A Transversely Isotropic Viscoelastic Constitutive Equation for Brainstem Undergoing Finite Deformation

2006 ◽  
Vol 128 (6) ◽  
pp. 925-933 ◽  
Author(s):  
Xinguo Ning ◽  
Qiliang Zhu ◽  
Yoram Lanir ◽  
Susan S. Margulies
Keyword(s):  
Shear Deformation ◽  
Transversely Isotropic ◽  
Material Model ◽  
Model Parameters ◽  
Shear Stresses ◽  
Element Analysis ◽  
Cross Sectional ◽  
Implementation Model ◽  
Finite Shear ◽  
The Matrix

The objective of this study was to define the constitutive response of brainstem undergoing finite shear deformation. Brainstem was characterized as a transversely isotropic viscoelastic material and the material model was formulated for numerical implementation. Model parameters were fit to shear data obtained in porcine brainstem specimens undergoing finite shear deformation in three directions: parallel, perpendicular, and cross sectional to axonal fiber orientation and determined using a combined approach of finite element analysis (FEA) and a genetic algorithm (GA) optimizing method. The average initial shear modulus of brainstem matrix of 4-week old pigs was 12.7Pa, and therefore the brainstem offers little resistance to large shear deformations in the parallel or perpendicular directions, due to the dominant contribution of the matrix in these directions. The fiber reinforcement stiffness was 121.2Pa, indicating that brainstem is anisotropic and that axonal fibers have an important role in the cross-sectional direction. The first two leading relative shear relaxation moduli were 0.8973 and 0.0741, respectively, with corresponding characteristic times of 0.0047 and 1.4538s, respectively, implying rapid relaxation of shear stresses. The developed material model and parameter estimation technique are likely to find broad applications in neural and orthopaedic tissues.

The Precise Determination of the Johnson–Cook Material and Damage Model Parameters and Mechanical Properties of an Aluminum 7068-T651 Alloy

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
B. Bal ◽  
K. K. Karaveli ◽  
B. Cetin ◽  
B. Gumus
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Physical Simulation ◽  
Damage Model ◽  
Rolling Direction ◽  
Stress Triaxiality ◽  
Material Model ◽  
Tensile Tests ◽  
Model Parameters ◽  
Element Analysis

Al 7068-T651 alloy is one of the recently developed materials used mostly in the defense industry due to its high strength, toughness, and low weight compared to steels. The aim of this study is to identify the Johnson–Cook (J–C) material model parameters, the accurate Johnson–Cook (J–C) damage parameters, D1, D2, and D3 of the Al 7068-T651 alloy for finite element analysis-based simulation techniques, together with other damage parameters, D4 and D5. In order to determine D1, D2, and D3, tensile tests were conducted on notched and smooth specimens at medium strain rate, 100 s−1, and tests were repeated seven times to ensure the consistency of the results both in the rolling direction and perpendicular to the rolling direction. To determine D4 and D5 further, tensile tests were conducted on specimens at high strain rate (102 s−1) and temperature (300 °C) by means of the Gleeble thermal–mechanical physical simulation system. The final areas of fractured specimens were calculated through optical microscopy. The effects of stress triaxiality factor, rolling direction, strain rate, and temperature on the mechanical properties of the Al 7068-T651 alloy were also investigated. Damage parameters were calculated via the Levenberg–Marquardt optimization method. From all the aforementioned experimental work, J–C material model parameters were determined. In this article, J–C damage model constants, based on maximum and minimum equivalent strain values, were also reported which can be utilized for the simulation of different applications.

A Simple Transversely Isotropic Hyperelastic Constitutive Model Suitable for Finite Element Analysis of Fiber Reinforced Elastomers

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Leslee W. Brown ◽  
Lorenzo M. Smith
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Energy Function ◽  
Strain Energy ◽  
Strain Energy Function ◽  
Transversely Isotropic ◽  
Material Model ◽  
Fiber Reinforced ◽  
Element Analysis ◽  
Material Tests

A transversely isotropic fiber reinforced elastomer’s hyperelasticity is characterized using a series of constitutive tests (uniaxial tension, uniaxial compression, simple shear, and constrained compression test). A suitable transversely isotropic hyperelastic invariant based strain energy function is proposed and methods for determining the material coefficients are shown. This material model is implemented in a finite element analysis by creating a user subroutine for a commercial finite element code and then used to analyze the material tests. A useful set of constitutive material data for multiple modes of deformation is given. The proposed strain energy function fits the experimental data reasonably well over the strain region of interest. Finite element analysis of the material tests reveals further insight into the materials constitutive nature. The proposed strain energy function is suitable for finite element use by the practicing engineer for small to moderate strains. The necessary material coefficients can be determined from a few simple laboratory tests.

Microtensile Specimen Attachment and Shape—Finite Element Analysis

2008 ◽  
Vol 87 (1) ◽  
pp. 89-93 ◽  
Author(s):  
C.J. Soares ◽  
P.V. Soares ◽  
P.C.F. Santos-Filho ◽  
S.R. Armstrong
Keyword(s):  
Stress Distribution ◽  
Shear Stresses ◽  
Element Analysis ◽  
Cross Sectional ◽  
Surface Attachment ◽  
Testing Specimen ◽  
Testing Region ◽  
Number Of Faces ◽  
Von Mises ◽  
Specimen Shape

Microtensile bond strength values are influenced by specimen shape and attachment method to the gripping device during testing. We hypothesized that stress distribution inside the testing specimen is affected by microtensile specimen shape and attachment method. Rectangular, hourglass-, and dumbbell-shaped specimens, all with a 1 mm2 cross-sectional testing region, were modeled as indirect ceramic restorations luted to dentin. Three specimen attachments were investigated: (1) posterior surface; (2) posterior, superior, and lateral surfaces; and (3) all surfaces. Qualitative and quantitative analyses were carried out according to von Mises’ criteria. Stress analysis showed a direct correlation between attachment modes and stress distribution, with shear stresses observed in models with less surface attachment. Increasing the number of faces for specimen attachment to the metallic gripping device resulted in a more homogeneous and regular distribution of stress, with tensile stress concentrated at the adhesive interface. Dumbbell-shaped specimens showed improved stress distribution compared with rectangular and hourglass-shaped specimens.

Geometrically nonlinear finite element simulation of smart laminated shells using a modified first-order shear deformation theory

2019 ◽  
Vol 30 (4) ◽  
pp. 517-535 ◽  
Author(s):  
Hanen Mallek ◽  
Hanen Jrad ◽  
Mondher Wali ◽  
Fakhreddine Dammak
Keyword(s):  
Finite Element ◽  
Shear Deformation ◽  
Deformation Theory ◽  
Piezoelectric Materials ◽  
Shear Deformation Theory ◽  
Nonlinear Finite Element ◽  
Shear Stresses ◽  
Geometrically Nonlinear ◽  
Element Analysis ◽  
First Order

This article investigates geometrically nonlinear and linear analysis of multilayered shells with integrated piezoelectric materials. An efficient nonlinear shell element is developed to solve piezoelastic response of laminated structure with embedded piezoelectric actuators and sensors. A modified first-order shear deformation theory is introduced in the present method to remove the shear correction factor and improve the accuracy of transverse shear stresses. The electric potential is assumed to be a linear function through the thickness of each active sub-layer. Several numerical tests for different piezolaminated geometries are conducted to highlight the reliability and efficiency of the proposed implementation in linear and geometrically nonlinear finite element analysis.

Effective Elastic Moduli of Ribbon-Reinforced Composites

1990 ◽  
Vol 57 (1) ◽  
pp. 158-167 ◽  
Author(s):  
Y. H. Zhao ◽  
G. J. Weng
Keyword(s):  
Aspect Ratio ◽  
Elastic Moduli ◽  
Volume Fraction ◽  
Transversely Isotropic ◽  
Isotropic Case ◽  
Effective Elastic Moduli ◽  
Cross Sectional ◽  
Isotropic Composite ◽  
The Matrix ◽  
The Hill

Based on the Eshelby-Mori-Tanaka theory the nine effective elastic constants of an orthotropic composite reinforced with monotonically aligned elliptic cylinders, and the five elastic moduli of a transversely isotropic composite reinforced with two-dimensional randomly-oriented elliptic cylinders, are derived. These moduli are given in terms of the cross-sectional aspect ratio and the volume fraction of the elliptic cylinders. When the aspect ratio approaches zero, the elliptic cylinders exist as thin ribbons, and these moduli are given in very simple, explicit forms as a function of volume fraction. It turns out that, in the transversely isotropic case, the effective elastic moduli of the composite coincide with Hill’s and Hashin’s upper bounds if ribbons are harder than the matrix, and coincide with their lower bounds if ribbons are softer. These results are in direct contrast to those of circular fibers. Since the width of the Hill-Hashin bounds can be very wide when the constituents have high modular ratios, this analysis suggests that the ribbon reinforcement is far more effective than the traditional fiber reinforcement.

Additional Guidance for Inelastic Ratcheting Analysis Using the Chaboche Model

2014 ◽  
Author(s):  
William F. Weitze ◽  
Timothy D. Gilman
Keyword(s):  
Finite Element Analysis ◽  
Stainless Steel ◽  
Cylindrical Shell ◽  
Kinematic Hardening ◽  
Material Model ◽  
Model Parameters ◽  
Temperature Dependent ◽  
Model Refinement ◽  
Element Analysis ◽  
Chaboche Model

This paper builds on PVP2013-98150 by Kalnins, Rudolph, and Willuweit [1], which documented two calibration processes for determining the parameters of the Chaboche nonlinear kinematic hardening (NLK) material model for stainless steel, and tested the material model using a pressurized cylindrical shell subjected to thermal cycling. The current paper examines (1) whether a Chaboche NLK model with only two terms (rather than four as in PVP-98150) is sufficiently accurate, (2) use of the ANSYS program for material model refinement and finite element analysis, and (3) analysis using temperature-dependent NLK model parameters, again using ANSYS.

Prediction of Elastic Properties in Discontinuous Composite Materials

2005 ◽  
Vol 297-300 ◽  
pp. 1265-1269
Author(s):  
Hong Gun Kim
Keyword(s):  
Stress Transfer ◽  
Shear Stresses ◽  
Shear Lag ◽  
Analysis Model ◽  
Concentration Effects ◽  
Element Analysis ◽  
Fiber Aspect Ratio ◽  
The Matrix ◽  
Elastic Loading ◽  
Shear Lag Theory

The shortcoming of conventional SLT (Shear Lag Theory) is due to the neglect of stress transfer across the fiber ends, which results in the inaccurate stress variation for the fiber when the fiber aspect ratio is small in elastic loading. Thus a new model called NSLT (New Shear Lag Theory) is developed considering the stress concentration effects that exists in the matrix regions near fiber ends. In this paper the prediction of elastic composite modulus is presented to evaluate the stress transfer mechanism using NSLT. A micromechanical FEA (Finite Element Analysis) model with axisymmetry is implemented to verify the results of fiber stresses and interfacial shear stresses. It is found that the proposed model gives a reasonable prediction compared with the results based on other models.

Hyperelastic Material Model Selection of Structural Silicone Sealants for Use in Finite Element Modeling

2017 ◽  
Author(s):  
Larry D. Carbary ◽  
Jon H. Kimberlain ◽  
John C. Oliva
Keyword(s):  
Finite Element ◽  
Material Model ◽  
Hyperelastic Material ◽  
Model Parameters ◽  
Element Analysis ◽  
Structural Silicone ◽  
Lab Experiments ◽  
Hyperelastic Model ◽  
Hyperelastic Models ◽  
Selection Of

Hyperelastic material model parameters have been developed to capture the behavior of silicone based construction sealants. Modern commercially available finite element analysis software makes it quite accessible to develop hyperelastic material models, automating the process of curve-fitting experimental lab data to specific hyperelastic formulations. However, the process of selecting a particular hyperelastic model from those supported is not straightforward. Here, a series of lab experiments are employed to guide the selection of the hyperelastic model that best describes various structural silicone glazings. A total of 10 different sealants are characterized with discussion of variations among the models. Comparisons of the best performing hyperelastic models for the different sealants are presented. Finally, an application is described in which these hyperelastic models have begun to be implemented in practice.

scholarly journals Finite-element modelling of NiTi shape-memory wires for morphing aerofoils

2020 ◽  
Vol 124 (1281) ◽  
pp. 1740-1760
Author(s):  
W.L.H. Wan A. Hamid ◽  
L. Iannucci ◽  
P. Robinson
Keyword(s):  
Finite Element ◽  
Shape Memory ◽  
Cantilever Beam ◽  
Material Model ◽  
Sensitivity Study ◽  
Niti Shape Memory Alloy ◽  
Element Analysis ◽  
Cross Sectional ◽  
Explicit Finite Element ◽  
Thermomechanical Behaviour

AbstractThis paper presents the development and implementation of a user-defined material (UMAT) model for NiTi Shape-Memory Alloy (SMA) wires for use in LS-DYNA commercial explicit finite-element analysis software. The UMAT focusses on the Shape-Memory Effect (SME), which could be used for actuation of aerostructural components. The actuation of a fundamental structure consisting of an SMA wire connected in series with a linear spring was studied first. The SMA thermomechanical behaviour obtained from the finite-element simulation was compared with that obtained from the analytical solution in MATLAB. A further comparison is presented for an SMA-actuated cantilever beam, showing excellent agreement in terms of the SMA stress and strain as well as the tip deflection of the cantilever beam. A mesh sensitivity study on the SMA wire indicated that one beam element was adequate to accurately predict the SMA thermomechanical behaviour. An analysis of several key parameters showed that, to achieve a high recovery strain, the stiffness of the actuated structure should be minimised while the cross-sectional area of the SMA wire should be maximised. The actuation of an SMA wire under a constant stress/load was also analysed. The SMA material model was finally applied to the design of morphing aluminium and composite aerofoils consisting of corrugated sections, resulting in the prediction of reasonably large trailing-edge deflections (7.8–65.9 mm).

Yield Surface Investigation of Alloys During Model Disk Spin Tests

2014 ◽  
Author(s):  
Anton N. Servetnik ◽  
Evgeny P. Kuzmin
Keyword(s):  
Experimental Approach ◽  
Eddy Currents ◽  
Material Model ◽  
Isotropic Hardening ◽  
Model Parameters ◽  
Element Analysis ◽  
Strain Fields ◽  
Von Mises ◽  
Yield Conditions ◽  
Incremental Theory Of Plasticity

Results of quasi-static numerical simulation of spin tests of model disk made from high-temperature forged alloy are presented. To determine stress-strain state of disk during loading finite element analysis is used. Simulation of elastic-plastic strain fields was carried out using incremental theory of plasticity with isotropic hardening. Model sensitivity from Von mises and Tresca yield conditions and hardening conditions was investigated. To identify the material model parameters an experimental approach of rim radial displacement measurement by eddy currents sensor during the load-unload of spin test was used. Calculation made using different material models were compared with the experimental results.

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