Measuring interfacial fracture toughness with the blister test

The adhesion of thin films to substrates can be quantified using the blister test, which measures the crack extension force (G) required to propagate a crack along the film/substrate interface. We summarize the derivation of crack extension force for the blister test, and discuss how blister tests can be conducted by measuring only the pressure and volume of liquid injected into the test system. We describe a way to calculate the velocity of the interface crack front. Data from blister tests of acrylate films (14 mu m thick) on nitride substrates are analyzed. The critical crack extension forces (G(C)) measured were 25 - 34 J/m(2) for samples which had a commercial adhesion promoter at the interface, and 0.5 - 2.0 J/m(2) without the adhesion promoter. G(C) was observed to increase with the velocity of the interface crack, and the dependence appears to obey a power-law.