The Effect of Stress Concentration on the Reliability of Composite Materials

A model is presented for predicting reliability of brittle composite structures with complex multiaxial stress states. This model allows all of the stress components to con tribute to the probability of material fracture. The model is applied to an off-axis geometry and to a center through-hole off-axis geometry using several different material systems. Results for the off-axis geometry demonstrate the importance of using the correct specimen configuration when performing a reliability analysis. Stresses induced by the end-constraint may cause an over prediction of reliability or an underutilization of material strength, depending on the overall stiffness and strength characteristics of the material. Results for the center-notched off-axis geometry demonstrate the effect of strength variability on the localization of fracture prob ability. Low variability materials exhibit a localization of high probability of failure regions, implying a high repeatability of fracture initiation site. High variability materials exhibit a smoothing of the high failure probability regions, which denotes less sensitivity to the stress concentration. Regions which contribute heavily to a loss in structure reliability may be identified before testing, so that a redesign may be effected.