The Tensile Yield Strength of Certain Steels under Suddenly Applied Loads

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Abstract
Dynamic tensile yield stresses are determined for eight steels, including one mild steel, two plain carbon steels, two carbon manganese steels, one heat-treated alloy, and two cast steels. The dynamic loads are applied by means of an impact machine of the falling weight type. An attachment is fitted to this machine to enable the peak load to be reached in 3 milli-seconds (0·003 second). Supplementary tests, in which the time to reach the peak load is 1 milli-second, are carried out on three of the steels. Electrical resistance strain gauges mounted directly on the specimens are used to record the loads. Comparison with static values reveals an increase in yield stress of from 21 to 36 per cent for the carbon steels under dynamic loading. This increase diminishes with increase in static yield strength. The annealed cast steels behave in a similar manner to the carbon steels, but the heat-treated alloy steel shows no appreciable increase in yield strength with increase in rate of loading. Comparison is also effected with some results of other investigators. A theory is put forward to account for the variation in sensitivity of yield strength to load rate. A division of tensile tests into three main types, on a basis of rate of loading, is suggested for future work.

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