Residual Stress Engineering for Aerospace Structural Forgings

ABSTRACT: Manufacturing of jet engine and aerospace structural components involve a series of thermo-mechanical processes such as forging, heat treatment, machining and joining processes. During thermo-mechanical processing, bulk residual stresses in the components evolve which may lead to part distortion. Surface residual stresses impact fatigue life. Managing residual stresses in the part during processing and under service condition is therefore critical to optimizing component performance. As the aerospace industry embarks on introducing new material system and starts to push the performance limits on the components, design and material engineers would need robust, reliable and validated predictions of residual stress distributions in the part. In this proposed Phase I program, Scientific Forming Technologies Corporation (SFTC) is teaming up with Hill Engineering LLC and Proto Manufacturing Inc to work closely with AFRL and jet engine OEMs including Pratt and Whitney, GE Aviation and Rolls Royce to establish a framework for quality assurance procedure to link residual stress modeling predictions with measurements. DEFORM residual stress modeling predictions need to account for uncertainties in processing conditions, material data and boundary conditions. It is critical to identify factors impacting bulk and surface residual stress measurement accuracy, repeatability and reliability of measurements and quantifying measurement errors and variations. A proof of concept procedure for a combined residual stress modeling and measurements quality assurance plan will be demonstrated. A detailed verification and validation plan for residual stress quality assurance program will be developed during Phase I in consultation with AFRL and OEMs which will be executed in subsequent Phase II part of this program. It is anticipated that a validated residual stress quality assurance program linking modeling predictions and measurements will be beneficial to OEMs in qualifying first article forgings and verifying periodic cutups from the perspective of optimizing fatigue life and managing part distortion during thermo-mechanical processing of components. BENEFIT: It is anticipated that the proposed work will result in establishing a residual stress assurance plan linking residual stress modeling results with both bulk and surface residual stress measurements. This proposed work aims to bridge the gap between residual stress modeling predictions and measurements. It is anticipated that a quality assurance procedure linking residual stress modeling and measurements will help in qualifying first article forgings through an improved, reliable understanding of part distortion during subsequent machining process, fatigue life and risk assessment This project will lead to robust, reliable and validated predictions and measurements of residual stresses. This will lead to better design and control of thermo-mechanical processes which in future may help to push the existing limits of jet engine performance in service conditions. This project will help in improved understanding of the interaction of residual stresses on fatigue life and part distortion during processing. Finally this project may play a small but significant role in accelerating the insertion of new material through a better understanding of processing, evolution of residual stresses and fatigue life.