Residual Stress Engineering for Aerospace Structural Forgings

ABSTRACT: Aircraft engine and structural components are being produced from forgings with increasingly complex geometries in a range of aerospace alloys. The forging process involves a number of steps required to attain favorable material properties (e.g., heat treatment, rapid quench, and cold work stress relieving). These processing steps, however, also result in the introduction of residual stress. Excessive bulk residual stresses can have negative consequences including: part distortion, reduced crack initiation life, and increased crack growth rates. While bulk residual stresses are often accounted for with simple approximations that ensure safety, there is an opportunity to improve the understanding of the bulk residual stress fields in forged parts and to monitor them as a routine part of quality assurance, which would reduce design uncertainty associated with residual stresses and would allow for higher performing structure. The proposed program will develop an approach for quality management of residual stresses in aerospace forgings, will develop technology to support quality system implementation, and will demonstrate the quality system in a production environment. The proposed quality system will combine advanced computational process modeling and residual stress measurement technology to establish a robust system of production control. BENEFIT: The proposed program offers a logical next-step in the continued improvement of structural engineering methods. Advances in residual stress technology over the past decade (or more) have resulted in improved tools for the analysis of residual stress effects on material performance. Technology is available, for example, to predict fatigue crack growth accounting for residual stress effects. By specifically accounting for residual stress effects in these calculations, designs can become more efficient and require lower safety margins. This leads to higher, more aggressive performance. One significant missing ingredient inhibiting the full accounting of residual stress in design is the fact that residual stress levels are typically not certified in the material supply chain. The development of a quality management system for residual stresses in forged aerospace components will enable material suppliers to certify the level of residual stress in their forged product, which will enable end users to specifically account for residual stress effects in design (and will result in significant positive benefit).