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Non-Destructive Quantification of Plastic Deformation in Steel: Employing X-Ray Diffraction Peak Broadening Analysis

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Technical Report

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The X-ray diffraction XRD pattern of an alloy, such as steel, reveals, among other propertiesex., phase composition, crystal structure, information about the strain state, crystallitedomain size and dislocation density. While well-established non-destructive methods are available to quantify elastic strain and residual stress, dislocation density has proven to be a particularly elusive quantity to evaluate non-destructively. Dislocation density provides important information about the state of a material and the extent to which it was deformed. This has a strong influence on the mechanical behavior of a material during and after deformation. The goal of this work is to examine the underpinning science behind XRD peak broadening analysis and develop a methodology for evaluating plastic deformation in ferromagnetic steel alloys. An overview of the principles of XRD, how the crystallographic structure of steel accommodates stress and how X-rays interact with steel structures are documented. A historical perspective on XRD peak broadening analysis is provided. Two approaches, the modified Williamson-Hall and Warren-Averbach, have been identified to enable quantification of dislocation density and crystallite size. Both approaches that account for strain anisotropy are believed to offer the best potential for success. A variety of potential defense applications have been identified and a possible way ahead for advancement of this technology has been mapped. It is thus recommended to modify the portable XRD hardware and software to enable calculation of the dislocation density and crystallite size using both these approaches. This, together with elastic strain residual stress analysis, would enable better evaluation of the current state of health of steel structures and components as they near predetermined life limits and assess the risk in extending these limits.

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  • Properties of Metals and Alloys

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