Fracture mechanics analysis of coating/substrate systems Part I: Analysis of tensile and bending experiments

A finite fracture mechanics model is used to predict the development of multiple cracks in the coating layer of coating/substrate systems. The stresses in a cracked coating are evaluated by a variational mechanics approach. These stresses are then used to calculate the total energy released due to the formation of a complete crack in the coating layer. The analysis can handle tensile loads or bending loads and includes the effect of residual thermal stresses. By assuming the next coating crack forms when the energy released due to the formation of a complete microcrack equals the in situ fracture toughness of coating, it is proposed that one can predict the number of coating cracks as a function of applied strain. Alternatively, it is proposed that experimental data for number of cracks vs. strain can be fit to the fracture analysis and be used to determine an in situ coating fracture toughness. (C) 2000 Elsevier Science Ltd. All rights reserved.