X-ray Diffraction as a Means to Assess Fatigue Performance of Shot-Peened Materials

Report No. ARL-TR-6039
Authors: Daniel J. Snoha and Scott M. Grendahl
Date/Pages: June 2012; 28 pages
Abstract: Residual compressive stresses can contribute significantly to the enhancement of fatigue performance. Conventional shot peening is a process for imparting beneficial stresses at the surface and into the near-surface region of a metal component. X-ray diffraction provides a method to nondestructively characterize residual stress by the direct measurement of elastic strain in the microscopic structure. Plastic strain can be evaluated by the width of the diffraction peak. This report presents elastic and plastic strain data from residual stress measurements performed on four aviation materials shot peened to various Almen A-scale intensities by two different vendors. Fatigue performance in terms of endurance limit was determined using unnotched, round Kt = 1 test specimens. In general, the deepest levels of compression were associated with higher shot-peening intensities. However, the best fatigue performance and highest surface residual compressive stresses were observed on the lower end of the peening intensity range.
Distribution: Approved for public release
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Last Update / Reviewed: June 1, 2012