Modelling Thermo-mechanical Fatigue Hysteresis Loops from Isothermal Cyclic Data

A simple TMF facility is described which is capable of 'in-phase', 'out of phase' and 'diamond' type strain-temperature cycling. Typical TMF loops are presented for the 'diamond' type cycle for the nickel-base alloys IN100, Nimonic 90, IN738 and directionally solidified CM247LC-DS over the temperature range 400 °C-1000 °C. Alongside these results, isothermal cyclic stress-strain data are provided for ascending and descending strain amplitudes at discrete temperatures encompassing the strain and temperature range of the TMF tests. Testing on any individual specimen was terminated after a fixed energy consumption. By superimposing the symmetrical isothermal loops about a common origin, the isothermal data are then used to predict the observed (asymmetrical) TMF behaviour. The method works well for materials which show history independence such as IN100. However, for some of the materials, slight modification to the procedure is required. The sensitivity of the method to the form of isothermal data is demonstrated.