X-ray diffraction has become a popular means of residual stress measurement in the aerospace materials field over the last 50 years. A proposed new guide being developed by ASTM International Committee E28 on Mechanical Testing will provide the necessary information to obtain the most reliable residual stress values as well as identify and evaluate potential errors in measurement, paving the way for future developments. ASTM WK28149, Guide for Residual Stress Measurement by X-Ray Diffraction for Aerospace Bearing Materials, is under the jurisdiction of Subcommittee E28.13 on Residual Stress Management.

"Residual stresses are the stresses that remain after the original cause of the stresses has been removed," says Scott McCarthy, X-ray diffraction technician, FAG Aerospace and chair of the task group developing ASTM WK28149. "Residual stress plays a major role in bearing life since the total stress experienced by a component is a combination of the applied stress and residual stress."

According to McCarthy, the beneficial or detrimental effects of many processes, such as shot peening, honing, turning, grinding, case hardening and other heat treatments can be quantified with residual stress measurement, which allows for process optimization and monitoring of process parameters.

"Periodic tracking of residual stress during a bearing component's life is also beneficial," says McCarthy. "This provides insight into the eventual failure mode as well as guidance on possible improvements to the initial residual stress state to lengthen component life. Residual stress has even been used to track and predict component life."

Interested parties are invited to participate in the development of ASTM WK28149. "The committee mainly consists of representatives from X-ray diffraction equipment producers and laboratories specializing in the field," says McCarthy. "More representatives from the customer side are encouraged to join, including aircraft engine producers and designers."