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An experimental study of dwell and normal cyclic fatigue behaviours was carried out using specimens from a Ti60 forging with a bimodal microstructure.Apparent decrease in the fatigue life was found under dwell fatigue condition as compared to that under normal cyclic condition.Strain produced in each cycle in dwell fatigued specimens was observed larger than that in its normal cyclic-fatigued counterparts.Interior crack initiation was found in most dwell fatigued specimens as compared to the subsurface crack initiation under normal cyclic fatigue condition.Flat and bright facets were found at crack initiation sites in both cases.The facet density is higher in dwell condition,which is consistent with the crystal orientation and Schmid factors analysis of a grains around secondary cracks using electron back-scattered diffraction(EBSD) methods.Dwell loading favours cleavage in a grains with their basal plane normals aligned no more than 15° to the loading axis,which may account for its lower fatigue life according to the present study.
An experimental study of dwell and normal cyclic fatigue behaviors was carried out using specimens from a Ti60 forging with a bimodal microstructure. Apparent decrease in the fatigue life was found under dwell fatigue condition as compared to that under normal cyclic condition. Strain produced in each cycle in dwell fatigued specimens was observed larger than that in its normal cyclic-fatigued counterparts. Interior crack initiation was found in most dwell fatigued specimens as compared to the subsurface crack initiation under normal cyclic fatigue conditions. Flat and bright facets were found at crack initiation sites in both cases. facet density is higher in dwell condition, which is consistent with the crystal orientation and Schmid factors analysis of a grains around secondary cracks using electron back-scattered diffraction (EBSD) methods. dwell loading favors cleavage in a grains with their basal plane normals aligned no more than 15 ° to the loading axis, which may account for its l ower fatigue life according to the present study.