Compressive fracture of layered hyperelastic materials with inter - And intralaminar defects

When a layered material is compressed along the layers, fracture due to interlaminar defects cannot be predicted using the classical Griffith-Irwin criterion or its generalisations, and therefore fracture due to mechanisms, specific to heterogeneous materials, needs to be considered. One of such mechanisms is internal instability, i.e. the loss of stability in the microstructure of the heterogeneous material. This paper investigates internal instability of layered hyperelastic materials with inter- and intralaminar defects undergoing large deformations under uniaxial or equi-biaxial loading. For interlaminar defects called "defects with connected edges", the upper and the lower bounds for the critical load are established. The bounds are based on the analytical solutions for 3-D internal instability problem, considered within the model of piecewise-homogeneous medium. It is suggested that the Equivalent Constraint Model could be used to account for the presence of intralaminar defects in the material. Numerical results for hyperelastic layered materials, with layers described by the neo-Hookean potentials, are presented and discussed. They indicate that the bounds give a good estimation for considered modes of internal instability and material properties.