Biaxial Mechanical Properties of the Natural and Glutaraldehyde Treated Aortic Valve Cusp—Part I: Experimental Results

1999 ◽  
Vol 122 (1) ◽  
pp. 23-30 ◽  
Author(s):  
K. L. Billiar ◽  
M. S. Sacks
Keyword(s):  
Aortic Valve ◽  
Constitutive Models ◽  
Collagen Fibers ◽  
Mechanical Anisotropy ◽  
Fiber Architecture ◽  
Biaxial Testing ◽  
Mechanical Coupling ◽  
Uniform Region ◽  
Strain Relationship ◽  
Function Relationship

To date, there are no constitutive models for either the natural or bioprosthetic aortic valve (AV), in part due to experimental complications related to the AV’s small size and heterogeneous fibrous structure. In this study, we developed specialized biaxial testing techniques for the AV cusp, including a method to determine the local structure–strain relationship to assess the effects of boundary tethering forces. Natural and glutaraldehyde (GL) treated cusps were subjected to an extensive biaxial testing protocol in which the ratios of the axial tensions were held at constant values. Results indicated that the local fiber architecture clearly dominated cuspal deformation, and that the tethering effects at the specimen boundaries were negligible. Due to unique aspects of cuspal fiber architecture, the most uniform region of deformation was found at the lower portion as opposed to the center of the cuspal specimen. In general, the circumferential strains were much smaller than the radial strains, indicating a profound degree of mechanical anisotropy, and that natural cusps were significantly more extensible than the GL treated cusps. Strong mechanical coupling between biaxial stretch axes produced negative circumferential strains under equibiaxial tension. Further, the large radial strains observed could not be explained by uncrimping of the collagen fibers, but may be due to large rotations of the highly aligned, circumferential-oriented collagen fibers in the fibrosa. In conclusion, this study provides new insights into the AV cusp’s structure–function relationship in addition to requisite data for constitutive modeling. [S0148-0731(00)00901-8]

Alterations in Finite Element Results Given Constitutive Models From Tubular and Planar Biaxial Testing of the Same Porcine Coronary Arteries

2012 ◽  
Author(s):  
Joseph T. Keyes ◽  
Danielle R. Lockwood ◽  
Jonathan P. Vande Geest
Keyword(s):  
Constitutive Models ◽  
Design Parameters ◽  
Stress Distributions ◽  
Fiber Architecture ◽  
Biaxial Testing ◽  
Form Versus ◽  
Planar Form ◽  
Progression Of Disease ◽  
Insight Into

The biomechanical characterization of tissue offers insight into items such as progression of disease and design parameters for implants1,2. To biomechanically evaluate the properties of blood vessels, biaxial testing is frequently performed because biological samples often exhibit anisotropy, and are most frequently under tension from the applied pressures and stretches3,4. Deciding whether to splay a tubular sample open to test in planar form versus performing pressure-inflation testing is a decision often determined by what testing equipment is available. The purpose of this abstract is to compare pressure-inflation behavior, stress distributions, and fiber architecture in planar versus tubular biaxial testing of the same arteries.

Experiment Study on Degradation Laws of Sulfuric Acid Corrosion Reinforcements

2018 ◽  
Vol 878 ◽  
pp. 23-27 ◽  
Author(s):  
Ming Qiang Lin ◽  
Feng Juan Dai ◽  
Jia Tao Li
Keyword(s):  
Sulfuric Acid ◽  
Acid Corrosion ◽  
Constitutive Models ◽  
Corrosion Damage ◽  
Uniform Corrosion ◽  
Steel Bars ◽  
Relationship Model ◽  
Strain Relationship ◽  
Sulfuric Acid Corrosion ◽  
Corrosion Of Steel

The corrosion of concrete structures is serious in sulfuric acid environments. Corrosion damage of reinforcements caused sulfuric acid corrosion is very serious. The rapid experiments of sulfuric acid corrosion steel bars were carried out, and the apparent morphology and mechanical properties of sulfuric acid corrosion steel bars were studied. The results show that the corrosion of steel bars is uniform corrosion. With the increase of corrosion rate, the yield platforms and the yield strengths and ultimate strengths are reduced. Based on the experimental datas, the relationship models between yield strengths and ultimate strengths and corrosion rates were obtained. The constitutive models of corrosion steel bars were established. The stress - strain relationship model is in good agreement with the experimental data.

Collagen fibers reduce stresses and stabilize motion of aortic valve leaflets during systole

2004 ◽  
Vol 37 (3) ◽  
pp. 303-311 ◽  
Author(s):  
J. De Hart ◽  
G.W.M. Peters ◽  
P.J.G. Schreurs ◽  
F.P.T. Baaijens
Keyword(s):  
Aortic Valve ◽  
Collagen Fibers ◽  
Aortic Valve Leaflets

scholarly journals Straightening of curved pattern of collagen fibers under load controls aortic valve shape

2014 ◽  
Vol 47 (2) ◽  
pp. 341-346 ◽  
Author(s):  
Peter E. Hammer ◽  
Christina A. Pacak ◽  
Robert D. Howe ◽  
Pedro J. del Nido
Keyword(s):  
Aortic Valve ◽  
Collagen Fibers

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.

The Effect of Collagen Fiber Directional Distribution on the Mechanical Response of the Vascular Wall

2009 ◽  
Author(s):  
Rana Rezakhaniha ◽  
Nikos Stergiopulos
Keyword(s):  
Constitutive Equations ◽  
Mechanical Response ◽  
Vascular Tissue ◽  
Constitutive Models ◽  
Morphological Characteristics ◽  
Nonlinear Behavior ◽  
Vascular Wall ◽  
Incompressible Material ◽  
Collagen Fibers ◽  
Strain Energy Functions

Constitutive equations reflecting well the microstructure are fundamental for the detailed stress analysis of the arterial tissue. Vascular tissue is an inhomogeneous and incompressible material which undergoes large deformations and shows highly anisotropic nonlinear behavior. These properties make strain energy functions (SEFs) a suitable tool to derive constitutive equations. Structural constitutive models try to integrate the histological and morphological characteristics of the tissue by introducing parameters with physical meaning, such as the fraction of each wall constituent, the elastic properties of single elastin or collagen fibers or the angle of collagen fibers.

Local Mechanical Anisotropy in Human Cranial Dura Mater Allografts

1998 ◽  
Vol 120 (4) ◽  
pp. 541-544 ◽  
Author(s):  
M. S. Sacks ◽  
M. C. Jimenez Hamann ◽  
S. E. Otan˜no-Lata ◽  
T. I. Malinin
Keyword(s):  
Dura Mater ◽  
Mechanical Tests ◽  
Mechanical Anisotropy ◽  
Fiber Architecture ◽  
High Mechanical Strength ◽  
Structural Symmetry ◽  
Symmetry Test ◽  
The Right ◽  
High Degree

Human cranial dura mater (CDM) allograft’s success as a repair biomaterial is partly due to its high mechanical strength, which facilitates its ability to form water-tight barriers and resist high in-vivo mechanical loads. Previous studies on CDM allograft mechanical behavior used large test specimens and concluded that the allograft was mechanically isotropic. However, we have quantified CDM microstructure using small angle light scattering (SALS) and found regions of well-aligned fibers displaying structural symmetry between the right and left halves (Jimenez et al., 1998). The high degree of fiber alignment in these regions suggests that they are mechanically anisotropic. However, identification of these regions using SALS requires irreversible tissue dehydration, which may affect mechanical properties. Instead, we utilized CDM structural symmetry to estimate the fiber architecture of one half of the CDM using computer graphics to flip the SALS fiber architecture map of the corresponding half about the plane of symmetry. Test specimens (20 mm × 4 mm) were selected parallel and perpendicular to the preferred fiber directions and subjected to uniaxial mechanical failure testing. CDM allografts were found to be locally anisotropic, having an ultimate tensile strength (UTS) parallel to the fibers of 12.76 ± 1.65 MPa, and perpendicular to the fibers of 5.21 ± 1.01 MPa (mean ± sem). These results indicate that uniaxial mechanical tests on large samples used in previous studies tended to mask the local anisotropic nature of the smaller constituent sections. The testing methods established in this study can be used in the evaluation of new CDM processing methods and post-implant allograft mechanical integrity.

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