Analysis of a wedge impression test for measuring the interface toughness between films/coatings and ductile substrates

The adhesion between thin elastic films/coatings and ductile substrates can be measured using a wedge test, wherein a long sharp edge is impressed through the film into the substrate. The resulting plastic deformation causes delamination between the film and the substrate. The extent of the delamination can be correlated with the crack driving force to determine the toughness of the interface. Results are presented that relate the energy release rate and mode-mixity to the stresses: both residual and those induced by the impression. Numerical and asymptotic results are presented for the strain transferred to the coating. The numerical results verify that the asymptotics provide accurate closed-form solutions when the delaminations exceed about seven contact widths. An example is provided for a thermal barrier coating system.