Probabilistic Analysis of Cold Expanded Holes

Many aircraft make use of cold expanded (Cx) holes to increase the life of select fastener holes. Currently there is not an accepted method to predict the life at Cx holes accounting for the physics of the process. The Engineered Residual Stress Implementation (ERSI) Working Group has been actively pursuing methods to accurately predict the fatigue crack growth life of Cx holes. Recently the ERSI working group led a round robin exercise focusing on how uncertainty in fatigue response due to the random variability in residual stresses at Cx fastener holes can be captured in damage tolerance analysis (DTA). The round robin was conducted in a single blind fashion. While most of the respondents to the round robin provided deterministic analysis, Southwest Research Institute (SwRI) also performed a probabilistic analysis to better account for random variables. By performing this probabilistic analysis, SwRI is able to identify the sensitivities in the DTA to the input parameters. Once the sensitivities are known, they can be used to determine the parameters that need to tracked for use in a digital twin. This paper demonstrates how progressively addressing parameter uncertainties can reduce the overall uncertainties in the crack growth prediction.