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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.


Carter B.J.,Fracture Analysis Consultants, Inc. | Carter B.J.,Cornell University | Schenck E.C.,Impact Technologies, LLC | Wawrzynek P.A.,Fracture Analysis Consultants, Inc. | And 3 more authors.
Engineering Fracture Mechanics | Year: 2012

Fretting nucleation models and three-dimensional finite element analyses are used to compute the fretting fatigue life for metallic components. The models predict crack nucleation cycles and location(s). Discrete crack growth simulations provide stress intensity factor histories, with multiple, non-planar, three-dimensional cracks possible. The histories are input into crack growth rate model(s) to compute propagation cycles. The sum of fretting nucleation plus propagation cycles is the total life. Experimental fretting data, including crack nucleation location and cycles, and crack growth trajectory and propagation cycles, are used to validate the approach. Predictions for a realistic turbine blade/disk are comparable to field observations. © 2012 Elsevier Ltd.


Davis B.R.,Cornell University | Wawrzynek P.A.,Fracture Analysis Consultants, Inc. | Carter B.J.,Fracture Analysis Consultants, Inc. | Ingraffea A.R.,Cornell University
Engineering Fracture Mechanics | Year: 2016

The energy-based growth formulation and accompanying simulation technique introduced in Part I of this series is generalized in this work to predict arbitrary, mixed-mode, non-planar crack evolution. The implementation uses a novel basis-function approach to generate a crack extension expression, rather than relying on the local, point-by-point approach described in Part I. The basis-function expression dampens the effect of numerical noise on crack growth predictions that could produce numerically unstable simulation results. Two simulations are presented to demonstrate the technique's ability to capture both general non-planar behavior, as well as local mixed-mode phenomena, e.g. "factory-roof" formation, along the crack front. © 2016 Elsevier Ltd.


Craig McClung R.,Southwest Research Institute | Wawrzynek P.,Fracture Analysis Consultants, Inc. | Lee Y.-D.,Southwest Research Institute | Carter B.J.,Fracture Analysis Consultants, Inc. | And 2 more authors.
Proceedings of the ASME Turbo Expo | Year: 2016

Most current tools and methodologies to predict the life and reliability of fracture critical gas turbine engine components rely on stress intensity factor solutions that assume highly idealized component and crack geometries, and this can lead to highly conservative results in some cases. This paper describes a new integrated methodology to perform these assessments that combines one software tool for creating high fidelity crack growth simulations (FRANC3D) with another software tool for performing probabilistic fatigue crack growth life assessments of turbine engine components (DARWIN). DARWIN employs finite element models of component stresses, while FRANC3D performs automatic adaptive re-meshing of these models to simulate crack growth. Modifications have been performed to both codes to allow them to share and exchange data and to enhance their shared computational capabilities. Most notably, a new methodology was developed to predict the shape evolution and the fatigue lifetime for cracks that are geometrically complex and not easily parameterized by a small number of degrees of freedom. This paper describes the integrated software system and the typical combined work flow, and it shows the results from a number of analyses that demonstrate the significant features of the system. © Copyright 2016 by ASME.


Pettit R.,FractureLab | Annigeri B.,Aerojet Rocketdyne | Owen W.,Aerojet Rocketdyne | Wawrzynek P.,Fracture Analysis Consultants, Inc.
Engineering Fracture Mechanics | Year: 2013

The damage tolerance assessment of complex aerospace structural components requires the capability of effective modeling of 3D cracks and their associated propagation and velocity and path under fatigue loads. A 3D mixed mode crack propagation theory is presented which includes the effect of KI, KII, and KIII, as well as non-proportional loading, elastic and fracture resistance anisotropy, and fracture mode asymmetry (viz. the ability to transition between competing tensile and shear modes of propagation). A modified strain energy release rate criterion including the modeling of crack closure is developed and presented for a representative problem. An elementary, mode I characterization of closure is used, leaving shear mode closure as fertile ground for further study. Use of the model is presented for an example problem with steady-vibratory interaction. © 2013 Elsevier Ltd.


Grant
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.


Grant
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.


Grant
Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase I | Award Amount: 99.77K | Year: 2011

ABSTRACT: The Air Force has been placing increased emphasis on probabilistic methods for predictions of design reliability of fracture critical engine components, including metallic turbine engine blades and disks. Current state-of-the-practice for these methods typically include a significant amount of conservatism in crack initiation and fatigue crack growth and inspection design criteria due to uncertainties in material properties, fatigue performance, crack growth analysis, stress analysis, residual stresses, damage mechanisms, and nondestructive inspection, among others. We propose to develop and demonstrate a new probabilistic life prediction methodology that will significantly reduce uncertainty and conservatism by employing an accurate mechanics based crack growth analysis. We will combine an existing high fidelity 3D crack growth simulator (FRANC3D) with an existing probabilistic life prediction code (DARWIN). Both codes are recognized as being the most mature and the most capable codes in their areas of specialization (high fidelity crack modeling and probabilistic life prediction , respectively). The new methodology is expected to reduce conservatism in probabilistic life predictions, thus extending component lives or inspection intervals. The proposed effort includes the involvement of a major engine OEM. BENEFIT: Current probabilistic methodologies for setting fatigue lives and inspection intervals for metallic engine components include a significant amount of conservatism due to uncertainties in the, among other things, crack growth analysis. The proposed effort will combine a high fidelity crack growth simulator (FRANC3D) with a probabilistic fatigue life calculator (DARWIN). The resulting tool and methodology is expected to reduce conservatism in probabilistic life predictions, thus increasing the predicted mean time to failure. For a constant relative probability of failure this will extend the allowable component life and inspection intervals. Extending component fatigue lives and inspection intervals will yield significant costs saving over the lifetime of the engine. The resulting methodology can be used in non-engine applications such as airframes, land and sea based turbines, and terrestrial vehicles.


Fracture Analysis Consultants, Inc. | Entity website

DARWIN & FRANC3D FAC along with SWRI recently finished a project funded by the US Air Force. The project combined the DARWIN and FRANC3D software ...


Fracture Analysis Consultants, Inc. | Entity website

Fracture Analysis Consultants, Inc (FAC) Specializing in fracture simulation and software development. Fracture Analysis Consultants, Inc ...

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