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It is well known that machining and cold working operations produce surface conditions that can either enhance or debit the fatigue life of production components. When surfaces are abusively machined, the resultant tensile residual stresses (RS) and microstructural damage often cannot be detected reliably by conventional nondestructive testing (NDT). However, nondestructive surface RS measurements via x-ray diffraction (XRD) can detect process induced surface damage or abusive machining in very thin layers before cracking occurs. Heretofore, XRD techniques have been limited in their ability to characterize stresses in small diameter holes and other limiting geometries. Recent advancements in XRD technology and instrumentation have allowed nondestructive RS measurements to be performed on the inner diameter (I.D.) surface of small diameter through holes. The same advanced XRD instrumentation can also be used to perform RS measurements at relatively low diffraction angles.

The processing of certain features in automotive components such as crankshafts, gears, shafts, springs, rotors, cylinder heads, engine blocks etc. pose several difficulties for manufacturers and it is often a challenge to produce a finished product with the superior material characteristics that may be required for a given application. Among material characteristics of interest, the residual stress can have a significant impact on the effective service life of a component. Since residual stresses are introduced in nearly every step in manufacturing, it follows that the effect of processing applied to failure-critical locations must be well understood, controlled and optimized. This paper discusses the key aspects of applying XRD to the measurement of residual stress and will cite examples where XRD has been applied to the characterization of some typical automotive components.