C. J. Szczepanski, S. K. Jha, Universal Technology Corporation, Dayton, OH; J. M. Larsen, Air Force Research Laboratory, Wright-Patterson AFB, OH; J. W. Jones, University of Michigan, Ann Arbor, MI
Commercial interest in very high cycle fatigue (VHCF) has been spurred by the safe-life extension of components in transportation and energy production systems. In the VHCF regime, cyclic plastic strains are very low, fatigue damage is very localized, and the propensity for significant damage accumulation is highly dependent on the characteristics of local microstructures. New techniques have been developed for characterizing VHCF behavior as well as new understanding of the role of microstructure-specific fatigue damage accumulation and short/small crack growth in fatigue. In this work, ultrasonic fatigue was used to characterize the VHCF behavior of Ti-6246 and three distinct categories of crack initiation sites are observed. Examination of the initiation sites indicates that crystallographic texture suitable for basal <a>-type slip is present within these critical microstructural locations. Insights into the process of fatigue crack initiation that consider the influence of textured regions in damage accumulation will be discussed.
Summary: This work focuses on the role of local microstructural neighborhoods in both fatigue crack initiation and propagation. The variability in fatigue lifetimes in the very high cycle fatigue regime results from fatigue crack initiation within microtextured regions.
