A new creep constitutive relationship for high temperature alloys

Abstract

From experimental creep rates of high temperature alloys, it is found they can be classified into three types: with creep rate decreasing only, with creep rate deceasing firstly but accelerating after a certain time, and with creep rate increasing slowly but accelerating after a certain time. These three typical creep types can be characterized in a unified form, by dividing creep process into two creep stages distinguished by the critical creep time. Before the critical time, the first stage has decreasing or slowly increasing creep rate only, after the critical time, the second stage also has accelerating creep rate besides the previous creep rate. A new generalized creep constitutive relationship with creep time and four stress-dependent parameters has then been proposed. The stress-dependent parameters can be interpolated from test results under various stress levels. It is found that the interpolation functions should be expressed in different styles according to the stress level distinguished by a critical creep stress. The critical creep stress can be determined just by the glass strain variation under various stress levels. More meaningfully, critical creep stress corresponds to the cross point in the bi-linear model of creep failure life in fact. It is also found there is a non-creep stress below which creep deformation can be neglected.