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Ithaca, NY, United States

Davis B.R.,Cornell University | Wawrzynek P.A.,Fracture Analysis Consultants, Inc. | Hwang C.G.,Seoul University of Venture and Information | Ingraffea A.R.,Cornell University
Engineering Fracture Mechanics | Year: 2014

A technique was implemented for decomposing 3-D mixed-mode energy release rates using the Virtual Crack Extension (VCE) method. The technique uses a symmetric/anti-symmetric approach to decompose local crack-front displacements that are substituted into the global VCE energy release rate form. The subsequent expansion leads to the mixed-mode energy release rate expressions. As a result of the expansion, previously unaddressed modal-interaction coupling terms are found to impact the mixed-mode energy release rates. This development expands the VCE method's advantages over similar procedures when simulating arbitrary crack growth by providing the means to calculate both mixed-mode energy release rates and their variations. © 2014 Elsevier Ltd.

Agency: Department of Defense | Branch: Navy | Program: SBIR | Phase: Phase II | Award Amount: 149.27K | Year: 2016

The US Navy is concerned with fretting fatigue as a controlling factor in aircraft component life, such as the dovetail contact of blade/disk assemblies and spline gears in helicopter transmissions. To model fretting fatigue crack nucleation and subsequent fatigue crack growth, the FRANC3D software was modified to include fretting nucleation models. These models, combined with finite element results predict fretting nucleation life and crack nucleation sites. Discrete crack insertion and growth is then simulated to predict total life. FRANC3D has been used to successfully simulate fretting fatigue in: dog-bone specimens, small scale dovetail specimens, a blade/disk assembly, helicopter transmission gear teeth, and a wind turbine shaft/bearing assembly. These simulations highlighted the need for additional fretting experiments, as fretting nucleation models require material dependent parameters. The Army Research Lab will conduct a suite of experiments on bare- and coated-steel dog-bone specimens with titanium fretting pins. This data will verify and validate the fretting nucleation models, and the FRANC3D simulations will provide benchmarks for simulating fretting fatigue in more complex components. Enhancements to the software will allow a straightforward transition from fretting nucleation to fatigue crack growth, thereby providing total life predictions for critical aircraft components.

Agency: Department of Defense | Branch: Navy | Program: SBIR | Phase: Phase II | Award Amount: 664.02K | Year: 2007

The US Navy is working towards providing more reliable estimates of fatigue life to reduce the risk of component failure during flight and to improve repair schedules while reducing costs. Fretting fatigue is seen as one of the controlling factors in the life of aircraft engine components where cyclic loading leads to contact and slip between mating parts. For instance, the disk/blade assemblies in turbine engines suffer fretting at the dovetail contacts. In the proposed analysis methodology, an analytical model of fretting fatigue crack nucleation based on the uncracked stresses in the contact region provides the component life up to the point of a measurable crack. A finite-element-based approach to model the discrete, arbitrary, 3D crack growth from the measurable, initial crack to the point of failure provides a stress intensity factor history and remaining life estimate. The marriage of the two approaches provides a cradle-to-grave analysis capability for modeling fretting fatigue. Fracture Analysis Consultants Inc. (FAC) along with Research Applications Inc. (RAI), in consultation with Pratt & Whitney, intend to develop and validate such a methodology starting from RAI’s analytical model of fretting fatigue crack nucleation and FAC’s finite-element-based fracture analysis software, Franc3D/NG.

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 712.25K | Year: 2007

This Phase II proposal describes the continued development of three-dimensional, nonlinear structural analysis methods for use in prognosis systems for aerospace, gas turbine, metallic components and component assemblies. In Phase I, Fracture Analysis Consultants Inc. (FAC) demonstrated the feasibility of using a three-dimensional fracture propagation program, Franc3D/NG, to automatically generate finite element models that relate sensor-measurable structural response to damage scenarios involving fatigue cracks. These numerical results were used to generate probabilistic predictions of remaining useful component life. In Phase II, FAC proposes to work closely with Pratt & Whitney to expand on the Phase I work with four key areas of emphasis. First, we propose to incorporate realistic engine loads, such as combined high and low frequency cycling, and realistic materials, such as single crystal alloys. Second, we propose to incorporate advanced 3D fracture mechanics, including mixed mode I, II, and III loading, orthotropic material behavior, and crack growth in residual stresses due to surface treatments. Third, we propose to verify the software using historical and newly generated test results. Fourth, we propose to verify the software and demonstrate its usefulness and usability in an actual engine development and production environment.

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 746.36K | Year: 2012

ABSTRACT: Over the past few years, the Air Force has increased the emphasis on probabilistic methods for design reliability predictions of fracture critical engine components, including metallic turbine engine blades and disks. A significant shortcoming and potential source of conservatism of most current life prediction tools and methodologies is the reliance on stress intensity factor values obtained from highly idealized component and crack geometries. In Phase I, we demonstrated that this shortcoming could be overcome by making an existing high fidelity 3D crack growth simulator work together with an existing probabilistic life prediction code. The resulting prototype software tool was used to perform a probabilistic life prediction for a geometrically complex engine component. For Phase II, we propose to develop the prototype software into a tool suitable for routine production use. This will include creating a unified graphical user interface, adding additional features, performing sensitivity studies that will assess accuracy/efficiency tradeoffs and develop best practices, and performing a series of analyses that include advanced life prediction topics. BENEFIT: The successful completion of Phase II will result in a high fidelity probabilistic fatigue life prediction tool for metallic turbine engine components. Such a tool will allow engine manufacturers to reduce uncertainty and conservatism in fatigue life assessments. This means that for current engine designs, component lives or inspection intervals can be extended with no increased risk of failure. For new engine designs, the tool can be used to help find the optimal point among performance, efficiency, and life cycle cost. The tool can be used by the government to perform high accuracy fracture risk assessments independent of the manufacturers. The tool can also be applied to other applications with fracture critical components, such as airframes and power generation turbines, among others.

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