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The plastic deformation of polycrystalline lead under controlled stress. Fox, Gary Wayne

Abstract

A qualitative analysis of current creep theory has been made by studying the creep of polycrystalline lead. The behaviour of the low temperature stress-strain curve with prior creep history, and the strain response to decreases in creep stress were examined. The effect of temperature and creep strain on the low temperature stress-strain curve was investigated over the temperature range 0.5Tm to 0.8Tm. Specimens were quenched to 77°K. after creep and strained to determine the stress-strain curve. The 77°K. yield stress was found to increase during primary creep and remain constant in steady state. Increasing the creep temperature drastically lowered the low temperature yield stress. The reversible flow stress ratio was found to decrease with increasing temperature. These observations were in qualitative agreement with both a reaction rate theory and a rearrangement model. Stress decrease tests were carried out by reducing the creep stress after deforming the specimen varying amounts into primary and steady state in the temperature range 0.5Tm to 0.85Tm . The strain response to a stress decrease in steady state was in best agreement with the simple recovery theory. The variation In yield stress due to non-regular obstacle spacing was found to be extremely small at all temperatures and did not behave in accordance with the qualitative predictions of the rearrangement theory.

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