過大荷重を負荷した試験片の疲労き裂進展加速の機構

抄録

The acceleration mechanism of crack growth after applying overload was investigated under baseline stress ratio R = -1. An overload was applied during fatigue crack growth test with constant stress amplitude by using carbon steel. Not only the overload level but also the cyclic stress condition affected the crack growth behavior after overloading. The effects of an overload on the rate of fatigue crack growth at constant amplitude have been of interest for some time, and much information has been gathered through which the crack growth was retarded. However there is relatively little information concerning the effects of an overload through which the crack growth was accelerated. Where the cyclic stress level was higher, the crack growth rate after overloading was kept higher level depending on the experimental conditions. Also, the acceleration of the crack growth was observed in some testing under plane stress conditions. Where the acceleration of crack growth was observed, the crack tips were blunted by applying overload. Thus the conditions of tensile overload affected zone were related to the acceleration of crack growth. It is discussed from the experimental results that the crack growth acceleration after overload was caused by the tensile residual stress developed in front of the crack tips due to applying compressive cyclic stress of which value exceeded a critical level.