Finite element modelling of the fracture behaviour of brittle coatings

During bending, the crack density in a brittle coating increases gradually with increasing load and can be monitored using the acoustic emission (AE) technique. It is also known that the formation of cracks in coatings results in stress relaxation around the crack which will also affect subsequent fracture behaviour. Up to now, the significance of stress relaxation due to cracking on subsequent acoustic emission behaviour has not been fully analysed. In this work, the AE response of a brittle coating is studied in terms of its fracture properties. A finite element model (FEM) of a brittle coating on an elastic substrate in four-point bending is presented. In the model, cracking is assumed to occur once the surface tensile stresses have exceeded a certain critical value. Results from the FEM show good agreement with work done by others. The development of the FEM makes it possible to study the effect of various coating parameters in isolation which is difficult to achieve in an experimental study.