THE BLISTER TEST FOR INTERFACE TOUGHNESS MEASUREMENT

The blister test for the measurement of interface fracture toughness for a thin film bonded to an elastic substrate has been analyzed. The load applied in order to debond the film is either hydrostatic pressure or a point load. Results for the energy release rate and mixity of modes 1 and 2 for the interface crack are presented for cases where the debond has been initiated and extends several film thicknesses. Analytical results are given in the two extremes of very small film deflections (weak interfaces) and very large film deflections (tough interfaces). Numerical results are presented in the intermediate zone based on the non-linear von Karman equations. Arbitrary and independent values of the elastic constants of the film and the substrate are allowed in the analysis. These basic crack tip quantities, energy release rate and mode mixity, may be used in a proper fracture criterion which incorporates the strong dependence of mode mixity for interface cracks.