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It is well known that manufacturing operations produce material conditions that can either enhance or debit the fatigue life of production components. One of the most critical aspects of material condition that can have a significant impact on fatigue life is residual stress (RS) [1, 2]. When springs are manufactured, the spring stock may undergo several operations during production. Additional operations may also be introduced for the purpose of imparting the spring with beneficial surface RS to extend its fatigue life and increase its ability to execute the task it was designed to perform. The resultant RS present in production springs as a result of the various fabrication and processing operations applied can be predicted and modeled, however, RS measurements must be performed in order to quantify the RS state with precision.

Automobile manufacturers have experienced increasing consumer and regulatory pressure to improve fuel efficiency and crashworthiness while simultaneously decreasing overall vehicle body weight. As such, the use of advanced high strength steels (AHSS) in body panels and other structural elements is becoming more and more prevalent because these advanced materials present an economical and elegant solution to the problem. To ensure the quality and safety of AHSS components, residual stress (RS) specifications (among others) have been introduced with the intent to minimize failures experienced both in the field and during production. Moreover, when welding processes are applied to AHSS components, the localized loss of ductility in combination with tensile RS can result in localized cracking, distortion, and/or failures.

Several residual stress (RS) measurement standards that employ x-ray diffraction (XRD) techniques are available for users in Europe, North America, Japan and other countries. Such standards are similar in principle however the detailed requirements for each standard are different. RS measurements performed on critical components require a good knowledge of XRD techniques and current best practices so that they can be correctly applied to the challenging geometries and exotic materials that often compose critical components of interest. This paper will compare the key requirements found in the various RS measurement guidelines and standards currently available to users while emphasizing and justifying current best practices as they apply to the measurement of RS on mechanical components used in the automotive and the aerospace industry.

Residual stress plays an important role in fatigue life resistance of automotive components. Due to the complex nature and combination of multiple processes used in the manufacturing of these components the residual stresses present may not always be uniform. Typically most components contain both surface and sub-surface stress gradients. This leads us to the conclusion that characterizing the residual stress at one location will not generate a sufficient understanding of the stresses present. Characterizing and understanding the stress gradients will help to manage the fatigue life of various components as well as help establish proper quality control practices to ensure the presence of beneficial residual stresses at critical locations.

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.