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A New Test Method for Measuring the Longitudinal and Shear Moduli of Fiber Reinforced Composites

Farid Taheri

Department of Civil Engineering, Dalhousie University, P.O. Box 1000, Halifax, Nova Scotia, Canada B3J 2X4

A new test method for the simultaneous evaluation of the longitudinal and the shear moduli of fiber reinforced plastic composites (FRPC) is introduced. Under the proposed method, specimens with different span to depth ratios (Llh) are subjected to three-point bending. Therefore, we name the method the "Varying Span Method" (VSM). The method builds on the inherent low shear modulus characteristics of FRPC. This characteristic leads to a flexural modulus which is a function of LMh. Eliminating the effect of local deformation from the test results, the flexural modulus (beside the geometry of the specimen) is a function of the longitudinal and the through-the-thickness shear moduli. These moduli can be obtained from the results of at least two tests on specimens with different Llh. For this, two distinctly different theories are introduced. A special apparatus is used to eliminate the effect of local deformations. The factors that may affect the accuracy and efficiency of the results are investigated and discussed. The validity of the proposed method is demonstrated by theoretical and experimental evaluations. The moduli of graphite/epoxy and Kevlar/epoxy composites, as measured by VSM, are reported. The measured values were found to be in very good agreement with the values evaluated by other standard methods.

Key Words: composite materials • fiber reinforced plastics • testing method • tensile modulus • through-the-thickness shear modulus • shear modulus • varying span method

Journal of Composite Materials, Vol. 33, No. 23, 2134-2160 (1999)
DOI: 10.1177/002199839903302301


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