Mode ‡U Fatigue Crack Growth Characteristics and Experimental Evaluation of the Crack Driving Force
Hideo NISHIZAWA and Takeshi OGAWA
Abstract:Mode II fatigue crack growth has been investigated for a high strength bearing steel, SUJ2, using a specially prepared fixture developed by Fujii et al. The fixture could apply large T-stress, I.e. compressive stress component parallel to the crack surface, which enabled us to grow the fatigue crack to the pure mode II direction. Detailed experiments for mode II as well as conventional mode I fatigue crack growth were performed, and the characteristics were compared. In order to investigate the net characteristics of mode II fatigue crack growth, deformation fields near the crack tip were measured under mode II loading by ESPI (Electronic Speckle Pattern Interferometry) method and used to derive effective stress intensity factor range using nonlinear least-squires based on Newton-Raphson method. The results revealed that the mutual contact of the crack surfaces reduced the crack driving force and the crack growth rate simultaneously. The mode II fatigue crack growth rate exhibited remarkable scatter due to the crack surface contacts at the deflected path of the mode II fatigue cracks. Key Words:Fatigue crack growth, Mode II, Effective stress intensity factor range, ESPI method, Deformation field