The aim of the presented work is to develop improved concepts for the prediction of fatigue lifetime under variable amplitude loading including plastic deformation and thermomechanical fatigue of welded joints made of the austenitic stainless steel 1.4550. Local strain amplitudes are located in the regime of low cycle fatigue, which is dominated by short crack growth. This can best be described by nonlinear fracture mechanics. To develop a fracture mechanics based lifetime model, different experiment types are carried out to estimate the influence of loading history, thermal cycling, and mean stresses. For the evaluation, different estimation concepts based on Palmgren-Miner's classic linear damage accumulation rule are used: solely calculated by strain ranges, damage parameter established by Smith, Watson and Topper, and a damage parameter based on the cyclic effective J-integral. The differences in the concepts are highlighted and used for further considerations on how to improve the lifetime prediction models.
