Integrating Residual Stress Analysis of Critical Fastener Holes into USAF Depot Maintenance
Abstract: The objective of this Rapid Innovation Fund (RIF) program is to integrate finite element simulations of residual stress fields, physically based life prediction methods, and inspections for cold worked (CX) fastener holes into depot maintenance practices. For decades, the aircraft industry has used cold working of fastener holes to enhance the service life (fatigue performance) of critical, highly stressed structure. Although the structure directly benefits and is much less prone to failure, current requirements for structural inspections are very stringent. This is because the current analysis methods used to set inspection intervals do not take into account the beneficial residual stress fields that result from the cold work process. The efforts under this program have shown that the United States Air Force (USAF) can increase inspection intervals by as much as five times if the physically based residual stress fields are incorporated into analysis procedures. This program has successfully integrated a series of tools to accomplish the objective for A-10 application and capture the Return-On-Investment afforded by the implementation.
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“As the United States Air Force continues to extend the service life of their aircraft the Aircraft Structural Integrity Program (ASIP) has had to refine the methods it uses to analyze and predict fatigue crack growth. Through the use StressCheck®, coupled with AFGROW, we in A-10 ASIP have been able to more accurately model, predict and analyze critical aircraft structure for the A-10 and other types of structure for non-A-10 system managers. This also allows us within the A-10 to more accurately assess risk for decision makers, streamline aircraft inductions into scheduled maintenance and reduce cost for total life cycle management.”
A-10 ASIP Manager