Shear characterization of unidirectional composites with the off-axis tension test

Abstract

The influence of end constraints on accurate determination of the intralaminar shear modulusG 12 from an off-axis tension test is examined both analytically and experimentally. The Pagano-Halpin model is employed to illustrate that, when the effect of end constraints is properly considered, the exact expression forG 12 is obtained. When the effect of end constraints is neglected, expressions for the apparent shear modulusG 12 * and apparent Young's modulusE * are obtained. Numerical comparison for various off-axis configurations and aspect ratios is carried out using typical material properties for graphite/polyimide unidirectional composites. It is demonstrated that the end-constraint effect influences accurate determination ofG 12 more adversely than it affects the laminate Young's modulusE xx in the low off-axis range. Experimental results obtained from off-axis tests on unidirectional Gr/Pi specimens confirm the above. Based on the presented analytical and experimental evidence, the 45-deg off-axis coupon is proposed for the determination of the intralaminar shear modulusG 12.