Original paper(Vol.49 No.5 pp.572)

Fracture Mechanics Analysis of Edge-Indentation Method for Evaluation of Delamination Strength of Coating

Dongkun Zhang, Masahiko Kato, Keijiro Nakasa

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 interracial 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-de1aminated interracial crack is pushed by the side of indenter, the critical value of interracial strain-energy release rate or the interfacial fracture toughness, 2g12, is expressed by the following equation :
2g12={1/8p2k2B1Ee1}{cos2q/tan2a}{P0/x}
where B1 is coating thickness, Eel is elastic constant of coating, q is a half of delamination angle, a is apex angle of indenter, P0 is indentation load at delamination, x is indentation distance from edge, and k is a constant. The interracial fracture toughness, 2g12, corresponds to the delamination energy, Ed, Which has been defined experimentally from indentation load vs. displacement curve in the previous paper.

Key Words:Delamination energy, Sprayed coating, Edge-indentation method, Elastic-plastic finite element method, Fracture mechanics analysis