Design Tools for Fatigue Life Prediction in Surface Treated Aerospace Components

Although surface treatments like low plasticity burnishing (LPB) and laser shock processing (LSP) impart deep compressive residual stresses that significantly improve damage tolerance, credit for the improved fatigue strength is not generally taken in design. The analytical tools needed to support taking design credit by predicting the fatigue life and optimizing the surface treatment process for the desired fatigue performance do not exist. The development of a suitable design tool is proposed that integrates the Fatigue Design Diagram (FDD) method developed at Lambda Research with FEA and LEFM analysis codes currently used in component design. The FDD is an extension of the Haigh or Goodman diagram in common use by designers, facilitating implementation and ease of use. Phase I will draw upon the extensive surface enhancement database available at Lambda Research for LPB and shot peening to test and demonstrate the feasibility of the FDD approach to predict the fatigue life of components for steels, Ti, Ni, and Al alloys damaged by corrosion, fretting and FOD. In Phase 2, FDD based design software tools will be created that interface with FEA codes currently used by designers. This comprehensive tool will allow the designer to predict fatigue life and distortion of components for a given combined residual and applied stress distribution, and to iteratively optimize residual stress distribution to achieve the desired fatigue life for a given failure mode and component geometry. Commercialization through licensed distribution of the software by FEA code providers will extend the technology to the aerospace, defense, automotive and general industrial markets.