抄録
It is well known that a tensile overload applied during constant amplitude cycling at a positive stress ratio R can lead to a retardation in the rate of subsequent crack propagation. On the other hand relatively little is known about crack growth behavior following a tensile overload when constant amplitude cycling is carried out at negative stress ratio R. To provide such information, in the present study the effect of a tensile overload was investigated at three R values; R=0, -1 and -1. 5. Also, the behavior of crack closure and propagation were compared, particularly at negative R values. In the experimental program, center cracked plates of a 0. 35% carbon steel were used. At a baseline of R=0, after an overload retardation in the crack propagation was observed.
However, in the case of R=-1. 0, little or no retardation was observed, and at R=-1. 5 the fatigue crack growth rate actually accelerated after a tensile overload. The crack propagation behavior is related to the blunting behavior of crack tips and the residual stress distributions.
The fatigue life became shorter by applying a single overload while the crack propagated under negative mean stress conditions. This behavior is very dangerous, if the overloading condition and the succeeding cyclic loading conditions are unknown.
