Fatigue Assessment with Special Respect to Size Effects and Material Behavior within Local Strain-Based Approaches

In vehicle design and engineering, the fatigue of materials is a size-dependent phenomenon, which occurs in every safety-relevant component. An inaccurate fatigue assessment, neglecting relevant influencing factors, may therefore either lead to considerable safety risks or to a significant oversizing of the component. Due to the size dependency of the microstructure and the related deformation and fatigue mechanisms, the fatigue life estimation requires an understanding of the cyclic material behavior as well as the damage mechanisms of materials on different scales. In this respect, local strain-based fatigue design concepts are advantageous for the estimation of the fatigue properties of components with arbitrary size and geometry, because the applicable material models allow an implementation of a realistic cyclic material behavior and a relation to different fatigue damage mechanisms in the elastic and the elastic-plastic load regime. As previous research indicates, an additional consideration of size effects may enhance the accuracy of fatigue design by accounting for the influence of component geometry and load conditions on the local fatigue properties. Considering complex load time histories, the transient material behavior may have to be taken into consideration, since the microstructure as well as the local material properties of engineering materials change continuously during cyclic deformation [1, 2, 3]. The presented work shows, how the application of appropriate fatigue damage and material parameters as well as size effects may reduce the numerical as well as experimental effort for the fatigue assessment of vehicle components.