Nondestructive Characterization of Residual Stresses in Small I.D. Through Holes via X-Ray Diffraction Techniques

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. These advancements will allow OEM's and their suppliers to improve fatigue life and product quality by characterizing and managing the RS present in the I.D. of connecting rods, bearing raceways, transmission and clutch components, etc. without the need to section the component.