The Experts below are selected from a list of 5373 Experts worldwide ranked by ideXlab platform
W C Hunter - One of the best experts on this subject based on the ideXlab platform.
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physically based Strain Invariant set for materials exhibiting transversely isotropic behavior
2001Co-Authors: John C Criscione, A S Douglas, W C HunterAbstract:Abstract A novel set of 5 Strain Invariants for materials exhibiting transversely isotropic behavior with respect to a reference configuration is developed through analysis of physical attributes of deformation. Experimental advantage for hyperelastic materials is demonstrated by showing that common tests can directly determine terms in W , the Strain energy per unit reference volume. An analysis of symmetry allows the general form of W to be refined a priori. Moreover, this kinematics framework is potentially useful for solving inverse problems since the 5 response terms in the Cauchy stress t are mostly orthogonal (9 of the 10 mutual inner products vanish). For small deformation they are fully orthogonal (all 10 inner products vanish). A response term in t consists of an Invariant response function multiplied by its associated kinematic tensor.
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an Invariant basis for natural Strain which yields orthogonal stress response terms in isotropic hyperelasticity
2000Co-Authors: John C Criscione, A S Douglas, J D Humphrey, W C HunterAbstract:A novel constitutive formulation is developed for finitely deforming hyperelastic materials that exhibit isotropic behavior with respect to a reference configuration. The Strain energy per unit reference volume, W, is defined in terms of three natural Strain Invariants, K1–3, which respectively specify the amount-of-dilatation, the magnitude-of-distortion, and the mode-of-distortion. Distortion is that part of the deformation that does not dilate. Moreover, pure dilatation (K2=0), pure shear (K3=0), uniaxial extension (K3=1), and uniaxial contraction (K3=−1) are tests which hold a Strain Invariant constant. Through an analysis of previously published data, it is shown for rubber that this new approach allows W to be easily determined with improved accuracy. Albeit useful for large and small Strains, distinct advantage is shown for moderate Strains (e.g. 2–25%). Central to this work is the orthogonal nature of the Invariant basis. If η represents natural Strain, then {K1,K2,K3} are such that the tensorial contraction of (∂Ki/∂η) with (∂Kj/∂η) vanishes when i≠j. This result, in turn, allows the Cauchy stress t to be expressed as the sum of three response terms that are mutually orthogonal. In particular (summation implied) t=Ai∂W/∂Ki, where the ∂W/∂Ki are scalar response functions and the Ai are kinematic tensors that are mutually orthogonal.
D Kelly - One of the best experts on this subject based on the ideXlab platform.
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Strain Invariant failure theory part 1 an extensible framework for predicting the mechanical performance of fibre reinforced polymer composites
2019Co-Authors: Garth Pearce, Nayeem Tawqir Chowdhury, A Mukkavilli, Shen Hin Lim, B G Prusty, A Crosky, D KellyAbstract:Abstract Failure prediction for composite materials is still a major area of interest within both the academic literature and the composite industry. This paper presents a modelling and experimental framework which has been developed for the application of Strain Invariant Failure Theory (SIFT), but which can be adapted to other failure prediction methods if required. SIFT is set of physics-based failure criteria developed to predict the onset of irreversible deformation of glassy polymers. The paper provides an overview of the available evidence for SIFT and provides a complete methodology for applying SIFT to predict the onset of failure in a composite component. Fundamental to the method presented is a modular and hierarchical dehomogenisation procedure; allowing for the evaluation of stress and Strain state variables within the constituent components of the composite. Due to the constant evolution of composite characterisation techniques, the method presented in this paper is designed to be extensible (i.e. accommodating of new materials and product forms) and modular (i.e. subsections of the method can be easily substituted or refined). Known limitations of the current method are clearly presented and discussed. A companion paper will present validation of the approach for simple uniaxial and biaxial coupon experiments and will discuss how the method can be applied to a range of existing composite characterisation testing standards.
Ruogang Zhao - One of the best experts on this subject based on the ideXlab platform.
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COMPARISON OF ANALYTICAL AND FINITE ELEMENT IMPLEMENTATION OF EXPONENTIAL CONSTITUTIVE MODELS FOR VALVE TISSUE UNDER MICROPIPETTE ASPIRATION SBC2010-19245
2020Co-Authors: Ruogang Zhao, Krista Lynn Sider, Craig A SimmonsAbstract:INTROUDUCTION Micropipette aspiration (MA) has been widely used to measure the biomechanical properties of cells and biomaterials The goal of this study was to determine whether aortic valve tissue material parameters estimated by the easily-implemented analytical approach [3] differ from those obtained by finite element (FE) analysis aortic valve tissue under MA. To do so, we implemented an exponential hyperelastic constitutive model in the FE model and used an inverse FE approach to predict material parameters METHODS AND MATERIALS Material models To fit the MA experimental measurements of the embryonic atrioventricular cushions, Butcher et al. implemented an exponential constitutive model [2] where W is the Strain energy, C and α are material constants and E is the Green's finite Strain with the 2 nd Piola-Kirchoff stress (S) being calculated by S = ∂W/∂E. To relate the stress and Strain in the constitutive model to experimental measurements, Butcher et al. directly assigned the measured aspiration length (L) to pipette radius (a) ratio as the Green's Strain, and the measured aspiration pressure ΔP as the Lagrangian stress T, which is calculated by T = λS with the stretch ratio in the aspiration direction (λ) given by λ = (E + 1) 0.5 To account for the multicomponent stress-Strain field in the valve tissue during MA process, we implemented an incompressible isotropic exponential constitutive model. The Strain energy density function of this model is expressed as where W is the Strain energy, C and α are material constants and I 1 is the first Strain Invariant, defined as I 1 = with λ 1 , λ 2 and λ 3 being the principal stretches. This isotropic exponential constitutiv
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a simple method to estimate the exponential material parameters of heart valve tissue based on analogy between uniaxial tension and micropipette aspiration
2013Co-Authors: Ruogang Zhao, Craig A SimmonsAbstract:Micropipette aspiration (MA) has been widely used to measure the biomechanical properties of cells and biomaterials. To estimate material parameters from MA experimental data, analytical half-space models and inverse finite element (FE) analyses are typically used. The half-space model is easy to implement but cannot account for nonlinear material properties and complex geometrical boundary conditions that are inherent to MA. Inverse FE approaches can account for geometrical and material nonlinearities, but their implementation is resource-intensive and not widely available. Here, by making analogy between an analytical uniaxial tension model and a FE model of MA, we proposed an easily implementable and accurate method to estimate the material parameters of tissues tested by MA. We first adopted a Strain Invariant-based isotropic exponential constitutive model and implemented it in both the analytical uniaxial tension model and the FE model. The two models were fit to experimental data generated by MA of porcine aortic valve tissue (45 spots on four leaflets) to estimate material parameters. We found no significant differences between the effective moduli estimated by the two models (\(p > 0.39\)), with the effective moduli estimated by the uniaxial tension model correlating significantly with those estimated by the FE model (\(p < 0.001; R^{2}= 0.96\)) with a linear regression slope that was not different than unity (\(p = 0.38\)). Thus, the analytical uniaxial tension model, which avoids solving resource-intensive numerical problems, is as accurate as the FE model in estimating the effective modulus of valve tissue tested by MA.
Zoltan Major - One of the best experts on this subject based on the ideXlab platform.
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Computational implementation and experimental validation of a micro-mechanics informed progressive damage Strain Invariant Failure Theory
2018Co-Authors: Emil Pitz, Matei-constantin Miron, Zoltan MajorAbstract:Abstract The current paper deals with the failure modelling in continuously reinforced composite structures taking into account the material's inherent microstructure. The implementation of a constitutive model for transversely isotropic damage in fibre reinforced composites is presented. Damage initiation in the orthotropic linear elastically modelled composite is governed by the Strain Invariant Failure Theory (SIFT), utilising the first Strain Invariant and the second deviatoric Strain Invariant for damage initiation. To phenomenologically account for the material's microstructure, the homogenised macro Strain is related to the micro Strain by means of Strain amplification factors determined from prior simulations of Repeating Unit Cells (RUCs) with different fibre arrangements utilising Periodic Boundary Conditions (PBCs). For validation of the numerically implemented model, experimental tests of composite laminates with varying layups are performed. The conducted experiments are simulated utilising the implemented models and the obtained results are validated with the experimental data.
Craig A Simmons - One of the best experts on this subject based on the ideXlab platform.
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COMPARISON OF ANALYTICAL AND FINITE ELEMENT IMPLEMENTATION OF EXPONENTIAL CONSTITUTIVE MODELS FOR VALVE TISSUE UNDER MICROPIPETTE ASPIRATION SBC2010-19245
2020Co-Authors: Ruogang Zhao, Krista Lynn Sider, Craig A SimmonsAbstract:INTROUDUCTION Micropipette aspiration (MA) has been widely used to measure the biomechanical properties of cells and biomaterials The goal of this study was to determine whether aortic valve tissue material parameters estimated by the easily-implemented analytical approach [3] differ from those obtained by finite element (FE) analysis aortic valve tissue under MA. To do so, we implemented an exponential hyperelastic constitutive model in the FE model and used an inverse FE approach to predict material parameters METHODS AND MATERIALS Material models To fit the MA experimental measurements of the embryonic atrioventricular cushions, Butcher et al. implemented an exponential constitutive model [2] where W is the Strain energy, C and α are material constants and E is the Green's finite Strain with the 2 nd Piola-Kirchoff stress (S) being calculated by S = ∂W/∂E. To relate the stress and Strain in the constitutive model to experimental measurements, Butcher et al. directly assigned the measured aspiration length (L) to pipette radius (a) ratio as the Green's Strain, and the measured aspiration pressure ΔP as the Lagrangian stress T, which is calculated by T = λS with the stretch ratio in the aspiration direction (λ) given by λ = (E + 1) 0.5 To account for the multicomponent stress-Strain field in the valve tissue during MA process, we implemented an incompressible isotropic exponential constitutive model. The Strain energy density function of this model is expressed as where W is the Strain energy, C and α are material constants and I 1 is the first Strain Invariant, defined as I 1 = with λ 1 , λ 2 and λ 3 being the principal stretches. This isotropic exponential constitutiv
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a simple method to estimate the exponential material parameters of heart valve tissue based on analogy between uniaxial tension and micropipette aspiration
2013Co-Authors: Ruogang Zhao, Craig A SimmonsAbstract:Micropipette aspiration (MA) has been widely used to measure the biomechanical properties of cells and biomaterials. To estimate material parameters from MA experimental data, analytical half-space models and inverse finite element (FE) analyses are typically used. The half-space model is easy to implement but cannot account for nonlinear material properties and complex geometrical boundary conditions that are inherent to MA. Inverse FE approaches can account for geometrical and material nonlinearities, but their implementation is resource-intensive and not widely available. Here, by making analogy between an analytical uniaxial tension model and a FE model of MA, we proposed an easily implementable and accurate method to estimate the material parameters of tissues tested by MA. We first adopted a Strain Invariant-based isotropic exponential constitutive model and implemented it in both the analytical uniaxial tension model and the FE model. The two models were fit to experimental data generated by MA of porcine aortic valve tissue (45 spots on four leaflets) to estimate material parameters. We found no significant differences between the effective moduli estimated by the two models (\(p > 0.39\)), with the effective moduli estimated by the uniaxial tension model correlating significantly with those estimated by the FE model (\(p < 0.001; R^{2}= 0.96\)) with a linear regression slope that was not different than unity (\(p = 0.38\)). Thus, the analytical uniaxial tension model, which avoids solving resource-intensive numerical problems, is as accurate as the FE model in estimating the effective modulus of valve tissue tested by MA.
