抄録
The authors have been carrying out a series of fatigue crack growth tests under two-step varying load conditions to reveal the fundamental characteristics of fatigue crack growth behavior under varying load conditions, and have established an empirical law governing the crack growth rate during the retardation period observed after the load change from high to low load amplitudes. This report describes the results of fatigue crack growth tests carried out on Al alloy CT specimen to investigate precisely the effects of pre-straining and aging treatment on the crack growth behavior during the retardation period under two-step varying load conditions. The results indicated that the crack growth rate under constant amplitude load conditions was not affected by the pre-straining and the aging treatment, but that the crack growth rate during the retardation period was remarkably influenced by these treatments. By taking the above mentioned crack growth behaviors into account, the analytical crack growth law to estimate the crack growth rate in the retardation period, derived empirically in our previous studies, was modified to be available for a wide range of material conditions. Furthermore, a reasonable crack growth model was also proposed.
