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Determination of Significant Failure Size for Finite Element Analysis (FEA)

Description:

TECHNOLOGY AREA(S): Materials 

OBJECTIVE: Determine threshold of finite element analysis “hot spot” characteristics where real-world degradation or failure effects become predictable and measureable. 

DESCRIPTION: Hill AFB Landing Gear (LG) office uses Finite Element Analysis (FEA) to predict LG part failures. Analyses will often reveal localized stress concentrations or “hot spots” where a limited number of elements are indicated by the software as exceeding material limits. Currently, determination as to when the hot spots would result in real-world part failure is based on the size of the area of elements stressed above yield or ultimate strength. This determination is subjectively based on the experience of the LG engineer performing the FEA, and can differ between engineers even for the same component in the same situation. For example, some have used the criteria in industry boiler and pressure vessel standard ASME BPVC Section VIII-2 to make this determination for LG hardware. The research and development effort shall produce a predictive relationship between FEA stress concentration characteristics and real-world hardware effects under the same loading conditions. Relevant characteristics of FEA hot spots may include but are not limited to mesh or part geometry, size, stress levels, location, distance between stress concentrations, and sensitivity to existing part defects/damage. Loading scenarios may include tension, compression, shear, and bending. Common LG part materials include Aluminum 7075-T73 and 7050-T73, Steel 300M and 4340. Alternative finite element software/meshing/analysis methods other than what Hill AFB currently uses are within scope of this study. The model predictions shall be verified and validated on physical test specimens according to ASTM E8 for tension. The contractor shall publish a commercial standard or specification for interpreting FEA stress concentrations based on the results of this effort. 

PHASE I: R&D solution that meets the above requirements and conduct preliminary business case analysis (BCA) to determine implementation costs, including a return-on-investment (ROI) calculation that compares anticipated savings to expected costs. Proof-of-concept prototype(s) shall be developed to demonstrate conformance to the requirements. 

PHASE II: Initiate and complete the test plan developed in Phase I. Proof-of-concept prototype(s) shall be refined to installation-ready article and shall undergo testing to verify and validate all requirements. This process may require multiple iterations before a final design is selected. Refine BCA/ROI based on the final design. 

PHASE III: If developed technologies are cost effective, passes verification / validation and qualification testing, then it shall proceed to transitioning and implementation of the technologies. With possible application to other AFSC sites. 

REFERENCES: 

1. ASME/BPVC sec VIII-2 "Boiler and Pressure Vessel Code (BPVC)"; 2. ASTM E 8 "Standard Test Methods for Tension Testing of Metallic Materials"; 3. “The Theory of Material Failure” By Richard M Christensen ISBN # (978-0-19-966211-1)

KEYWORDS: Finite Element Analysis, FEA, Hotspots, Landing Gear 

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