โ Scribed by Y.W. Chung; W.J. Lee
No coin nor oath required. For personal study only.
Low cycle fatigue behaviors in Nb-bearing high strength, low alloy (HSLA) steel have been studied at plastic strain amplitudes Aep/2 ranging from 1 x 10 -5 to 1 x 10 -2 in air and in ultrahigh vacuum (UHV). Microcracks are initiated along slip lines both in air and in UHV, and grain boundaries act as effective barriers to the propagation of microcracks. Coffin-Manson relations are reasonably satisfied for the microcrack initiation life N~ and the fatigue life Nf both in air and in UHV. The accumulated total cyclic plastic strain energy W~ required for fatigue crack initiation and the accumulated total cyclic plastic strain energy Wf required for fatigue failure are expressed mathematically in the form of K(Aep/2) N.
The computed values of W~ and Wf are in good agreement with the values determined experimentally. The vacuum environment enhances N~, Nf, W~ and Wf. The environmental effect becomes greater as the plastic strain amplitude decreases.
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