Mechanical Description of Viscoplastic and Damage Behaviour Under Variable Temperature in Presence of Microstructural Instabilities

Structure calculations on refractory alloys at variable temperature must take into account the microstructural instabilities which may lead to important hardening. This paper describes an experimental and numerical study involving the following points: such a metallurgical effect can be macroscopically described by a mechanical model which is built up in the framework of the thermodynamics with internal variables, this model is numerically identified for a Nickel-Base alloy, IN100, in high temperature range, by using specially performed cyclic creep tests with discrete temperature changes, the possibilities of this model for predicting mechanical behaviour under cyclic non-isothermal loadings are shown, and compared to experimental results, finally we present some comments concerning the influence of non-isothermal conditions on lifetime, since it has been noticed from tests that, although mechanical behaviour is drastically changed, the rupture time is not very much affected.