エッジインデンテーション皮膜はく離強度評価法の破壊力学的検討

抄録

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=1/8π²k²B₁E_e1cos²θ/tan²α(P₀/x)²
where B₁ is coating thickness, E_e1 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, E_d, which has been defined experimentally from indentation load vs. displacement curve in the previous paper.