A RANDOM CRITICAL-CORE THEORY OF MICRODAMAGE IN INTERPLY HYBRID COMPOSITES .1. 1ST FAILURE AND HYBRID EFFECT

This paper presents a statistical analysis for the tensile first failu re and hybrid effect (which is part of the synergistic effect) of unid irectional interply hybrid composites. A shear-lag model is applied to solve the stress redistributions after the breakage of low-elongation fibers. By applying the random critical core model, the probabilistic first failure strain of hybrids is evaluated first, and the hybrid ef fect for strains is consequently evaluated. Reduction of the stress co ncentration factor and ineffective length of the low-elongation fibers in hybrids and differences between microdamage mechanisms in hybrids and single fiber composites provide a theoretical explanation of the h ybrid effect. The present theoretical results show reasonable agreemen t with the existing experimental results.