COMPRESSION OF LAMINATED COMPOSITE BEAMS WITH INITIAL DAMAGE

Compression testing is conducted for specimens with well-documented initial damage states obtained from three-point bend testing. Strengths and failure modes are determined for specimens with four quasi-isotropic stacking sequences and two thicknesses. Initial damage prior to compression testing is divided into three classifications based on the extent and location of the damage. These are (1) specimens with short delaminations distributed evenly through the specimen thickness, (2) specimens with few long delaminations, and (3) specimens with local fiber damage in the surface plies under the three-point bend contact point. Specimens without initial damage are also tested in order to determine the effects of the initial damage on the final compression strength and failure modes. It was found that specimens with short multiple delaminations experienced the greatest reduction in compression strength compared to the undamaged specimens. All of the sublaminates formed by the delaminations failed at the same time with no indication of sublaminate buckling. Individual sublaminate buckling was observed for longer, isolated delaminations near the surface of the laminate. Single delaminations far from the specimen surface had little effect on the final compression strength, with moderate strength reduction observed for specimens with localized surface ply damage.