The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Philip V Bayly - One of the best experts on this subject based on the ideXlab platform.
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on the accuracy and fitting of transversely Isotropic Material models
Journal of The Mechanical Behavior of Biomedical Materials, 2016Co-Authors: Yuan Feng, Ruth J Okamoto, Guy M Genin, Philip V BaylyAbstract:Fiber reinforced structures are central to the form and function of biological tissues. Hyperelastic, transversely Isotropic Material models are used widely in the modeling and simulation of such tissues. Many of the most widely used models involve strain energy functions that include one or both pseudo-invariants (I4 or I5) to incorporate energy stored in the fibers. In a previous study we showed that both of these invariants must be included in the strain energy function if the Material model is to reduce correctly to the well-known framework of transversely Isotropic linear elasticity in the limit of small deformations. Even with such a model, fitting of parameters is a challenge. Here, by evaluating the relative roles of I4 and I5 in the responses to simple loadings, we identify loading scenarios in which previous models accounting for only one of these invariants can be expected to provide accurate estimation of Material response, and identify mechanical tests that have special utility for fitting of transversely Isotropic constitutive models. Results provide guidance for fitting of transversely Isotropic constitutive models and for interpretation of the predictions of these models.
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estimation of Material parameters from slow and fast shear waves in an incompressible transversely Isotropic Material
Journal of Biomechanics, 2015Co-Authors: Dennis J Tweten, Ruth J Okamoto, Philip V Bayly, John L Schmidt, Joel R GarbowAbstract:This paper describes a method to estimate mechanical properties of soft, anIsotropic Materials from measurements of shear waves with specific polarization and propagation directions. This method is applicable to data from magnetic resonance elastography (MRE), which is a method for measuring shear waves in live subjects or in vitro samples. Here, we simulate MRE data using finite element analysis. A nearly incompressible, transversely Isotropic (ITI) Material model with three parameters (shear modulus, shear anisotropy, and tensile anisotropy) is used, which is appropriate for many fibrous, biological tissues. Both slow and fast shear waves travel concurrently through such a Material with speeds that depend on the propagation direction relative to fiber orientation. A three-parameter estimation approach based on directional filtering and isolation of slow and fast shear wave components (directional filter inversion, or DFI) is introduced. Wave speeds of each isolated shear wave component are estimated using local frequency estimation (LFE), and Material properties are calculated using weighted least squares. Data from multiple finite element simulations are used to assess the accuracy and reliability of DFI for estimation of anIsotropic Material parameters.
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Measurments of mechanical anisotropy in brain tissue and implications for transversely Isotropic Material models of white matter
Journal of Mech Behav Biomed Maetr, 2013Co-Authors: Yuan Feng, Ravi Namani, Ruth J Okamoto, Guy M Genin, Philip V BaylyAbstract:White matter in the brain is structurally anIsotropic, consisting largely of bundles of aligned, myelin-sheathed axonal fibers. White matter is believed to be mechanically anIsotropic as well. Specifically, transverse isotropy is expected locally, with the plane of isotropy normal to the local mean fiber direction. Suitable Material models involve strain energy density functions that depend on the I 4 and 5 pseudo-invariants of the Cauchy–Green strain tensor to account for the effects of I relatively stiff fibers. The pseudo-invariant 4 is the square of the stretch ratio in the fiber I direction; I 5 contains contributions of shear strain in planes parallel to the fiber axis. Most, if not all, published models of white matter depend on I 4 but not on 5. Here, we explore the small strain I limits of these models in the context of experimental measurements that probe these dependencies. Models in which strain energy depends on I 4 but not 5 can capture differences in Young’s I (tensile) moduli, but will not exhibit differences in shear moduli for loading parallel and normal to the mean direction of axons. We show experimentally, using a combination of shear and asymmetric indentation tests, that white matter does exhibit such differences in both tensile and shear moduli. Indentation tests were interpreted through inverse fitting of finite element models in the limit of small strains. Results highlight that: (1) hyperelastic models of transversely Isotropic tissues such as white matter should include contributions of both the I 4 and 5 strain pseudo- I invariants; and (2) behavior in the small strain regime can usefully guide the choice and initial parameterization of more general Material models of white matter.
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identification of a transversely Isotropic Material model for white matter in the brain
ASME 2012 International Mechanical Engineering Congress and Exposition, 2012Co-Authors: Yuan Feng, Ravi Namani, Ruth J Okamoto, Guy M Genin, Philip V BaylyAbstract:Axonal fiber tracts in white matter of the brain form anIsotropic structures. It is assumed that this structural anisotropy causes mechanical anisotropy, making white matter tissue stiffer along the axonal fiber direction. This, in turn, will affect the mechanical loading of axonal tracts during traumatic brain injury (TBI). The goal of this study is to use a combination of in-vitro tests to characterize the mechanical anisotropy of white matter and compare it to gray matter, which is thought to be structurally and mechanically Isotropic. A more complete understanding of the mechanical anisotropy of brain tissue will provide more accurate information for computational simulations of brain injury.Copyright © 2012 by ASME
Alfred Sevidzem Yenwongfai - One of the best experts on this subject based on the ideXlab platform.
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progress in the analysis of non axisymmetric wave propagation in a homogeneous solid circular cylinder of a piezoelectric transversely Isotropic Material
Physics Procedia, 2010Co-Authors: A G Every, Alfred Sevidzem Yenwongfai, M ShatalovAbstract:Abstract Non-axisymmetric waves in a free homogeneous piezoelectric cylinder of transversely Isotropic Material with axial polarization are investigated on the basis of the linear theory of elasticity and linear electromechanical coupling. The solution of the three dimensional equations of motion and quasi-electrostatic equation is given in terms of seven mechanical and three electric potentials. The characteristic equations are obtained through the application of the mechanical and two types of electric boundary conditions at the surface of the cylinder. A convenient method of calculating dispersion curves and phase velocities is discussed, and resulting curves are presented for propagating and evanescent waves for the piezoelectric ceramic Material PZT-4 for non-axisymmetric modes of circumferential wave number m = 1 . It is observed that the dispersion curves are sensitive to the type of the imposed boundary conditions as well as to the strength of the electromechanical coupling.
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wave propagation in a homogenous piezoelectric solid cylinder of transversely Isotropic Material
2009Co-Authors: Alfred Sevidzem YenwongfaiAbstract:The ultrasonic nondestructive evaluation (NDE) of composite cylinders is dependent on the thorough understanding of the propagation characteristics of the wave modes in these Materials. In this dissertation the propagation of free harmonic non-axisymmetric (flexural) waves in a homogeneous piezoelectric solid cylinder of transversely Isotropic Material is studied, on the basis of the linear theory of elasticity and linear electromechanical coupling of the elastic and electric variables. The equations of motion of the cylinder are developed using the constitutive relations of a piezoelectric Material possessing transversely Isotropic symmetry properties, with the symmetry direction collinear with the axis of the cylinder. The physically allowed boundary conditions are derived from Hamilton’s variational principle. Four displacement and three electric potentials satisfying Helmholtz’s equation are used to solve the equations of motion of the cylinder. The characteristic equation (dispersion relation) is obtained by the application of the boundary conditions satisfied by the elastic and electric variables. The characteristic equation is solved numerically by a novel method which makes use of the three dimensional plot of the log of the modulus of the left hand side of the characteristic equation. The results are numerically illustrated via dispersion curves of a sample PZT-4 composite cylinder. Significant changes in the propagating wave modes are revealed by the dispersion curves, when compared with a corresponding non-piezoelectric model of a PZT-4 cylinder. It is also observed that the dispersion curves are sensitive to the form of the electric boundary conditions.
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analysis of non axisymmetric wave propagation in a homogeneous piezoelectric solid circular cylinder of transversely Isotropic Material
International Journal of Solids and Structures, 2009Co-Authors: A G Every, M Shatalov, Alfred Sevidzem YenwongfaiAbstract:A study concerning the propagation of free non-axisymmetric waves in a homogeneous piezoelectric cylinder of transversely Isotropic Material with axial polarization is carried out on the basis of the linear theory of elasticity and linear electro-mechanical coupling. The solution of the three dimensional equations of motion and quasi-electrostatic equation is given in terms of seven mechanical and three electric potentials. The characteristic equations are obtained by the application of the mechanical and two types of electric boundary conditions at the surface of the piezoelectric cylinder. A novel method of displaying dispersion curves is described in the paper and the resulting dispersion curves are presented for propagating and evanescent waves for PZT-4 and PZT-7A piezoelectric ceramics for circumferential wave numbers m = 1, 2, and 3. It is observed that the dispersion curves are sensitive to the type of the imposed boundary conditions as well as to the measure of the electro-mechanical coupling of the Material.
M Shatalov - One of the best experts on this subject based on the ideXlab platform.
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progress in the analysis of non axisymmetric wave propagation in a homogeneous solid circular cylinder of a piezoelectric transversely Isotropic Material
Physics Procedia, 2010Co-Authors: A G Every, Alfred Sevidzem Yenwongfai, M ShatalovAbstract:Abstract Non-axisymmetric waves in a free homogeneous piezoelectric cylinder of transversely Isotropic Material with axial polarization are investigated on the basis of the linear theory of elasticity and linear electromechanical coupling. The solution of the three dimensional equations of motion and quasi-electrostatic equation is given in terms of seven mechanical and three electric potentials. The characteristic equations are obtained through the application of the mechanical and two types of electric boundary conditions at the surface of the cylinder. A convenient method of calculating dispersion curves and phase velocities is discussed, and resulting curves are presented for propagating and evanescent waves for the piezoelectric ceramic Material PZT-4 for non-axisymmetric modes of circumferential wave number m = 1 . It is observed that the dispersion curves are sensitive to the type of the imposed boundary conditions as well as to the strength of the electromechanical coupling.
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analysis of non axisymmetric wave propagation in a homogeneous piezoelectric solid circular cylinder of transversely Isotropic Material
International Journal of Solids and Structures, 2009Co-Authors: A G Every, M Shatalov, Alfred Sevidzem YenwongfaiAbstract:A study concerning the propagation of free non-axisymmetric waves in a homogeneous piezoelectric cylinder of transversely Isotropic Material with axial polarization is carried out on the basis of the linear theory of elasticity and linear electro-mechanical coupling. The solution of the three dimensional equations of motion and quasi-electrostatic equation is given in terms of seven mechanical and three electric potentials. The characteristic equations are obtained by the application of the mechanical and two types of electric boundary conditions at the surface of the piezoelectric cylinder. A novel method of displaying dispersion curves is described in the paper and the resulting dispersion curves are presented for propagating and evanescent waves for PZT-4 and PZT-7A piezoelectric ceramics for circumferential wave numbers m = 1, 2, and 3. It is observed that the dispersion curves are sensitive to the type of the imposed boundary conditions as well as to the measure of the electro-mechanical coupling of the Material.
Mahbube Subhani - One of the best experts on this subject based on the ideXlab platform.
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Reducing the effect of wave dispersion in a timber pole based on transversely Isotropic Material modelling
Construction and Building Materials, 2016Co-Authors: Mahbube Subhani, Jianchun Li, Bijan Samali, Keith CrewsAbstract:Round timbers are used for telecommunication and power distribution networks, jetties, piles, short span bridges etc. To assess the condition of these cylindrical shape timber structures, bulk and elementary wave theory are usually used. Even though guided wave can represents the actual wave behaviour, a great deal complexity exists to model stress wave propagation within an orthotropic media, such as timber. In this paper, timber is modelled as transversely Isotropic Material without compromising the accuracy to a great extent. Dispersion curves and mode shapes are used to propose an experimental set up in terms of the input frequency and bandwidth of the signal, the orientation of the sensor and the distance between the sensors in order to reduce the effect of the dispersion in the output signal. Some example based on the simulated signal is also discussed to evaluate the proposed experimental set up.
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A comparative study of guided wave propagation in timber poles with Isotropic and transversely Isotropic Material models
Journal of Civil Structural Health Monitoring, 2013Co-Authors: Mahbube Subhani, Jianchun Li, Bijan SamaliAbstract:Guided wave (GW) has been used for many years in non-destructive testing (NDT). There are various ways to generate the guided wave, including impact or impulse either manually or using devices. Although the method of impact or impulse is considered to be simple and practical in guided wave generation, it produces waves with broadband frequencies, which often make analysis much more difficult. The frequency bandwidth produced by manual impacts is usually at the low end, and is therefore justified when dealing with one dimensional wave propagation assumption in low strain integrity testing of cylindrical structures. Under such assumption if the velocity is known accurately, NDTs can produce reasonably good results for the condition assessment of the structure. However, for guided wave propagation in timber pole-like structures, it is rather complicated as timber is an orthotropic Material and wave propagation in an orthotropic medium exhibits different characteristics from that in Isotropic medium. It is possible to obtain solutions for guided wave propagation in orthotropic media for cylindrical structures, even though the orthotropic Material greatly complicates GW propagation. In this paper, timber has been considered as a transversely Isotropic (i.e. simplified orthotropic) Material and a comparative study of GW propagation in a timber pole is conducted considering Isotropic and transversely Isotropic modelling. Phase velocity, group velocity and attenuation are the main parameters for this comparative study. Moreover, traction-free situation and embedded geotechnical condition are also taken into consideration to evaluate the effect of boundary. Displacement profile, wave propagation pattern and power flow at particular frequency are utilized to determine different displacement components of longitudinal and flexural waves along and across the timber pole. Effect of temperature and moisture content (in terms of modulus of elasticity) in timber pole is also compared to show the variation in phase velocity.
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effect of elastic modulus and poisson s ratio on guided wave dispersion using transversely Isotropic Material modelling
Advanced Materials Research, 2013Co-Authors: Mahbube Subhani, Hauke Gravenkamp, Bijan SamaliAbstract:Timber poles are commonly used for telecommunication and power distribution networks, wharves or jetties, piling or as a substructure of short span bridges. Most of the available techniques currently used for non-destructive testing (NDT) of timber structures are based on one-dimensional wave theory. If it is essential to detect small sized damage, it becomes necessary to consider guided wave (GW) propagation as the behaviour of different propagating modes cannot be represented by one-dimensional approximations. However, due to the orthotropic Material properties of timber, the modelling of guided waves can be complex. No analytical solution can be found for plotting dispersion curves for orthotropic thick cylindrical waveguides even though very few literatures can be found on the theory of GW for anIsotropic cylindrical waveguide. In addition, purely numerical approaches are available for solving these curves. In this paper, dispersion curves for orthotropic cylinders are computed using the scaled boundary finite element method (SBFEM) and compared with an Isotropic Material model to indicate the importance of considering timber as an anIsotropic Material. Moreover, some simplification is made on orthotropic behaviour of timber to make it transversely Isotropic due to the fact that, analytical approaches for transversely Isotropic cylinder are widely available in the literature. Also, the applicability of considering timber as a transversely Isotropic Material is discussed. As an orthotropic Material, most Material testing results of timber found in the literature include 9 elastic constants (three elastic moduli and six Poisson's ratios), hence it is essential to select the appropriate Material properties for transversely Isotropic Material which includes only 5 elastic constants. Therefore, comparison between orthotropic and transversely Isotropic Material model is also presented in this article to reveal the effect of elastic moduli and Poisson's ratios on dispersion curves. Based on this study, some suggestions are proposed on selecting the parameters from an orthotropic model to transversely Isotropic condition.
Keith Crews - One of the best experts on this subject based on the ideXlab platform.
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Reducing the effect of wave dispersion in a timber pole based on transversely Isotropic Material modelling
Construction and Building Materials, 2016Co-Authors: Mahbube Subhani, Jianchun Li, Bijan Samali, Keith CrewsAbstract:Round timbers are used for telecommunication and power distribution networks, jetties, piles, short span bridges etc. To assess the condition of these cylindrical shape timber structures, bulk and elementary wave theory are usually used. Even though guided wave can represents the actual wave behaviour, a great deal complexity exists to model stress wave propagation within an orthotropic media, such as timber. In this paper, timber is modelled as transversely Isotropic Material without compromising the accuracy to a great extent. Dispersion curves and mode shapes are used to propose an experimental set up in terms of the input frequency and bandwidth of the signal, the orientation of the sensor and the distance between the sensors in order to reduce the effect of the dispersion in the output signal. Some example based on the simulated signal is also discussed to evaluate the proposed experimental set up.
