Constitutive modeling of high strength steels; application to the analytically strengthening of thick-walled tubes using the rotational autofrettage

Abstract

This paper focuses on high-strength and hardness steels which are used as an upgraded material in the construction of high-pressure vessels. Their mechanical behavior shows that these steels have perfectly plastic or linear hardening behavior with slight slopes during their loading phase. In contrast, their reversed loading behavior is nonlinear and quite easily affected by the prior plastic strain, in a way that the Bauschinger effect factor, trend, and nonlinearity degree of the reversed loading plastic part are strongly dependent on the prior plastic strain level. At first, a constitutive model was proposed to capture the test data of the nonlinear part of the stress-strain curve and the Bauschinger effect factors, as a function of prior plastic strain. Furthermore, this model should be proposed so that its application in solving boundary value problems such as thick-walled tubes leads to a closed-form analytical solution. To this end, the proposed model was adjusted to find a closed-form analytical solution for the analysis of thick-walled tubes under rotational autofrettage. In the following, the optimum autofrettage level for strengthening a thick-walled tube made of high-strength steel is obtained for proposed and other simplified constitutive models. By comparing the results, it was concluded that consideration of the dependency of mechanical behavior of this material on the prior plastic strain makes significant changes on the equivalent stresses.