Robust Methods for the Measurement of Bulk Residual Stress

ABSTRACT: Aircraft engine and structural components are being produced from forgings with increasingly complex geometries in a wide range of aerospace alloys. The forging process involves a number of steps required to attain favorable material properties (e.g., heat treatment, rapid quench, cold work stress relieving, and artificial aging). These processing steps, however, also result in the introduction of residual stress. Excessive bulk residual stresses can have negative consequences including: part distortion during machining and/or during service, reduced crack initiation life, increased crack growth rates, and an overall reduction in part life. While bulk residual stresses are often accounted for with simple approximations that ensure safety, improved understanding of bulk residual stress fields would enable higher quality design and analysis methods. This could lead to overall higher performing structure. The proposed work plan will develop improved technology for the measurement of bulk residual stress and will demonstrate the effectiveness of this approach under representative conditions. BENEFIT: The proposed residual stress measurement technology is a significant improvement that would fill a critical gap in capability for bulk residual stress measurement, enabling high-quality measurements in aerospace materials. This technology is important to the aerospace community, and is applicable to many other industries as well. For example, pressure vessels, turbines, industrial facilities, ships, and heavy equipment all contain critical structure with significant amounts of residual stress. As design and analysis techniques evolve to incorporate residual stress effects, it is important to have residual stress measurement techniques capable of providing the necessary supporting data with a high degree of accuracy. The proposed technology expands residual stress measurement capability to support these important challenges.