STUDY OF FATIGUE-CRACK PROPAGATION BEHAVIOR OF FILM MATERIALS (FATIGUE TESTING METHOD AND FACTORS CONTROLLING FATIGUE-CRACK PROPAGATION RATES)

At present, materials with small dimensions such as thin films are oft en used in electronic packaging. This study concerns a film fatigue te sting method, which makes it possible to observe the fatigue crack pro pagation behavior on a film bonded to a through-hole in a base plate s ubjected to push-pull cyclic loads. An analytical model for this testi ng method is presented using a boundary element method, so that the fi lm fatigue fracture can be treated quantitatively in terms of fracture mechanics (K-values and J-integrals). The fatigue crack growth proper ties were examined for commercial-grade iron films with 100 mu m thick ness bonded to either a circular or an elliptical hole in the base pla te. As a result, using the stress intensity factor based on the measur ed crack opening displacement, Delta K-est, the fatigue crack propagat ion behavior of the film could be understood in terms of the effective stress intensity factor widely used in the bulk specimen, Delta K-eff .