Identifying micron-scale fatigue crack initiation by correlating temporal dynamic compliance with Computed Tomography

Fatigue failure is ubiquitous in engineering applications. While the total fatigue life is critical to understanding a component's operational life, the characterization of crack initiation life is important for safety, regulatory compliance, and predictive maintenance. Traditionally, initiation life is evaluated by potential drop method, acoustic emission technique, and strain-based measurements. However, the primary challenge with these methods lies in the necessity of calibration for each new material system. The difficulties become even more aggravated for additively manufactured components, where fatigue properties are reported to vary widely in the open literature. In this work, an analytical methodology is utilized to evaluate the initiation life of two different materials: AlSi10Mg and SS316L, fabricated via laser-powder bed fusion (L-PBF) technique. The processing parameters are selected such that AlSi10Mg behaves like a brittle material while SS316L shows ductile behavior. A custom fatigue testing apparatus is used inside Computed Tomography (CT) equipment for evaluating micron-scale fatigue crack initiation. The apparatus reports load-displacement data, which is post-processed using an analytical approach to calculate the evolution of dynamic compliance. The results indicate that micron-scale crack initiation during fatigue loading is indicated by a marked change in dynamic compliance. The findings suggest that dynamic compliance monitoring may potentially be used to identify fatigue crack initiation in different materials.