In-plane shear properties of cross-ply composite laminates with different off-axis angles

Abstract

A modified Iosipescu test fixture has been designed and manufactured to investigate the in-plane shear properties of cross-ply composite laminates with different off-axis angles. A cross-ply [0/90]2s glass fiber reinforced epoxy composite laminate was manufactured using the hand lay-up technique. This laminate was cut at different off-axis angles (0°, 15°, 30°, 45°, 60°, 75° and 90°) to give specimens with different stacking sequences ([0/90]2s, [15/-75]2s, [30/-60]2s, [45/-45]2s, [60/-30]2s, [75/-15]2s and [90/0]2s respectively). The tensile properties (strength, modulus and Poisson's ratio) of cross-ply laminate were determined experimentally. Shear modulus and the tensile elastic properties of cross-ply laminate with different off-axis angles were predicted theoretically from the elastic properties of the constituent materials. The results show that Young's modulus measured from the stress-strain diagram drawn using strain gauge readings in the tension test is more than six orders of magnitude higher than those determined from the stress-strain diagram of the testing machine. The predicted value of the Young's modulus of cross-ply specimen, [0/90]2s, has excellent agreement with the experimental results. The maximum in-plane shear strength is found for specimens with 45° and 60° off-axis angles, i.e. for [45/-45]2s and [60/-30]2s specimens respectively. On the other hand specimens with 0° and 90° off-axis angles have the minimum in-plane shear strength. The predicted values of in-plane shear modulus of cross-ply laminate with different off-axis angles (0-90°) agree very well with the experimental results. Failure modes of cross-ply specimens with different off-axis angles in Iosipescu shear test have been investigated. © 2003 Elsevier Ltd. All rights reserved.