Buckling of a Sublaminate in a Quasi-Isotropic Composite Laminate

Abstract

Buckling of a delaminated region can cause high interlaminar stresses which, in turn, lead to delamination growth. Hence, buckling strain is an important parameter in assessing the potential for strength loss due to the delamination. The objective of this study was to predict the buckling of an elliptic delamination embedded near the surface of a thick quasi-isotropic laminate. The thickness of the delaminated ply group (the sublaminate) was assumed to be small compared to the total laminate thickness. Finite- element and Rayleigh-Ritz methods were used for the analyses. The Rayleigh-Ritz method was found to be simple, inexpensive, and accurate, except for highly anisotropic delaminated regions. Effects of delamination shape and orientation, material anisotropy, and layup on buckling strains were examined. Results showed that (1) the stress state around the delaminated region is biaxial, which may lead to buckling when the laminate is loaded in tension, (2) buckling strains for multi-directional fiber sublaminates generally are bounded by those for the 0 deg and 90 deg unidirectional sublaminates, and (3) the direction of elongation of the sublaminate that has the lowest buckling strain correlates with the delamination growth direction.