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

Critical strains in heterogeneous materials with cleavage type delaminations ('defects with connected edges') loaded in compression have been estimated. The upper and lower bounds were determined for critical strains for laminated materials in compression along such interlaminar defects, using the results for perfectly bonded and sliding layers. Substantiation of the bounds was based on the general principle of mechanics, which states that the release from a part of the connections inside the mechanical system cannot increase the value of the critical load. The method is illustrated by numerical results. The influence of critical strains on the shear and extension modes of stability loss was determined as a function of layer properties. Numerical results for composites undergoing uniaxial or biaxial compression show that the derived strain bounds are a reasonable estimation for certain fibre volume fractions and mechanical properties. PRC/1679