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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requirements for accurate estimation of anIsotropic Material parameters by magnetic resonance elastography a computational study
Magnetic Resonance in Medicine, 2017Co-Authors: Dennis J Tweten, Ruth J Okamoto, Philip V BaylyAbstract:Purpose To establish the essential requirements for characterization of a Transversely Isotropic Material by magnetic resonance elastography (MRE). Theory and Methods Three methods for characterizing nearly incompressible, Transversely Isotropic (ITI) Materials were used to analyze data from closed-form expressions for traveling waves, finite-element (FE) simulations of waves in homogeneous ITI Material, and FE simulations of waves in heterogeneous Material. Key properties are the complex shear modulus μ2, shear anisotropy ϕ=μ1/μ2−1, and tensile anisotropy ζ=E1/E2−1. Results Each method provided good estimates of ITI parameters when both slow and fast shear waves with multiple propagation directions were present. No method gave accurate estimates when the displacement field contained only slow shear waves, only fast shear waves, or waves with only a single propagation direction. Methods based on directional filtering are robust to noise and include explicit checks of propagation and polarization. Curl-based methods led to more accurate estimates in low noise conditions. Parameter estimation in heterogeneous Materials is challenging for all methods. Conclusions Multiple shear waves, both slow and fast, with different propagation directions, must be present in the displacement field for accurate parameter estimates in ITI Materials. Experimental design and data analysis can ensure that these requirements are met. Magn Reson Med 78:2360–2372, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
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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
Ruth J Okamoto - One of the best experts on this subject based on the ideXlab platform.
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requirements for accurate estimation of anIsotropic Material parameters by magnetic resonance elastography a computational study
Magnetic Resonance in Medicine, 2017Co-Authors: Dennis J Tweten, Ruth J Okamoto, Philip V BaylyAbstract:Purpose To establish the essential requirements for characterization of a Transversely Isotropic Material by magnetic resonance elastography (MRE). Theory and Methods Three methods for characterizing nearly incompressible, Transversely Isotropic (ITI) Materials were used to analyze data from closed-form expressions for traveling waves, finite-element (FE) simulations of waves in homogeneous ITI Material, and FE simulations of waves in heterogeneous Material. Key properties are the complex shear modulus μ2, shear anisotropy ϕ=μ1/μ2−1, and tensile anisotropy ζ=E1/E2−1. Results Each method provided good estimates of ITI parameters when both slow and fast shear waves with multiple propagation directions were present. No method gave accurate estimates when the displacement field contained only slow shear waves, only fast shear waves, or waves with only a single propagation direction. Methods based on directional filtering are robust to noise and include explicit checks of propagation and polarization. Curl-based methods led to more accurate estimates in low noise conditions. Parameter estimation in heterogeneous Materials is challenging for all methods. Conclusions Multiple shear waves, both slow and fast, with different propagation directions, must be present in the displacement field for accurate parameter estimates in ITI Materials. Experimental design and data analysis can ensure that these requirements are met. Magn Reson Med 78:2360–2372, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
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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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automated estimation of elastic Material parameters of a Transversely Isotropic Material using asymmetric indentation and inverse finite element analysis
ASME 2015 International Mechanical Engineering Congress and Exposition, 2015Co-Authors: Yuan Feng, Chunghao Lee, Lining Sun, Ruth J OkamotoAbstract:Anisotropy exists in many soft biological tissues. The most common anisotropy is transverse isotropy, which is typical for fiber-reinforced structures, such as the brain white matter, tendon and muscle. Although many methods have been proposed to determine tissue properties, techniques to characterize Transversely Isotropic Materials remain limited. The goal of this study is to investigate the feasibility of asymmetric indentation coupled with numerical optimization based on inverse finite element (FE) simulation to characterize Transversely Isotropic soft biological tissues. The proposed approach combining indentation and optimization may provide a useful general framework to characterize a variety of fiber-reinforced soft tissues in the future.Copyright © 2015 by ASME
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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.
Yuan Feng - One of the best experts on this subject based on the ideXlab platform.
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characterizing white matter tissue in large strain via asymmetric indentation and inverse finite element modeling
Journal of The Mechanical Behavior of Biomedical Materials, 2017Co-Authors: Yuan Feng, Chunghao Lee, Lining Sun, Xuefeng ZhaoAbstract:Characterizing the mechanical properties of white matter is important to understand and model brain development and injury. With embedded aligned axonal fibers, white matter is typically modeled as a Transversely Isotropic Material. However, most studies characterize the white matter tissue using models with a single anIsotropic invariant or in a small-strain regime. In this study, we combined a single experimental procedure - asymmetric indentation - with inverse finite element (FE) modeling to estimate the nearly incompressible Transversely Isotropic Material parameters of white matter. A minimal form comprising three parameters was employed to simulate indentation responses in the large-strain regime. The parameters were estimated using a global optimization procedure based on a genetic algorithm (GA). Experimental data from two indentation configurations of porcine white matter, parallel and perpendicular to the axonal fiber direction, were utilized to estimate model parameters. Results in this study confirmed a strong mechanical anisotropy of white matter in large strain. Further, our results suggested that both indentation configurations are needed to estimate the parameters with sufficient accuracy, and that the indenter-sample friction is important. Finally, we also showed that the estimated parameters were consistent with those previously obtained via a trial-and-error forward FE method in the small-strain regime. These findings are useful in modeling and parameterization of white matter, especially under large deformation, and demonstrate the potential of the proposed asymmetric indentation technique to characterize other soft biological tissues with Transversely Isotropic properties.
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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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automated estimation of elastic Material parameters of a Transversely Isotropic Material using asymmetric indentation and inverse finite element analysis
ASME 2015 International Mechanical Engineering Congress and Exposition, 2015Co-Authors: Yuan Feng, Chunghao Lee, Lining Sun, Ruth J OkamotoAbstract:Anisotropy exists in many soft biological tissues. The most common anisotropy is transverse isotropy, which is typical for fiber-reinforced structures, such as the brain white matter, tendon and muscle. Although many methods have been proposed to determine tissue properties, techniques to characterize Transversely Isotropic Materials remain limited. The goal of this study is to investigate the feasibility of asymmetric indentation coupled with numerical optimization based on inverse finite element (FE) simulation to characterize Transversely Isotropic soft biological tissues. The proposed approach combining indentation and optimization may provide a useful general framework to characterize a variety of fiber-reinforced soft tissues in the future.Copyright © 2015 by ASME
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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
Kathryn R Nightingale - One of the best experts on this subject based on the ideXlab platform.
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full characterization of in vivo muscle as an elastic incompressible Transversely Isotropic Material using ultrasonic rotational 3d shear wave elasticity imaging
IEEE Transactions on Medical Imaging, 2021Co-Authors: Anna E Knight, Ned C Rouze, Mark L Palmeri, Courtney A Trutna, Lisa D Hobsonwebb, Annette Caenen, Felix Q Jin, Kathryn R NightingaleAbstract:Using a 3D rotational shear wave elasticity imaging (SWEI) setup, 3D shear wave data were acquired in the vastus lateralis of a healthy volunteer. The innate tilt between the transducer face and the muscle fibers results in the excitation of multiple shear wave modes, allowing for more complete characterization of muscle as an elastic, incompressible, Transversely Isotropic (ITI) Material. The ability to measure both the shear vertical (SV) and shear horizontal (SH) wave speed allows for measurement of three independent parameters needed for full ITI Material characterization: the longitudinal shear modulus μL, the transverse shear modulus μT, and the tensile anisotropy χE. Herein we develop and validate methodology to estimate these parameters and measure them in vivo, with μL = 5.77 ± 1.00 kPa, μT = 1.93 ± 0.41 kPa (giving shear anisotropy χμ = 2.11 ± 0.92), and χE = 4.67 ± 1.40 in a relaxed vastus lateralis muscle. We also demonstrate that 3D SWEI can be used to more accurately characterize muscle mechanical properties as compared to 2D SWEI.
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tractable calculation of the green s tensor for shear wave propagation in an incompressible Transversely Isotropic Material
Physics in Medicine and Biology, 2020Co-Authors: Ned C Rouze, Mark L Palmeri, Kathryn R NightingaleAbstract:Assessing Material properties from observations of shear wave propagation following an acoustic radiation force impulse (ARFI) excitation is difficult in anIsotropic Materials because of the complex relations among the propagation direction, shear wave polarizations, and Material symmetries. In this paper, we describe a method to calculate shear wave signals using Green's tensor methods in an incompressible, Transversely Isotropic (TI) Material characterized by three Material parameters. The Green's tensor is written as the sum of an analytic expression for the SH propagation mode, and an integral expression for the SV propagation mode that can be evaluated by interpolation within precomputed integral functions with an efficiency comparable to the evaluation of a closed-form expression. By using parametrized integral functions, the number of required numerical integrations is reduced by a factor of 102-109 depending on the specific problem under consideration. Results are presented for the case of a point source positioned at the origin and a tall Gaussian source similar to an ARFI excitation. For an experimental configuration with a tilted Material symmetry axis, results show that shear wave signals exhibit structures that are sufficiently complex to allow measurement of all three Material parameters that characterize an incompressible, TI 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.
