Modeling short crack propagation under variable structural and thermal loadings

In the present work, a new concept for the prediction of fatigue life under variable structural and thermal loads is presented based on the modeling of short crack propagation by the effective cyclic J‐integral. Stresses in the range below the initial endurance limit up to plastic deformations can be considered. The development and validation of the concept is based on the large database of constant and variable amplitude loading tests for the austenitic stainless steel X6CrNiNb18‐10 (1.4550, AISI 347). Taking into account the influence of notches and welding process, tests were performed for specimens with different stress concentration factors and even with specimens of nonhomogeneous microstructure due to welding or its physical simulation (Gleeble). The input for the developed model is based on local stress–strain hysteresis in the order of their occurrence. This is the basis for considering load sequence effects; the new J‐based model considers several types of them. The model as well as the identification of the parameters will be presented in detail. Validation to experimental results is also shown against the background of common fatigue concepts. Basic aspects of the model are discussed.