Reliable in-plane shear modulus for pultruded-fibre-reinforced polymer sections

Abstract

A simple test method to determine the in-plane shear properties of pultruded materials, where the mat reinforcement is of randomly oriented continuous fibres, is presented. Existing standard test methods have a number of weaknesses, but a number of them can be overcome by using the 10° off-axis tensile test method proposed by Chamis and Sinclair in 1976. Straight-sided specimens have unidirectional fibre reinforcement oriented at 10° to the direction of tensile load. Tension generates a biaxial in-plane stress state that, by employing stress and strain transformations, enables the shear modulus to be determined. The mean shear moduli of web material in four shapes, from 20 coupon tests in batches of five, were found to be consistent at 4·2–4·8 GPa. Given that 10° off-axis coupons are easy to prepare, with no technical difficulties, this non-standard method is recommended to characterise the in-plane shearing of pultruded materials having continuous-filament (or strand) mat reinforcement.