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Amir Sohrabi M.,Cooper Tire and Rubber Company | Muliana A.H.,Texas A&M University | Srinivasa A.R.,Texas A&M University
Finite Elements in Analysis and Design | Year: 2017

This study presents simulations of shape changing in active truss structures that undergo non-linear and time dependent response. The truss structure comprises of slender members with electro-active (piezoelectric) components joined by pins, allowing for large deformations due to rotations at the pins. A nonlinear time-dependent electro-mechanical constitutive model is considered for the piezoelectric components in the truss systems. In order to find the actuation inputs to achieve a desired shape, the required shape is defined with respect to reference configuration for a equivalent 3 dimensional continuum. The mapping between reference and current configuration is used to calculate the macroscopic strains in the continuum. The corresponding strains along the longitudinal axes of the truss members whose ends coincide with certain material points in the continuum are then calculated. The strains corresponding to the predefined shapes are achieved by applying electric field through the piezoelectric materials, and as a result the truss system undergoes the desired shape changes. The shape changing behaviors in electro-active truss systems are analyzed using a finite element (FE) method, incorporating nonlinear material and geometry. Numerical implementation of the active truss structures is also presented. Two types of truss configurations are considered which are planar and beam configurations. The planar configuration is formed by arrangement of cubical truss elements while the beam configuration consists of several tetrahedral truss elements. Several shape configurations of the planar and beam truss structures are shown as examples. While considerable amount of work has been done with piezo-actuated truss systems under the assumption of linear piezoelectric response, we study the influence of the nonlinear hysteretic electro-mechanical behavior and highlight the differences in the deformations of the truss structures when the nonlinear and time-dependent electro-mechanical and linear electro-mechanical models are considered for the piezoelectric components. © 2017 Elsevier B.V.


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.


Mars W.V.,Cooper Tire and Rubber Company
Rubber Chemistry and Technology | Year: 2011

In compounded material systems, such as rubber, a wide range of properties can be achieved by design. This flexibility poses a challenge-how to balance stiffness against other considerations, such as energy dissipation under dynamic loading, fatigue, etc. Negotiating this balance requires that adequate account be taken of how a given mechanical input (i.e., strain, stress, energy) is controlled, and how other mechanical outputs vary as the stiffness changes.We outline here a simple analysis bywhich these considerations can be managed. The analysis is based on a novel split of the elasticity law into work-conjugate parts: one representing generally that which is to be held constant, and the other representing that which occurs in reaction to imposed control. The split gives rise to a scalar parameter suitable for quantifying the degree to which a given 1D mechanical process is strain-, energy-, or stress-controlled. The physical sense of the parameter is illustrated through the example of a two-spring system, where one spring represents the subject material, and the other represents the mechanical environment in which the material operates. The example shows that the parameter concisely summarizes the effects of the environment on the operating conditions of the material.We also provide a simple example illustrating how the parameter can be used to rank the fatigue performance of a set of compounds, taking into account the stiffness and the test control mode.


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.


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.


Ait-Bachir M.,CNRS Research Institute in Civil Engineering and Mechanics | Mars W.V.,Cooper Tire and Rubber Company | Verron E.,CNRS Research Institute in Civil Engineering and Mechanics
International Journal of Non-Linear Mechanics | Year: 2012

The energy release rate of a small crack in an infinite hyperelastic medium, and subjected to large strain multiaxial loading conditions, is derived by considering the balance of configurational stresses acting on two planes: one cutting the center of the crack face, and the other at an infinite distance in front of the crack tip. The analysis establishes that the energy release rate of a small crack is always proportional to the size of the crack, irrespective of the loading conditions and the crack orientation. The balance of configurational stresses is illustrated for several benchmark cases including simple extension, pure shear and equibiaxial extension, and for perpendicular and inclined cracks. © 2012 Elsevier Ltd. All rights reserved.


Chen H.,Indiana University – Purdue University Indianapolis | Slipchenko M.N.,Purdue University | Liu Y.,Indiana University – Purdue University Indianapolis | Liu Y.,Cooper Tire and Rubber Company | And 4 more authors.
Journal of Applied Physiology | Year: 2013

The microstructural deformation-mechanical loading relation of the blood vessel wall is essential for understanding the overall mechanical behavior of vascular tissue in health and disease. We employed simultaneous mechanical loading-imaging to quantify in situ deformation of individual collagen and elastin fibers on unstained fresh porcine coronary adventitia under a combination of vessel inflation and axial extension loading. Specifically, the specimens were imaged under biaxial loads to study microscopic deformation-loading behavior of fibers in conjunction with morphometric measurements at the zero-stress state. Collagen fibers largely orientate in the longitudinal direction, while elastin fibers have major orientation parallel to collagen, but with additional orientation angles in each sublayer of the adventitia. With an increase of biaxial load, collagen fibers were uniformly stretched to the loading direction, while elastin fibers gradually formed a network in sublayers, which strongly depended on the initial arrangement. The waviness of collagen decreased more rapidly at a circumferential stretch ratio of λθ= 1.0 than at λθ= 1.5, while most collagen became straightened at λθ= 1.8. These microscopic deformations imply that the longitudinally stiffer adventitia is a direct result of initial fiber alignment, and the overall mechanical behavior of the tissue is highly dependent on the corresponding microscopic deformation of fibers. The microstructural deformationloading relation will serve as a foundation for micromechanical models of the vessel wall. Copyright © 2013 the American Physiological Society.


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.


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


Singh H.K.,Virginia Polytechnic Institute and State University | Singh H.K.,Cooper Tire and Rubber Company | Chakraborty A.,Virginia Polytechnic Institute and State University | Chakraborty A.,University of Minnesota | And 2 more authors.
Holzforschung | Year: 2010

An experimental evaluation of mixed mode fracture tests conducted on adhesively bonded wood specimens using a dual actuator load frame is presented. This unit allows the fracture mode mixity to be easily varied during testing of a given specimen, providing improved consistency, accuracy, and ease of testing over a range of loading modes. Double cantilever beam (DCB) type specimens made of southern yellow pine (Pinus spp.) wood substrates bonded with a commercially available one part polyurethane adhesive were tested over a wide range of mode mixities from pure mode I to pure mode II. The critical strain energy release rate (SERR) values were calculated from the measured load, displacement, and crack length data, in combination with material properties and specimen geometric parameters, and compared on a GI versus GII fracture envelope plot. Mean quasi-static fracture energy values were calculated to be 390 J m-2 and 420 J m-2 for mode I and mode II fracture, respectively. For various mixed mode phase angles, the critical SERR values were partitioned into mode I and mode II components. In mixed mode loading conditions the cracks were typically driven along the interface, which resulted in lower total fracture energy values when compared with those measured under pure mode I loading conditions. A drop in measured fracture energy of approximately 45% was observed with mode mixity phase angles as small as 16°, implying that engineering designs based on results from the popular mode I DCB test could be nonconservative in some situations. Fracture surfaces obtained at different mode mixities are also discussed. An improved understanding of fracture behavior of adhesively bonded wood joints under mixed mode loading through generation of fracture envelopes could lead to improved designs of bonded wood structures. Copyright © by Walter de Gruyter.

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