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

A modified losipescu 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 losipescu shear test have been investigated. (C) 2003 Elsevier Ltd. All rights reserved.