Critical strains in layered composites with interfacial defects loaded in uniaxial or biaxial compression

Critical strains in heterogeneous materials with cleavage type delamination s ('defects with connected edges') loaded in compression have been estimate d. The upper and lower bounds were determined for critical strains for lami nated materials in compression along such interlaminar defects, using the r esults for perfectly bonded and sliding layers. Substantiation of the bound s was based on the general principle of mechanics, which states that the re lease from a part of the connections inside the mechanical system cannot in crease the value of the critical load. The method is illustrated by numeric al results. The influence of critical strains on the shear and extension mo des of stability loss was determined as a function of layer properties. Num erical results for composites undergoing uniaxial or biaxial compression sh ow that the derived strain bounds are a reasonable estimation for certain f ibre volume fractions and mechanical properties.