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Wang Z.G.,University of Iowa | Wang Z.G.,Prudential Insurance Company | Liu Y.,Cooper Tire and Rubber Company | Wang G.,Virginia Polytechnic Institute and State University | Sun L.Z.,University of California at Irvine
International Journal of Biomedical Imaging | Year: 2011

Quantification of the mechanical behavior of normal and cancerous tissues has important implication in the diagnosis of breast tumor. The present work extends the authors' nonlinear elastography framework to incorporate the conventional X-ray mammography, where the projection of displacement information is acquired instead of full three-dimensional (3D) vector. The elastic parameters of normal and cancerous breast tissues are identified by minimizing the difference between the measurement and the corresponding computational prediction. An adjoint method is derived to calculate the gradient of the objective function. Simulations are conducted on a 3D breast phantom consisting of the fatty tissue, glandular tissue, and cancerous tumor, whose mechanical responses are hyperelastic in nature. The material parameters are identified with consideration of measurement error. The results demonstrate that the projective displacements acquired in X-ray mammography provide sufficient constitutive information of the tumor and prove the usability and robustness of the proposed method and algorithm. Copyright © 2011 Z. G. Wang et al.

Liu Y.,Cooper Tire and Rubber Company | Wang G.,Rensselaer Polytechnic Institute | Sun L.Z.,University of California at Irvine
Journal of Engineering Mechanics | Year: 2014

Many engineering and biological media can be described as the combination of several heterogeneous constituent phases. For instance, a tumor-containing organ can be approximated as two phases: tumor and tissue media. A nonlinear elastography method is developed in this paper to identify the distribution of mechanical properties in two-phase media, based solely on the measurement of displacements and forces on the external boundary. The two-phase distribution is approximated with a general continuous material parameter field, for which a designed grouping technique is applied to reduce the number of unknowns. The numerical efficiency of the minimization-based reconstruction is further enhanced by user-supplied gradients of the objective function, which are computed with minimal cost using a nonlinear adjoint method. Sample reconstruction is performed to identify two irregular inclusions in a two-dimensional nonlinear medium. © 2014 American Society of Civil Engineers.

Hoo Fatt M.S.,University of Akron | Chen L.,Cooper Tire and Rubber Company
Journal of Cellular Plastics | Year: 2014

A phenomenological constitutive model for Divinycell PVC H100 foam undergoing crushing and hysteresis under cyclic compression loading was developed. Cyclic compression tests were done with strain amplitudes from 0.02 to 0.1 and strain rates ranging from 0.0005's-1 to 5 s-1. Within this test range, the PVC H100 foam exhibited strain rate-dependency, damage, and hysteresis. Damage that occurred in the foam after yielding followed the pattern of Mullins damage, i.e. the damage was essentially fixed at a given strain amplitude, and more damage occurred with increasing the strain amplitude. A constitutive model based on damage initiation and viscoelastic damage evolution of the foam was proposed. A simple damage initiation criterion based on critical compressive strain was proposed to separate undamaged and damaged foam response. A standard model, an elastic spring in parallel with Maxwell element, was used to describe viscoelastic behavior before and after damage. Before damage, spring and damper constants were evaluated from the test data. The rate-dependent undamaged stress-strain response and flow stress were found to be in good agreement with the test results. After damage, the spring and dashpot resistances were found to be the functions of strain amplitude and flow stress, which depended on strain rate. These viscoelastic damage functions were shown to give very good predictions of the hysteresis and strain rate-dependent behavior of the foam after damage. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Klein J.E.,Virginia Polytechnic Institute and State University | Divoux G.M.,Virginia Polytechnic Institute and State University | Singh H.K.,Virginia Polytechnic Institute and State University | Singh H.K.,Cooper Tire and Rubber Company | And 7 more authors.
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2011

Proton exchange membrane fuel cells typically consist of stacks of membrane electrode assemblies sandwiched between bipolar plates, effectively combining the individual cells in series to achieve the desired voltage levels. Elastomeric gaskets are commonly used between each cell to insure that the reactant gases are isolated; any failure of a fuel cell gasket can cause the reactants to mix and can lead to failure of the fuel cell. An investigation of the durability and lifetime of these fuel cell seals was performed by using accelerated characterization methods. A hydrocarbon sealant was tested in five different environments to simulate fuel cell conditions. Material properties such as secant modulus at 100% strain, tensile strength and strain at failure were determined using dogbone samples aged at several different imposed strains and aging times in environments of interest. Tearing energy was evaluated using trouser test samples tested under different rates and temperatures after various environmental aging conditions. Viscoelastic properties of these seals were analyzed using momentary and relaxation compressive stress tests. A viscoelastic and mechanical property characterization of these elastomeric seals under accelerated aging conditions could help understand their behavior and predict their durability in the presence of mechanical and environmental loading. ©2010 Society for Experimental Mechanics Inc.

Song C.R.,University of Mississippi | Adhikari S.,Fugro | Kidd J.T.,Cooper Tire and Rubber Company
International Journal of Geotechnical Engineering | Year: 2016

Many sections of floodwalls in New Orleans, LA were damaged or suffered catastrophic failure as a result of Hurricane Katrina. One of the key triggering mechanisms of failure reported is the gap development between the floodwall and soil. This study developed an effective retrofitting technique to prevent this gap development by introducing a buried layer of self-sealing sand and bentonite mixture. This self-sealing layer was expected to swell fast enough so that it could seal the gap without any time delay and to exert insignificant swelling pressure to the levee so that it did not affect the stability of the levee. Among several mixtures of sand and bentonite, the mixture of 70% sand and 30% bentonite (by dry weight) proved to be a more effective one among laboratory and large scale model tests conducted in this study by swelling fast enough to seal the gap (approximately 10% swelling strain in 2 days), but exerting insignificant swelling pressure (162.03 kPa in 2 days) to the levee. From the numerical analysis using FLAC3D, it was confirmed that the stability of the levee was actually increased by sealing the gap even with the minor swelling pressure from the self-sealing layer. From 1/64th scale centrifuge tests, the wall with the self-sealing layer did not fail at 64 g, while the one without the self-sealing layer failed at 25 g acceleration. © 2016 Informa UK Limited, trading as Taylor & Francis Group

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