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X-Ray Diffraction Residual Stress Analysis Using High Precision Centroid Shift Measurement Techniques - Application to Uranium-0.75 Weight Percent Titanium Alloy
Published online by Cambridge University Press: 06 March 2019
Abstract
The standard three-point parabola technique has been used extensively in residual stress analysis for peak location with precisions (standard deviation) of peak shift measurements in the range of 0.01° to 0.03° (20). While this level of precision produces useful data for peaks at high diffraction angles, it becomes untenable when a material with high elastic modulus is encountered whose only suitable peak falls below approximately 140° 20. Uranium-0.75 weight percent titanium alloy, which is the material of interest in this investigation, falls into this category.
A technique has been developed by which diffraction peak centroid shifts are determined with a precision of 0.002° of diffraction angle (Δ20). The method consists of step-scanning over the peak of interest to acquire data in digital form. A small Computer is then used to locate the diffraction line by calculating its centroid from digital data.
The use of a special probe consisting of four distance transdueers (LVDT) to achieve precise alignment of the specimen surface on a Siemens back-reflection stress diffractometer will also be described.
A calibration experiment was performed on uranium-0.75 titanium tensile specimens in which the X-ray diffraction response was measured as a function of various levels of applied stress in order to determine the experimental elastic moduli. It was found that repetitive analyses on a single area of a cylinder had a standard deviation on the measured diffraction centroid shift of 0.002 degree which is approximately an order of magnitude smaller than that achieved by the standard parabola fitting technique. Thus, the residual stress can be defined to a precision of ∼ 2,000 psi, as opposed to 30,000 psi, at best, were the measurements obtained by the conventional procedure.
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- Research Article
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- Copyright © International Centre for Diffraction Data 1973
References
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