An Overview of the Engineered Residual Stress Implementation Working Group

Abstract The Engineered Residual Stress Implementation (ERSI) working group was formed in 2016 with a mission to “develop a holistic paradigm for the implementation of engineered residual stresses into lifing of fatigue and fracture critical components”. ERSI emerged from within the United States Air Force (USAF) aircraft structural integrity community as a forum for individuals and organizations to collaborate constructively, transition technology and data to the public sphere, and consult on policy/best practices concerning the incorporation of residual stresses with other entities such as the FAA, DoD, ASTM, SAE, etc. ERSI members represent a broad diversity of interests and backgrounds, both domestic and international, from military, academia, and industry. The primary focus of ERSI so far has been the transition of a classic engineered residual stress technology, cold expansion of holes, into life extension for USAF weapon systems. Although hole cold expansion is known to provide significant structural fatigue life extension, the full potential improvement has not been included in certified airworthiness limits. With extensive support from ERSI, the USAF recently issued a Structures Bulletin which allows aircraft structural integrity managers to utilize cold expansion benefits for initial and recurring inspection intervals, a significant achievement for both platform availability and fleet-wide cost savings. This achievement is a holistic product from the three primary focus areas, or committees, within ERSI that represent different technical disciplines of aircraft structural integrity: 1) analysis and test, 2) residual stress characterization, and 3) nondestructive inspection/evaluation, quality assurance, data management. These three committees work together to identify and address technical gaps, define the requirements and guidelines for implementation, and collaboratively develop and accomplish new round robin activities that advance the state-of-the-art. This paper describes recent work performed by the ERSI working group across these three committees.