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

A push-pull impact fatigue testing apparatus and relevant testing proc edure designed by the authors are presented. Based on the principles o f Hopkinson's bar, the specimens are subjected to trapezoidal wave loa ds. 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 40 Cr steel, while ordinary low-cycle fatigue tests were conducted in par allel. The results showed that there was no obvious overstress under i mpact loading. Reversal impact loading did not produce an apparent Bau schinger 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. Therefor e low-cycle impact fatigue is considered more dangerous than ordinary low-cycle fatigue.