Abstract
Tension-compression and torsional low-cycle fatigue tests were conducted on specimens containing an artificial small hole. Even in the range of low-cycle fatigue, the plastic strain range which can be detected from hysteresis is extremely small. The relationship between total strain range (Δet, Δγt) and fatigue life (Nf) is expressed byΔe4.18tNf=2.06×l0-5(Nf≤3000) for tension-compression andΔγ2.90tNf=5.48×10-2 (Nf≤2000) for torsion. Fatigue life is mostly spent by the propagation of small cracks except for the case of Nf>104 in tension-compression fatigue. The prior fatigue history hardly influences crack growth rate in later cyclic loading and this assures Miner's rule to hold under variable amplitude loading. In torsional fatigue, cracks initiated not only at the edge of an artificial small hole but also in the vicinity of the hole, and therefore not only cracks with ±45 degrees angle against specimen axis but also axial and circumferential cracks were observed. This crack initiation mechanism can be explained by the elastic-plastic analysis based on the combination of the finite element method and the body force method.
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