実用機械材料の結晶粒径分布による加工硬化指数の変化

概要

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Grain-size distributions of commercially pure aluminum, copper and 6・4 brass are approximated well with a log-normal distribution function, and it is shown that the median and the standard-deviation of distributions increase the strain-hardening exponent of sheet specimens of copper and 6・4 brass under tension. Both the simple equal-strain and equal-stress models of a composite flow curve are introduced, which are based on the flow stress rule of nth-power curve relation, connecting with the distribution function whose upper grain-size is bounded with 3・5 times the mean-grain diameter. The equal-strain model gives the lower flow stress limit, and the equal-stress model yields the upper one, and the experimental flow stress appears in between or closely around these two neighboring limits. Both models prove analytically that the median and the standard-deviation of distributions increase the strain-hardening exponent of a sheet metal under tension. The former model predicts the upper bound of the strain-hardening exponent and the latter one predicts the lower one, and experimental data on 6・4 brass are shown to appear in between them.
1986-07-25