Influence of mixed-mode-loading on the fatigue crack growth in components and structures

During the product life cycle variable loads can appear on a structure. In some circumstances these loads can crucially change the local stress situation on an existing failure and thereby significantly affect structure's durability. With respect to the fatigue crack growth, this thesis mainly focuses on fatigue crack growth under combined loading conditions, the so-called mixed-mode-loadings. In this context, experimental investigations are presented dealing with aspects regarding characteristic fracture mechanical values at 3D-mixed-mode and the effect of varying loading directions and loading levels on crack growth. These experiments are performed by using both available and specially developed concepts of specimens and loading devices. Due to the resultant crack front segmentation arisen from the presence of mode III in mixed-mode-loadings, a separate chapter is created to deal with this issue explicitly. Furthermore, a loading device concept, that is developed within this thesis, enabling experimental crack growth simulations at different out-of-phase mixed-mode-loading conditions, is comprehensively illustrated and accordingly applied. Based on characteristic values identified, the experimental researches confirm that existing criteria are conservative and can continue to be applied. As a final conclusion, the variation in loading directions and loading levels, as well as the out-of-phase mixed-mode-loadings, influence the crack's growth rate and its orientation.