The Effect of Cyclic Stress Hysteresis at Elevated Temperature on the Crack Propagation Behavior in Smooth Specimens of O.45% Carbon Steel

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The specimens prestressed at 200℃ and 375℃ were fatigued at room temperature in rotating bending. As long as no fatigue crack initiated during prestressing at 375℃, the number of cycles required for crack initiation at room temperature, n_c, was increased. The increase in n_c becomes greater as the prestress becomes higher. The prestress at 375℃ contributes to a decrease in crack propagation rate, dl/dn. the wellknown relationship dl/dn=c(ΔK)^m has been proved to be applicable regardless of the precrack length. Both constants c and m become smaller and larger, respectively, as the prestress becomes higher. The increase in n_c and the decrease in dl/dn may be explained as the result of a rapid strain aging occurring during cyclic stressing at 375℃. With the specimens prestressed at 200℃, the decrease in dl/dn depended on the prestress too, but the effect was less remarkable than that at 375℃.
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