Fatigue Crack Propagation Behavior and Its Controlling Factor for Diffusion Bonding Interface (Noting Crack Tip Opening Displacement Relating to Interface Strength between Same Metals)
Koki ISHIDA, Tashiyuki TORII and Kenichi SHIMIZU
Abstract:It is necessary to separate two important factors of dissimilar materials and interface strength, in order to discuss fatigue crack propagation behavior along the interface of composite materials. As model specimens with different interface strength, a diffusion bonding between the same materials (SK7s) is expected to have different interface strength with different bonding temperature. In addition, a fatigue testing was conducted under a certain displacement constrained by base plate so that the fatigue crack propagation behavior could be observed stably even for the interface without sufficient strength. As a result, the fatigue crack showed almost continuous propagation along the interface bonded at higher temperature, but slow and then abrupt propagation behavior intermittently on the interface bonded at lower temperature even under smaller stress amplitude condition. This abrupt propagation was related closely to crack tip opening displacement increased gradually during fatigue, which was understood by a cohesive crack model relating to a decrease of cohesive force near the crack tip in terms of liner fracture mechanics. The increase of crack tip opening displacement due to stress cycling was discussed using a potential-energy model in connection with fatigue damage. Key Words:Diffusion bonding, Interface strength, Interface crack, Fatigue crack propagation, Crack tip opening displacement