Macro pattern of fatigue-broken surface of inclined surface cracks under biaxial loading

Abstract The fatigue test scheme and some results for 16MnR steel under the conditions that the biaxial loading ratio is equal to 0, 0·5 and 1, and the angle of crack inclination is equal to 0, 30, and 45°, respectively, are reported, with emphasis on the variations in the macro patterns of fatigue-broken surfaces of the surface cracks. This macro pattern may be classified into two categories: in the first category the fatigue-broken surface is smooth and flat, and in the second category it is discontinuous and curved. The present research work suggests that the discontinuity of the fatigue-broken surface of the surface crack is mainly caused by the mutual action by mode I and mode III crack driving forces. The variation rule for the mode I and mode III normalized stress intensity factors (SIFs) with the angle of crack inclination and with the biaxial loading ratio is presented. Based on the variation rule of the mode I and mode III normalized SIFs, the variation features of the macro patterns of the fatigue-broken surfaces of inclined surface cracks with the biaxial loading ratio and with the angle of crack inclination can be explained and predicted.