Theoretical assessment of influence of deformation induced heating on mechanical behaviour at elevated temperatures

Abstract

When a material is deformed, most of the work done by the applied stress is dissipated as heat. For low rates of deformation or for small blocks of material, the loss of heat to the surroundings is rapid relative to the rate of heat generation and the temperature rise is therefore minimal. Under the opposite conditions however, a significant temperature profile can develop within the material. For thermally activated deformation at elevated temperatures, this can have a significant effect on the mechanical response. This is investigated theoretically in the present work. It is evident that the creep of materials in the presence of a temperature profile is central to the understanding and an analysis of this forms the first part of the paper, where creep under uniaxial stress, in bending and in torsion are treated. In the next section, deformation heating under adiabatic conditions is considered and finally, numerical analyses are given for cases where deformation heating occurs with concurrent conduction to the surroundings. Some examples where deformation self-heating is likely to be important are discussed. These include superplastic behaviour, thermal fatigue, rapid stress rupture tests, depressurisation of nuclear reactors, and the deformation of planetary material.