Abstract

Fatigue damage is one of the most ubiquitous sources of structural degradation during both nominal and off-nominal operations in engineering components. While model-based computational methods for assessing structural damage evolution are available, difficulty in achieving the required accuracy due to inadequacy in capturing the dynamical behavior of fatigue damage at the grain level makes them difficult to solely rely on. The random distribution of microstructural flaws such as inclusions and defects produce a wide uncertainty in the crack initiation phase. Such defects become even more critical in additive manufactured components which typically consist of an array of microstructural features such as lack of fusion defects and pores that are radically different from their cast counterparts. The defects coupled with microstructural anisotropy in AM-fabricated parts renders the prediction of fatigue crack evolution near to intractable through computational modeling only. The objective of the current work is to investigate the evolution of fatigue failure in Hastelloy X parts fabricated using a laser powder directed energy deposition process and having varying degree of flaws. An in-situ fatigue testing setup integrated with ultrasonic transducers and a confocal microscope allowed for the systematic study of fatigue crack evolution in the presence of varied degree of sflaws. The resulting data from experimentation, characterization, and analysis were integrated to gain unprecedented insights into the evolution of fatigue failure in Hastelloy X parts.