COMPRESSION OF LAMINATED COMPOSITE BEAMS WITH INITIAL DAMAGE

Compression testing is conducted for specimens with well-documented in itial damage states obtained from three-point bend testing. Strengths and failure modes are determined for specimens with four quasi-isotrop ic stacking sequences and two thicknesses. Initial damage prior to com pression testing is divided into three classifications based on the ex tent and location of the damage. These are (1) specimens with short de laminations distributed evenly through the specimen thickness, (2) spe cimens 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 determin e the effects of the initial damage on the final compression strength and failure modes. It was found that specimens with short multiple del aminations 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 subla minate buckling. Individual sublaminate buckling was observed for long er, isolated delaminations near the surface of the laminate. Single de laminations far from the specimen surface had little effect on the fin al compression strength, with moderate strength reduction observed for specimens with localized surface ply damage.