Journal of Composite Materials current issue

Development, Dielectric, and Thermal Studies on HAF Carbon-filled Polyester Gradient Composites

Chand, N., Nigrawal, A. — Wed, 04 Nov 2009 09:16:38 PST

In this study, high abrasion furnace carbon having particle size 28—36 nm has been incorporated in unsaturated polyester resin to develop gradient composites. Dielectric measurements have been conducted on the graded composites by using a LCR meter. Effect of temperature and frequency variation on dielectric constant (^'), dielectric dissipation factor (tan ) and on a. c. conductivity (_a.c.) of the samples have been determined. Dielectric measurements have been performed in the temperature range from 30°C to 150°C and in the frequency range 1—10 kHz. Dielectric constant increases gradually with the increase of filler content in the direction of centrifugal force, which shows the existence of gradient structure in the composite. This is confirmed based on the microstructures observed at different positions in the graded composites. On increase of frequency, reduction in dielectric constant in carbon-filled polyester composites has been formed. Dielectric constant and a.c. conductivity increased with increase in temperature. ^' variation with temperature shows a plateau which shifts from 145°C to 125°C on increase of carbon content. Linear dependence of ln ₀ on E_a follows the compensation law for HAF carbon-filled polyester gradient composite, which is similar to semi conducting composite behavior. T_g obtained by DSC plots for samples 1—4 are higher as compared to polyester resin.

Wood Flour -- Recycled Polyol Based Polyurethane Lightweight Composites

Racz, I., Andersen, E., Aranguren, M. I., Marcovich, N. E. — Wed, 04 Nov 2009 09:16:38 PST

This work is focused on the production and characterization of lightweight polyurethane (PU) composites reinforced with pine wood flour (WF), which can have applications in car interior panels, construction, and acoustic insulation. A crosslinked PU formulated from a recycled polyol was used as matrix. The mechanical performance of the reinforced composites was studied through tensile, three point bending, and dynamic mechanical tests. The strength, modulus, and storage modulus increased with filler concentration.The addition of Al(OH)₃ did not reduce the flammability of the composites with low WF concentrations; however, some improvements were found in the case of composites prepared with 20 wt% WF.

Delamination Analysis in Drilling of CFRP Composites Using Response Surface Methodology

Krishnamoorthy, A., Boopathy, S. R., Palanikumar, K. — Wed, 04 Nov 2009 09:16:38 PST

Carbon fiber reinforced plastic (CFRP) composite materials are finding increased applications in many industries due to their excellent properties. Drilling of CFRP composites is needed for joining of these composite structures. During drilling, delamination is an important factor, which affects the property of the drilled hole. In this work experiments are conducted to analyze the delamination in drilling of CFRP composites. The cutting parameters considered are spindle speed, feed rate, and drill diameter. The tool material used for the present investigation is ‘‘BRAD and SPUR’’ type made of carbide. Second-order mathematical relation is established using response surface methodology for predicting delamination in drilling of CFRP composites. The results indicate that the model can be effectively used to predict the delamination in drilling of CFRP composites. The effect of different parameters in drilling of CFRP composites is analyzed and presented in detail.

Modeling VARTM Processes with Hybrid Media Incorporating Gravity Effects

Yoon, M.-K., Chen, H., Simacek, P., Heider, D., Gillespie, J. W. — Wed, 04 Nov 2009 09:16:38 PST

Vacuum-assisted resin transfer molding (VARTM) processes are increasingly used in manufacturing scale-up composite applications. Accordingly, gravity can significantly influence the flow behavior in tall-structure composite manufacturing processes. The present study developed a closed-form analytic solution incorporating gravity effects with the equivalent parameter approach in order to predict the resin flow behavior in a tall structure resin infusion. A hybrid model was used that consists of thin distribution media and a fibrous preform. An analytic solution was developed and validated with experiments as well as numerical methods in terms of the resin flow front shape, lag length, and the flow front location with time for the horizontal, upward, and downward infusion cases. The flow front locations were monitored using time domain reflectometry sensors embedded in the fabric layers. The lag length was constant in the horizontal infusion case, but decreased and increased in the upward and downward infusion cases, respectively, as resin progressed. The downward infusion case showed the fastest fill time, which corresponds to the previous results using a homogenous model. However, the flow became unstable at a certain location where the local flow front speeds increased suddenly along the distribution media. These phenomena were not observed in a model with homogenous media but were observed in a model with hybrid media, only in the downward infusion cases. The analytic solution also identified the stable flow conditions with the mold angles. The results obtained in the present study can be used to estimate stable process conditions in designing VARTM processes for manufacturing large-scale tall composite structures.

On the Sensitivity of the Nanostructural Parameters on Young's Modulus of PLSNs in Fully Intercalated Structures

Yazdi, A. Z., Bagheri, R., Kazeminezhad, M. — Wed, 04 Nov 2009 09:16:38 PST

Polymer-layered silicate nanocomposites have been observed to demonstrate enhanced mechanical properties particularly at low weight fractions of silicate. Experimental and theoretical investigations reveal that numerous structural parameters strongly influence the modulus of such nanocomposites. A multiscale micromechanical model is developed which considers a wide range of different affecting parameters including the particle aspect ratio, the number of silicate layers per stack, the d-spacing ratio between the layers, the penetration of polymer chains along silicate sheets, the intercalation feature, and the particle volume fraction. The developed model illustrates the accuracy and flexibility superiorly compared with the conventional models proposed in the literature. Moreover, good agreement is found between the experimental data and the modeling results.

Experimental Investigation of the Dynamic Response of a Symmetric Laminated Composite Beam Via Laser Vibrometry

Kiral, Z., Malgaca, L., Akdag, M., Kiral, B. G. — Wed, 04 Nov 2009 09:16:38 PST

This article reports the experimental analysis of free and forced vibrations of a cantilever symmetric laminated composite beam with different lay-up sequences. The free vibrations generated due to initial displacements are recorded by two laser displacement sensors. The damping ratios for different ply orientations are determined by using the ratios between the successive peaks in the free vibration responses and the corresponding envelope curves. The dynamic response of the beam to a moving load with constant velocity is also investigated. The pressured air is blown out onto the beam to create the load and the movement of the load is achieved by an industrial robot manipulator. The moving load mechanism is peculiar to this study. The free and moving load responses are also examined by the finite element method. A commercial finite element package ANSYS^® is used for numerical analyses. The results reported in this study show that the lay-up sequence has an important role on the dynamic response of the laminated composites and the velocity of the moving load affects the dynamic response considerably, especially for [90]_2s lay-up.

The Effects of Composite Plate Design Parameters on Linear Vibrations by Discrete Singular Convolution Method

Secgin, A., Atas, C., Sarigul, A. S. — Wed, 04 Nov 2009 09:16:38 PST

This study is devoted to some specific free vibration analysis of thin composite plates based on discrete singular convolution (DSC) approach. As the first analysis, a parametric study is performed on the basis of number of lamination, boundary condition, and orientation angle of symmetrically laminated composite plates. As the second, the effects of material type, boundary condition, and stacking sequence on the modal characteristics of laminated plates made of E-glass/epoxy, Kevlar/epoxy, and carbon/epoxy are investigated. Thirdly, linear modal characteristics of fiber metal laminates are specifically analyzed due to their common use in aircraft design. Hopefully, the results presented in the article may be practically of interest for engineers and designers. This study displays the applicability of the DSC method for real-life problems.

Compression Strength Degradation of Nanocomposites after Lightning Strike

Mall, S., Ouper, B.L., Fielding, J.C. — Wed, 04 Nov 2009 09:16:38 PST

This study investigated five conductive nanocomposites for their compressive strength degradation after subjecting them to a simulated lightning strike. These systems consisted of a ply of nickel-coated carbon woven fabric as lightning strike protection component besides the four plies of standard carbon fibers (AS4) fabric embedded in the epoxy (EPON 862). The other four systems had an additional protection system, which was nickel-nanostrand veil (NiNS), aligned buckypaper, random buckypaper, or mixed buckypaper made up of vapor-grown carbon fibers and single-walled nanotubes. All other buckypapers were made of single-walled nanotubes. Failure and damage mechanisms were also investigated. The ultimate compressive strength reduced by about 75—30% from a simulated lightning strike. This reduction as well as the damage was maximum with NiNS and minimum with random buckypaper. Damage from the lightning strike was related to the electrical conductivity and degradation in the compressive strength of the tested systems.

Expanded Waste Ground Rubber Tire Powder/Polypropylene Composites: Processing-Structure Relationships

Wed, 04 Nov 2009 09:16:38 PST

The usage of waste tire powder as dispersed phase in polypropylene matrix offers an interesting opportunity for recycling of the waste tire. In order to obtain ‘value added products’ from polypropylene (PP)/waste ground rubber tire powder (WGRT) composites, in this study, the processing of foamedPP/WGRT composites was investigated using a single-screw foam extrusion setup and chemical blowing agent. The regression models were constructed to study the relationships between the foam structure (i.e., void fraction, average cell size, and cell density) of foamed PP/WGRT composites, the processing conditions (extruder’s die temperature and screw speed), and the formulation compositions (WGRT content and blowing agent concentration) by applying a four-factor central composite design (CCD) statistical approach. The response surface plots generated using the regression models allow the rapid selection of the proper process parameters to obtain PP/WGRT composite foams with the desired density and morphology.