Summary of Recent Round Robin Life Prediction Efforts for Crack Shape and Residual Stress Effects

Abstract

Two round-robin life prediction efforts were conducted to assess the ability to perform blind life predictions for test data obtained for corner cracks at centered and offset holes in 7075-T651 and 2024-T351 Aluminum alloys. The first round robin effort was conducted as part of a recent AFGROW Crack Growth Life Prediction Software Workshop focused on the ability to accurately predict crack shape evolution, and the second was conducted by the Engineered Residual Stress Initiative (ERSI) Workshop on the effect of split sleeve cold-working. The goal of the ERSI round-robin was to quantify specific sources of systematic uncertainties based on fixed input data provided to each participant. The blind predictions of crack growth life for the AFGROW Workshop were in very good agreement with the test data, and the predictions for the ERSI effort were generally within the statistical variation of the test data. However, the predictions of crack shape evolution did not show good agreement with the test results for either effort. The crack growth predictions for each crack direction were made using a single crack growth rate model based on the test specimen grain orientation and crack growth in the radial direction from the hole (L-T orientation). On further investigation, it was determined that different crack growth rate models (L-T and L-S) were required to predict crack shape changes as the initial corner cracks grew through the thickness of the test specimens. This paper will summarize the results of each blind round robin effort and compare the crack shape predictions made using single and dual crack growth rate models.