A Model for Aortic Growth Based on Fluid Shear and Fiber Stresses

1998 ◽  
Vol 120 (3) ◽  
pp. 348-354 ◽  
Author(s):  
L. A. Taber
Keyword(s):  
Finite Elasticity ◽  
Rat Aorta ◽  
Opening Angle ◽  
Published Data ◽  
Fluid Shear ◽  
Volumetric Growth ◽  
Fiber Stress ◽  
Rates Of Change ◽  
Smooth Muscle Fiber ◽  
Global And Local

Stress-modulated growth in the aorta is studied using a theoretical model. The model is a thick-walled tube composed of two pseudoelastic, orthotropic layers representing the intima/media and the adventitia. Both layers are assumed to follow a growth law in which the time rates of change of the growth stretch ratios depend linearly on the local smooth muscle fiber stress and on the shear stress due to blood flow on the endothelium. Using finite elasticity theory modified to include volumetric growth, we computed temporal changes in stress, geometry, and opening angle (residual strain) during development and following the onset of sudden hypertension. For appropriate values of the coefficients in the growth law, the model yields results in reasonable agreement with published data for global and local growth of the rat aorta.

An annotated checklist of the main representatives of meiobenthos from inland water bodies of Central and Southern Vietnam. I. Roundworms (Nematoda)

Zootaxa ◽  
2017 ◽  
Vol 4300 (1) ◽  
pp. 1 ◽  
Author(s):  
VLADIMIR A. GUSAKOV ◽  
VLADIMIR G. GAGARIN
Keyword(s):  
Taxonomic Composition ◽  
Published Data ◽  
Southern Vietnam ◽  
Annotated List ◽  
Freshwater Bodies ◽  
Freshwater Habitats ◽  
Inland Water Bodies ◽  
Bodies Of Water ◽  
Global And Local ◽  
Annotated Checklist

This paper presents an annotated list of nematode taxa found in the course of investigations of meiobenthic communities in various freshwater bodies in central and southern Vietnam. Data on the structure and abundance of populations, ecology, and global and local distribution are given along with taxonomic and other comments. The occurrence and level of taxonomic richness of roundworms in the studied bodies of water and biotopes are discussed briefly. In total, 127 taxa of 10 orders and 38 families of nematodes are listed. The number of recorded genera is 60; 72 representatives of these genera are identified to species level. The listing includes 48 taxa that had not been previously recorded from Vietnamese territory and 17 species originally collected, analyzed, and described as new to science from this country. The results of these investigations and an overview of the previously published data indicate that taxonomic composition and diversity of Nematoda in Vietnamese freshwater habitats remain poorly studied, except for certain areas. 

The Effect of Age on Residual Strain in the Rat Aorta

1996 ◽  
Vol 118 (4) ◽  
pp. 440-444 ◽  
Author(s):  
A. Badreck-Amoudi ◽  
C. K. Patel ◽  
T. P. C. Kane ◽  
S. E. Greenwald
Keyword(s):  
Residual Stress ◽  
Wall Thickness ◽  
Residual Strain ◽  
Normal Growth ◽  
Rat Aorta ◽  
Opening Angle ◽  
Steady Increase ◽  
The Relationship ◽  
Effect Of Age ◽  
Intravascular Pressure

Residual stress is observed in many parts of the cardiovascular system and is thought to reduce transmural stress gradients due to intravascular pressure. Its development is closely associated with normal growth and pathological remodeling, although there appear to be few previous reports of the relationship between aging and residual stress. We have estimated residual strain (an indicator of the magnitude of residual stress) at ten sites along the aorta of rats aged 2.5 to 56 weeks by measuring the degree to which rings of vessel spring open when cut (opening angle). At all ages the opening angle decreased along the aorta, reaching a minimum near the renal arteries and increasing toward the aorto-iliac bifurcation, a result that confirms previous studies. During growth, although the unloaded circumference of the aorta increased steadily, the wall thickness and medial surface area fell to a minimum at the age of 6 weeks before continuing a steady increase. Similarly, the opening angle decreased between the ages of 2.5 and 6 weeks, thereafter increasing with age. In the abdominal aorta, a strong correlation between opening angle and wall thickness relative to midwall radius (h/R) was seen; whereas in the thoracic segment, in which no increase in h/R with age occurred, no such relationship was found. These observations are in keeping with a recently proposed hypothesis that residual stress will change in response to growth-related changes in vessel geometry driven by a tendency to minimize the nonuniform stress distribution inevitably found in pressurized thick-walled cylinders.

Application of a Simplified Constant Crack Tip Opening Angle Model to Crack Propagation Analyses in Steel Pipelines

2020 ◽  
Author(s):  
Chris Bassindale ◽  
Xin Wang ◽  
William R. Tyson ◽  
Su Xu
Keyword(s):  
Crack Tip ◽  
Propagation Model ◽  
Simplified Model ◽  
Computational Time ◽  
Opening Angle ◽  
Recent Experimental Data ◽  
Published Data ◽  
Velocity Data ◽  
Crack Tip Opening Angle ◽  
Crack Tip Opening

Abstract In this paper, a simplified constant crack tip opening angle (CTOA) model is presented and used to analyze two different pipeline steels. The steels examined in this work were an American Petroleum Institute (API) Standard X65 steel and a Japanese Industrial Standard (JIS) steel with the grade designation of STPG370. The commercial finite element (FE) code ABAQUS 2017x was used to generate the models and solve the analyses. The proposed propagation model was first verified through comparing the numerical results with published data. The steady-state fracture velocity data from the simplified model matched the data from literature within a maximum difference of 2% while drastically reducing the computational time required by an order of magnitude. Following the verification of the simplified model, it was then used to analyze recent experimental data. The model was able to match the experimental crack velocity data within a difference of 4%.

Torsional stress distributions in tubes with external and internal notches

2012 ◽  
Vol 47 (6) ◽  
pp. 331-340 ◽  
Author(s):  
Michele Zappalorto ◽  
Paolo Lazzarin
Keyword(s):  
Shear Stress ◽  
Opening Angle ◽  
Local Geometry ◽  
Outer Diameter ◽  
Stress Distributions ◽  
Large Bulk ◽  
Notch Tip ◽  
Global And Local ◽  
Axisymmetric Tube ◽  
Good Agreement

Practical expressions useful to assess the elastic stress distribution in a torque loaded axisymmetric tube, weakened by circumferential U- and blunt V-shaped notches, are presented. The solution is obtained as an extension of a previous analytical solution valid for axisymmetric solid shafts. It accounts for the local geometry (notch tip root radius and notch opening angle) as well as for the global geometry (inner and outer diameter of the tube). Shear stress fields are written as a function of the shear stress at the notch tip. Varying global and local geometries, the obtained equations are compared with a large bulk of finite element results, showing a good agreement.

scholarly journals A Phenomenological Model for Mechanically Mediated Growth, Remodeling, Damage, and Plasticity of Gel-Derived Tissue Engineered Blood Vessels

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
Julia Raykin ◽  
Alexander I. Rachev ◽  
Rudolph L. Gleason
Keyword(s):  
Blood Vessels ◽  
Damage Mechanics ◽  
Time Course ◽  
Material Behavior ◽  
Published Data ◽  
Mechanical Stimuli ◽  
Volumetric Growth ◽  
Model Framework ◽  
Modeling Framework ◽  
Tissue Engineered Blood Vessels

Mechanical stimulation has been shown to dramatically improve mechanical and functional properties of gel-derived tissue engineered blood vessels (TEBVs). Adjusting factors such as cell source, type of extracellular matrix, cross-linking, magnitude, frequency, and time course of mechanical stimuli (among many other factors) make interpretation of experimental results challenging. Interpretation of data from such multifactor experiments requires modeling. We present a modeling framework and simulations for mechanically mediated growth, remodeling, plasticity, and damage of gel-derived TEBVs that merge ideas from classical plasticity, volumetric growth, and continuum damage mechanics. Our results are compared with published data and suggest that this model framework can predict the evolution of geometry and material behavior under common experimental loading scenarios.

scholarly journals Mathematical Modelling of Residual-Stress Based Volumetric Growth in Soft Matter

2021 ◽  
Author(s):  
Ruoyu Huang ◽  
Raymond W. Ogden ◽  
Raimondo Penta
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Mathematical Modelling ◽  
Soft Matter ◽  
Direct Evidence ◽  
Deformation Gradient ◽  
Opening Angle ◽  
Spherically Symmetric ◽  
Volumetric Growth ◽  
Incompressibility Constraint

AbstractGrowth in nature is associated with the development of residual stresses and is in general heterogeneous and anisotropic at all scales. Residual stress in an unloaded configuration of a growing material provides direct evidence of the mechanical regulation of heterogeneity and anisotropy of growth. The present study explores a model of stress-mediated growth based on the unloaded configuration that considers either the residual stress or the deformation gradient relative to the unloaded configuration as a growth variable. This makes it possible to analyze stress-mediated growth without the need to invoke the existence of a fictitious stress-free grown configuration. Furthermore, applications based on the proposed theoretical framework relate directly to practical experimental scenarios involving the “opening-angle” in arteries as a measure of residual stress. An initial illustration of the theory is then provided by considering the growth of a spherically symmetric thick-walled shell subjected to the incompressibility constraint.

Constitutive branching in elastic materials

1982 ◽  
Vol 92 (1) ◽  
pp. 167-181 ◽  
Author(s):  
R. Hill
Keyword(s):  
General Theory ◽  
Work Function ◽  
Finite Elasticity ◽  
Stress And Strain ◽  
Elastic Materials ◽  
Material Response ◽  
Critical States ◽  
Global And Local ◽  
Homogeneous Strain ◽  
Conjugate Stress

AbstractIn finite elasticity a homogeneous strain is not always determined uniquely by the conjugate stress. The phenomenon is investigated for any constitutive work-function, and in both its global and local aspects. Uniqueness is lost in specific critical states. Basic properties of their aggregates in the stress and strain spaces are derived, and shown to be fundamental for the material response near individual critical states. The geometry of local branches is analyzed in detail. Further properties resulting from material isotropy are obtained. The general theory is illustrated by examples typifying the responses of metal crystals and rubberlike polymers.

Exploring accessibility from spatial interaction data: An evaluation of the Essential Air Service (EAS) program in the contiguous US air transport system

2016 ◽  
Vol 49 (4) ◽  
pp. 930-951 ◽  
Author(s):  
Yongha Park ◽  
Morton E O’Kelly
Keyword(s):  
Spatial Interaction ◽  
Interaction Model ◽  
Air Transportation ◽  
Continental Scale ◽  
Routing Schemes ◽  
Rates Of Change ◽  
Subsidy Program ◽  
Global And Local ◽  
Air Carriers ◽  
Accessibility Measure

This paper is primarily concerned with the accessibility of airports located in small and geographically isolated communities. Specifically, it carries out a sensitivity analysis to derive rates of change for the parameters of a spatial interaction model applied to empirical air passenger trip data, and interprets the results focusing on the local airports subsidized by the Essential Air Service program. An empirical trip based accessibility measure is developed for individual airports in the contiguous US air transportation system. The measure enables us to capture the distinctive roles of small airports, which primarily function as regional associates of nearby cities and entrances for long-haul trips via major hub(s) to continental-scale connections. We observe the geographic and temporal variability of accessibility among airports, regarding the external factors including the dynamics of air carriers’ routing schemes, as well as global and local circumstances. Their impacts on passenger journey lengths are substantial at the local airports due to the few available connections. This issue has received less attention in existing subsidy program assessments. Furthermore, we explore the geographic distribution of non-subsidized local airports showing similar accessibility conditions. This paper enhances prior development by showing that the rates of change in accessibility scores are largely stable over recent national air passenger data.

A Model for Stress-Induced Growth in the Developing Heart

1995 ◽  
Vol 117 (3) ◽  
pp. 343-349 ◽  
Author(s):  
I-En Lin ◽  
L. A. Taber
Keyword(s):  
Diastolic Pressure ◽  
Wall Stress ◽  
Rate Of Change ◽  
Embryonic Chick ◽  
Local Growth ◽  
Volumetric Growth ◽  
Differential Growth ◽  
Elevated Pressures ◽  
Developing Heart ◽  
Global And Local

Mechanical loads affect growth and morphogenesis in the developing heart. Using a theoretical model, we studied stress-modulated growth in the embryonic chick ventricle during stages 21–29 (4–6 days of a 21-day incubation period). The model is a thick-walled, compressible, pseudoelastic cylinder, with finite volumetric growth included by letting the rate of change of the local zero-stress configuration depend linearly on the Cauchy stresses. After investigating the fundamental behavior of the model, we used it to study global and local growth in the primitive ventricle due to normal and abnormal cavity pressures. With end-diastolic pressure taken as the growth-modulating stimulus, correlating theoretical and available experimental results yielded the coefficients of the growth law, which was assumed to be independent of time and loading conditions. For both normal and elevated pressures, the predicted changes in radius and wall volume during development were similar to experimental measurements. In addition, the residual stress generated by differential growth agreed with experimental data. These results suggest that wall stress may be a biomechanical factor that regulates growth in the embryonic heart.

Acute Thoracic Vertebral Injury Thresholds

2004 ◽  
Author(s):  
Mari S. Truman ◽  
Lisa A. Ferrara ◽  
Ryan Milks ◽  
Illya Gordon ◽  
Jason Eckhardt
Keyword(s):  
Thoracic Spine ◽  
Intervertebral Discs ◽  
Acute Injury ◽  
Published Data ◽  
Thoracic Vertebrae ◽  
Injury Threshold ◽  
Thoracic Disc ◽  
Global And Local ◽  
Local Stiffness ◽  
Non Destructive

This study measures select static and dynamic characteristics of the human mid-thoracic spine, and compares them to previously published data for the thoraco-lumbar and cervical regions. Little information is available on the acute injury threshold for mid-thoracic intervertebral discs. The aim of this study was to characterize injury thresholds for the thoracic spine. Non-destructive combined flexion-compression loading experiments were conducted on 5 fresh human T5-T10 functional spinal units (FSU) at quasi-static and physiologic strain rates, and the resulting load-deflection responses were converted into global and local stiffness. Subsequently, 29 thoracic vertebrae (T5-T10) from 6 spines were subjected to moderate to severe impact loading in flexion. The peak forces and pressures were not statistically different between the thoracic disc levels. However, the mean injury forces and pressures were statistically different from mean failure forces found in the literature for both the lumbar and cervical spine regions, with the thoracic values falling between the cervical and lumbar values.

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