A COMPUTATIONAL MODEL FOR DAMAGE EVOLUTION IN CERAMIC COATINGS: EFFECT OF RANDOM MICROSTRUCTURE

A novel numerical model is proposed to investigate effects of microstructure on damage and fracture evolution in ceramic coatings under mechanical loading. Random microstructures of coatings are generated by the Monte Carlo method based on the Poisson distribution of the number of microdefects and stereological size-shape distribution of voids in plasma-sprayed ceramic coatings. The initial damage distribution and corresponding effective material properties linked to the microstructures and element dimensions are determined for all elements with the use of an analytical method. Processes of failure evolution at the microscopic level are introduced into mesoscopic considerations using the framework of a continuum damage mechanics (CDM). The approach is extended to non-uniaxial stress states to describe damage evolution in the porous coatings. Initiation and growth of local microcracks linked to local failures affect damage evolution due to changes in elastic anisotropy at the level of elements and subsequent modifications of stress and strain fields. Based on the proposed algorithm, the constitutive relationship for the coatings with damage is included in the finite element code NASTRAN as an additional material subroutine. Effects of porosity, voids attributes (size, shape and numbers) of the coatings on their loading behaviours are evaluated quantitatively and qualitatively in a three point bending simulation. The results indicate that system is capable of predicting anisotropic damage growth and crack initiation in ceramic coatings.