CRACK BRIDGING IN FUNCTIONALLY GRADED COATINGS

A crack bridging analysis is carried out to predict crack propagation in coatings made of functionally graded materials (FGM). The FGM coati ng is taken to be a ceramic/metal composite with its gradation charact erized by the local volume fractions of metal and ceramic phases. Frac ture in the FGM coating is resisted by the plastic deformation of meta l ligaments in the crack wake that bridge the crack; the crack bridgin g, however, is not uniform. A position-dependent crack bridging model is developed taking into account the coating gradation and metal plast icity. The model is subsequently used ina finite element analysis to p redict the reduced fracture driving force. It is found that crack brid ging in the FGM coating can significantly reduce the crack tip stress intensity. It is also found that coating gradation has a strong influe nce on the fracture driving force and the crack length at arrest. The present finite element model can be extended readily to study the effe ct of large-scale plastic deformation on-crack growth in a FGM coating . (C) 1997 Elsevier Science Ltd.