Fatigue Crack Propagation in Surface Film-Bonded Materials Using Pure Copper and Commercial Grade Iron Films

Abstract

As model specimens of surface film-bonded materials with or without resin interlayer, pure copper or commercial grade iron films were bonded to the surface of steel base plates by epoxy resin bonding or by diffusion bonding. The film thickness was 100 and 50µm for the copper and 100µm for the iron, respectively. In the fatigue testing results using these specimens, very few slips were observed around the crack initiated relatively early during fatigue on the film bonded with epoxy resin, while many slips were observed during fatigue on the film bonded by diffusion. As for the fatigue life, the epoxy bonding layer restrains the fatigue crack propagation from the surface film to the inner base plate, thus increasing the fatigue crack propagation life of the film-bonded plates with epoxy resin. In this connection, both the compressive residual stress on the iron film and the smaller tensile residual stress on the thinner copper film increased the fatigue crack propagation life significantly as compared with the larger tensile residual stress on the thicker copper film. Finally, the effect of the epoxy bonding layer on the fatigue crack propagation rate of the surface film was discussed in terms of the measured crack opening displacement range at 250µm from behind the crack tip, Δ φ250.