SBIR-STTR Award

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

The goal of this program is to develop a validated design tool to predict fatigue behavior in components subjected to residual compression inducing surface treatments. This design tool will be based on the Fatigue Design Diagram (FDD) model developed at Lambda Technologies to predict the optimum magnitude of compression needed to mitigate damage and restore or exceed the original performance of aerospace components. An FDD code will be developed in this Phase II SBIR program that will be capable of interfacing with most commercial finite element analysis (FEA) codes. Several design analysis options will be available, including the prediction of optimum residual stress distribution, life estimation, damage tolerance design, etc. The FDD code will be validated with test results from PRATT & WHITNEY’s F100-PW220 HPC 4-6 surface treated blades. Also, additional tests are planned to test the limits applicability of the FDD. Commercialization plan includes providing seat licenses to OEMs and DoD agencies, and also by providing training and on a trial limited time basis free beta-version of the FDD code to users.

Benefit:
The specific benefits of the prediction tool will be: a) Expansion of the range of application of existing alloys to higher stress levels b) Extension of the life of components by mitigating damage mechanisms c) Lower cost of ownership by reducing inspection and maintenance requirements d) Reduced need and associated cost of using specialty alloys e) Improved performance of existing components without changing material or design f) Improved performance with reduced weight and cost for new designs Specific benefits to DoD foreseen from this Phase II SBIR program The development of the FDD code under this SBIR program is expected to revolutionize the way fatigue-limited aircraft components will be designed/inspected/repaired/replaced in the future. The code will help in identifying critical regions in aircraft components at the early stages of design and by appropriate RS design, engineers will be able to take design credit by way of increased performance, reduced weight, increased damage tolerance. In legacy engines and aircrafts, the FDD code will help in accomplishing life extension. Even previously retired components may be reworked to restore through the use of the FDD code. In summary, the following specific benefits are foreseen: a) An engineering method to take RS design credit in new engine parts b) Legacy engine life extension by RS design at critical regions c) Reduced inspection and MRO by increasing damage tolerance d) Improved time on wing due to reduced inspection and MRO e) Aging aircraft life extension by RS design at critical regions

Keywords:
fatigue design diagram, surface enhancement, Life Extension, aircraft engine components, compressive residual stress, LSP, LPB, aircraft structural components