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It is well known that machining operations produce surface conditions that can either enhance or debit the fatigue life of production components. Furthermore it has been well established that the thermal gradients produced during the solidification process of a casting operation can also generate detrimental residual stress loads. Cast cylinder blocks can sustain life limiting stress gradients from these processes. Due to their complex geometry it has historically been very difficult if not impossible to fully characterize the residual stresses present at critical locations in cylinder blocks. Recent advances in x-ray diffraction (XRD) have reduced the minimum clearance required for an accurate measurement from 200mm to 70mm. This now allows XRD to be used as a non destructive test (NDT) on features such as cylinder liners and bores, bulk heads and assembled journals.

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.