Experimental investigation on cumulative damage indices for steel members under ultra-low-cycle loading

Notched bending specimens and axial load specimens were tested under different ultra-low cycle loadings to investigate the plastic deformation capacity and plastic energy capacity of steel members. A total of 53 experiments were performed in cyclic axial and bending configurations. The effect of notch shape, the order of mixed amplitudes, the average deformation of the amplitude, and the environmental temperature on plastic deformation capacity of steel members are studied. Four cumulative damage indices, including the ductility damage index, the normalized plastic energy damage index, the max-side ductility damage index, and the max-side normalized plastic energy damage index were compared for ductile fracture evaluation of these specimens under different ultra-low cycle loadings. The results indicated that the standard deviation of the normalized plastic energy damage index is the smallest among the four damage indices, which shows the lowest data dispersity. The max-side ductility damage index is larger than the ductility damage index, and the max-side normalized plastic energy damage index is larger than the normalized plastic energy damage index, both achieving a safety evaluation. Among the four damage indices, the max-side normalized plastic energy damage index achieves the maximum reliability. [Display omitted] •Notched specimens were tested to investigate the plastic deformation capacity and plastic energy capacity.•The effect of notch shape, order of mixed amplitudes and average deformation on plastic deformation capacity are studied.•Four cumulative damage indices were compared for ductile fracture evaluation of specimens under ultra-low cycle loadings.•Among the four damage indices, the max-side normalized plastic energy damage index achieves the maximum reliability.