Design Tools for Fatigue Life Prediction in Surface Treated Aerospace Components Navy SBIR FY2005.1 Sol No.: Navy SBIR FY2005.1 Topic No.: N05-026 Topic Title: Design Tools for Fatigue Life Prediction in Surface Treated Aerospace Components Proposal No.: N051-026-0480 Firm: Lambda Technologies 5521 Fair Lane Cincinnati, Ohio 45227 Contact: Narayanan Jayaraman Phone: (513) 561-0883 Web Site: lambda-research.com Abstract: 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. Benefits: New surface treatment technologies have emerged that can mitigate a variety of damage mechanisms to greatly improve fatigue performance and damage tolerance. The design tool to predict fatigue life in the presence of compressive residual stress that will be developed in this program will allow credit to be taken for these beneficial surface treatments. The FEA coupled design tool will provide the means of optimizing the magnitude and shape of the compressive residual stress distribution produced by surface treatment to achieve a desired fatigue strength and life for the component geometry, load spectrum and damage mechanism. The specific benefits of the comprehensive design tool will be: 1) To extend the range of application in existing alloys to higher stress levels. 2) To extend the life of existing and new components by mitigating damage mechanisms. 3) To reduce the cost of ownership by reducing inspection and maintenance requirements. 4) To reduce the need for, and cost of, using specialty alloys. 5) To improve the performance of existing components without changing either material or design. 6) Ultimately, to incorporate residual compression into initial component designs for cost and weight savings with improvement of performance. This design tool is expected to have far-reaching commercial applications, in areas where fatigue, corrosion fatigue, stress corrosion cracking, fretting fatigue, and other damage processes that can be mitigated by the use of compressive residual stresses. These include the fields of aerospace, military, marine, automotive, biomedical, and structural engineering applications where fatigue failure is a concern. Return