A Structural Continuum Constitutive Model for a Two-Phase Soft Tissue

2010 ◽  
Author(s):  
Silvia Wognum ◽  
Michael S. Sacks
Keyword(s):  
Mechanical Behavior ◽  
Soft Tissues ◽  
Bladder Wall ◽  
Constitutive Models ◽  
Tissue Level ◽  
Model Parameters ◽  
Two Phase ◽  
Tissue Properties ◽  
Highly Nonlinear ◽  
Cord Injury

Due to the complexity in determining multi-constituent tissue properties, most structural constitutive models for soft tissues focus on a single constituent. However, many tissues contain multiple load-bearing constituents, such as collagen fibers and smooth muscle (SM) cells. Moreover, to elucidate how observed changes in tissue components are related to altered net mechanical behavior at the tissue level, structural constitutive models require physiological relevant model parameters and formulations for changes in referential configuration when one component is physically removed. As an excellent example application that underscores these issues, we have examined the urinary bladder wall (UBW), which undergoes large deformations and exhibits highly nonlinear and anisotropic mechanical behavior [1,2]. Moreover, it undergoes profound remodeling in response to different pathologies such as spinal cord injury (SCI) [1,2].

Experimental Validation Technique for Constitutive Models Describing Behavior of Soft Tissue Surrogates During Projectile Penetration

2010 ◽  
Author(s):  
Ericka K. Amborn ◽  
Karim H. Muci-Ku¨chler ◽  
Brandon J. Hinz
Keyword(s):  
Soft Tissue ◽  
Mechanical Behavior ◽  
High Speed ◽  
Soft Tissues ◽  
Constitutive Models ◽  
Model Parameters ◽  
Channel Deformations ◽  
Single Term ◽  
Sensitivity Studies ◽  
Element Erosion

Numerical simulations of ballistic penetration of soft tissues are particularly difficult to validate because relevant experimental data is not readily available. Efficient, controlled, high strain rate experiments involving large deformations must be developed for that purpose. This paper proposes an axisymmetric experiment to validate constitutive models describing the bulk mechanical behavior of soft tissue surrogates. The need to use techniques such as element erosion and re-meshing or to consider material failure is avoided by using a cylindrical target with a small pre-made cylindrical channel along its axis. Cavitation is excited by firing a spherical projectile through the pre-made channel whose diameter is smaller than that of the projectile. The transient response of the channel is recorded using a high speed camera and the images collected are analyzed using a digital image tracking software to measure the channel deformations. As an example to demonstrate the usefulness of the proposed experiment, measurements from a test involving a ballistic gelatin cylinder are used to evaluate the quality of numerical results produced by finite element analyses performed with ABAQUS/Explicit. The mechanical behavior of the soft tissue surrogate is represented in the simulations using a single-term Ogden model. Different values are attempted for the required material properties and friction coefficient based on data available in the literature and simple sensitivity studies. The experimental results are used to assess the results corresponding to each set of model parameters.

scholarly journals A Contemporary Look at Biomechanical Models of Myocardium

2019 ◽  
Vol 21 (1) ◽  
pp. 417-442 ◽  
Author(s):  
Reza Avazmohammadi ◽  
João S. Soares ◽  
David S. Li ◽  
Samarth S. Raut ◽  
Robert C. Gorman ◽  
...  
Keyword(s):  
Mechanical Behavior ◽  
Constitutive Models ◽  
Underlying Structure ◽  
Model Parameters ◽  
Specific Test ◽  
Future Directions ◽  
Passive Components ◽  
Biomechanical Models ◽  
The Past ◽  
And Function

Understanding and predicting the mechanical behavior of myocardium under healthy and pathophysiological conditions are vital to developing novel cardiac therapies and promoting personalized interventions. Within the past 30 years, various constitutive models have been proposed for the passive mechanical behavior of myocardium. These models cover a broad range of mathematical forms, microstructural observations, and specific test conditions to which they are fitted. We present a critical review of these models, covering both phenomenological and structural approaches, and their relations to the underlying structure and function of myocardium. We further explore the experimental and numerical techniques used to identify the model parameters. Next, we provide a brief overview of continuum-level electromechanical models of myocardium, with a focus on the methods used to integrate the active and passive components of myocardial behavior. We conclude by pointing to future directions in the areas of optimal form as well as new approaches for constitutive modeling of myocardium.

scholarly journals Contribution of Collagen Fiber Undulation to Regional Biomechanical Properties Along Porcine Thoracic Aorta

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Shahrokh Zeinali-Davarani ◽  
Yunjie Wang ◽  
Ming-Jay Chow ◽  
Raphaël Turcotte ◽  
Yanhang Zhang
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Thoracic Aorta ◽  
Aortic Wall ◽  
Multiphoton Microscopy ◽  
Constitutive Models ◽  
Tensile Tests ◽  
Biomechanical Properties ◽  
Model Parameters ◽  
Extracellular Matrix Components

As major extracellular matrix components, elastin, and collagen play crucial roles in regulating the mechanical properties of the aortic wall and, thus, the normal cardiovascular function. The mechanical properties of aorta, known to vary with age and multitude of diseases as well as the proximity to the heart, have been attributed to the variations in the content and architecture of wall constituents. This study is focused on the role of layer-specific collagen undulation in the variation of mechanical properties along the porcine descending thoracic aorta. Planar biaxial tensile tests are performed to characterize the hyperelastic anisotropic mechanical behavior of tissues dissected from four locations along the thoracic aorta. Multiphoton microscopy is used to image the associated regional microstructure. Exponential-based and recruitment-based constitutive models are used to account for the observed mechanical behavior while considering the aortic wall as a composite of two layers with independent properties. An elevated stiffness is observed in distal regions compared to proximal regions of thoracic aorta, consistent with sharper and earlier collagen recruitment estimated for medial and adventitial layers in the models. Multiphoton images further support our prediction that higher stiffness in distal regions is associated with less undulation in collagen fibers. Recruitment-based models further reveal that regardless of the location, collagen in the media is recruited from the onset of stretching, whereas adventitial collagen starts to engage with a delay. A parameter sensitivity analysis is performed to discriminate between the models in terms of the confidence in the estimated model parameters.

scholarly journals Enhancing Constitutive Models for Soils: Adding the Capability to Model Nonlinear Small Strain in Shear

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
S. Seyedan ◽  
W. T. Sołowski
Keyword(s):  
Yield Surface ◽  
Constitutive Models ◽  
Strain Range ◽  
Small Strain ◽  
Deviatoric Stress ◽  
Triaxial Tests ◽  
Engineering Practice ◽  
Model Parameters ◽  
Highly Nonlinear ◽  
Strain Relationship

The deviatoric stress-deviatoric strain relationship in soils is highly nonlinear, especially in the small strain range. However, the constitutive models which aim to replicate the small strain nonlinearity are often complex and rarely used in geotechnical engineering practice. The goal of this study is to offer a simple way for updating the existing constitutive models, widely used in geotechnical practice, to take into account the small strain shear modulus changes. The study uses an existing small strain relationship to derive a yield surface. When the yield surface is introduced to an existing soil model, it enhances the model with the nonlinear deviatoric stress-deviatoric strain relationship in the small strain range. The paper also gives an example of such a model enhancement by combining the new yield surface with the Modified Cam Clay constitutive model. The validation simulations of the undrained triaxial tests on London Clay and Ham River sand with the upgraded constitutive models replicate the experiments clearly better than the base models, without any changes to existing model parameters and the core source code associated with the base model.

Simulation of the Aging Face

2006 ◽  
Vol 129 (4) ◽  
pp. 619-623 ◽  
Author(s):  
E. Mazza ◽  
O. Papes ◽  
M. B. Rubin ◽  
S. R. Bodner ◽  
N. S. Binur
Keyword(s):  
Finite Element ◽  
Mechanical Behavior ◽  
Soft Tissues ◽  
Constitutive Relations ◽  
Three Dimensional ◽  
Mechanical Tests ◽  
Specific Reference ◽  
Human Face ◽  
Highly Nonlinear ◽  
Aging Function

A three-dimensional finite element program is described which attempts to simulate the nonlinear mechanical behavior of an aging human face with specific reference to progressive gravimetric soft tissue descent. A cross section of the facial structure is considered to consist of a multilayered composite of tissues with differing mechanical behavior. Relatively short time (elastic-viscoplastic) behavior is governed by equations previously developed which are consistent with mechanical tests. The long time response is controlled by the aging elastic components of the tissues. An aging function is introduced which, in a simplified manner, models the observed loss of stiffness of these aging elastic components due to the history of straining as well as other physiological and environmental influences. Calculations have been performed for 30 years of exposure to gravitational forces. The deformations and stress distributions in the layers of the soft tissues are described. Overall, the feasibility of using constitutive relations which reflect the highly nonlinear elastic-viscoplastic behavior of facial soft tissues in finite element based three-dimensional mechanical analyses of the human face is demonstrated. Further developments of the program are discussed in relation to possible clinical applications. Although the proposed aging function produces physically reasonable long-term response, experimental data are not yet available for more quantitative validation.

Tissue-Level Structural Constitutive Models

2000 ◽  
Author(s):  
Michael S. Sacks
Keyword(s):  
Mechanical Behavior ◽  
Constitutive Models ◽  
Biological Tissues ◽  
Tissue Level ◽  
Chemical Treatments ◽  
Strain Energy Density Function ◽  
Fundamental Goal ◽  
The Matrix ◽  
Device Applications ◽  
Underlying Mechanisms

Abstract A fundamental goal in constitutive modeling is the ability to predict the mechanical behavior of a material under a generalized loading state. To achieve this goal, rigorous experimentation involving all relevant deformations is necessary to obtain both the form and material constants of a strain-energy density function. For both natural biological tissues and tissue-derived soft biomaterials, there exist many physiological, surgical, and medical device applications where rigorous constitutive models are required. Although able to fit the biaxial data well, phenomenological models cannot be used to determine the underlying mechanisms of tissue mechanical behavior. In particular, the respective roles of the fibers and the matrix and how these may change with growth or chemical treatments are unknown. Structurally based constitutive models avoid ambiguities in material characterization and offer insights into the function, structure, and mechanics of tissue components. In the present work a structural constitutive model for the aortic valve is presented as an example of a structural approach. Ongoing issues in practically applying structural models to other tissues are also addressed.

Improvement of Predictive Accuracy on Subchannel Analysis Code (NASCA) for Tight-Lattice Rod Bundle Tests: Optimization of UEDA’S Entrainment Model Parameter and Cross Flow Model Parameters

2006 ◽  
Author(s):  
Hiromasa Chitose ◽  
Akitoshi Hotta ◽  
Akira Ohnuki ◽  
Ken Fujimura
Keyword(s):  
Nuclear Reactor ◽  
Predictive Accuracy ◽  
Constitutive Models ◽  
Cross Flow ◽  
Heat Removal ◽  
Model Parameters ◽  
Two Phase ◽  
Energy Agency ◽  
Rod Bundle ◽  
Subchannel Analysis

The Reduced-Moderation Water Reactor (RMWR) is being developed at Japan Atomic Energy Agency and demonstration of the core heat removal performance is one of the most important issues. However, operation of the full-scale bundle experiment is difficult technically because the fuel rod bundle size is larger, which consumes huge electricity. Hence, it is expected to develop an analysis code for simulating RMWR core thermal-hydraulic performance with high accuracy. Subchannel analysis is the most powerful technique to resolve the problem. A subchannel analysis code NASCA (Nuclear-reactor Advanced Sub-Channel Analysis code) has been developed to improve capabilities of analyzing transient two-phase flow phenomena, boiling transition (BT) and post BT, and the NASCA code is applicable on the thermal-hydraulic analysis for the current BWR fuel. In the present study, the prediction accuracy of the NASCA code has been investigated using the reduced-scale rod bundle test data, and its applicability on the RMWR has been improved by optimizing the mechanistic constitutive models.

Simulation of mechanically stirred two-phase liquid-gas flow

1986 ◽  
Vol 51 (5) ◽  
pp. 1001-1015 ◽  
Author(s):  
Ivan Fořt ◽  
Vladimír Rogalewicz ◽  
Miroslav Richter
Keyword(s):  
Spatial Distribution ◽  
Velocity Field ◽  
Gas Flow ◽  
Liquid Velocity ◽  
Model Parameters ◽  
Two Phase ◽  
Mean Velocity ◽  
Rushton Turbine ◽  
Low Viscosity ◽  
Volumetric Gas Flow Rate

The study describes simulation of the motion of bubbles in gas, dispersed by a mechanical impeller in a turbulent low-viscosity liquid flow. The model employs the Monte Carlo method and it is based both on the knowledge of the mean velocity field of mixed liquid (mean motion) and of the spatial distribution of turbulence intensity ( fluctuating motion) in the investigated system - a cylindrical tank with radial baffles at the wall and with a standard (Rushton) turbine impeller in the vessel axis. Motion of the liquid is then superimposed with that of the bubbles in a still environment (ascending motion). The computation of the simulation includes determination of the spatial distribution of the gas holds-up (volumetric concentrations) in the agitated charge as well as of the total gas hold-up system depending on the impeller size and its frequency of revolutions, on the volumetric gas flow rate and the physical properties of gas and liquid. As model parameters, both liquid velocity field and normal gas bubbles distribution characteristics are considered, assuming that the bubbles in the system do not coalesce.

On the Natural Lubrication of Synovial Joints: Normal and Degenerate

1977 ◽  
Vol 99 (2) ◽  
pp. 163-172 ◽  
Author(s):  
Joseph M. Mansour ◽  
Van C. Mow
Keyword(s):  
Articular Cartilage ◽  
Solid Phase ◽  
Articular Surface ◽  
Moving Load ◽  
Frictional Resistance ◽  
Elastic Solid ◽  
Surface Load ◽  
Two Phase ◽  
Tissue Properties ◽  
Synovial Joints

Fluid flow and mass transport mechanisms associated with articular cartilage function are important biomechanical processes of normal and pathological synovial joints. A three-layer permeable, two-phase medium of an incompressible fluid and a linear elastic solid are used to model the flow and deformational behavior of articular cartilage. The frictional resistance of the relative motion of the fluid phase with respect to the solid phase is given by a linear diffusive dissipation term. The subchondral bony substrate is represented by an elastic solid. The three-layer model of articular cartilage is chosen because of the known histological, ultrastructural, and biomechanical variations of the tissue properties. The calculated flow field shows that for material properties of normal healthy articular cartilage the tissue creates a naturally lubricated surface. The movement of the interstitial fluid at the surface is circulatory in manner, being exuded in front and near the leading half of the moving surface load and imbibed behind and near the trailing half of the moving load. The flow fields of healthy tissues are capable of sustaining a film of fluid at the articular surface whereas pathological tissues cannot.

Inverse analysis of constitutive models: Biological soft tissues

2007 ◽  
Vol 40 (4) ◽  
pp. 936-940 ◽  
Author(s):  
Fulin Lei ◽  
A.Z. Szeri
Keyword(s):  
Inverse Analysis ◽  
Soft Tissues ◽  
Constitutive Models
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