Damage index for crack initiation of structural steel under cyclic loading

A damage index for crack initiation (DICI) with damage accumulation effects considered was introduced in this study. Cyclic tension and compression tests of notched bars were used to verify the proposed DICI. The local cyclic elasto-plastic stress-strain responses, used to calculate DICI, were analyzed using the incremental plasticity procedures of ABAQUS finite element code for various strain amplitudes. Two crack initiation criteria with DICI used, single point criterion and characteristic length criterion, were employed to investigate the crack initiation behavior of the specimens. The single point criterion for crack initiation is met when DICI exceeds 1 at any point of the continuum. The characteristic length criterion for crack initiation is met when DICI exceeds 1 over a critical length equal to the characteristic length. It was found that the single point criterion is applicable to fatigue crack initiation and ductile crack initiation separately, while the characteristic length criterion is feasible to simulate fatigue crack initiation and ductile crack initiation simultaneously.