A study is presented on the influence of strain rate and strain rate history on the flow stress of several metals. Experiments were performed on specimens of four polycrystalline metals: 1100-0 aluminum, OFHC copper, AZ31 B magnesium, and commercially pure zinc. The experiments involve, the use of a modified Kolsky bar to increase abruptly the imposed strain rate, initially 2 × 10−4 s−1, by a factor of more than 106. Tests were performed at selected temperatures in the range T ≤ (1/2)Tm. The results include complete stress-strain curves for deformation at constant strain rates as well as for deformation involving a sharp increment in strain rate. The difference in flow stress at a given value of strain for stress-strain curves obtained at constant but different strain rates provides one measure of the influence of strain rate on the flow stress. However, the results of the incremental strain rate experiments show that both strain rate and strain rate history contribute to this difference in flow stress. Hence, interpretation of both the incremental and the constant strain rate tests offers a means for distinguishing between the effects of strain rate as opposed to those of differences in strain rate history.

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