Comparative Creep Life Evaluation of HR3C Using Creep Damage Models

Recently, due to both environmental and energy efficiency, the designed life cycle of many power plant have been extended and also their operating temperature increased. When a material is exposed to high temperature over 50% of its melting temperature, it often shows unusual creep behavior in which the long time exposure of high temperature causes a microstructural degradation in the material and leads to creep rupture at a stress much lower than yield. Thus, there is a great significance in evaluating the creep life of high temperature components in power plant. In this study, accelerated uniaxial creep tests have been conducted to obtain material properties of HR3C at high temperature. The material properties of three damage models were derived from the accelerated short term creep tests in different stress conditions and the constitutive equation was the form of a power-law for the Kachanov and Liu-Murakami damage models and a hyperbolic sine function for the Dyson model, respectively. Based on these three damage models, the long term creep life was also evaluated. Using the creep rupture envelope, a modified grain boundary constrained cavitation coefficient function is proposed to resolve the constant failure strain problem. Also another modifications is made to the aging coefficient calculation by suggesting a new type of optimization function. By this, the classical problem of rupture time underestimation in the original Dyson model has been resolved. Consequently, the suggested creep life evaluation technique with a simple uniaxial creep example can be extended to more complicated engineering components at high temperature.