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

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 Poissonʹs 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 Youngʹs 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 Youngʹs 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.