Abstract
A combined experimental and numerical study of the compression response and the failure characteristics of various quasi-isotropic coupons with a hole obtained from a [±45/90/0]s quasi-isotropic laminate was carried out. Specimens with various quasi-isotropic stacking sequences of [±45+ l=O//90 + l=O/l=O]s, were acquired by cutting the coupons at various angles k from the quasi-isotropic laminate. Analysis of the coupons based on 2-D and 3-D finite element models were performed to evaluate the stresses around the hole. Two different compressive failure prediction techniques based on distinctly different failure modes, namely fiber kinking and delamination, have been evaluated. The validity of these techniques was measured against experimental data of quasiisotropic coupons tested.
The failure of the laminated coupons with a hole has been shown to be sensitive to the stacking sequence. It is also shown that a 2-D finite element model does not provide the required stacking sequence sensitivity. Thus, a 3-D analysis of the stress state in the vicinity of the hole is necessary. The study shows that no one mode of failure is responsible for limiting the strength for all laminate off-axis orientations, but rather the failure mode changes with change in stacking sequence. The analysis also substantiates the experimental data presented, that the peak strength of the laminate is achieved for a stacking sequence of [32.5/-57.5/77.5/-12.5], which corresponds to an off-axis angle of 12.5 with respect to the loading direction.