Effects of dwell time on thermo-mechanical fatigue - An import influence factor for dimensioning components of engines

Out-of-phase thermo-mechanical fatigue tests are performed for different dwell times at the particular maximum temperature to investigate the influence of dwell times on cyclic deformation and fatigue behaviour. The umbrella terms stress hardening and softening for the cyclic deformation behaviour at TMF loading are separated and drawn in a damage map displaying maximum temperature versus dwell time at the maximum temperature. The sub-areas result from plastification effects during heating-up, cyclic stress relaxation effects, grain growth and volume growth effects, aging effects during service time and in-/decrease of mean stresses - whereas their interaction causes nonsymmetric deformation behaviour at TMF loading. Moreover, phenomenological concepts to draw an interaction between different TMF dwell times as well as the interaction with LCF data are presented.