Abstract
Fatigue crack growth behavior under varying amplitude load conditions can not be estimated presisely from the fatigue crack growth data under constant amplitude load conditions, even when discussed from the view point of the effective stress intensity factor, because it depends upon other factors such as crack tip blunting. Hitherto, crack growth under repeated block load (i.e., two-step) conditions has been ordinarily discussed microscopically, and on the other hand, those after single and multiple peak overloads have been discussed macroscopically. It is preferable to relate the above two approaching methods with each other in order to evaluate the crack growth behavior under varying load conditions systematically.
In order to clarify the transient phenomena of fatigue crack growth behaviors under two-step varying load conditions, a series of fatigue crack growth tests were carried out on aluminum alloy (A2017-T3) CT specimens. An analytical crack growth law during the transient period was established through the empirical simulation between crack growth length and stress cycles in this period. The procedure presented in this study is useful to predict fatigue crack growth under other types of varying load conditions.
