Study on Strength and Nonlinear Stress-Strain Response of Plain Woven Glass Fiber Laminates under Biaxial Loading

Abstract

Strength and stress-strain properties are investigated for plain woven glass fiber laminates using thin tubular specimens under biaxial static and cyclic loadings. Some composites show large distortion and fiber reorientation close to failure under biaxial load ing. For such composites the usage of the 2nd Piola-Kirchhoff stress instead of the nominal stress is proposed for strength evaluation. The experimental result reveals that the Tsai-Wu criterion fits the biaxial strength expressed by the 2nd Piola-Kirchhoff stress much better than the strength expressed by the nominal stress. Strong interaction between axial and shear deformations is found beyond the knee/yield points while, within the elastic range no interaction is found between the axial and shear stiffness. Fiber misalignment with the loading axis affects the observed stress-strain behavior under cyclic loading. More than two S-S curves are distinguishable when the fiber misalignment is higher than 2°. Such stress-strain relations are successfully simulated using an incremental method in conjunc tion with updating fiber orientation. Good agreement between the calculated result and ex perimental one confirms that the proposed model which considers fiber misalignment can explain the observed stress-strain response under biaxial fatigue loading.