Evaluating fatigue crack propagation properties using miniature specimens

Standard fatigue crack propagation (FCP) test placed strict requirement on specimen size. FCP rate in subsize specimen was found to be slightly but consistently slower than that in the standard specimens. Based on a critical study on two aluminum alloys and two steels, we found the lower rates can be attributed to the plane stress state in the miniature specimens being different from that in the standard specimens. By taking account of crack closure, the miniature specimen data are brought in line with the standard specimen results and may serve as an upper bound estimate of FCP properties.

► We tested miniature crack growth specimens of two Al alloys and two steels.
► Their FCP rates are often lower than that in the standard specimen.
► The discrepancy is associated with a difference in stress state.
► Miniature and standard specimen data fall in line if crack closure is considered.
► FCP rates versus ΔKeff, relation may serve as an upper bound for life prediction.