HIGH STRAIN-RATE LOW-CYCLE IMPACT FATIGUE OF A MEDIUM-CARBON ALLOY-STEEL

A push-pull impact fatigue testing apparatus and relevant testing procedure designed by the authors are presented. Based on the principles of Hopkinson's bar, the specimens are subjected to trapezoidal wave loads. The strain rates in the specimens may reach 400 s-1. In this study low-cycle impact fatigue tests were carried out on quench-tempered 40Cr steel, while ordinary low-cycle fatigue tests were conducted in parallel. The results showed that there was no obvious overstress under impact loading. Reversal impact loading did not produce an apparent Bauschinger effect, which reveals a deformation mechanism different from ordinary low-cycle fatigue. The high strain rates in low-cycle impact fatigue make the steel brittle and amenable to early failure. Therefore low-cycle impact fatigue is considered more dangerous than ordinary low-cycle fatigue.