Application of stress intensity factor superposition in residual stress fields considering crack closure. (15th February 2021) - Keller, S.
Highlights: Clarification of stress intensity factor superposition under crack closure phenomena. Importance of crack geometry changes by crack closure for stress intensity factor superposition is demonstrated. Proposal and discussion of two alternative residual and applied stress intensity factor definitions. Discussion of crack face contact modelling for stress intensity factor calculation in fatigue load cycles. Abstract: The correlation between stress intensity factor (SIF) range and fatigue crack growth is a powerful tool for fail-safe design approaches applied to lightweight structures. The key role is precise calculation of the SIFs of fatigue load cycles. Advanced material processing can shape residual stresses and makes SIF calculation a challenging task. While the consideration of tensile residual stresses is successfully tackled by SIF superposition, the treatment of compressive residual stresses needs still clarification. This work demonstrates the application of the SIF superposition principle in regions containing high compressive residual stresses leading to crack closure effects. Crack closure depends on the combined load of residual and applied stresses and is interpreted as a change of crack geometry in this work. Thus the relation between the source, i.e. the applied or residual stress, and its consequence, i.e. the corresponding SIFs, depends on the interaction of the sources, i.e. the combined load. Due to this interaction, residual stress-induced changes of the fatigue behaviour cannot be linked to the residual or applied SIF only. This work proposes two alternative definitions of applied and residual SIF, allowing a clear correlation between either residual or applied SIF to fatigue behaviour changes.