Microstructure based fatigue life predictions for thick plate 7050-T7451 airframe alloys

The purpose of this work was to test a microstructure based fatigue life prediction Monte-Carlo model for potential use in quantifying fatigue quality and reliability of metallic structural alloys. The model used was of the crack growth type with the sizes of crack initiating pores, local crack geometry and crack tip texture as random variables. The model was verified using data for 7050-T7451 plate alloy fatigue tested in smooth sample configuration at σ_max of 241 and 276 MPa and R=0.1. The mechanical testing was supplemented with characterizations of the size distributions of the fatigue performance limiting bulk porosity and measurements of the actual sizes of the fatigue crack initiating pores. Predicted fatigue lives were in good agreement with the experimental results and the model identified the size distribution of the crack initiating pores as the dominant variable controlling fatigue performance. The distributions of those pores were predicted from the bulk pore size data using the statistics of extremes. The developed approach proved effective in incorporating microstructural information in modeling fatigue and could be used in ranking fatigue quality and reliability of materials based on microstructural data.