Bringing to Life a Newly Discovered Signature of Fatigue Crack Initiation via Multimodal Characterizations

Abstract

Fatigue is the most prevalent failure mode in structural materials, yet remains challenging to study due to the seemingly unpredictable nature of crack initiation. To elucidate the driving forces of crack initiation in ductile polycrystalline metals, we employ a multimodal approach to identify and track grains with a suspected potential to initiate fatigue cracks via a newly founded signature. We discover this crack initiation potential (CIP) signature under the hypothesis that slip localization, a well-known precursor to crack initiation, is linked to intragrain misorientation, which can be quantified through single grain orientation distributions. We verify the CIP signature in an Inconel-718 material via static two-dimensional and three-dimensional electron microscopy and “bring to life” the dynamics of the CIP signature via in-situ synchrotron X-ray diffraction. With this CIP signature, we move to better focus studies of fatigue crack initiation on the individual grains and processes that drive fatigue failure.