PLASTIC INSTABILITY IN RATE-DEPENDENT MATERIALS
BROWN UNIV PROVIDENCE RI DIV OF ENGINEERING
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The paper presents a theoretical analysis of the time variation of strain gradients in a tensile specimen of rate-dependent material, the analysis being based on the assumption that the strain rate in the material is a function of the local values of stress and strain. The theory is used to determine the criterion for the growth of strain gradients, and it is shown that for a given material there exists a region of the stress-strain plane in which these gradients increase indefinitely with time. The theory is applied to materials with specific types of rate-dependence, and the results are related to experimental data obtained at constant rates of strain.