Mesh Independent Probabilistic Residual Life Prediction of Metallic Airframe Structures

Global Engineering and Materials, Inc. (GEM) along with its team members, Clarkson University and LM Aero, propose to develop a mesh independent probabilistic residual life prediction tool for metallic airframe structures. The deterministic solver of this probabilistic analysis tool will be developed by integrating our cutting edge extended finite element toolkit for Abaqus (XFA) with a novel small time-scale fatigue crack growth model for mesh independent fatigue crack growth prediction of a complex airframe structural component subjected to multiaxial and variable amplitude loading. The fast matching and narrow band technique will be implemented to track a curvilinear 3D crack growth without remeshing. Both the versatility and the high computational efficiency will make the XFA an ideal solution model for the probabilistic life prediction where the initial defect shape and location can be treated as random variables without user intervention. After the integration of XFA with a general purpose probabilistic analysis framework (PFA), the resulting probabilistic version of the XFA (PXFA) will enable the following: 1) fatigue reliability assessment of an aging component; 2) evaluation of design variables to meet a targeted reliability level; and 3) provision of operational decision support using SHM data on repair, maintenance, and life extension options.

Structural aging under fatigue loading is one of the most common failure mechanisms in civilian structures such as buildings, bridges, power lines, pressure vessels, and ship structures. The developed probabilistic fatigue life prediction tool can be used effectively and efficiently to assist a designer and rule-maker to answer the following questions: 1) How tolerant of cracks is the location? 2) How long to repair a crack in service? 3) What is the impact of an operational profile change? 4) How often should inspections be made? and 5) How can SHM input be used best? The tool can be used to assist commercial and military industries to reduce the cost of test-driven design and process iterations with the use of the virtual testing tool. Finally, teaming with LM, a highly visible airplane manufacturer, will considerably shorten our development cycle from producing a prototype research orientated tool to commercially accessible design software.

The results from this research will have significant benefits to enhance the aviation safety program in NASA. It will result in: 1) a commercially viable, accurate, computationally efficient, and user-friendly probabilistic residual life assessment tool for charactering fatigue crack growth and perform damage analysis with the presence of uncertainties in design and loading parameters; 2) an integrated analysis framework for fatigue damage prognosis and health management of air platform; 3) a virtual testing tool to reduce current certification and qualification costs which are heavily driven by experimental testing under various stress conditions; and 4) innovative probabilistic methods and reliability assessment procedures to facilitate the structural health management. The developed tool integrates advanced computational mechanics, innovative fatigue damage modeling, and efficient probabilistic methods into a seamless framework for probabilistic crack growth analysis and structural damage prognosis.

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