Biaxial Mechanical Properties of the Native and Glutaraldehyde-Treated Aortic Valve Cusp: Part II—A Structural Constitutive Model

2000 ◽  
Vol 122 (4) ◽  
pp. 327-335 ◽  
Author(s):  
Kristen L. Billiar ◽  
Michael S. Sacks
Keyword(s):  
Aortic Valve ◽  
Constitutive Model ◽  
Heart Valves ◽  
Low Pressure ◽  
Model Material ◽  
Biaxial Stress ◽  
Mechanical Anisotropy ◽  
Biaxial Test ◽  
Stress Strain ◽  
Strain Behavior

We have formulated the first constitutive model to describe the complete measured planar biaxial stress–strain relationship of the native and glutaraldehyde-treated aortic valve cusp using a structurally guided approach. When applied to native, zero-pressure fixed, and low-pressure fixed cusps, only three parameters were needed to simulate fully the highly anisotropic, and nonlinear in-plane biaxial mechanical behavior. Differences in the behavior of the native and zero- and low-pressure fixed cusps were found to be primarily due to changes in the effective fiber stress–strain behavior. Further, the model was able to account for the effects of small <10deg misalignments in the cuspal specimens with respect to the biaxial test axes that increased the accuracy of the model material parameters. Although based upon a simplified cuspal structure, the model underscored the role of the angular orientation of the fibers that completely accounted for extreme mechanical anisotropy and pronounced axial coupling. Knowledge of the mechanics of the aortic cusp derived from this model may aid in the understanding of fatigue damage in bioprosthetic heart valves and, potentially, lay the groundwork for the design of tissue-engineered scaffolds for replacement heart valves. [S0148-0731(00)00504-5]

scholarly journals Study of biaxial mechanical properties of the passive pig heart: material characterisation and categorisation of regional differences

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Fulufhelo Nemavhola
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Computational Models ◽  
Heart Diseases ◽  
Interventricular Septum ◽  
Model Material ◽  
Biaxial Test ◽  
Material Behaviour ◽  
Material Parameters ◽  
Biaxial Tests

AbstractRegional mechanics of the heart is vital in the development of accurate computational models for the pursuit of relevant therapies. Challenges related to heart dysfunctioning are the most important sources of mortality in the world. For example, myocardial infarction (MI) is the foremost killer in sub-Saharan African countries. Mechanical characterisation plays an important role in achieving accurate material behaviour. Material behaviour and constitutive modelling are essential for accurate development of computational models. The biaxial test data was utilised to generated Fung constitutive model material parameters of specific region of the pig myocardium. Also, Choi-Vito constitutive model material parameters were also determined in various myocardia regions. In most cases previously, the mechanical properties of the heart myocardium were assumed to be homogeneous. Most of the computational models developed have assumed that the all three heart regions exhibit similar mechanical properties. Hence, the main objective of this paper is to determine the mechanical material properties of healthy porcine myocardium in three regions, namely left ventricle (LV), mid-wall/interventricular septum (MDW) and right ventricle (RV). The biomechanical properties of the pig heart RV, LV and MDW were characterised using biaxial testing. The biaxial tests show the pig heart myocardium behaves non-linearly, heterogeneously and anisotropically. In this study, it was shown that RV, LV and MDW may exhibit slightly different mechanical properties. Material parameters of two selected constitutive models here may be helpful in regional tissue mechanics, especially for the understanding of various heart diseases and development of new therapies.

scholarly journals Identification of orthotropic material parameters for acute, necrotic, fibrotic and remodelling myocardial infarcts in the rat

2019 ◽  
Author(s):  
Mazin S. Sirry ◽  
Laura Dubuis ◽  
Neil H. Davies ◽  
Jun Liao ◽  
Thomas Franz
Keyword(s):  
Constitutive Model ◽  
Orthotropic Material ◽  
Constitutive Models ◽  
Biaxial Stress ◽  
Percentage Error ◽  
Fe Model ◽  
Stress Strain ◽  
Material Parameters ◽  
Strain Data ◽  
Tensile Experiment

AbstractFinite element (FE) models have been effectively utilized in studying biomechanical aspects of myocardial infarction (MI). Although the rat is a widely used animal model for MI, there is a lack of material parameters based on anisotropic constitutive models for rat myocardial infarcts in literature. This study aimed at employing inverse methods to identify the parameters of an orthotropic constitutive model for myocardial infarcts in the acute, necrotic, fibrotic and remodelling phases utilizing the biaxial mechanical data developed in a previous study. FE model was developed mimicking the setup of the biaxial tensile experiment. The orthotropic case of the generalized Fung constitutive model was utilized to model the material properties of the infarct. The parameters of Fung model were optimized so that the FE solution best fitted the biaxial experimental stress-strain data. A genetic algorithm was used to minimize the objective function. Fung orthotropic material parameters for different infarct stages were identified. The FE model predictions best approximated the experimental data of the 28 days infarct stage with 3.0% mean absolute percentage error. The worst approximation was for the 7 days stage with 3.6% error. This study demonstrated that the experimental biaxial stress-strain data of healing rat infarcts could be successfully approximated using inverse FE methods and genetic algorithms. The material parameters identified in this study will provide an essential platform for FE investigations of biomechanical aspects of MI and the development of therapies.

scholarly journals Uniform Nonlinear Constitutive Model and Parameters for Clay in Different Consolidation Conditions Based on Regression Method

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Tao Cheng ◽  
Keqin Yan ◽  
Huazhi Zhang ◽  
Xianfeng Luo ◽  
Shengfang Li
Keyword(s):  
Constitutive Model ◽  
Initial Conditions ◽  
Constitutive Relations ◽  
Test Sample ◽  
Maximum Relative Error ◽  
Compression Tests ◽  
Stress Strain ◽  
Strain Behavior ◽  
Nonlinear Constitutive Model ◽  
Isotropic Consolidation

The nonlinear constitutive relations of clay are investigated considering different initial conditions. Highly compressible clay is selected as the test sample. Two groups of tri-axial compression tests are performed, respectively, afterK0consolidation and isotropic consolidation. On the basis of the framework ofE~vmodel, a uniform nonlinear constitutive model is proposed by fitting the test data. With the average slope of the unloading-reloading curve selected as the unloading modulus, the unloading function is constructed as the loading-unloading criterion. Moreover, a comparison between the experimental stress-strain curves and the results predicted by the constitutive model is made. It is shown that the prediction is reasonable, which can reflect the stress-strain behavior of the soil under theK0consolidation and isotropic consolidation conditions. The maximum relative error of the two series of curves is not remarkable, less than 6%.

Protein Forced Unfolding and Its Effects on the Finite Deformation Stress-Strain Behavior of Biomacromolecular Solids

2005 ◽  
Vol 874 ◽  
Author(s):  
H. Jerry Qi ◽  
Christine Ortiz ◽  
Mary C. Boyce
Keyword(s):  
Constitutive Model ◽  
Single Molecule ◽  
Biological Networks ◽  
Finite Deformation ◽  
State Theory ◽  
Force Extension ◽  
Stress Strain ◽  
Strain Behavior ◽  
Mechanics Model ◽  
Deformation Stress

AbstractMany proteins have been experimentally observed to exhibit a force-extension behavior with a characteristic repeating pattern of a nonlinear rise in force with imposed displacement to a peak, followed by a significant force drop upon reaching the peak (a “saw-tooth” profile) due to successive unfolding of modules during extension. This behavior is speculated to play a governing role in biological and mechanical functions of natural materials and biological networks composed of assemblies of such protein molecules. In this paper, a constitutive model for the finite deformation stress-strain behavior of crosslinked networks of modular macromolecules is developed. The force-extension behavior of the individual modular macromolecule is represented using the Freely Jointed Chain (FJC) statistical mechanics model together with a two-state theory to capture unfolding. The single molecule behavior is then incorporated into a formal continuum mechanics framework to construct a constitutive model. Simulations illustrate a relatively smooth “yield”-like stress-strain behavior of these materials due to activate unfolding in these microstructures.

scholarly journals Stress-Strain Behavior of Perfluorosulfonic Acid Membranes at Various Temperatures and Humidities: Experiments and Phenomenological Modeling

2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Ahmet Kusoglu ◽  
Yaliang Tang ◽  
Michael H. Santare ◽  
Anette M. Karlsson ◽  
Simon Cleghorn ◽  
...  
Keyword(s):  
Constitutive Model ◽  
Flow Behavior ◽  
True Strain ◽  
Plastic Behavior ◽  
Stress Strain ◽  
True Strain Rate ◽  
Material Constants ◽  
Strain Behavior ◽  
Constitutive Response ◽  
Perfluorinated Sulfonic Acid

The constitutive response of perfluorinated sulfonic acid (PFSA) membranes based on tensile testing is investigated, and a phenomenological constitutive model for the elastoplastic flow behavior as a function of temperature and humidity is proposed. To this end, the G’Sell–Jonas (1979, “Determination of the Plastic Behavior of Solid Polymers at Constant True Strain Rate,” J. Mater. Sci., 14, pp. 583–591) constitutive model for semicrystalline polymers is extended by incorporating, in addition to temperature, relationships between the material constants of this model and the measured relative humidity. By matching the proposed constitutive model to the experimental stress-strain data, useful material constants are found. Furthermore, correlations between these material constants and Young’s modulus and proportional limit stress are investigated. The influence of material orientation, inherited from processing conditions, on the stress-strain behavior is also studied. The proposed model can be used to approximate the mechanical behavior of PFSA membranes in numerical simulations of a fuel cell operation.

Development of a Flow Evolution Network Model for the Stress–Strain Behavior of Poly(L-lactide)

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Maureen L. Dreher ◽  
Srinidhi Nagaraja ◽  
Jorgen Bergstrom ◽  
Danika Hayman
Keyword(s):  
Finite Element ◽  
Constitutive Model ◽  
Computational Modeling ◽  
Medical Devices ◽  
Constitutive Models ◽  
Constitutive Relationship ◽  
Displacement Curve ◽  
Stress Strain ◽  
Strain Behavior ◽  
Flow Evolution

Computational modeling is critical to medical device development and has grown in its utility for predicting device performance. Additionally, there is an increasing trend to use absorbable polymers for the manufacturing of medical devices. However, computational modeling of absorbable devices is hampered by a lack of appropriate constitutive models that capture their viscoelasticity and postyield behavior. The objective of this study was to develop a constitutive model that incorporated viscoplasticity for a common medical absorbable polymer. Microtensile bars of poly(L-lactide) (PLLA) were studied experimentally to evaluate their monotonic, cyclic, unloading, and relaxation behavior as well as rate dependencies under physiological conditions. The data were then fit to a viscoplastic flow evolution network (FEN) constitutive model. PLLA exhibited rate-dependent stress–strain behavior with significant postyield softening and stress relaxation. The FEN model was able to capture these relevant mechanical behaviors well with high accuracy. In addition, the suitability of the FEN model for predicting the stress–strain behavior of PLLA medical devices was investigated using finite element (FE) simulations of nonstandard geometries. The nonstandard geometries chosen were representative of generic PLLA cardiovascular stent subunits. These finite element simulations demonstrated that modeling PLLA using the FEN constitutive relationship accurately reproduced the specimen’s force–displacement curve, and therefore, is a suitable relationship to use when simulating stress distribution in PLLA medical devices. This study demonstrates the utility of an advanced constitutive model that incorporates viscoplasticity for simulating PLLA mechanical behavior.

A Cyclic Stress-Strain Constitutive Model for Polycrystalline Magnesium Alloy and its Application

2007 ◽  
Vol 546-549 ◽  
pp. 81-88
Author(s):  
Xiang Guo Zeng ◽  
Qing Yuan Wang ◽  
Jing Hong Fan ◽  
Zhan Hua Gao ◽  
Xiang He Peng
Keyword(s):  
Magnesium Alloy ◽  
Constitutive Model ◽  
Cyclic Stress ◽  
Stress And Strain ◽  
Slip Systems ◽  
Stress Strain ◽  
Strain Behavior ◽  
Cast Magnesium ◽  
Magnesium Alloy Am60 ◽  
Good Agreement

The stress-strain behavior of cast magnesium alloy (AM60) was investigated by strain-controlled cyclic testing carried out on MTS. In order to describe the cyclic stress and strain properties of AM60 by means of the energy storing characteristics of microstructure during irreversible deformation, a plastic constitutive model with no yielding surface was developed for single crystal by adopting a spring-dashpot mechanical system. Plastic dashpots reflecting the material transient response were introduced to describe the plasticity of slip systems. By utilizing the KBW self-consistent theory, a polycrystalline plastic constitutive model for Magnesium alloy was formed. The numerical analysis in the corresponding algorithm is greatly simplified as no process of searching for the activation of the slip systems and slip directions is required. The cyclic stress-strain behavior, based on this model, is discussed. The simulation results show good agreement with the experimental data for AM60.

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