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Determination of residual strength in notched APC-2 cross-ply composite laminates at elevated temperature

The residual strength of notched AS-4/polyetheretherketone (PEEK) composite (APC-2) laminates with a central hole at elevated temperature was systematically investigated by both analytical and empirical methods. First, APC-2 cross-ply [0/90]4s panels were fabricated and cut into samples. A circular hole with one of five diameters was drilled in the center of each sample. The samples were subjected to quasi-static tensile tests at elevated temperatures to measure their mechanical properties – strength and longitudinal stiffness. Stress concentration and high temperature were found to remarkably affect the residual strength of composite. Point stress criterion (PSC) above was found to be unsatisfactory in predicting the residual strength. A modified PSC combined with the equation of thermal degradation was able to predict the characteristic length at elevated temperature. The residual strengths predicted by the extended modified PSC model were in very close agreement with the empirical data.