1986 Volume 35 Issue 394 Pages 772-778
It is well known that the fatigue crack propagation rate is affected by stress history and thus crack propagation retardation or acceleration will occur. Consequently, many attempts to develop a suitable fatigue crack propagation model under varying loads have been made by various investigators. However, it seems that models developed until now have some problems.
In the previous report, the present authors proposed a new fatigue crack propagation model based on the results of crack propagation tests under programmed or random load by using CT type specimens. However, these results were obtained for the case of stress ratio (R) equals 0.1. So, it is posibble to observe such a different crack propagation behavior that retardation is relieved or acceleration is increased by the compressive part of stress range when R equals -1. Accordingly the authors have investigated about this behavior by executing fatigue crack propagation tests under random loading in which stress ratio is fixed to R=0 and R=-1 using CCT specimen. Then a more reasonably improved model than that proposed in the previous report is proposed in this paper.
As a result it is made clear that the fatigue crack propagation life under stationally random loading can be estimated accurately enough by the linear model when R=-1, and that for the case of R=0 it can be estimated most accurately when the new proposed model is employed.