| For the theoretical discussion of the crack advance phenomena, many models have been suggested. However, most of them could not suggest the exact processes of the crack-tip region in the low cycle fatigue conditions, but only rough approximations in terms of LEFM for the damage of crack-tip region. Recently, Oh and Nam suggested a new model of crack advance and life prediction based on the damage formation in fatigue process zone, where the concentrated degradation of the material occurred with crack advance. In the previous studies a parameter of α₁ which is the term of correcting plastic zone size was suggested to be constant by many researchers in a fixed temperature. But the experimental results for 1Cr-Mo-V steel showed that α₁ is a function of temperature, and the microhardness tests proved that the smaller the value of α₁ in high temperature, the smaller the size of cyclic plastic zone(n). |
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