Change in Properties of the Glycocalyx Affects the Shear Rate and Stress Distribution on Endothelial Cells

2006 ◽  
Vol 129 (3) ◽  
pp. 324-329 ◽  
Author(s):  
Wen Wang
Keyword(s):  
Endothelial Cells ◽  
Structural Change ◽  
Shear Rate ◽  
Stress Distribution ◽  
Drag Coefficient ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Force Balance ◽  
Endothelial Glycocalyx ◽  
The Matrix

The endothelial glycocalyx mediates interactions between the blood flow and the endothelium. This study aims to evaluate, quantitatively, effects of structural change of the glycocalyx on stress distribution and shear rate on endothelial cells. In the study, the endothelial glycocalyx is modeled as a surface layer of fiber matrix and when exposed to laminar shear flow, the matrix deforms. Fluid velocity and stress distribution inside the matrix and on cell membranes are studied based on a binary mixture theory. Parameters, such as the height and porosity of the matrix and the drag coefficient between fluid and matrix fibrils, are based on available data and estimation from experiments. Simple theoretical solutions are achieved for fluid velocity and stress distribution in the surface matrix. Degradation of the matrix, e.g., by enzyme digestion, is represented by reductions in the volume fraction of fibrils, height, and drag coefficient. From a force balance, total stress on endothelial surface remains constant regardless of structural alteration of the glycocalyx. However, the stress that is transmitted to endothelial cells by direct “pulling” of fiber branches of the glycocalyx is reduced significantly. Fluid shear rate at the cell membrane, on the other hand, increases. The study gives quantitative insight into the effect of the structural change of the glycocalyx on the shear rate and pulling stress on the endothelium. Results can be used to interpret experiments on effects of the glycocalyx in shear induced endothelial responses.

A 1-D model to explore the effects of tissue loading and tissue concentration gradients in the revised Starling principle

2006 ◽  
Vol 291 (6) ◽  
pp. H2950-H2964 ◽  
Author(s):  
Xiaobing Zhang ◽  
Roger H. Adamson ◽  
Fitz-Roy E. Curry ◽  
Sheldon Weinbaum
Keyword(s):  
Tight Junction ◽  
Tissue Concentration ◽  
Three Dimensional ◽  
Force Balance ◽  
Endothelial Glycocalyx ◽  
Surrounding Tissue ◽  
Concentration Gradients ◽  
Rat Mesentery ◽  
The Matrix ◽  
D Model

The recent experiments in Hu et al. ( Am J Physiol Heart Circ Physiol 279: H1724–H1736, 2000) and Adamson et al. ( J Physiol 557: 889–907, 2004) in frog and rat mesentery microvessels have provided strong evidence supporting the Michel-Weinbaum hypothesis for a revised asymmetric Starling principle in which the Starling force balance is applied locally across the endothelial glycocalyx layer rather than between lumen and tissue. These experiments were interpreted by a three-dimensional (3-D) mathematical model (Hu et al.; Microvasc Res 58: 281–304, 1999) to describe the coupled water and albumin fluxes in the glycocalyx layer, the cleft with its tight junction strand, and the surrounding tissue. This numerical 3-D model converges if the tissue is at uniform concentration or has significant tissue gradients due to tissue loading. However, for most physiological conditions, tissue gradients are two to three orders of magnitude smaller than the albumin gradients in the cleft, and the numerical model does not converge. A simpler multilayer one-dimensional (1-D) analytical model has been developed to describe these conditions. This model is used to extend Michel and Phillips’s original 1-D analysis of the matrix layer ( J Physiol 388: 421–435, 1987) to include a cleft with a tight junction strand, to explain the observation of Levick ( Exp Physiol 76: 825–857, 1991) that most tissues have an equilibrium tissue concentration that is close to 0.4 lumen concentration, and to explore the role of vesicular transport in achieving this equilibrium. The model predicts the surprising finding that one can have steady-state reabsorption at low pressures, in contrast to the experiments in Michel and Phillips, if a backward-standing gradient is established in the cleft that prevents the concentration from rising behind the glycocalyx.

Short Fibre Polymer Composites: a Fracture-Based Theory of Fibre Reinforcement

1994 ◽  
Vol 28 (7) ◽  
pp. 588-606 ◽  
Author(s):  
Michael R. Piggott
Keyword(s):  
Volume Fraction ◽  
Force Balance ◽  
Short Fibre ◽  
Standard Theory ◽  
Fibre Reinforcement ◽  
Minimum Volume ◽  
Stress Strain ◽  
Reinforced Polymers ◽  
Fibre Composites ◽  
The Matrix

The interphase between reinforcing fibers and polymers is brittle, and does not behave in the way it was assumed to when the standard theory for composite strength was developed. Futhermore, this theory predicts curved stress-strain plots for aligned short fibre composites, yet the evidence for this is unconvincing, and there is much new evidence that these stress-strain curves are straight. The time has therefore come to abandon this approach and take into account, instead, the apparent brittleness and sudden failure of aligned fibre reinforced polymers. This paper presents the evidence, and introduces the new approach. This involves microcrack development in composites from stress concentrations at the fibre ends. Since such failure initiation can occur simultaneously at many sites, the stress required to cause abrupt failure across the whole cross section can be estimated by a simple force balance. This analysis gives the familiar expressions used for short fibre composites, with one important difference. For carbon reinforced polymers, the polymer has to reach its breaking strength before failure, so that there is no minimum volume fraction for reinforcement with these composites. With glass, on the other hand, which has a higher breaking strain than most thermosets used for composites, the matrix appears unable to exert its full strength. Thus low fibre volume fraction glass fibre composites can be weaker than the matrix, and a minimum volume fraction for reinforcement exists.

scholarly journals Effect of Temperature on the Viscoelastic Properties of Carbon Nanotube Reinforced Polypropylene Composites

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Jun Huang ◽  
Denis Rodrigue ◽  
Ling Dong
Keyword(s):  
Mechanical Properties ◽  
Carbon Nanotubes ◽  
Carbon Nanotube ◽  
Stress Distribution ◽  
Viscoelastic Properties ◽  
Volume Fraction ◽  
Axial Direction ◽  
Effect Of Temperature ◽  
Polypropylene Composites ◽  
The Matrix

Finite element method (FEM) is used to analyze the mechanical properties of carbon nanotubes (CNTs) reinforced polypropylene (PP) composites. Firstly, polypropylene is assumed as a viscoelastic material, while carbon nanotubes are assumed as linear elastic materials to study the effect of temperature on the mechanical properties of neat PP and CNT/PP nanocomposites. Secondly, to compare the viscoelastic properties of neat PP and CNT/PP nanocomposites, the relaxation time at a specific temperature is used to investigate the relaxation of the nanocomposites for fixed tensile displacements. Thirdly, the effect of CNT volume fraction on the viscoelastic properties of nanocomposites is studied at different temperatures. Finally, to better understand the stress distribution along the CNT axial direction, a single carbon nanotube is isolated in the matrix to compare the stress distribution with nonisolated CNTs.

Study of Thermal Stress of Iron-Boron Alloy Casing

2011 ◽  
Vol 311-313 ◽  
pp. 1039-1043
Author(s):  
Yun Zhang ◽  
Yong Di Li ◽  
Jian Jun Wu
Keyword(s):  
Thermal Stress ◽  
Stress Distribution ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Internal Surface ◽  
Stressed Condition ◽  
Fiber Volume ◽  
The Matrix ◽  
Thermal Stress Distribution ◽  
Properties Of Composites

The outer casing of heater made of iron-boron alloy is brittle fractured easily. It is a an effective way to add continuous fibers in brittleness material to improve the mechanical properties of composites. Temperature and thermal stress distribution of iron-boron alloy casing and the influence of thickness on the thermal stress of the casing is computed with finite element method, and the thermal stress distribution and influence of fiber volume fraction of continuous fiber-reinforced composites is studied. The result indicates that the external surface is in tensile stressed condition, and the internal surface is in compression stressed condition; the thermal stress increases with the thickness. The compression stress of the matrix decreases and the tensile stress increases with the increasing of the fiber volume fraction.

Formation of Persistent Slip Band in Fatigued Copper Single Crystals

1982 ◽  
Vol 40 ◽  
pp. 470-471
Author(s):  
N. Y. Jin
Keyword(s):  
Volume Fraction ◽  
Fatigue Cracks ◽  
Wall Structure ◽  
Matrix Structure ◽  
Dislocation Dipole ◽  
Slip Bands ◽  
Persistent Slip Bands ◽  
The Matrix ◽  
Hard Shell ◽  
Copper Single Crystals

Localised plastic deformation in Persistent Slip Bands(PSBs) is a characteristic feature of fatigue in many materials. The dislocation structure in the PSBs contains regularly spaced dislocation dipole walls occupying a volume fraction of around 10%. The remainder of the specimen, the inactive "matrix", contains dislocation veins at a volume fraction of 50% or more. Walls and veins are both separated by regions in which the dislocation density is lower by some orders of magnitude. Since the PSBs offer favorable sites for the initiation of fatigue cracks, the formation of the PSB wall structure is of great interest. Winter has proposed that PSBs form as the result of a transformation of the matrix structure to a regular wall structure, and that the instability occurs among the broad dipoles near the center of a vein rather than in the hard shell surounding the vein as argued by Kulmann-Wilsdorf.

Preparation of Electron Transparent Metal-Matrix Composites

1968 ◽  
Vol 26 ◽  
pp. 334-335 ◽  
Author(s):  
M. R. Pinnel ◽  
A. Lawley
Keyword(s):  
Stainless Steel ◽  
Load Transfer ◽  
Volume Fraction ◽  
Steel Wire ◽  
Initial Step ◽  
Interfacial Region ◽  
Matrix Composites ◽  
Specific Test ◽  
The Matrix ◽  
The One

Numerous phenomenological descriptions of the mechanical behavior of composite materials have been developed. There is now an urgent need to study and interpret deformation behavior, load transfer, and strain distribution, in terms of micromechanisms at the atomic level. One approach is to characterize dislocation substructure resulting from specific test conditions by the various techniques of transmission electron microscopy. The present paper describes a technique for the preparation of electron transparent composites of aluminum-stainless steel, such that examination of the matrix-fiber (wire), or interfacial region is possible. Dislocation substructures are currently under examination following tensile, compressive, and creep loading. The technique complements and extends the one other study in this area by Hancock.The composite examined was hot-pressed (argon atmosphere) 99.99% aluminum reinforced with 15% volume fraction stainless steel wire (0.006″ dia.).Foils were prepared so that the stainless steel wires run longitudinally in the plane of the specimen i.e. the electron beam is perpendicular to the axes of the wires. The initial step involves cutting slices ∼0.040″ in thickness on a diamond slitting wheel.

scholarly journals Stress analysis of infinite laminated composite plate with elliptical cutout under different in plane loadings in hygrothermal environment

2021 ◽  
Vol 8 (1) ◽  
pp. 1-12
Author(s):  
Ashok Magar ◽  
Achchhe Lal
Keyword(s):  
Stress Concentration ◽  
Stress Distribution ◽  
Composite Plate ◽  
Volume Fraction ◽  
Elliptical Hole ◽  
Laminated Composite ◽  
Laminated Composite Plate ◽  
Concentration Changes ◽  
Hygrothermal Environment ◽  
Plate Analysis

Abstract This paper presents the solution of stress distribution around elliptical cutout in an infinite laminated composite plate. Analysis is done for in plane loading under hygrothermal environment. The formulation to obtain stresses around elliptical hole is based on Muskhelishvili’s complex variable method. The effect of fibre angle, type of in plane loading, volume fraction of fibre, change in temperature, fibre materials, stacking sequence and environmental conditions on stress distribution around elliptical hole is presented. The study revealed, these factors have significant effect on stress concentration in hygrothermal environment and stress concentration changes are significant with change in temperature.

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

scholarly journals Continuous Cooling Transformation Behaviour and Bainite Transformation Kinetics of 23CrNi3Mo Carburised Steel

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 48
Author(s):  
Wenjun Song ◽  
Min Lei ◽  
Mingpan Wan ◽  
Chaowen Huang
Keyword(s):  
Phase Transformation ◽  
Volume Fraction ◽  
Austenite Formation ◽  
Steel Matrix ◽  
Transformation Kinetics ◽  
Bainite Transformation ◽  
Continuous Cooling ◽  
The Matrix ◽  
Dimensional Growth ◽  
Kinetics Of

In this study, the phase transformation behaviour of the carburised layer and the matrix of 23CrNi3Mo steel was comparatively investigated by constructing continuous cooling transformation (CCT) diagram, determining the volume fraction of retained austenite (RA) and plotting dilatometric curves. The results indicated that Austenite formation start temperature (Ac1) and Austenite formation finish temperature (Ac3) of the carburised layer decreased compared to the matrix, and the critical cooling rate (0.05 °C/s) of martensite transformation is significantly lower than that (0.8 °C/s) of the matrix. The main products of phase transformation in both the carburised layer and the matrix were martensite and bainite microstructures. Moreover, an increase in carbon content resulted in the formation of lamellar martensite in the carburised layer, whereas the martensite in the matrix was still lath. Furthermore, the volume fraction of RA in the carburised layer was higher than that in the matrix. Moreover, the bainite transformation kinetics of the 23CrNi3Mo steel matrix during the continuous cooling process indicated that the mian mechanism of bainite transformation of the 23CrNi3Mo steel matrix is two-dimensional growth and one-dimensional growth.

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