The steady state creep behavior in an isotropic functionally graded composite cylinder, subjected to internal pressure has been investigated. The cylinder is assumed to be made of composite containing silicon carbide particles in a matrix of pure aluminum. The creep behavior of the material has been described by threshold stress based creep law with a stress exponent of five. The effect of imposing linear particle gradient on the distribution of stress and strain rates in the composite cylinder has been investigated. The study reveals that for the assumed linear particle distribution, the radial stress decreases throughout the cylinder with increase in particle gradient, whereas the tangential, axial, and effective stresses increase significantly near the inner radius but show significant decrease toward the outer radius. The strain rates in the composite cylinder could be reduced significantly by employing gradient in the distribution of reinforcement while keeping the same average amount of reinforcement.

This article presents a theoretical and experimental study on the measurement and prediction of die pressure in the extrusion process of wood-plastic composite (WPC). Die pressure is an important parameter in processing of WPCs as it governs the product strength, quality, and the final output rate, which directly affects the economy of the production. In this research work, a modular die was designed to accommodate for various circular die inserts to produce rod-shaped products having various diameters. Experimentation was carried out to record the pressure for each product. To develop a theoretical formulation for die pressure, two different schemes were considered and modified: non-Newtonian flow and hot extrusion. The comparison of the experimental and theoretical results demonstrated that the experimental values are between the values predicted by the two theoretical schemes. However, it was shown that by applying a correction factor (based on the compaction ratio of die) into the hot extrusion scheme, a theoretical ground can be suggested for pressure prediction in WPC processing. It appeared that the WPC flow in the die resembles more of a plug flow.

The main goal of this research is the fatigue simulation of cross-ply laminates under cyclic tension–tension loading conditions. For this purpose, a progressive fatigue damage model is developed based on two main assumptions. First, it is assumed that off-axis plies are responsible for stress redistribution into the laminate. Second, on-axis plies are responsible for strength reduction and control failure of the laminate. Developed model is capable of predicting the fatigue life and residual strength of cross-ply laminates with a limited experimental data and acceptable accuracy. The results of the model are compared with the experimental data provided in the second part of the present article.

The bistability of unsymmetric cross-ply [0_n/90_n]_T laminates has already been investigated in much detail. In this work a new type of bistable laminate is presented which has a symmetric lay-up. Bistability derives from an unsymmetric fiber prestress applied to the laminate. The experimental procedure used to apply this fiber prestress is presented in detail. Experimental results are compared with analytical and finite element models which have the ability to model fiber prestress accurately. As well as having minimal hygrothermal variability, it is noted that the snap-through loads for a prestressed symmetric laminate can be much higher than its unstressed [0_n/90_n]_T equivalent.

In this work the influence of a uniaxial carbon fabric layer on the mechanical performances of a glass mat/epoxy composite used for marine applications has been studied. All the structures have been made, at room temperature, by vacuum bagging technique. Tension and flexural tests have been carried out in order to evaluate the specific mechanical properties of the composite and to compare these with those of the marine aluminium alloy 6016-T4. The glass composites have higher specific strength but lower specific modulus than aluminium alloy. To increase the specific modulus of the composites, each layer of glass mat has been replaced with a layer of uniaxial carbon fabric. In addition, a simplified numerical model has been proposed to understand better the relevant dependence of the specific mechanical properties from the position and the orientation of the fibers. The comparison of the predicted numerical results with experiments has shown the accuracy of this model.

This article presents the results of an experimental investigation of static and fatigue behavior of unidirectional and cross-ply T700/Cycom 890 composite laminates. Test specimens are fabricated by using vacuum-assisted resin transfer molding technique. The ply configurations are: unidirectional [0₁₀] and [90₁₀] and cross-ply ([0/90]_4s, [0/90₅/0], and [0/90₄]_s) composites. Unidirectional specimens are tested under static and fatigue conditions to provide fundamental input data to run the progressive fatigue damage model developed in the first part of this article. To evaluate the capability of the progressive fatigue damage model, cross-ply laminates are tested under static and fatigue loading. The comparison between model predictions and the experiments shows a good correlation.

Drilling carbon/epoxy laminates is a common operation in manufacturing and assembly. However, it is necessary to adapt the drilling operations to the drilling tools correctly to avoid the high risk of delamination. Delamination can severely affect the mechanical properties of the parts produced. Production of high quality holes with minimal damage is a key challenge. In this article, delamination caused in laminate plates by drilling is evaluated from radiographic images. To accomplish this goal, a novel solution based on an artificial neural network is employed in the analysis of the radiographic images.

Polypropylene/montmorillonite (iPP/MMT) has been investigated as an alternative to isotactic polypropylene (iPP) as a matrix for glass mat thermoplastic (GMT) composites. The melt viscosity increased significantly on MMT addition, but iPP/5.9 wt% MMT-based hybrid GMT preforms were fully impregnated after 30 s of compression molding, which is consistent with GMT industrial cycle times. The flexural modulus and strength increased monotonically with MMT content in consolidated hybrid GMT specimens prepared by compression molding, although the impact strength decreased. Moreover, the increases in the flexural modulus were greater than predicted from a conventional rule of mixtures taking into the measured Young’s moduli of the iPP/MMT matrices. Possible reasons for this are discussed.

New bimetal magnesium/aluminium macrocomposites containing millimeter-scale Al-based core reinforcement were fabricated using solidification processing followed by hot coextrusion. Two approaches were attempted for enhancing the performance of AZ31: (a) AZ31 shell integration with pure Al core (pure Al core approach) and (b) AZ31 shell integration with AA5052 core (AA5052 core approach), in that order. In the AA5052 core approach eventually, macrointerface width was increased by 2 orders of magnitude (compared to that in the macrocomposite obtained using the pure Al core approach), while stiffness was increased (+36%), 0.2%YS was unchanged and UTS was increased (+14%) (compared to monolithic AZ31). The evolution of the Mg-Al macrointerface and its effect on microstructure and mechanical properties is investigated in this article.

Further implications of a fatigue model based on the cycle-by-cycle probability of failure are presented. A model for the residual strength is developed based on a linear relation between the residual strength at any cycle level and its derivative. This model is shown to be in excellent agreement with published test results. The model is also shown to lead to a constant cycle-by-cycle probability of failure under constant amplitude loading thus verifying the assumption of constant probability of failure made previously. The model is then used to construct constant life (Goodman) diagrams for composite structures and its predictions are compared to published test results. The model follows the test data well but needs further improvement for negative R values. The approach is then extended to the determination of the truncation level required for a structure to meet a certain fatigue life. The truncation level is a function of R ratio and the amount of statistical scatter for static tension and compression tests. Using representative values for the scatter, the predicted truncation level of 38% is shown to cover most applications. Possible reasons for discrepancies and areas where more work is needed are identified.

Quasi-static compressive tests were performed on carbon fiber reinforced polymer (CFRP) circular tubes to examine their axial crushing behaviors. Stable progressive crushing processes with brittle fracturing crushing mode were observed during the experiments. It is found that the crushing triggers including the ply drop off trigger and the shape memory alloy (SMA) trigger introduced in the specimens can efficiently initiate a stable progressive crushing process and significantly improve the specific energy absorption (SEA) as well as the crushing load efficiency (CLE) of the specimens. It is important to mention that the SMA trigger provides 37.2% increase of the SEA and 28.0% increase of the CLE, respectively, as compared with the specimens without a crushing trigger. Moreover, the SEA and the CLE of the composite tubes with the SMA trigger are 22.8% and 4.3% higher than those of specimens with the ply drop off trigger. In addition, the significant improvement of the SEA and the CLE is achieved with only a little increase of the initial peak-specific crushing stress.

In this article, a new kind of hydroxyapatite-zirconia-carbon nanotube (HA-ZrO₂-MWCNT) ceramic composites was fabricated to enhance the mechanical properties of a hydroxyapatite (HA) ceramic for satisfying various requirements in bone rehabilitation. A new dispersing process was proposed to ensure a homogeneous distribution of multi-wall carbon nanotubes (MWCNTs) in the HA ceramic matrix. The flexural strength and fracture toughness of the HA-ZrO₂-CNT composites were enhanced by about 126% and 124%, respectively, as compared with those of the unmodified HA ceramics. The X-ay diffraction analysis revealed that a small quantity of HA decomposed in the composites with introduction of strengthening phases. The in vitro test results showed that the sample surfaces were covered with a new apatite layer after immersion in simulated body fluid for 10 days, indicating good biocompatibility of the composites.

This article proposes an experimental study on the mode I interlaminar fracture of glass/polyester composites by using acoustic emission (AE) to analyze the damage evolution and evaluate the interlaminar performance of polymeric composites. A delamination process simulated with a double cantilever beam in opening mode (Mode I) coupled with an AE technique has been employed. The microscopic observation (scanning electron microscopy) is used to determine the correlation between different fracture mechanisms and their corresponding AE signal frequency content. Selected emissions are classified as matrix cracking, fiber breakage, or interface processes (fiber–matrix debonding) based on their total power in defined frequency intervals of the spectral power density. A correlation was established between the mechanical energy release rate and the AE energy rate. Analysis in the frequency domain shows AE parameters are powerful indicators of the intensity of the damage.

In this article, an attempt has been made to the development of magnesium (AM50)-based hybrid composites with graphite nanofiber (GNFs)/alumina short fiber (Al₂O_3sf) hybrid preforms by infiltration method. The main objective of the present work is to investigate the effect of higher volume percentage of GNFs with the mechanical properties of the Mg/Al₂O_3sf composites system. Based on the SEM observations, it has been confirmed that the Al₂O_3sf are good dispersed within the matrix metal. However, the GNFs were formed agglomerated within the matrix metal due to the higher volume percentage of GNFs while preforming. The mechanical properties such as hardness, tensile strength, and compressive strength of composites improved upto a threshold of 10% volume fraction of fibers. When the volume fraction of fibers was above 10% the properties showed to decreasing trend due to the presence of GNFs agglomerations. In the present hybrid composites, even though GNFs existed as clusters their distribution within the array of Al₂O_3sf network are found to be relatively good. It suggests that a critical amount of GNFs agglomerates may actually be beneficial for the mechanical properties of the composites.

This article is on the numerical determination of the mechanical properties of adhesively bonded hollow sphere structures (HSS). Two types of morphologies, namely syntactic and partial HSS, are considered. In the case of syntactic HSS, the hollow steel spheres are completely embedded in adhesive matrix, whereas for partial HSS the adhesive is concentrated at the contact points of neighbouring spheres. In addition to the elastic properties of the structure, the initial tensile and compressive yield strengths and the 1% offset yield strengths are calculated and compared for both configurations. Here, the anisotropic behavior of the adhesive in the tensile and compressive regime is incorporated. It could be shown that both configurations reveal quite different behavior on the macro-scale and therefore can be chosen according to specific requirements. Furthermore, the applicability of the adhesive as design parameter for the mechanical properties of HSS is shown.

The fusion devices currently being developed present several challenges for magnet designers. One challenge lies within the electrical insulation, which must be able to withstand extreme temperatures, large shear and compressive stresses, high operating voltages, and high levels of incident radiation. To address the need for better performing insulation systems, Composite Technology Development (CTD), Inc. has developed CTD-403, a cyanate ester resin with increased radiation resistance, ease of processing and fabrication, low moisture absorption characteristics, and high mechanical and electrical strength at cryogenic and elevated temperatures. The moisture absorption trends of CTD-403/S2 glass composite insulation were studied. The effects of humidity exposure on interlaminar shear strength (ILSS), compressive strength, dielectric strength, and glass transition temperature were also studied. The saturation level of the insulation was seen to increase with the relative humidity of the aging environment. Fickian behavior was seen at room temperatures below 97% relative humidity exposure. Non-Fickian behavior was seen at elevated temperatures. Saturation levels after 6 months exposure were seen to be below typical epoxy-based insulation systems, averaging 0.5% weight gain. Degradation of mechanical and electrical properties was seen with increased humidity exposure and moisture absorption. ILSS showed an average retention rate of 75% after 6 months exposure. The compressive strength showed no decrease after 6 months exposure at room temperature, and show retention rates greater than 90% at 75°C/79% RH. An average dielectric strength of 98.6 kV/mm was seen for all specimens at room temperature (above 90% retention) after 6 months exposure.

SiCp-reinforced copper matrix composites with the reinforcement content of 30–50 vol.% were fabricated by hot pressing using Cu-coated and uncoated SiC powder. The microstructure and mechanical properties of the composites were studied. The results showed that with the increasing of SiCp volume fraction, the Brinell hardness of the composites increased first and arrived at a peak value, then decreased, while the bending strength decreased continuously. On the condition of same volume fraction of SiCp, the Brinell hardness and bending strength of the composites using coated powder were higher than that of the composites using uncoated powder. The annealing treatment lowered the Brinell hardness and bending strength of the composites. When the volume fraction of SiCp was 30 vol.%, the fracture mechanism of the composites showed a mixed manner of dimple and quasi-cleavage fracture. While the volume fraction of SiCp was 50 vol.%, the fracture behavior of the composites dominated in quasi-cleavage manner with seldom dimples.

Composite material usage is necessary on NASA’s future launch vehicles in order to obtain a low mass vehicle. While aircraft and launch vehicles that utilize load-bearing composite components have many similar damage tolerance requirements, the distinct differences between a part that has a lifetime of ~500 s (one launch) and can be inspected in detail before use and one that has a lifetime of many tens of thousands of flight hours and can only undergo a ‘walk around’ inspection before each flight (commercial transport) needs to be taken into account. This article presents these differences and uses data from the ARES I composite interstage as an example of how to arrive at preliminary compression after impact strength values for the sandwich structure in the acerage of this part using residual strength curves. Results show that if severity of damage can be quantified by a nondestructive method (other than dent depth), the mass of the structure can be reduced due to better characterization of the damage.

Many years ago, free edge effects were studied extensively, perhaps excessively, for ordinary tape laminate composites. Various techniques were used to show that the free edge effects extended only a short distance from the free edge and that stacking sequence had a significant impact on interlaminar stresses, which could cause premature failure. In contrast, the analytical study of woven composites has focused on periodic analysis of unit cells. Since such analyses assume an infinite array of unit cells, free edge effects were not considered. This article investigates the significance of traction free surfaces on stresses in woven composites. Effects due to both free edge and free lateral surfaces (due to finite thickness) were investigated. The significance of the free edge effect was found to be sensitive to the waviness of the plain weave mat. Also, the stress distribution is quite different for finite and infinitely thick stacks of woven mats.

In the present study, new light weight nanocomposites (AZ31-1.5Al₂O₃-Ca) based on magnesium alloy AZ31B are developed using disintegrated melt deposition technique. Microstructural characterization studies revealed equiaxed grain structure, minimal porosity, and good matrix-reinforcement interfacial integrity. The results also showed that addition of both nano-Al₂O₃ and Ca led to a simultaneous improvement in 0.2% yield compressive strength (0.2% YCS), ultimate compressive strength (UCS), and work of fracture (WoF) of the AZ31B magnesium alloy while failure strain was slightly compromised. Moreover, excellent oxidation resistance of this composite was realized when compared to AZ31B up to 500°C. The results suggest that this composite formulation can be used in diverse engineering applications requiring light weight structural materials.

Nowadays, the market demand for environmentally friendly materials is rapidly increasing. Biodegradable fibers and biodegradable polymers, mainly extracted from renewable resources, are expected to be a major contribution to the production of new industrial high performance biodegradable composites, partially solving the problem of waste management. At the end of its lifetime, a structural biodegradable composite can be crushed and recycled through a controlled industrial composting process. Bodros et al. [1] showed that biodegradable L-polylactide acid (PLLA)/flax fibers mat composites exhibiting specific tensile properties equivalent to glass fiber polyester composites can be manufactured by an un-optimized film-stacking process. In our study, the process has been investigated more extensively. Indeed, the compaction of flax mats requires a higher load than for glass mats of similar areal weight. The transverse permeability of flax mats has also been shown to be lower than for glass mats. In both cases, this is due to a higher degree of entanglement of the flax fibers within the mat. However, the range of permeability and compressibility values of the flax mats are well within the values that allow a good through-the-thickness impregnation. Flax fibers cannot sustain long exposures at the impregnation temperature of the mats by PLLA resin. Through-the-thickness impregnation of flax mats processes such as film stacking are more suitable than in-plane impregnation processes such as resin transfer molding because the flow of resin is limited on short distances and allows short times of impregnation.

The strength of unidirectional composites is essentially dependent on the mechanical behavior of their reinforcement. The variability in mechanical properties of glass fibers has been studied using bundles of about 1400 filaments. This article proposes an experimental study on the fiber fracture strength distributions during tensile test by using acoustic emission (AE) in order to verify individual filament failures. AE monitoring of a bundle of E-glass fibers provides a convenient and relatively quick method to obtain the Weibull parameters of strength distribution. Results show that AE can be used as an effective tool to recognize the failure strength distribution as well as flaw population of fibers.

This article presents the results of an experimental and analytical study on the behavior of concrete cylinders externally wrapped with fiber-reinforced polymer (FRP) composites and internally reinforced with steel spirals. The experimental work was carried out by testing twenty-four 150 x 300 mm² concrete cylinders subjected to pure compression with various confinement ratios and types of confining material. The test results show that the compressive response of concrete confined with both FRP and steel spirals cannot be predicted by summing the individual confinement effects obtained from FRP and steel spirals. This is largely attributable to differences in the inherent material properties of FRP and steel. A new empirical model to predict the axial stress–strain behavior of concrete confined with FRP and steel spirals is proposed. Comparisons between experimental results and theoretic predictions show agreement.

ZrB₂—20 vol.% SiC ceramics with additional 20 vol.% short carbon fibers were developed to promote graceful failure using hot-pressing technique. The influence of short carbon fiber on the strength, and modulus of composite was analyzed and estimated using a modified rule of mixtures. The calculation results showed that a little decrease in flexural strength from 502 to 445 MPa and elastic modulus from 414 to 322 GPa was due to the lower elastic modulus of short carbon fiber. An apparent increase in fracture toughness from 2.0 to 6.56 MPa m^1/2 was obtained with the addition of short carbon fiber. And the fracture toughness was analyzed and calculated based on the toughening mechanisms of crack deflection, fiber pullout, and crack bridging. Calculated results were in good agreement with experimental results.

In view of the shape and distribution of fillers, a model predicting the effective thermal conductivity of filled polymer composites is proposed on the basis of the percolation theory. Compared to other models proposed in the literatures, theoretical results obtained with the percolation model agree better with the experimental data. Methods of determining the percolation threshold V _c and the exponent n in the percolation model are also discussed.

Finite element models based on X-ray tomography of the carbon foam morphology are developed to characterize response of multifunctional carbon foams. These models incorporate ligament anisotropy as well as coating layers and provide comprehensive information for adapting processing and performance parameters. Illustrations at multiple scales are presented to explore the range of properties in coupled-field environments that are crucial for the emerging multifunctional devices. The results highlight the importance of anisotropy and the impact of common processing defects in tailoring properties. Specifically, coating coverage and quality interfaces are critical in delivering the desired thermoelectrical response.

Varying amounts of three different carbons (carbon black, synthetic graphite particles, and carbon nanotubes) were added to polypropylene, and the resulting single-filler composites were tested for thermal conductivity using the nanoflash test method. In addition, the effects of single fillers and combinations of different carbon fillers were studied via a factorial design. Each single filler caused a statistically significant increase in through-plane thermal conductivity at the 95% confidence level, with synthetic graphite causing the largest increase, followed by carbon nanotubes, and then carbon black. The synthetic graphite/carbon nanotube formulations, followed by the carbon black/synthetic graphite formulations also caused a statistically significant increase in composite through-plane thermal conductivity. Composites containing 75 and 80 wt% synthetic graphite in polypropylene had an in-plane thermal conductivity of 24 and 34 W/m^.K, respectively. This meets the thermal conductivity target of >20 W/m^.K for fuel cell bipolar plates.

Impact damage of textile composite and aluminum are the most common phenomenon in aircrafts and high-speed vehicles as impact loadings often occur. This article presents a comparative study of the impact responses of two kinds of 3D textile composites (named as 3D spacer weft-knitted composite and 3D orthogonal woven composite) and aluminum circular plates tested with a modified split Hopkinson pressure bar apparatus. Finite element analyses of the impact behavior of the composites and aluminum were also presented to uncover the impact damage mechanisms. Furthermore, the quasi-static indentation tests were carried out for comparing the different damage modes between quasi-static and impact loading. The 3D textile composites have resin crack and fiber breakage under quasi-static indentation tests while only elasto-plastic deformation has been found in aluminum. The energy absorption of the 3D textile composite is greater than aluminum. While under impact loading, the 3D textile composites absorb lower impact energy than aluminum because the lower impact damages were found in the composite circular plate. More importantly, no impact delamination was found in both of the 3D textile composites. This manifestation of the 3D textile composites is tougher than aluminum in impact loading and more suitable for aircrafts and high-speed vehicles design.

This article analyzes the effect of devising a new failure envelope by the combination of the most commonly used failure criteria for the composite laminates, on the design of composite structures. The failure criteria considered for the study are maximum stress and Tsai–Wu criteria. In addition to these popular phenomenological-based failure criteria, a micromechanics-based failure criterion called failure mechanism-based failure criterion is also considered. The failure envelopes obtained by these failure criteria are superimposed over one another and a new failure envelope is constructed based on the lowest absolute values of the strengths predicted by these failure criteria. Thus, the new failure envelope so obtained is named as most conservative failure envelope. A minimum weight design of composite laminates is performed using genetic algorithms. In addition to this, the effect of stacking sequence on the minimum weight of the laminate is also studied. Results are compared for the different failure envelopes and the conservative design is evaluated, with respect to the designs obtained by using only one failure criteria. The design approach is recommended for structures where composites are the key load-carrying members such as helicopter rotor blades.

Al–(1, 3, 5, 7, 10 vol%) SiC nanocomposites were produced by mechanical alloying (MA) and double pressing/sintering route. The characteristics of the milled powders and the consolidate specimens were examined using high resolution scanning electron microscopy and X-ray diffraction method. Compression and hardness tests were used to study the effect of SiC volume fraction on the strength of Al–SiC nanocomposites. It was shown that with increasing the SiC volume fraction, finer particles with narrower size distribution and smaller crystallite size are obtained after MA. During sintering close to the melting point of aluminum, the presence of nanometer-scaled SiC particles was found to hinder the grain growth significantly. The Al matrix with a higher SiC content exhibited more potential for grain boundary pinning, i.e., smaller grain size was obtained at higher SiC volume fractions. Consequently, an improved mechanical strength was obtained. The processing method (MA/pressing/sintering) can be used for fabrication of near-net shape Al matrix nanocomposites.

Four-point bending beam tests are applied to investigate the bending behavior of asphalt composites strengthened by grid reinforcements made of carbon, glass, and polyester fiber grids. Both experimental and analytical predictions are compared considering the deflection behavior of carbon grid-reinforced beams. This study especially shows significant structural improvement and better crack resistance of asphalt composite beams by carbon grids. Temperature and loading rate dependencies are also evaluated and compared for both reinforced and unreinforced asphalt composite beams. The maximum bending forces of carbon grid-reinforced beams significantly decrease with decreasing loading rate and increasing the temperature. The deflection behavior of asphalt composite beams reinforced by carbon grids is reasonably predicted using a bilinear damage-based model and a viscoelastic beam theory. The layer-parallel direct shear test is conducted for investigating the interlayer shear behavior of asphalt composite beams.

Large structures made with composites (e.g., wind turbine rotor blades, yachts, and airplane fuselages) employ fabrics with small tow sizes especially when fabricated by vacuum-assisted resin transfer molding (VARTM). Simulation tools are frequently used to aid the manufacturing process development for large structures. This article details the development of a low cost VARTM manufacturing process for a 3.2 m long aeroelastically tailored rotor blade that has been completed without an infusion modeling tool. This robust VARTM-based process has been developed for very large tow sized fabrics with very poor permeability. Changes in the manufacturing process are made based on a parametric matrix until the desired part quality is achieved. Principal in-plane permeability is measured using 1D channel flow method for various fibers used in this study. Details of the methods employed to assemble the final blade are presented. The final process results in the fabrication of six rotor blades each with different lay up and fiber constituents. Problems and solutions related to migrating from a small-scale VARTM process to larger structures are detailed. Final blade quality is determined by full-scale mechanical testing under static and fatigue loading conditions. All the manufactured blades fail at least 160% above the proof load indicating compliance with the design quality criteria.

This article studied a possible mechanism of a failure from a thick hoop layer of a filament-wound rocket motor case with long cylindrical portion analytically and numerically. The hoop-wound fibers at the cylindrical portion was slightly inclined from the circumferential direction as a finite width prepreg tape was wound without overlapping or gap by alternately feeding in forward and backward direction. Fiber stress concentration in the hoop layer due to possible damage states was assessed through analytical studies and a rough estimate of the stress concentration was given by explicit functions. The possible damage consisted of transverse cracks slightly inclined from each other and debonding of the interface between the hoop layer and the base layer. The approximate analytical solution agreed well with the numerical results in spite of simplification. The results could show the possibility of stress enhancement due to damage in the thick hoop layer made of two slight inclined fibers and important guideline for the design of filament winding pressure vessels.

Transverse stress–strain constitutive relations are required for structural analysis of thick-section composites. A standard technique for assessment of transverse shear properties is the V-notched beam method. Such technique is based on strain gage measurements, which require a large specimen thickness for strain gage placement and impose tight geometry tolerances to minimize variations of strain at the gage location. A full-field strain measurement capability could enable simpler test specimen designs. A method for assessment of shear stress–strain relations using a short-beam shear (SBS) test and a digital image correlation (DIC) technique is presented in this work. The DIC technique is based on quantifying locations of a random texture on a surface to measure surface shape and deformation. V-notched-beam and SBS test results are compared for a glass/epoxy tape composite. To illustrate accuracy of SBS stress calculations, finite element results are obtained. Highly nonlinear interlaminar stress–strain relations are documented.

A phenomenological anisotropic theory of viscoplasticity that takes account of the difference between the nonlinear rate-dependent behaviors of unidirectional carbon fiber-reinforced composites under off-axis tensile and compressive loading conditions is presented. The plane-stress representation of the effective stress associated with the pressure-modified Hill’s anisotropic yield criterion is modified into a new form that allows consideration of the difference between the shear flow stress levels under transverse tension and compression, i.e., a shear flow differential effect, as well as of the difference between the transverse tensile and compressive flow stress levels, i.e., a transverse flow differential effect. The shear flow differential effect is modeled in two ways by assuming the sensitivity and insensitivity to transverse stress, respectively. The rate-dependent plastic deformation of unidirectional composites is modeled on the basis of the concept of overstress and the irreversible thermodynamics with internal variables. The viscoplasticity model proposed in the present study can be reduced to the form developed in an earlier study, which facilitates identification of material constants and comparison with other existing theories. Validity of the proposed viscoplasticity model is evaluated by comparing with the off-axis tension and compression test results on a unidirectional carbon/epoxy composite at different strain rates. It is demonstrated that consideration of both the transverse and shear flow differential effects is crucial for accurate prediction of the different nonlinear rate-dependent behaviors of unidirectional composites under off-axis tensile and compressive loading conditions and those two kinds of flow differential effects have successfully been modeled in the proposed theory of viscoplasticity.

A natural polyol was prepared from castor oil by alcoholysis with triethanolamine. The oil and the oil-based polyol were characterized by infrared spectroscopy and through the analytical determination of their functional groups, both techniques indicating that the hydroxyl content increased significantly after the alcoholysis reaction. The modified oil was subsequently used as the polyol component in the formulation of rigid polyurethane foams. Wood flour was chosen to be incorporated as filler in these materials. Physical, thermal, and mechanical properties of the neat and reinforced foams were measured, analyzed, and compared to a reference commercial system. The chemical reaction between wood flour and isocyanate strongly affected the composites’ response to thermo-gravimetric tests. Compression modulus and yield strength decreased as wood flour content increased. The effect of the foam density on the compression properties was also investigated.

In the present work, the elastic behavior of different hypoeutectic and hypereutectic Al–Si alloys and different Al₂O₃ short fiber and SiC particle reinforced materials (SFRM and PRM, respectively) is studied. The effective Young’s modulus (E) of materials was experimentally measured and compared with the different theoretical predictions of Hashin–Strikman, Tuchiniskii, shear lag, and the rule of mixtures (ROM). The unreinforced alloys present an interconnected lamellar Si structure after fast solidification, which increases the Young’s modulus up to that of the Tuchiniskii prediction for interpenetrating skeletal structures. On the other hand, alloys presenting isolated and coarse Si particles (after spheroidization treatment at 540°C) are well described by the lower bound of the ROMs. Similarly, the interconnected Si–SiC structure observed in 10 and 70 vol% SiC reinforced AlSi7Mg and AlSi7 matrices in the as cast condition is responsible for the higher stiffness of the composite, if compared with that of Al99.5 or spheroidized AlSi7 matrices. An analogous behavior is observed in the SFRMs in the as cast condition, where the Si lamellae bridge the Al₂O₃ fibers, increasing the Young’s modulus of the composites, if compared with the conditions of spheroidized Si. Furthermore, the primary Si particles produce an improvement in the Young’s modulus by connecting several fibers in the case of a short fiber-reinforced hypereutectic AlSi18 matrix.

X-truss/foam sandwich structure with prominent compression and shear strength has broad application prospects as primary structure in aircraft, truck, and other fields. But unsuitable molding pressure usually causes quality defects such as poor skin–core adhesion or broken Z-pins, which seriously decreases the structure's mechanical property and induces too much thickness error. In order to obtain a suitable molding pressure, the hot pressing process was analyzed. It was found that the suitable molding pressure is mainly determined by the property of the foam core, the resisting force of Z-pin inserting into the face sheets, as well as Z-pin inserting angle and density. In the calculated suitable molding pressure, X-truss/foam sandwich structures were successfully fabricated using carbon fiber Z-pins and face sheets together with polymethacrylimide foam core. The thickness of sandwich structures and final inserting angle of Z-pins were basically consistent with the calculations.

This study is aimed to evaluate the influence of a number of parameters within the context of composite structure optimization. In particular, the nature of the component materials and all of the possible orientations were studied. Problems optimizing elementary plates and structures modeled using finite elements were treated using a genetic algorithm. The results were used to define the relative importance of these parameters and to derive simple design rules that would reliably obtain a high-performance configuration.

A finite element method is presented for predicting the mechanical performance of discontinuous fiber mesostructures typically produced by directed carbon fiber preforming. High-filament count bundles are modeled using beam elements to enable large representative volume elements to be studied. The beams are attached to a regular grid of 2D continuum elements, which represent the matrix material, using an embedded element technique. The model is validated by comparing simulations with experimental data for random and aligned fiber architectures produced with different tow sizes (6 and 24 K) and fiber lengths (28, 58, and 115 mm). Stiffness and strength predictions are generally within 10% for 6 K preforms, but this error increases up to 40% with increasing tow size because of the assumption that the fiber bundles are circular in cross-section.

Multiwalled carbon nanotubes (MWCNTs) have been first coated with cobalt ferrites by a simple wet method. Transmission electron microscopy images show that ferrite nanoparticles (average diameter of 10 nm) were deposited on the sidewall of the MWCNTs. X-ray diffraction pattern exhibits representative diffraction peaks corresponding to spinel structure, and the structure of the MWCNTs is not distorted. X-ray photoelectron spectroscopy spectrum shows the proportion of the content of Fe and Co is about 2:1, which coincides with the stoichiometric proportion of CoFe₂O₄.

The organic–inorganic hybrid involving hydroxyl-terminated polydimethylsiloxane (HTPDMS)-modified epoxy, filled with organo-modified flurohectorite clay of various percentages (1–5 wt%) were prepared via in situ polymerization using -amino propyltriethoxysilane as cross-linking agent in the presence of dibutyltindilaurate catalyst. The reactions involved during the curing process between epoxy and siloxane were confirmed by FT-IR. The results of differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperatures of the clay-filled hybrid epoxy systems are lower than that of neat epoxy. The data obtained from the thermal studies indicated that improved thermal stability was due to the incorporation of nanoclay into siloxane-modified epoxy hybrid systems. The morphologies of the siloxane containing epoxy–clay hybrid systems show heterogeneous character, due to the partial incompatibility of HTPDMS. Scanning electron microscopy indicates the phase separation, induced by the polymerization, occurs in the HTPDMS-modified epoxy hybrids to yield spherical particles of siloxane-rich phase, which are uniformly dispersed in the continuous epoxy matrix. Microstructures of nanocomposites were ascertained from X-ray diffraction (XRD) and transmission electron microscopy. The formation of exfoliated structure of organoclay was confirmed from the XRD pattern and shows interlayer spacing between 3.42 and 8.50 Å. Hybrid epoxy nanocomposites containing higher percentage composition of organo-modified flurohectorite clay contents (up to 5 wt%) display more pronounced improvements in thermal properties and moisture resistance than corresponding unmodified epoxy matrices.

The properties of polymers are greatly enhanced when they are incorporated with silicate-layered clays as they find many applications in the fields of electronics, automobile industry, packaging, and construction. In this study a thermoplastic polymer poly(vinyl alcohol) (PVA) and montmorillonite (MMT) clay were used to prepare MMT-PVA nanocomposites and their mechanical properties were investigated. In general PVA is used in paper coating and packaging where their tensile strength and tearing strength are vital. The MMT-PVA nanocomposites displayed more than 60% increase in the tensile strength and young’s modulus where as the tearing energy doubles the value of neat PVA. This is a substantial enhancement compared to that reported so far. The enhancement was achieved at low clay content probably due to its exfoliated structure. The dispersed clay layers are well embedded with PVA matrix via strong interatomic interactions leading to better material properties.

The impact resistance properties of T300/epoxy composite laminates are experimented at different velocities of 10–300 m/s striking on the laminates [(45/-45)₄]_s, [(0/45/90/-45)₂]_s, and [(0/45/90/-45)₄]_s. The striking and residual velocities of bullets shot by a high-speed gas gun are measured by laser velocity measurement device. In the tests, the whole penetration process is recorded by high-speed camera from the front side of targets, and then the fracture and the energy absorption of specimens are analyzed. Under the high-velocity impact, the in situ stress distribution is investigated through the reading of strain gages installed on specimens. Failure models of target laminates are discussed at three types of bullet striking velocities, classified as the less, equal, and lager than the ballistic limit velocity.

Single diaphragm forming (SDF) has been used in manufacturing high-quality thermoplastic composite sheet parts with complex geometries. However, temperature gradients through the thickness may exist in the composites, especially for thick, high temperature, semicrystalline composites. The thermal gradient may introduce residual stresses, which may degrade the mechanical properties or warp the part. Therefore, investigating temperature profile through the thickness during processing can improve the quality of SDF composite parts. A laboratory scale SDF with a cooling system was built for the temperature study through the thickness. Carbon fiber reinforced polyphenylene sulphide (carbon/PPS) was used for the temperature study, and the effect of cooling rate on the nonisothermal crystallization of the carbon/PPS was also investigated using differential scanning calorimeter. The start crystallization temperature and the peak crystallization temperature decrease with increasing cooling rates. A combination of Avrami and Ozawa theory was successfully used in the work for describing the crystallization kinetics, and the crystallization activation energy was determined for the carbon fiber reinforced PPS.

A hyperelastic constitutive model is developed for textile composite reinforcement at large strain. A potential is proposed, which is the addition of two tension and one shear energies. The proposed potential is a function of the right Cauchy Green and structural tensor invariants whose choice corresponds to textile composite reinforcement mechanical behavior which exhibits weak elongations in the fiber directions and large angular variations in the fabric plane.

The model is implemented in a Vumat user routine of ABAQUS/Explicit. Some elementary tests are performed in order to identify the model and verify its validity. It is then used to simulate the hemispherical punch forming of balanced and unbalanced fabrics. A correct agreement is obtained with experimental forming processes.

An approach for the prediction of growth of delaminations in laminated composites made of plies of fiber-reinforced polymers is proposed. It allows to handle arbitrary combinations of force, displacement, temperature, and moisture loads. Quasi-static load cases can be treated as well as load cases where some load components are constant and some load components are cyclic. The proposed approach is based on the Griffith criterion, which is evaluated by means of some finite element procedure. It provides a complete picture of a delamination problem in a given structure and offers systematic understanding of the influence of size and position of a delamination on the growth, on the growth stability, and on the structural response. Two examples, a curved laminate and a T-joint, are investigated in detail to underline the capabilities of the proposed approach.

Hydroxyapatite (HA) impregnated poly-(acrylamide) nanocomposites were synthesized using -radiations and the prepared composites were characterized by different instrumental techniques. Fourier transform infrared spectroscopy studies revealed the presence of carbonated HA, while the X-ray diffraction analysis showed the mean particle size of HA to be nearly 6.53 nm and width 1.278 nm. The nanosize of the hydroxyapatite crystals were also confirmed by Transmission electron microscopy analysis. The crystallinity of material was found to be 76.10% with interchain separation between 0.1998 and 0.1933 nm for native HA and HA nanocomposites, respectively. Thermogravimetric analysis studies resulted in the thermogram that resembled with that of the natural bone. Scanning electron microscope results revealed the pore size of prepared composite ranging between 50 and 100 µm. The modulus and compressive strength of prepared materials were found to be 726.40 and 39.55 MPa, respectively. Water uptake capacity of the prepared nanocomposites was quantified in terms of swelling ratio and the data were used to calculate network parameters of HA–PAm composites. The in vitro – blood compatibility results confirmed a fair level of blood compatibility of the prepared composites.

Metal matrix composites are engineered materials with a combination of two or more dissimilar materials, (at least one of which is a metal) to obtain enhanced properties. In the present investigation Al-4.5% Cu alloy was used as the matrix and fly ash and silicon carbide (SiC) as reinforcements. The hybrid metal matrix composite was produced using conventional foundry techniques. The fly ash and SiC were added in 5%, 10%, and 15% by weight (equal proportion) to the molten metal. The hybrid composite was tested for fluidity, hardness, density, mechanical properties, impact strength, dry sliding wear, slurry erosive wear, and corrosion. The microstructure examination was done using scanning electron microscope to assess the distribution of particulates in the aluminum matrix. The results show that there is an increase in hardness with increase in the particulates content. The density decreases with increase in fly ash and SiC content. The tensile strength, compression strength, and impact strength increases with increase in fly ash and SiC. The resistances to dry wear and slurry erosive wear increases with increase in fly ash and SiC content. Corrosion increases with increase in fly ash and SiC content. This material can be used as bearing material.

The present composite structure models assume that reinforcement particles are located in a repeated arrayed order through metal matrix. This study investigates the effect of both random particle distribution and particle volume fraction on the indentation behavior of Al 1080/SiC particle reinforced metal–matrix composites under a spherical indenter. The ceramic particles were distributed randomly in a certain particle volume fraction through aluminum matrix in order to achieve a similar structure to a real particulate composite structure as possible. The particle volume fraction strongly affects permanent indentation surface profiles and indentation depths. The indentation profile becomes smoother, and the peak indentation depth increases as the particle volume fraction decreases. The random particle distribution has a small effect on the peak indentation depth but affects strongly the permanent indentation profiles as well as the residual stress and strain fields in the indentation region. A small increase appears in the local particle concentration in the indentation region and is affected considerably by the random particle distribution. The hardness tests as well as the scanning electron microscopy micrographs of the indentation regions of specimens with different particle volume fractions are in good agreement with theoretical analysis.

Accurate matrix-dominated constitutive properties can be a key to accurate failure models for polymer–matrix composites. This work shows the effect of nonlinear interlaminar shear stress–strain relations on delamination failure predictions for thick IM7/8552 carbon/epoxy tape laminates with wavy plies. Nonlinear finite element model (FEM) predictions and subsequent test correlations are presented. The interlaminar shear stress–strain relations are generated using short-beam shear tests and a digital image correlation full-field strain measurement technique. Test data for the wavy-ply coupons show that nonlinear shear stress–strain response is required for accurate failure prediction.

Parametric appraisal of a dry sliding wear process is presented for a set of new composites consisting of polyester as the matrix, flakes of pine-bark as the fibrous reinforcing component, and the kiln-dust of a cement plant as the filler. The filler content in the composites is fixed at 50 wt%, while the weight fraction of fiber reinforcement is varied (0–12 wt%) so as to obtain composite samples of three different compositions. Wear tests are carried out with the help of a pin-on-disc test rig employing the design of experiments approach based on Taguchi’s orthogonal arrays. The findings of the experiments indicate that the rate of wear is greatly influenced by various control factors. An optimal parameter combination is determined, which leads to minimization of wear rate. Analysis of variance is performed on the measured data and signal-to-noise (S/N) ratios. A mathematical correlation, consistent with the experimental observations is proposed as a predictive equation for estimation of sliding wear rate of these composites. Finally, optimal factor settings for minimum wear are determined using genetic algorithm.

In this article, the experimental results of hybrid-fiber engineered cementitious composite (HFECC)-strengthened masonry walls subjected to quasi-static out-of-plane loadings are reported. The aim is to assess the extent to which HFECC-strengthening systems can improve the out-of-plane resistance of unreinforced masonry walls. A total of 12 masonry panels were fabricated and tested in the laboratory under both patch load and uniformly distributed load. Test results showed significant improvement of HFECC-strengthened masonry wall’s performance against out-of-plane loadings. To provide design aid for such HFECC-strengthened masonry walls, simplified theoretical models were also developed to predict its out-of-plane ultimate load-carrying capacities based on the observed failure mechanisms. The theoretically predicted values compared favorably with experimental data.

A 3D orthogonal woven S2-glass composite is investigated using finite element micromechanics to characterize the stiffness and the strength. The methods are applied to a targeted parametric investigation of the effects of stitch density on strength properties and potential benefits of through-thickness reinforcement, such as resistance to transverse shear and delamination, with some consequent loss of in-plane properties. Direct modeling of the exact microstructure from scanning electron microscope visualization provides a precise knowledge of the mechanics and the failure modes of the microstructure under various loading conditions. Modeling results are verified by comparison to experimental data. In-plane stiffness and strength are predicted with 90% or better accuracy. Transverse shear stiffness was less well predicted, but strength was still predicted within 86% accuracy.

Novel fluoroalkyl end-capped oligomers/hydrogarnet (katoite) nanocomposites were prepared by the hydrothermal reactions of a stoichiometric mixture of Ca(OH)₂, Al(OH)₃, and Al₂Si₂O₅(OH)₄ in the presence of the corresponding fluorinated acrylic acid, acryloylmorpholine, and N,N-dimethylacrylamide oligomers. These fluorinated katoite nanocomposites thus obtained are nanometer size-controlled, and were found to exhibit a good dispersibility in water, methanol, ethanol, and tetrahydrofuran. Fluoroalkyl end-capped oligomers were also applied to the dispersion of parent katoite into these solvents; however, a poor dispersiblity for these solvents was observed. On the other hand, fluoroalkyl end-capped 2-methacryloyloxyethanesulfonic acid oligomer [R_F–(MES)_n–R_F] was able to solubilize katoite into water to afford the transparent colorless solution. The obtained R_F–(MES)_n–R_F/katoite nanocomposites were found to exhibit a good antibacterial activity against Staphylococcus aureus, and were also applied to the surface modification of poly(vinyl alcohol) to exhibit a good oleophobicity imparted by fluorine on the surface.

The research is aimed to investigate the compressive strengths of glass/epoxy nanocomposites, containing various loadings of spherical silica nanoparticles. Through a sol–gel technique, the silica particles with a diameter of 25 nm were exfoliated uniformly into the epoxy resin. Subsequently, by inserting the silica–epoxy mixture into the unidirectional glass fiber through a vacuum hand lay-up process, the glass fiber/epoxy composite laminates with 10, 20, and 30 wt% of silica nanoparticles were fabricated. Quasi-static and dynamic compression tests were conducted on the brick composite specimens with fiber orientations of 0°, 5°, 10°, 15°, and 90° using a hydraulic MTS machine and a split Hopkinson pressure bar, respectively. Observations on the failure specimens indicated that for fiber orientations less than 15°, the fiber microbuckling is the dominant failure mechanism. On the other hand, for the 90° samples, the out-of-plane shear failure is the main failure mechanism. In addition, it was denoted that as the silica contents increase, the compressive strengths of the glass/epoxy composites are improved accordingly. The enhancing mechanism in the compressive strengths can be properly explicated using the microbuckling model.

A study was undertaken to evaluate the effect of atmospheric plasma treatments on the surface chemistry, morphology, and mechanical properties of graphite/epoxy composites. Characterization included contact angle measurements, XPS, FTIR, SEM and AFM. Treatment was shown to increase strength by as much as 50% relative to untreated specimens. The improvement was related to the number of passes and can be attributed to chemical surface modifications. While the total amount of oxygen on the surface stabilized quickly after a few plasma passes, the concentration of the carboxyl groups was shown to continuously increase, and correlated well with observed increases in strength.

Stiffened plates are used in several applications, such as aircrafts, ships, and aerospace structures. Dynamic analysis of stiffened and unstiffened composite laminated plate is presented in this work using a high-order finite element. The shear effect has been taken into consideration in the derivation of the element. This technique gives us the ability to avoid the problem of unsymmetry of stiffness matrix due to large deformation effect. The accuracy of the proposed derivation of the element has been verified through the comparison of the results with published, software (ANSYS-11) and experimental results. The effects of the number of layers and degree of orthtropy are studied with different case studies by different boundary conditions and thickness-to-span ratio. A comparison with different kind of elements is presented.

The research aims to investigate the interlaminar fracture toughness of glass fiber/epoxy composites, which consist of the silica nanoparticles and the rubber particles. Two kinds of rubber particles, one is the reactive liquid rubber (CTBN) and the other is the core-shell rubber (CSR), were employed to modify the fracture toughness of epoxy resin. In general, the disadvantage of adding rubber particles into polymeric resin is the dramatic reduction of stiffness although the toughness could be modified accordingly. In order to enhance the fracture toughness of the fiber composites without sacrificing their stiffness, the silica nanoparticles in conjunction with the rubber particles were introduced into the epoxy matrix to form a hybrid nanocomposite. Experimental results obtained from tensile tests on bulk epoxy confirm the presumption that the reduction of the epoxy stiffness because of the presence of rubber particles can be effectively compensated by the silica nanoparticles. Furthermore, the fracture tests conducted on the double cantilever beam specimens revealed that the inclusion of silica nanoparticles together with the CSR particle can appreciably increase the fracture toughness of the glass/epoxy composites up to 82%. On the other hand, when the epoxy matrices were modified with CTBN rubber particles and silica nanoparticles, the improvement of the interlaminar fracture toughness was around 48%. It is noted that the role of the silica nanoparticles on the fracture toughness of fiber composites with rubber-modified epoxy matrix is different. For the CSR-modified epoxy matrix, the contribution of silica nanoparticle on the fracture toughness is destructive. In contrast, for the CTBN-modified epoxy matrix, the silica nanoparticles can synchronously improve the fracture toughness of composites.

Coir yarn-reinforced polypropylene (PP)-based unidirectional composites were prepared by compression molding. Coir yarn content in the composite was optimized and 20% yarn content showed higher mechanical properties. Jute yarns (20%–100%) were incorporated into the coir-based composites. It was found that 20% coir and 80% jute-reinforced PP matrix composites performed the best results. All the materials (coir, jute, and PP) were irradiated with gamma radiation from 400 to 1000 krad. PP-based composites (20% coir and 80% jute) showed the highest mechanical properties at 600 krad of total gamma dose. Starch (2–10% in aqueous solution) was used as stiffening agent for the yarns and it was found better unidirectional position of the yarns inside composite over the untreated composite. It was reported that composites prepared with 5% starch treated yarns (coir and jute) for 5 min soaking time demonstrated the best results. Scanning electron microscopy, thermal degradation, water uptake, and electrical properties were also studied.

The fabrication and use of fiber Bragg grating (FBG) sensors, which operates in near infrared region (Bragg wavelength _B = 830 nm) to monitor the damage accumulation in composite is reported. The spectra ~830 nm of the embedded FBG sensor in 0°/90° woven cloth/vinyl ester composite were distorted and broadened due to fatigue loading, as expected. These distortions in FBG spectra indicate asymmetric and nonuniform strain distributions along the grating length of the FBG sensors due to the accumulation of damage during fatigue loading regimes. This information is useful for formulating a fundamental relationship between FBG spectral changes and the damage accumulation of composite structures. The results demonstrate that the sensitivity and durability of the embedded FBG sensors fabricated by conventional writing techniques at 830 nm range and monitored using inexpensive Si-based source and arrays were excellent for health monitoring of composite structures.

The research is aimed to investigate the mechanical behaviors of epoxy-based nanocomposites reinforced with spherical nanoparticles. Five different contents of silica nanoparticles – 5, 10, 15, 20, and 40 wt% – were introduced in the samples. Through a sol–gel technique, the silica particles with a diameter of 25 nm were exfoliated uniformly in the epoxy matrix. Experimental results obtained from tensile tests indicate that the modulus of nanocomposites increases with the increment of particulate inclusions, and the enhancing behavior is coincided with the model predictions obtained from the Mori–Tanaka micromechanical model. In addition, the fracture tests conducted on single-edge-notch bending specimens reveal that the inclusion of nanoparticles can effectively increase the fracture toughness of the nanocomposites. Furthermore, the extent of the enhancement is more appreciable in the brittle matrix system rather than in the ductile matrix system. Subsequently, by inserting the silica epoxy mixture into the unidirectional glass fiber through a vacuum hand lay-up process, the glass fiber/silica/epoxy composite samples were fabricated. Results depicted that the in-plane shear strength increases until the increment of particle loadings are up to 10 wt%. In addition, results obtained from the compression tests revealed that the glass/epoxy specimens with 20 wt% silica loading exhibit superior compressive strengths than those that do not contain any silica particles.

The purpose of the present study is to propose a strategy for identifying the mechanical characteristics of fibers and the damage in composite materials, based on an inverse method coupled with homogenization. It consists, in a general and systematic way, in coupling a homogenization procedure chosen by the user, with an appropriate numerical optimization algorithm. The method can be interpreted as a procedure for passage from macroscopic to mesoscopic scale. In this respect, it is shown that our method is capable of providing estimates of mesoscopic properties that are difficult to obtain experimentally. The proposed identification method is applied to examples of damaged and undamaged composites including those made of woven and unwoven natural fibers of Alfa and a polyester resin matrix. Identification results obtained by the proposed inverse method are compared to data taken from the literature to show its effectiveness.

An innovative methodology for the thermo-mechanical simulation of the laser transmission welding (LTW) process for thermoplastic components is presented. The work consists of two parts. In the first part, a finite element (FE) thermal model is developed, for the prediction of the transient spatial temperature history developing during the LTW process. Experimental measurements have been used for the calibration of the developed thermal model. Through this thermal model, a parametric study on the main welding parameters is performed, in order to investigate their effect on the maximum temperature. Using the parametric study results, the optimal combination of the welding parameters is derived taking into account the welding cost. In the second part, the optimized set is used in a model developed for the thermo-mechanical simulation of the LTW process and the calculation of the thermal stresses, strains, and distortions of the welded parts. The benefit of the proposed methodology is that it offers the capability of optimizing the LTW process, and also provides a reliable estimation of the developed temperature, as well as the thermal stress and strain fields reducing the experimental effort.

The hot deformation behavior of extruded Mg/nano-Al₂O₃ composite has been studied in the temperature and strain rate ranges of 300–500°C and 0.0003–10 s^-1. In the lower strain rate regime (<0.1 s^-1), the apparent activation energy evaluated is much higher than that for lattice self-diffusion. At higher strain rates, the behavior of the composite is similar to that of the matrix material and is controlled by grain boundary self diffusion. The prior particle boundaries in the composite, which are decorated by the nano-alumina particles, are stable and only kink under compression parallel to the extrusion direction.

Thermoplastic hydroxyl-terminated polyurethane (HTPU) elastomer in different proportions (1, 2, 3, 4, and 5 wt%) was incorporated into DGEBA-based epoxy resin and cured with triethylene tetramine. The several matrices involved were subjected to mechanical strength analysis, and among the combinations of blend matrices studied, the one that showed highest strength, namely, 1 wt% of HTPU in epoxy, was chosen to prepare composites. Mechanical properties of pure epoxy and HTPU-toughened epoxy composites filled with fly ash were studied with respect to varying weight fractions of fly ash loading. In this article, the mechanical properties studied are compression and impact. Fractographic studies of the toughened resin matrix and its composites have been carried out using scanning electron microscopy.

This article deals with the new development of a family of router milling tools for the high-performance milling of carbon fiber reinforced plastics. The new milling tools are shaped by multiple left-hand and right-hand helical edges, which form small pyramidal edges along the cutting length. Several substrates and coatings have been tested including AlTiN and the new naCO with nanocrystalline structure. After the analysis of tests and modifications on the tool prototypes, the final result is a series of routing endmills optimized for carbon fiber composites defining the influence of each of milling tool features on tool performance, which was not clearly established till date. The specific cutting forces, tool wear, and others aspects are discussed in detail.

Attempts have been made to encapsulate silica within poly(lactic acid) (PLA), prepared by nanoprecipitation and emulsification–diffusion methods, in order to modify their surface properties. We have shown that silica–PLA colloidal nanocomposites can be readily obtained through nanoprecipitation and emulsion–diffusion. The nanoprecipitation method coats a thin-nanolayer on the surface of the silica particles, as per transmission electron micrographs analysis. In the case of emulsion–diffusion method, the free PLA nanospheres were embedded around the silica particles. Both methods proved to be successful in coating or encapsulation of the inorganic surface through polymer precipitation.

The dynamic responses of a new kind of multi-structured knitted composite T-beam under transverse impact were investigated with a modified split Hopkinson pressure bar. The multi-structured knitted composite is composed of two knitted fabrics: biaxial warp-knitted fabric and weft double-faced interlock knitted fabric. The impact load–displacement curves were obtained to analyze the influences of impact velocity and flange height on the damage of the T-beam. A user-defined material behavior and critical damage area failure criterion were developed to calculate the impact damage evolution. The failure mechanisms of the T-beam with different flange height were discussed from the finite element results.

This study explores how substituting a new high molecular mass oligomeric poly(ethylene glycol) extended urethane dimethacrylate (UDMA) (PEG-U) for 2-hydroxyethyl methacrylate (HEMA) in photo-activated UDMA resins affects degree of vinyl conversion (DC), polymerization shrinkage (PS), stress development (PSSD) and biaxial flexure strength (BFS) of their amorphous calcium phosphate (ACP) composites. The composites were prepared from four types of resins (UDMA, PEG-U, UDMA/HEMA, and UDMA/PEG-U) and zirconia-hybridized ACP. Introducing PEG-U improved DC, while not adversely affecting PS, PSSD, and the BFS of composites. This improvement in DC is attributed to the long, more flexible structure between the vinyl groups of PEG-U and its higher molecular mass compared to poly(HEMA). The results imply that PEG-U has the potential to serve as an alternative to HEMA in dental and other biomedical applications.

A program of scaled tests on unnotched and open-hole tension and compression specimens is summarized. Quasi-isotropic IM7/8552 carbon-fiber epoxy specimens have been tested using two different scaling techniques: sub-laminate-level ([45/90/ - 45/0]_ns) and ply-level scaling ([45_n/90_n/ - 45_n/0_n]_s), independently varying the thickness and in-plane dimensions. Significant scaling effects are shown, with both strength and failure mechanisms changing with specimen size and the thickness scaling method having a particularly important effect. Failure mechanisms and scaling behavior are compared between tension and compression and models presented that predict the observed size effects from fundamental material parameters without any fitting factors.

This article discusses a simplified approach to analyze mechanical properties of randomly distributed short fiber composites. Mechanical properties of three different randomly oriented short fiber composites, cotton, nylon, and aluminium with vinylester resins, were experimentally investigated. The analytical results were compared with experimental results and a very good correlation was found. Further, the experimental results and the predictions showed that the strength of the composites is less than the strength of the matrix material, for all three composites tested.

Varying amounts of three different carbons (carbon black, synthetic graphite particles, and carbon nanotubes) are added to polypropylene and the resulting single filler composites are tested for viscosity. In addition, the effects of single fillers and combinations of different carbon fillers are studied via a factorial design. Each single filler and all the combinations of different fillers cause a statistically significant increase in composite viscosity. For synthetic graphite/polypropylene composites, the viscosity increase is due to a volume filling effect. Composites containing carbon black and/or carbon nanotubes show viscosity increases above those containing only synthetic graphite.

The propagation characteristics of Lamb waves activated and collected by an active piezoelectric sensor network in a carbon fibre (CF)/epoxy (EP) composite panel of five stiffeners were investigated. In particular, attenuation and dispersion of Lamb waves induced by reinforced stiffeners were evaluated, and angular dependence of propagating velocity of Lamb waves in the composite structure was studied. The interaction between Lamb wave modes and damage (a through-thickness hole) was subsequently examined. An inverse algorithm based on correlations between the digital damage fingerprints (DDFs) of wave signals in the benchmark and damaged structures was developed for damage identification. DDFs extracted from the captured wave signals were used to achieve efficient data compression for the calculation of correlation coefficients. Different combinations of actuator–sensor paths were used to estimate the location of damage. The results confirm that the proposed algorithm is able to identify damage in such a complex composite structure.

Clamps have recently gained interest due to possibility of their use in low-invasiveness operations. The work presents the mechanical tests made on connecting clamps manufactured from carbon fiber–epoxy resin composite (CF/Epoxy). The CF/Epoxy unidirectional composites were prepared with the use of different carbon fiber amount and their elasticity was analyzed. Mechanical characteristics of composite clamps was compared to typical metallic clamps. Stress relaxation tests were made on the composite clamps in simulated body fluid (SBF) at 37°C to determine their mechanical stability. It was shown that the mechanical strength of composite clamps is similar to that of metallic clamps, whereas their stiffness is comparable to bone tissue. The average variations of mechanical stability of the composite clamps kept in SBF under a constant strain were not significant at the end of 6 months aging.

A facile two-step melt extrusion processing method was used to prepare high performance thermoplastic starch (TPS)/urea modified montmorillonite (UMMT) nanocomposites in this work. X-ray diffraction (XRD) and transmission electron microscope (TEM) demonstrated that urea could destruct the multilayer and platelet structure of montmorillonite during the first melt extrusion processing, which was propitious to form intercalated or exfoliated nanocomposites in the second melt extrusion processing. UMMT, starch, and 30 wt% plasticizers (formamide and urea (1 : 2 wt%)) based on the starch could form partially exfoliated nanocomposites proved by XRD and TEM, respectively. Fourier transform infrared proved intense interactions existed in UMMT and TPS/UMMT nanocomposites. So high UMMT content could obviously increase the thermal stability and mechanical properties of nanocomposites, especially the tensile strength, Young’s modulus, and energy break could reach to 17.8 MPa, 210 MPa, and 760 J/m³, respectively. Finally, the increasing montmorillonite contents also decreased the water absorption and water vapor permeability of TPS material.

A methodology for analysing the degradation and collapse in postbuckling composite structures is proposed. One aspect of the methodology predicts the initiation of interlaminar damage using a strength criterion applied with a global-local analysis technique. A separate approach represents the growth of a pre-existing interlaminar damage region with user-defined multi-point constraints that are controlled based on the Virtual Crack Closure Technique. Another aspect of the approach is a degradation model for in-plane ply damage mechanisms of fiber fracture, matrix cracking, and fiber-matrix shear. The complete analysis methodology was compared to experimental results for two fuselage-representative composite panels tested to collapse. For both panels, the behavior and structural collapse were accurately captured, and the analysis methodology provided detailed information on the development and interaction of the various damage mechanisms.

This study aims to investigate the shear performance of partially precracked Reinforced Concrete (RC) T-beams bonded externally with bi-directional Carbon Fiber Reinforced Polymer (CFRP) discrete strips. A series of twelve RC T-beams are fabricated with internal transverse steel reinforcement and subjected to four-point and three-point bending systems. The external CFRP reinforcement strips are applied on the web and soffit of the beam with two-component epoxy system. The parameters investigated in the experimental program included (i) longitudinal tensile reinforcement ratio, (ii) shear span to effective depth ratio, (iii) spacing, and (iv) orientation of discrete CFRP strips. The experimental results show that the bi-directional CFRP discrete strip reinforcement significantly increases the shear capacity between 18 and 54% over the control beams. It is found that the test variables have significantly influenced the shear capacity of the CFRP strengthened beams. This study also validates the obtained experimental results with different existing theoretical models.

This article is concerned with the implementation of a coupled damage-elastic-plastic constitutive model for the matrix material of a 2D triaxial braided carbon fiber composite (2DTBC) subjected to compression loads. Damage in the matrix of 2DTBC is in the form of matrix microcracking which is observed in laboratory experiments of 2DTBC coupons subjected to cyclic loading. In the model, the matrix is treated as a continuously evolving solid governed by a coupled elastic-plastic damage theory which is modified from the classical elasto-plastic theory. With this description of the matrix, the response of 2DTBC to compression loading is studied through the adoption of a representative unit cell that consists of a progressively damaging matrix and elastic-plastic progressively damaging fiber tows. Results from the analysis are compared against a model without evolving damage and also against available experimental data to understand the significance of matrix damage and its influence on compression load bearing capability.

One major problem when using bonded fiber-reinforced plastic laminates to strengthen and upgrade existing structures is the high stresses in the adhesive layer, in the area close to the end of the laminate, which might govern the failure of the joint. One method that has been put forward as a means of reducing the stress concentration in this area, is to taper the end of the laminate. Although this method has been suggested by some design guidelines, no specific information is usually provided about the tapering type, required tapering length, and limitations associated with this method. A parametric study has been carried out to investigate the effect of tapering length and the material properties of joint constituents, i.e., stiffness of the laminate and adhesive, on stress distribution in adhesive joints using the finite element method. Two different configurations, including normal and reverse tapering, were considered. The results indicated that the effect of tapering on stress distribution is highly dependent on the stiffness of the laminate and the adhesive used in the joint. It was concluded that tapering is more effective in joints with softer laminates and stiffer adhesives. Reverse tapering was found to have more favorable effects on stress reduction in comparison to normal tapering.

A new approach for determining in-plane and out-of-plane stresses due to thermal and mechanical loading, in un-symmetric [0_n/90_m] cross-ply curved laminated strips is presented in this work. This approach can also be applicable to bi-modulus curved laminated strips. Predictions of curvatures, displacements, and stresses based on the superposition principle are carried out. In-plane stresses are calculated considering classical beam theory. In addition, out-of-plane stresses are predicted by using the Airy’s stress function in polar coordinates. The new approach satisfies the continuity conditions at the interface between 0° and 90° layers. Results show that in-plane and out-of-plane stresses are particularly sensitive to the thickness ratio and to geometric conditions. Finally, thermo-mechanical predictions have revealed that out-of-plane stresses are much lesser than in-plane stresses for initially flat laminates. For laminates with high imposed curvatures out-of-plane stresses are high, leading to delamination failure.

In this work, the role of SMC constituent components in controlling the moisture absorption of the final molded panels is discussed. A variety of polyester resins, low profile additives, and fillers were exposed to high humidity, defined as 90% relative humidity at 40°C, for extended hours. It was concluded that calcium carbonate, which is the most common filler for SMC, at a 0.12 wt% moisture absorption level, is the second lowest in moisture absorption. The comparison of the calculated and measured moisture absorption numbers indicated that rule of mixtures can be used to accurately predict the behavior of SMC based on the polymeric matrix. However, the polymeric matrix moisture uptake has to be measured experimentally and cannot be predicted using the mixing rule for its constituent ingredients due to the complexity of the interactions in the mixture. It was also identified that MgO, which is the most commonly used thickening agent, has a significant impact on moisture uptake of SMC. Based on the generated information, two low moisture absorbing SMC formulations were developed and their properties were measured.

A damage zone method based on 3D finite element analysis was proposed to predict the failure loads of single-lap bonded joints with dissimilar composite-aluminum materials. To simulate delamination failure, interply resin layers between any two adjacent orthotropic laminas of composite adherend were assumed with a thickness of one-tenth of a composite lamina. Geometrically nonlinear effects due to the large rotation of the single-lap joint were included in the analysis. Analysis also considered the material nonlinearity of the aluminum adherend due to the stress exceeding yield level. Based on the experimental observation that the failure modes of the specimens were dominated by delamination and debonding, the Ye-criterion was applied to account for the out-of-plane failure of composite adherend and the Von Mises strain criterion was applied for the adhesive layer. The failure indices were multiplied to the predicted damage zone as a weight factor and the calculated damage zones were divided by an area or volume considering the joint geometry. Predicted failure loads show deviation within 18% from experimental results for nine different bonding lengths or adherend thicknesses.

PVC/nano CaCO₃ composites were prepared on Brabender Plasticorder. For comparison purposes, commercial CaCO₃ composites were also prepared. Characterization of the nano CaCO₃ and nanocomposites were done using scanning electron microscope (SEM) and transmission electron microscope (TEM). Their mechanical and thermal properties were also studied. Exfoliation was observed with the addition of different sizes of nano CaCO₃ filled in PVC composites. Best properties were observed with 9 nm CaCO₃ PVC composites. Tensile strength and modulus improved significantly even though the amount of addition of nano filler is low. Thermal properties of PVC/nanocomposites were found to be better compared to that of commercial filled CaCO₃ in PVC composites.

Stepwise-graded composite layer of M2 tool steel and 17-4PH stainless steel was fabricated by a simple powder layering technique and the isothermal and nonisothermal sintering response of the bilayer were examined. It was shown that the materials exhibit poor compatibility during co-sintering, i.e., the amount of mismatch shrinkage is significant. An improved compatibility was obtained by adding 0.2 wt% B to the stainless steel powder. Formation of relatively dense layer at the bonding zone indicated an enhanced densification rate at the interface. Microstructural studies showed formation of a ferritic interface in M2/17-4PH composite and elongated grains with an intergranular boride phase and martensitic matrix at the bonding zone of M2/17-4PH + B. Increasing the sintering temperature broadened the interface width along with formation of more ferrite and coarser grains at the interface. Mechanical tests indicated higher shear strength and hardness of the interface zone in the composite compared with the individual layers.

The objective of this research was to develop environment-friendly Hwangtoh binder for application of Hwangtoh for interior wall finishing materials in the housing. To mix with Hwangtoh powder, water soluble melamine-polyurethane copolymer (MPU) resin with ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), CaCO₃, and inorganic fillers were designed. Far infrared ray irradiation, total VOC (TVOC) emission behavior, surface bonding strength, and surface crack behavior were studied by comparing to epoxy/Hwangtoh blend as control. For TVOC emission behavior, the 20 L small chamber method was used and the results satisfied the requirements of the excellent grade of TVOC of Korea Air Clean Association. To utilize the advantage of Hwangtoh, such as high absorbency, self-purification, deodorizing, sanitizing properties, and radiation of far infrared rays in the field of modern housing, this study was the foundation to develop environment-friendly binders for Hwangtoh.

In order to improve the in situ oxidation kinetic condition of Al in copper matrix, Cr, instead of Al was in situ oxidized to form Cu/Cr₂O₃ composites in the present investigation, Cu–Cr powders with different solubilities after mechanical activation were utilized to synthesize Cu/Cr₂O₃ composites, and their microstructure and stability were analyzed. The results show that although the Cu–Cr powders suffer from the same mechanical activation, Cr₂O₃ particles formed by the powders with different solubilities have great differences in size, amount, and distribution. In the range of experiments conducted, the Cu/Cr₂O₃ composite formed by Cu–Cr powders with 67% solution has large amounts of finer Cr₂O₃ particles uniformly distributed in the copper matrix and exhibited the best stability at elevated temperatures.

Adhesion and loading bearing properties of polyurethane (PU) foams and sandwich composite with metallic inserts are studied. Metal or solid polymer anchors are used as the load transfer components for PU foam and sandwich composites when they are used as the structural element in design. The traditional method of fixation of these components in foams is gluing and fastening. In this work, the anchors are in the form of inserts and are imbedded in the PU during the foaming process. Flexural testing was conducted on PU with and without metallic inserts to establish typical interaction trends. The load-deflection response, mode of failure, and fracture stresses of the PU structures are elucidated. Results show that long taper and leaf inserts imbedded in foam and sandwich composite provide better load carrying capacity. Comparisons between the taper and leaf inserts are documented. Leaf inserts inside a foam and sandwich composite show better results as compared to taper inserts in terms of adhesion and failure stresses. A linear elastic fracture model is also developed for the foam beam, and the fracture toughness is calculated. FEA analyses of the interaction between the inserts and the PU and sandwich composites under different loads were carried out. The FEA modeling results coincide with the experimental ones, hence validating the model.

The focus of this experimental investigation is the sizing-test fluid interaction reported to result in variable flow behavior in and permeability values for porous media. The flow behavior is studied for Vacuum Assisted Resin Transfer Molding (VARTM). Three types of sizing and three test fluids were chosen for the experiments. Two carbon stitch and two glass stitch bonded fabrics of different tow sizes were used for flow characterization. The present study uses two fluids with the same viscosity for each fabric to determine fluid-sizing interaction. The results show that the permeability values are the same with the fluids of same viscosity. The saturated flow behavior due to the heterogeneous nature of the media is different from the one observed in RTM processes. For VARTM processes the dual scale flow characteristics is not observed for a variety of tow sizes.

The compressive response of an alumina-filled epoxy composite material was characterized at various strain rates using a Kolsky bar and universal testing frame (MTS). In the Kolsky-bar experiments, dynamic stress equilibrium and constant strain-rate deformation in specimens were achieved using pulse-shaping techniques. The effects of specimen aspect ratio and interfacial friction on the dynamic response of the material were examined. Compressive stress–strain curves for the composite were obtained at strain rates ranging from 9.4 x 10^-4 to 1.35 x 10³ s^-1 which exhibited strong strain-rate sensitivity. A material response model, which agrees well with the experimental measurements for the strain rates examined in this study, is also described.

Dry oxidizing methods have been widely used to modify surface properties of polymer and ceramic substrates. Compared to other dry oxidizing methods, ultraviolet light/ozone (UV/O₃) treatment has hitherto attracted less attention, mainly due to relatively weak oxidizing power. With optimized processing conditions, however, UV/O₃ treatment can be better capable of offering desired effects associated with appropriate surface modifications. Incorporation of nanoscale reinforcements, e.g., carbon nanotubes (CNTs) and graphite, into a polymer matrix creates a new class of composites that possess unique mechanical and functional capabilities. A proper surface treatment is critical to dispersing the reinforcements in the matrix, hence to provide adequate adhesion between the reinforcements and the matrix. In this article, a review is provided on the underlying mechanisms of and the advantages arising from UV/O₃ treatment of polymer substrates and nanoscale carbon materials. Special focus is placed on the relationship between the changes in chemical composition, morphology, functional groups of the treated surface and the corresponding improvements in adhesion and wettability of the substrate, dispersion of nano-reinforcements, as well as the properties of the nanocomposites made therefrom.

Tests on stable unbonded (SU) square carbon fiber-reinforced elastomeric isolator (FREI) bearings were conducted to investigate their lateral and vertical response. The bearings are intended for seismic isolation of low-rise buildings including those of ordinary importance. To simulate the in-place application of SU-FREI bearings, the contact surfaces of the bearings were not bonded to the platens of the test machine. This unbonded application permitted stable rollover deformation to occur which enhances the bearing’s isolation efficiency. The bearings were shown to safely sustain large lateral displacements. When subjected to large lateral displacements, their originally vertical faces completely contacted the horizontal surfaces of the upper and lower platens, which created a stiffening response and ensured the stability of these very large displacements. The sensitivity of SU-FREI bearings to lateral displacement history and vertical pressure applied on the bearings were investigated. Regarding the latter parameter, it was found that the effect of variations in vertical pressure on the lateral response can be neglected when the SU-FREI bearings are subjected to relatively light vertical pressures such as considered for low-rise buildings.

The article presents an analysis of the damping of sandwich composites, made of PVC foam cores and laminated skins. Damping parameters are investigated using beam test specimens and an impulse technique. Damping modeling is developed using a finite element analysis which evaluated the different energies dissipated in the material directions of the core and the layers of the skins. The results obtained show that this analysis describes fairly well the experimental results. Next, finite element analysis is applied to investigate the influence of different parameters of the core and skins. The finite element analysis considered can be applied to complex shape structures.

This work was initiated to explore the possibility of preparing porous scaffold, using microwave energy under vacuum technique. The hypothesis was that microwave energy under vacuum may promote effective cross-linking of the biopolymers during drying as well as to lead desirable physical characteristics of composites for hard tissue-like bone regeneration. Three different percentages of hydroxyapatite (HA) was reinforced with gelatin–starch polymer network to prepare porous scaffolds. EDS result of the prepared scaffold composite showed that Ca/P ratio of the HA phase was the same for all the HA percentages, 1.7, which is slightly higher than the standard value of 1.67. FTIR results showed the existence of a carbonate group along with the peaks of phosphate groups and hydroxyls, the functional group of HA. The scaffold composite obtained by microwave energy under vacuum technique had good mechanical and structural properties, which showed a promising potential for bone-substitution applications.

In this study, Al99–SiC composites were produced using PM method. In the composites produced, the reinforcement rates of SiC were 0, 5, 10, and 20 (%wt). The matrix Al 99 powders were mechanically mixed with SiC particulates. These powders were compacted at room temperature at 500 MPa for 5 x 10 x 60 mm specimens and followed by sintering at 600 and 620°C for 1 h. Composite specimens were joined by CO₂ laser welding method. Rofin–Sinar SM2000 machine was used for the welding process. The microstructure of melted region was investigated by optical, scanning, and X-ray microchemical analysis techniques. The hardness test, tensile test, and three-point bend test results were presented. The effect to CO₂ laser welding method at different reinforcement rates and different sintering temperatures in Al 99 powder was investigated. Because of the lower thermal conductivity of Al99–SiC composites, melting zone is wide. It was observed that 0.5 m/min laser welding velocity was suitable for composites with low SiC rate (0% and 5% SiC), and with increasing SiC (10 and 20%), laser welding velocity of 0.3 m/min was suitable.

Lattice Boltzmann method is used to simulate numerically the fiber suspension flow through a parallel plate channel containing a cylinder in the dilute and concentrated regimes (nL² = 0.125 and 2.0, here n and L are the number density and the length of fiber, respectively). The numerical results of fiber orientation distribution based on a statistical scheme are obtained and consistent qualitatively with the experimental ones. The results showed that the cylinder in the channel results in a change in the fiber orientation distribution downstream of the cylinder along the flow and transverse directions. The influences of the cylinder on the fiber orientation distribution are more significant for the concentrated suspensions than the dilute ones. The initial fiber orientations at inlet have significant and small effects on the fiber orientation distribution upstream and downstream of the cylinder, respectively.

Flexible matrix composites (FMCs), consisting of high-elongation, low modulus elastomers reinforced with high-stiffness continuous fibers, offer a high degree of elastic tailorability not found in typical structural polymer matrix composites. In the current investigation, the frequency- and time-dependent anisotropic viscoelastic behavior of an FMC material is characterized at the lamina level using a fractional derivative approach. The viscoelastic lamina properties are input to an elasticity model to predict the viscoelastic properties of filament-wound, angle-ply FMC driveshafts. The model is validated with experiments carried out using shafts of various fiber angles under tensile and torsional loadings. A thermal and mechanical analysis of a spinning, misaligned shaft is then carried out to predict self-heating in the shaft. Comparisons of the self-heating behavior with experiments indicate good agreement for several different shaft fiber angles. The models proposed in this investigation can be used to minimize the number of experiments that need to be done to predict the viscoelastic self-heating of FMC shafts as well as other types of composite shafts.

Polymeric nanocomposites consisting of the thermoplastic blend of PP and PA6 (70/30 by weight) and the varied amount of the TDI-functionalized TiO₂ nanoparticles varied from 0 to 7 phr as a compatilizer, were prepared via melt compounding method. The mechanical performances of the prepared nanocomposites are examined on injection-molded specimens in terms of the tensile and flexural tests. The results showed that the mechanical strength of the nanocomposites increases with the content of functionalized-TiO₂ and the best result is achieved when its content is 3 phr. However, for TiO₂ content to exceed 3 phr, the nanocomposites become increasingly brittle, as indicated by the decrease in both tensile and flexural strength. The enhanced mechanical strength may be attributed to improved compatibilization of PA6 in PP matrix by virtue of functionalized-TiO₂. This conclusion is strongly supported by the evidence from the SEM photographs of the fracture of the nanocomposites, where the better dispersion of the PA6 phase in the PP can be clearly observed. In addition, the dispersion of TiO₂ in the nanocomposites was also investigated using a TEM. The result of TEM suggests that the functionalized-TiO₂ was well dispersed in the nanocomposites in a nanoscale, because the –NCO groups located at the surface of the TiO₂ can chemically associate with PA6, thus improving the compatibility between the TiO₂ and the PA6.

Thermogravimetric and dynamic mechanical behavior of extruded and injection molded polypropylene (PP) samples with additives and varying volume fractions (0, 4.5, 14, 21, and 39 vol%) of soft magnetic iron silicon (FeSi) particles with a mean particle diameter of 58 µm were analyzed. With increasing filler volume fraction, thermogravimetry shows enhanced thermal stability of PP. Dynamic mechanical analysis (DMA) was performed at temperatures between 200 and 400 K at discrete vibrating frequencies between 10^-1 and 10¹ Hz. Loss factor tan of all examined materials shows typical peaks (, ' and β) of phase transitions in the crystalline and amorphous polymer structure of PP in this temperature range. Storage modulus E' at 200 K starts at 2283 MPa for PP with additives (stabilizers, antioxidants, lubricants, desactivators, and surface activators) and increases up to 7175 MPa for 39 vol% iron silicon fraction. The activation energy at –peak reduces with increasing filler volume fractions.

The effect of ZrSiO₄ (zircon) content on friction performance and friction surfaces of semimetallic brake friction materials is discussed. The experimental results indicate that the varying content of zircon affects the friction performance as well as plays crucial role in the iron film formation on the friction surfaces. The friction layers, formed during friction process, were carefully characterized using scanning electron microscopy with energy dispersive X-ray microanalysis, and X-ray diffraction methods. The phenomenon of two different types of iron film formation (film I and film II) on the friction surfaces is proposed and their formation and destruction mechanism is described. Despite the compositions of both iron films being similar, film I is formed by steel wool itself and film II by the debris from either disc or steel wool. The relationships among formulation, friction performance, and friction surfaces are summarized.

In order to predict the long-term durability of polymer matrix composite materials submitted to humid environments, the moisture diffusion behavior has to be investigated. The knowledge of the effective diffusivity is actually required, for estimating the moisture content of polymer-based fiber-reinforced materials, even when a basic behavior such as Fick's law is assumed to occur. The original contribution of the present work is to provide new analytical solutions for the effective diffusivities from the solving of unit cell problems on representative volume elements by means of several multi-scale approaches. Composite materials with impermeable or permeable fibers are extensively investigated. The proposed approaches are extended to the practical case of composite materials containing realistic voids volume fractions.

This study evaluated influence of press temperature and press time on scratch and abrasion resistance of particle board panels overlaid by melamine resin impregnated paper. Three-layer experimental particleboard panels were made from mixed particles of beech (Fagus orientalis Lipsky.), poplar (Populus tremula L.), and Scotch pine (Pinus sylvestris L.) with an average density of 0.75 g/cm³. Panels were overlaid by melamine impregnated papers using temperature levels of 170, 185, and 205°C and press times ranging from 18 to 46 s. Both scratch and abrasion resistance of the specimens were determined employing two different apparatus. Based on the findings of work both properties of the samples increased with increasing press time for each press temperature level. It appears that increasing press temperature from 185°C to 205°C did not make any significant difference on scratch and abrasion resistance of the panels that were pressed using various press times at 95% confidence level. It was found that 170°C press temperature and 46 s press time resulted in the best characteristics of overlaid samples. It was also determined that effect of melamine resin pick-up ranging from 30% to 60% was an important parameter on both properties of the samples mentioned above.

The polyamides have replaced many traditional metallic materials due to excellent property profile. Even though polyamides are produced as near net shapes, machining has to be performed in the final stage of production. In this article, an attempt was been made to study the effects of cutting speed and feed rate on machining force, cutting power, and specific cutting pressure during turning of PA6 and PA66 GF30 polyamides with K10 carbide tool. The response surface methodology (RSM) based parametric analysis reveals that machining force and cutting power increase with cutting conditions, while specific cutting pressure decreases with increase in feed rate.

Full field warpage profiles of the co-cured composite T section structure are measured using the digital speckle correlation method. Both the measurement principle and the optical calibration method are introduced in detail. The shape profile from the side view and the underneath view of the composite T structure are measured, respectively. Finally, the whole warpages of the T section are obtained using image linking technology. These results will play an important role in designing and manufacturing of composite T section structures.

This article is a summary of computational research conducted to assess the relationship between fold-crack resistance and bending stiffness in coated papers. Though this article is based on theoretical research, an experimental pilot coating program was undertaken in conjunction with the modeling. The objective of the computational work was to suggest ways in which coated paper could be optimized to maximize fold-crack resistance as well as bending stiffness, both of which are inversely related. Models were developed to calculate the bending stiffness, to predict the onset of failure, and based on this prediction, to calculate the residual load-carrying capacity of coated paper composites. Optimization of the coated paper composite was taken as a function of the number of coating layers used, the individual layer thickness, and the mechanical properties of the coating layers during both tension and compression. Simulations were conducted for single-, double-, and triple-coated papers keeping the properties and dimensions of the base paper substrate constant throughout. But the elastic moduli of the coatings were varied independently, though failure stress values were kept constant in order to vary the strain to failure stress and stiffness simultaneously. The optimal coating lay-up as per the hypothesis was a triple coating comprising of a thin, stiff inner coating layer; a thick, low-stiffness middle coating; and a thin, low-stiffness outer coating. The hypothesis was confirmed by the pilot coating trials.

In this study the feasibility of applying two kinds of mudar (Calotropis gigantea) fibers, namely bark fibers and seed fibers, as an alternative raw material for fiber-reinforced composite (FRC) is investigated. The chemical analysis of the bark and seed fibers indicates that their main components are holocellulose 76 and 69%, cellulose 57 and 49%, lignin 18 and 23%, and alkali soluble substances 17 and 15%, respectively. There are statistically significant differences in the bark and seed fiber dimensions. The bark fibers are long, with a thin wall relative to their diameter, and are therefore lightweight. The seed and bark fibers are very similar to hard- and soft-woods, in terms of chemical compositions and fiber dimensions, respectively. The mechanical properties of the mudar bark fibers are: tensile strength 381 MPa, strain at break 2.1% and Young's modulus 9.7 GPa. In general, both types of fibers have enough potential for replacing or supplementing other fibrous raw materials as reinforcing agent.

Different wood species can be expected to affect the properties of wood–polymer composites (WPCs) differently, as they have different chemical compositions. The chemical composition (cellulose, lignin, hot water, and ethanol/cyclohexane extractive contents) of acacia, eucalyptus, pine, and oak and the morphological properties such as wood fiber length distribution were determined in order to investigate this effect. Composites of linear low-density polyethylene and 10 wt% of each of the wood species were prepared, using polyvinyl alcoholco-ethylene as a compatibilizer. Significant differences were found between the wood species in terms of both chemical composition and wood fiber length distribution. These affected the properties of the WPCs in different ways. Use of acacia resulted in a WPC with superior mechanical properties and thermal stability compared with the other species, due to its higher cellulose and lignin contents and a favorable wood fiber length distribution; however, acacia composites also showed a higher water absorption rate due to the higher cellulose content. We also found that WPCs containing wood species with a high lignin and extractive content, such as acacia and oak, had a higher resistance to UV degradation.

The efficiency of growth of nanocrystalline magnesium oxide–germanium dioxide nanocomposite powders at room temperature was investigated in the presence of the amino acids histidine, aspartic acid, and the biopolymer poly-l-lysine under varying conditions. It was observed that of the three, poly-l-lysine and histidine were more efficient and formed higher yields of the products. The growth of the nanocomposties was found to be pH-sensitive as indicated by zeta potential as well as TEM, and dynamic light scattering analyses. Furthermore, the nanocomposite powders were found to have significant antibacterial activity against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria.

Many previous studies had reported the improvement in the mechanical properties of vinyl ester resin reinforced with SLG. Among these material properties, fracture toughness and flexural properties are important material characteristics. This article investigates the relationship between these two sets of material properties in envirospheres (SLG)-reinforced phenolic composites. The material properties of the phenolic resin composites containing different percentage by weight of SLG are experimentally measured using the short bar method and the three-point test. The findings indicated that the PF/E-SPHERES (30%) constitute the best compromise with respect to cost, fracture toughness, and flexural strength. It is hoped that the discussion and results in this work would not only contribute towards the development of SLG-reinforced phenolic composites with better material properties, but also be useful for the investigations of fracture toughness and flexural strength in other composites.

Radial flow experiment is often used to measure the permeability of fibrous porous media by the composites processing community. However, very little work has been done to calibrate the radial flow set-up with media of known permeability. This article presents a new method for calibrating the permeability measuring set-ups based on radial flows. A reference medium in the form of two concentric annular slits is created for the radial flow mold whose permeability is estimated analytically and numerically. It is observed that the experimentally measured permeability deviates from the theoretical and numerical permeabilities with an increase in the flow rate for an injection setup using a gear pump as well as a piston-cylinder pump. The deviation can be attributed to two possible reasons: one is the leakage between the calibration device and mold plate surfaces because of a slight mold deformation at higher flow rates, the other one is the increase in the gap clearance of the reference medium because of the higher gap pressures at higher flow rates. No such deviation is observed while measuring the permeability of a fiber mat at different flow rates. Hence, the proposed reference medium can calibrate a conventional radial flow-based permeability measuring setups at low flow rates; the accuracy thus obtained can be extended to higher flow rates as well if permeability of a fiber mat can be shown to remain constant with the flow rate.

Advanced composites are hybridized by the integration of alumina nanoparticles into the matrix and onto the fabric surface. Alumina was pre-dispersed by sonication. Pre-processing of alumina was carried out by resin modification or fiber modification, prior to the consolidation into composite laminates. Alumina nano-particles were also functionalized by silane coupling agent tris-2-metoxyethoxy vinyl silane (T2MEVS). Vacuum assisted resin transfer molding (VARTM) was used to fabricate the composite panels for mechanical performance evaluation and characterization. Material property characterization for tensile, fatigue life and inter-laminar fracture toughness were determined for these hybrid composites and compared with the traditional fiber–matrix composite system as a baseline. Experimental characterization indicated that mode-I fracture toughness was significantly improved with the inclusion of alumina nanoparticles as well as by the functionalization of alumina nano-particles. However, the influences on the tensile behavior and tension/tension un-notched fatigue behavior in [0/90] configuration were not significant. In applications that involve only tension/tension fatigue loading, hybrid composites with nano-particulate inclusions can provide improved delamination failure characteristics without impacting the fatigue life and tensile behavior significantly.