Fatigue Crack Propagation Behavior in the Field of Residual Stress Distribution

Abstract

In the previous paper, a simulation model of fatigue crack opening and closing phenomena in an arbitrary stress distribution field for the purpose of obtaining RPG load is shown.From the calculation and experimental results of RPG load, the effects of stress ratio and delayed retardation on fatigue crack propagation are quantitatively assessed. Moreover it becomes clear that the stopping condition of fatigue crack propagation is ΔKRP≤0.In this paper, fatigue crack propagation tests in residual stress distribution field are carried out. Two types of center notched specimens are prepared : one is that gas heating is made at the center line of the specimen which leads to tensile residual stress field in the middle part of the specimen, the other at near the edges of the specimen which leads to compressive residual stress field in the middle part of the specimen. It becomes clear that tensile residual stress descends RPG load and compressive residual stress raises RPG load. Moreover if the large compressive residual stress exists, crack closes even when tensile yield zone generates at the crack tip under loading process. In this case, plastic zone could not grow until crack becomes fully open.Simulated RPG load is in good agreement with experimental one even in the field of residual stress distribution. And compressive residual stress has a large effect of decreasing the fatigue crack propagation rate. These effects can be successfully estimated by the simulation model.