Abstract
In order to discuss the delamination energy obtained by the edge-indentation method on a viewpoint of fracture mechanics, the crack initiation and propagation behavior were examined by the microscopic observation along interface under the indenter as well as the three dimensional finite-element stress analysis of the zone. The results show that the interfacial crack starts at a little distant position from the indentation center, and the triangular-shaped delamination of coating extends stably for a certain distance with increasing indentation load. When an apex of the triangular-shaped coating with partially delaminated interfacial crack is pushed by the side of indenter, the critical value of interfacial strain-energy release rate or the interfacial fracture toughness, 2γ12, is expressed by the following equation:
2γ12=1/8π2k2B1Ee1cos2θ/tan2α(P0/x)2
where B1 is coating thickness, Ee1 is elastic constant of coating, θ is a half of delamination angle, α is apex angle of indenter, P0 is indentation load at delamination, x is indentation distance from edge, and k is a constant. The interfacial fracture toughness, 2γ12, corresponds to the delamination energy, Ed, which has been defined experimentally from indentation load vs. displacement curve in the previous paper.
