A Two-Parameter Model for Mixed-Mode Fatigue Crack Growth and Multiaxial Fatigue 2015-01-0541

Engineering components and systems are usually subjected to mixed-mode and multiaxial fatigue loadings, and these conditions should be considered in product durability and reliability design and the maintenance of aging equipment, especially mission-critical components and systems. However, modeling the damage and degradation processes under these complex loading conditions is difficult and challenging task because not only the concepts, such as range, mean, peak, valley etc., developed for uniaxial loading usually cannot be directly transferred to mixed-mode and multiaxial loadings, but also some very unique phenomena related to these complex loading conditions. One such a phenomenon is the loading path effect that can be simply described as: out-of-phase loading is more damaging than in-phase loading for some ductile materials. To capture the loading path effect as observed in both mixed-model fatigue crack growth and multiaxial fatigue life test data, a new two-parameter driving force model (i.e., maximum principal stress and path length) has been proposed and some preliminary analyses have been conducted and qualitative descriptions have been given. In this paper, the mixed-mode fatigue crack growth and the multiaxial fatigue life data are reanalyzed with a more rigorous approach, and quantitative results are obtained.