Creep and Stress Rupture

Abstract

Creep phenomenon. Creep curve and its different stages. Strain–time relations to describe the basic shapes of creep curves mathematically. A general empirical equation for time laws of creep. Creep rate–stress–temperature relations, showing influence of stress and temperature on steady-state creep rate. Effect of grain size on steady-state creep rate. Activation energy for creep, its determination and relation with activation energy for self-diffusion. Creep deformation mechanisms: dislocation glide, dislocation creep or climb–glide creep, diffusional creep (Nabarro–Herring creep and Coble creep), and grain boundary sliding. Deformation mechanism map. Stress-rupture test and its difference with the creep test. Concept of equicohesive temperature (ECT) and deformation features at ECT. Fracture at elevated temperature. Creep cavitation: wedge-shaped cracks and round or elliptically shaped cavities. Presentation of engineering creep data, and prediction of creep strength and creep-rupture strength. Prediction of long-time properties by means of parameter methods, such as Larson–Miller parameter, Orr–Sherby–Dorn parameter, Manson–Haferd parameter, Goldhoff–Sherby parameter and limitations of parameter methods. Stress-relaxation and step-down creep test. Creep-resistant materials for high-temperature applications and rules to develop increased creep resistance at elevated temperatures. Creep under multiaxial stresses. Indentation creep and method to obtain creep curve using Rockwell hardness tester. Problems and solutions.