高ひずみ速度下における炭素鋼の下降伏応力のひずみ速度依存性

概要

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By utilizing a simple Arrhenius-type equation, the strain rate dependence of the lower yield stress of plain carbon was characterized in a wide range of strain rate from a conventional low strain rate to a high strain rate (ε^^・=10^3〜5×10^4/s). For pure iron and a mild steel, the strain rate dependence was well expressed by (p,q)=(1/2,1) when the activation energy was given by ΔG∝{1-σ^*/σ^*_m)^p}^q (σ^* ; the thermal component of the stress, σ^*_m ; the σ^* at 0K). For a low carbon (C=0.1〜0.2%) and a medium carbon (C〜0.45%) steel,it became clear that (p,q)=(1/2,3/2) and (1/2,2) were suitable to characterize the dependence,respectively. By applying the equation with (p,q)=(1/2,3/2) to the experimental data of double shear impact tests (Campbell and Ferguson, 0.12%C steel) which are often quoted to exemplify the dislocation damping mechanism at extremely high rates of strain, the data were re-analyzed in order to discuss whether or not the strain rate dependence can be expressed by the thermally activated process. Except at 195K,the calculated rate-dependence coincided fairly well with the experimental one. This suggests that in steel, the single thermally activated process is still predominant up to an extremely high rates of strain(ε〜5×10^4/s).
1986-10-15