A mesomechanical analysis of plastic strain and fracture localization in a material with a bilayer coating

The deformation and fracture of a coated material with an interlayer is investigated. A dynamic boundary-value problem in a plane strain formulation is solved numerically by the finite-difference method. The mechanical responses of a steel substrate, interlayer material and iron-boride coating is simulated by means of an isotropic strain-hardening model and a fracture criterion taking into account crack initiation and growth in regions experiencing tensile stresses. Numerical experiments on tension and compression of two- and three-phase microstructures were conducted. The average mechanical properties of the interlayer material are considered. The coating-interlayer and interlayer-substrate interface geometries correspond to configurations found experimentally and are accounted for explicitly in the calculations. Local regions of bulk tension are shown to form near the interfaces even under simple uniaxial compression of coated materials, which controls the fracture mechanisms at the mesoscale level. The influence of the interlayer on macroscopic homogenized strength of coated materials and on localized plastic flow and cracking patterns is examined.