A Tension-Torsion Testing Technique

Abstract

Although the creep behaviour of metals has been investigated since the beginning of the twentieth century (Andrade, 1910), a limited amount of data are available to describe this process, in the case of non-proportional, variable load conditions. The majority of tests have been performed under constant uniaxial load and do not coincide with those encountered in real components which operate under variable and complex states of stress. Such simple loading conditions do not show many of the effects found under complex stress states and which play an important role for some loading programmes (material softening observed after change in the principal component of the stress tensor, directional character of damage, etc.). So, because of modern design requirements for components such as nuclear power stations, chemical plants and so on, and due to the necessity of better knowledge of material behaviour and to the formulation of credible material models, it is necessary to obtain results of creep tests for complex stress state and variable loadings. Such experiments have not been carried out in a systematic way until relatively recently because of the technical difficulties in experimentation. Tests have been carried out basically for plane stress conditions (σ _l≠0,σ4 2≠0,σ ₃=0) using different test techniques.