This paper starts with an overview of the application of the three guidelines (GL) of the German Research Association of Mechanical Engineers (FKM). Each of these provides algorithms for calculating fatigue lives of components under constant or variable amplitude loading, however, with underlying different failure criteria, i.e. technical crack initiation life (GL-nonlinear), fatigue crack growth life (GL-fracture mechanics), and total fracture life (GL-linear). This paper introduces the U-Concept which has been evaluated from a large structural durability database. The U-Concept is a small add-on to the Local Strain Approach (LSA) which is the backbone of the GL-nonlinear. It enables 1) to directly calculate the fatigue life to total fracture based on elastic-plastic material behaviour according to the LSA, or 2) to estimate the remaining fatigue life from crack initiation to fracture without a crack growth simulation.

Concepts for crack propagation as well as fatigue assessment under variable mechanical and thermal loadings are unestablished. For variable mechanical loadings, the damage parameter PJ is well known, for thermal loadings the damage parameter DTMF is established. Both parameters base on the effective cyclic J-Integral, still the definition is different. The damage parameters PJ considers the effective stress and strain ranges from the upper reversal point of each load cycle to the point of crack closure. Depending on the loading sequence the point of crack closure is treated as a history variable. In addition, with a crack length dependant fatigue limit, the most important sequence effects are considered. A new PJ-based concept is developed by considering additional sequence effects. In comparison to experimental results, the developed concept is able to reduce scattering in the range of constant amplitude loading tests.