Tire Treadwear — A Comprehensive Evaluation of the Factors: Generic Type, Aspect Ratio, Tread Pattern, and Tread Composition Part IV: Laboratory Measurement of Mechanical Properties and Mechanical Actions of Tires Relating to Treadwear

1986 ◽  
Vol 14 (4) ◽  
pp. 264-291
Author(s):  
K. L. Oblizajek ◽  
A. G. Veith
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Contact Zone ◽  
Flexural Rigidity ◽  
Comprehensive Evaluation ◽  
Shear Stiffness ◽  
Shear Stresses ◽  
Lateral Shear ◽  
Band Bending ◽  
Tread Rubber

Abstract Treadwear is explained by specific mechanical properties and actions of tires. Rubber shear stresses in the contact zone between the tire and the road become large at large slip angles. When normal stresses are insufficient to prevent sliding at the rear of the footprint, wear occurs at a rate that depends on test severity. Two experimental approaches are described to relate treadwear to tire characteristics. The first uses transducers imbedded in a simulated road surface to obtain direct measurements of contact stresses on the loaded, freely-rolling, steered tires. The second approach is developed with the aid of a simple carcass, tread-band, tread-rubber tire model. Various tire structural configurations; characterized by carcass spring rate, edgewise flexural band stiffness, and tread rubber shear stiffness; are simulated and lateral shear stress response in the contact zone is determined. Tires featuring high band stiffness and low carcass stiffness generate lower lateral shear stress levels. Furthermore, coupling of tread-rubber stiffness and band flexural rigidity are important in determining level of shear stresses. Laboratory measurements with the described apparatus produced values of tread-band bending and carcass lateral stiffness for several tire constructions. Good correlation is shown between treadwear and a broad range of tire stiffness and test course severities.

scholarly journals Biomechanical Characterization of Endothelial Cells Exposed to Shear Stress Using Acoustic Force Spectroscopy

2021 ◽  
Vol 9 ◽  
Author(s):  
Giulia Silvani ◽  
Valentin Romanov ◽  
Charles D. Cox ◽  
Boris Martinac
Keyword(s):  
Mechanical Properties ◽  
Endothelial Cells ◽  
Shear Stress ◽  
Actin Filament ◽  
Force Spectroscopy ◽  
Shear Stresses ◽  
Cell Periphery ◽  
Static Conditions ◽  
Cells Cultured ◽  
Cell Cell

Characterizing mechanical properties of cells is important for understanding many cellular processes, such as cell movement, shape, and growth, as well as adaptation to changing environments. In this study, we explore the mechanical properties of endothelial cells that form the biological barrier lining blood vessels, whose dysfunction leads to development of many cardiovascular disorders. Stiffness of living endothelial cells was determined by Acoustic Force Spectroscopy (AFS), by pull parallel multiple functionalized microspheres located at the cell-cell periphery. The unique configuration of the acoustic microfluidic channel allowed us to develop a long-term dynamic culture protocol exposing cells to laminar flow for up to 48 h, with shear stresses in the physiological range (i.e., 6 dyn/cm2). Two different Endothelial cells lines, Human Aortic Endothelial Cells (HAECs) and Human Umbilical Vein Endothelial Cells (HUVECs), were investigated to show the potential of this tool to capture the change in cellular mechanical properties during maturation of a confluent endothelial monolayer. Immunofluorescence microscopy was exploited to follow actin filament rearrangement and junction formation over time. For both cell types we found that the application of shear-stress promotes the typical phenotype of a mature endothelium expressing a linear pattern of VE-cadherin at the cell-cell border and actin filament rearrangement along the perimeter of Endothelial cells. A staircase-like sequence of increasing force steps, ranging from 186 pN to 3.5 nN, was then applied in a single measurement revealing the force-dependent apparent stiffness of the membrane cortex in the kPa range. We also found that beads attached to cells cultured under dynamic conditions were harder to displace than cells cultured under static conditions, showing a stiffer membrane cortex at cell periphery. All together these results demonstrate that the AFS can identify changes in cell mechanics based on force measurements of adherent cells under conditions mimicking their native microenvironment, thus revealing the shear stress dependence of the mechanical properties of neighboring endothelial cells.

BIOMIMETIC ELECTROSPUN GELATIN–CHITOSAN POLYURETHANE FOR HEART VALVE LEAFLETS

2010 ◽  
Vol 10 (04) ◽  
pp. 563-576 ◽  
Author(s):  
CYNTHIA WONG ◽  
PATEL SHITAL ◽  
RUI CHEN ◽  
AMAL OWIDA ◽  
YOS MORSI
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Heart Valve ◽  
Exposure Time ◽  
Heart Valves ◽  
Retention Rate ◽  
Proper Function ◽  
Shear Stresses ◽  
Cell Retention ◽  
Electrospun Gelatin

Native heart valve leaflets are subjected to continuous pulsatile and homodynamic forces and can be as thin as 300 μm. For a proper function of the valve the materials selected for the leaflets need to be biocompatible, robust, flexible, and have comparable mechanical properties to the natural ones. In this paper, biocompatibility and cell retention ability for gelatin–chitosan polyurethane (PU), polyglycolide (PGA)/PLA and collagen-coated bovine pericardium were examined and their mechanical properties were tested. Endothelial cells, isolated from ovine carotid arteries were seeded onto these materials and exposed to a range of shear-stresses for a period of 1–3 h. The findings indicated that throughout the exposure time and the shear-stress range tested, a mean cell retention rate of 80% was obtained in the gelatin–chitosan PU group. However, for PGA/PLA and pericardium groups it was found that as the exposure time of shear-stress increased, a significant cell reduction was observed. Noticeably for all the range of physiological flow conditions tested, the electrospun gelatin–chitosan PU demonstrated good biocompatibility and cell retention properties and could be potentially used as a biomaterial for tissue engineering of heart valves.

Study on the Mechanical Properties of Discontinuity under Shearing

2011 ◽  
Vol 261-263 ◽  
pp. 900-904
Author(s):  
Qing Zhao Zhang ◽  
Ming Rong Shen
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Shear Strength ◽  
Empirical Formula ◽  
Shear Test ◽  
Slope Angle ◽  
Shear Stiffness ◽  
Roughness Coefficient ◽  
Normal Stresses ◽  
Fundamental Research

This paper presents a fundamental research in the mechanical properties of the regular jagged discontinuity under various normal stresses in the shear test. The mechanical properties of the regular jagged discontinuity under shear stress and their principal regularities are described. The strength and roughness of discontinuity under shear stress are investigated by the analysis of the data obtained. The calculation of shear stiffness of discontinuity and an empirical formula between the slope angle and roughness coefficient of discontinuity are proposed. The changing regularity of the parameters of the shear strength of discontinuity under shear stress is investigated, and an empirical formula is established to evaluate the shear strength of discontinuity.

Study on the Mechanical Properties of Discontinuity under Shearing

2011 ◽  
Vol 243-249 ◽  
pp. 3043-3049
Author(s):  
Chuan Sheng Chen ◽  
Shi Zhi Wen
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Shear Strength ◽  
Empirical Formula ◽  
Morphological Characteristics ◽  
Shear Stiffness ◽  
Jointed Rock ◽  
Roughness Coefficient ◽  
Fundamental Research ◽  
Mechanism Of Failure

The mechanical properties of discontinuity are different from those of a whole rock. And the shear strength of discontinuity is closely related to its morphological characteristics. The study of the mechanism of failure of jointed rock mass under shear stress is to reveal its mechanical behavior and its mechanism of failure. This paper presents a fundamental research in the mechanical properties of the regular jugged discontinuity under various normal stresses in the shear test. And it describes the mechanical properties of the regular jugged discontinuity under shear stress and their principal regularities. The strength and roughness of discontinuity under shear stress are investigated by the analysis of the data obtained. And this paper study the calculation of shear stiffness of discontinuity and proposed an empirical formula between the slope ratio and roughness coefficient of discontinuity. Also the changing regularity of the parameters of the shear strength of discontinuity under shear stress is investigated, and an empirical formula is developed to evaluate the shear strength of discontinuity in this paper.

scholarly journals The Effect of Crevassing on The Radiative Absorptance of a Glacier Surface (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 353 ◽  
Author(s):  
Tad Pfeffer
Keyword(s):  
Heat Transfer ◽  
Mechanical Properties ◽  
Surface Roughness ◽  
Shear Stress ◽  
Uniform Distribution ◽  
Absorptive Capacity ◽  
Surface Melting ◽  
Lateral Shear ◽  
Ice Surface ◽  
Temperature Distributions

Surface melting has been observed on the lower, floating half of Byrd Glacier, Antarctica, during the height of the summer ablation season, in spite of regional air temperatures consistently below 0°C. The thickness of ice in this area is about 2 500 m, but surface crevasses penetrate to a depth of about 20 m, and bottom crevasses, being water-filled, may extend all the way up to sea-level. This leaves a zone of uncrevassed ice between which is of the order of 200 m in thickness, across which lateral shear stress due to drag against fjord walls will be concentrated. Variations in the mechanical properties of ice in this zone, specifically variations in hardness due to temperature changes, will obviously have a significant effect on the dynamics of the ice stream. A model of the rough ice surface has been constructed, in which large crevasse furrows are represented by cylindrical V-grooves. These form the upper boundary of a solid conduction region which is semiinfinite below, and whose transient temperature distribution is calculated using the finite element method. The free surface boundary condition, that of sunlight warming the rough ice surface, is calculated by the construction and solution of coupled Fredholm integral equations of the second kind; these represent the energy absorbed at a point on the V-groove surface as being due to (1) energy directly incident from the sun, if the point is not in shadow, and (2) indirect radiation reflected from the opposite wall of the V-groove. This formulation takes into account all multiple reflections of radiation between the walls of the V-groove cavity. Additionally, the reflectivity of the ice surface is not given a constant value, but is allowed to vary, increasing as the angle of incidence departs from the surface normal. The purpose of the model is to compare temperature distributions with a rough surface to the same model with a smooth surface. Due to the many simplifications made with regard to surface heat transfer, it is imprudent to make assertions about actual temperature distributions based on the model results, but the difference between the rough and smooth model results will provide a lower bound on the actual enhancement effect of surface roughness, i.e. future, more comprehensive, modeling of energy exchange at an ice surface will be in error by at least the predicted amount if the surface is treated as if it were flat. The major effects of the surface roughness are greater absorptive capacity and non-uniform distribution of the absorbed energy. The greater absorptive capacity of a V-groove cavity is well known from studies in radiation heat transfer. Non-uniform distribution is due to two mechanisms: (1) the cavity effect is most pronounced at the apex of the V-groove, and (2) when surface melting occurs, energy is transported in the form of latent heat of melting from wherever the melting occurs to below the apex of the V-groove where the melt water refreezes. The possibility that lateral shear stress is concentrated in a zone only 200 m thick means that temperature perturbations due to surface roughness need only penetrate on the order of 200 m, or possibly even less, to have a significant effect on the mechanical properties of the ice, and in turn on the dynamics of the ice stream.

scholarly journals A Hysteretic Constitutive Model for Reinforced Concrete Panel Elements

2019 ◽  
Vol 13 (1) ◽  
Author(s):  
Kutay Orakcal ◽  
Leonardo M. Massone ◽  
Denizhan Ulugtekin
Keyword(s):  
Shear Stress ◽  
Reinforced Concrete ◽  
Constitutive Model ◽  
Shear Stiffness ◽  
Constitutive Relationship ◽  
Shear Stresses ◽  
Response Characteristics ◽  
Strain Behavior ◽  
Concrete Panels ◽  
Global And Local

Abstract A simple yet effective constitutive model-referred to as the “Fixed Strut Angle Model” (FSAM)-is presented in this paper for simulating the nonlinear axial/shear behavior of reinforced concrete membrane (panel) elements subjected to generalized and reversed cyclic loading conditions. In the formulation of the FSAM, normal stresses in cracked concrete are calculated along fixed crack (strut) directions. Shear stresses developing along crack surfaces, which are calculated using a simple friction-based constitutive relationship, are superimposed with the concrete stresses along the struts, for obtaining the total stress field in concrete. Model predictions were compared with panel tests results available in the literature, at various global and local response levels. The model was demonstrated to reasonably capture the overall response characteristics of reinforced concrete panels, including hysteretic shear stress vs. strain behavior, shear stress capacity, hysteretic shear stiffness attributes, ductility, pinching behavior, governing failure mode, principal strain and stress directions, and local deformations.

scholarly journals Biomechanical characterization of endothelial cells exposed to shear stress using acoustic force spectroscopy

2020 ◽  
Author(s):  
Giulia Silvani ◽  
Valentin Romanov ◽  
Charles D. Cox ◽  
Boris Martinac
Keyword(s):  
Mechanical Properties ◽  
Endothelial Cells ◽  
Shear Stress ◽  
Cell Movement ◽  
Microfluidic Channel ◽  
Elastic Behavior ◽  
Shear Stresses ◽  
Cell Periphery ◽  
Experimental Conditions ◽  
Apparent Stiffness

AbstractCharacterizing mechanical properties of cells is important for understanding many cellular processes, such as cell movement, shape, and growth, as well as adaptation to changing environments. In this study, we explore mechanical properties of endothelial cells that form the biological barrier lining blood vessels, whose dysfunction leads to development of many cardiovascular disorders. Stiffness and contractile prestress of living endothelial cells were determined by Acoustic Force Spectroscopy (AFS) focusing on the displacement of functionalized microspheres located at the cell-cell periphery. The specific configuration of the acoustic microfluidic channel allowed us to develop a long-term dynamic culture protocol exposing cells to laminar flow, reaching shear stresses in the physiological range (i.e. 8 dyne cm-2) within 48 hours of barrier function maturation. A staircase-like sequence of increasing force steps, ranging from 186 pN to 3.5 nN, was applied in a single measurement revealing a force-dependent apparent stiffness in the kPa range. Moreover, our results show that different degrees of stiffening, defining the elastic behavior of the cell under different experimental conditions, i.e. static and dynamic, are caused by different levels of contractile prestress in the cytoskeleton, and are modulated by shear stress-mediated junction development and stabilization at cell borders. These results demonstrate that the AFS is capable of fast and high-throughput force measurements of adherent cells under conditions mimicking their native microenvironment, and thus revealing the shear stress dependence of mechanical properties of neighbouring endothelial cells.

scholarly journals The Effect of Crevassing on The Radiative Absorptance of a Glacier Surface (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 353-353 ◽  
Author(s):  
Tad Pfeffer
Keyword(s):  
Heat Transfer ◽  
Mechanical Properties ◽  
Surface Roughness ◽  
Shear Stress ◽  
Uniform Distribution ◽  
Absorptive Capacity ◽  
Surface Melting ◽  
Lateral Shear ◽  
Ice Surface ◽  
Temperature Distributions

Surface melting has been observed on the lower, floating half of Byrd Glacier, Antarctica, during the height of the summer ablation season, in spite of regional air temperatures consistently below 0°C. The thickness of ice in this area is about 2 500 m, but surface crevasses penetrate to a depth of about 20 m, and bottom crevasses, being water-filled, may extend all the way up to sea-level. This leaves a zone of uncrevassed ice between which is of the order of 200 m in thickness, across which lateral shear stress due to drag against fjord walls will be concentrated. Variations in the mechanical properties of ice in this zone, specifically variations in hardness due to temperature changes, will obviously have a significant effect on the dynamics of the ice stream.A model of the rough ice surface has been constructed, in which large crevasse furrows are represented by cylindrical V-grooves. These form the upper boundary of a solid conduction region which is semiinfinite below, and whose transient temperature distribution is calculated using the finite element method. The free surface boundary condition, that of sunlight warming the rough ice surface, is calculated by the construction and solution of coupled Fredholm integral equations of the second kind; these represent the energy absorbed at a point on the V-groove surface as being due to (1) energy directly incident from the sun, if the point is not in shadow, and (2) indirect radiation reflected from the opposite wall of the V-groove. This formulation takes into account all multiple reflections of radiation between the walls of the V-groove cavity. Additionally, the reflectivity of the ice surface is not given a constant value, but is allowed to vary, increasing as the angle of incidence departs from the surface normal.The purpose of the model is to compare temperature distributions with a rough surface to the same model with a smooth surface. Due to the many simplifications made with regard to surface heat transfer, it is imprudent to make assertions about actual temperature distributions based on the model results, but the difference between the rough and smooth model results will provide a lower bound on the actual enhancement effect of surface roughness, i.e. future, more comprehensive, modeling of energy exchange at an ice surface will be in error by at least the predicted amount if the surface is treated as if it were flat.The major effects of the surface roughness are greater absorptive capacity and non-uniform distribution of the absorbed energy. The greater absorptive capacity of a V-groove cavity is well known from studies in radiation heat transfer. Non-uniform distribution is due to two mechanisms: (1) the cavity effect is most pronounced at the apex of the V-groove, and (2) when surface melting occurs, energy is transported in the form of latent heat of melting from wherever the melting occurs to below the apex of the V-groove where the melt water refreezes.The possibility that lateral shear stress is concentrated in a zone only 200 m thick means that temperature perturbations due to surface roughness need only penetrate on the order of 200 m, or possibly even less, to have a significant effect on the mechanical properties of the ice, and in turn on the dynamics of the ice stream.

Finite Element Analysis of Tire/Rim Interface Forces Under Braking and Cornering Loads

1992 ◽  
Vol 20 (2) ◽  
pp. 83-105 ◽  
Author(s):  
J. P. Jeusette ◽  
M. Theves
Keyword(s):  
Finite Element ◽  
Shear Stress ◽  
Contact Pressure ◽  
Element Model ◽  
Shear Stresses ◽  
Detailed Knowledge ◽  
Stress Distributions ◽  
Element Analysis ◽  
Plane Shear ◽  
Normal Contact

Abstract During vehicle braking and cornering, the tire's footprint region may see high normal contact pressures and in-plane shear stresses. The corresponding resultant forces and moments are transferred to the wheel. The optimal design of the tire bead area and the wheel requires a detailed knowledge of the contact pressure and shear stress distributions at the tire/rim interface. In this study, the forces and moments obtained from the simulation of a vehicle in stationary braking/cornering conditions are applied to a quasi-static braking/cornering tire finite element model. Detailed contact pressure and shear stress distributions at the tire/rim interface are computed for heavy braking and cornering maneuvers.

Determination of the transverse shear stress in layered composites

2020 ◽  
Vol 86 (2) ◽  
pp. 44-53
Author(s):  
Yu. I. Dudarkov ◽  
M. V. Limonin
Keyword(s):  
Shear Stress ◽  
Transverse Shear ◽  
Composite Beam ◽  
Layered Composite ◽  
Equivalent Model ◽  
Shear Stresses ◽  
Transverse Shear Stress ◽  
Layered Composites ◽  
Laminate Composites ◽  
Transverse Shear Stresses

An engineering approach to estimation of the transverse shear stresses in layered composites is developed. The technique is based on the well-known D. I. Zhuravsky equation for shear stresses in an isotropic beam upon transverse bending. In general, application of this equation to a composite beam is incorrect due to the heterogeneity of the composite structure. According to the proposed method, at the first stage of its implementation, a transition to the equivalent model of a homogeneous beam is made, for which the Zhuravsky formula is valid. The transition is carried out by changing the shape of the cross section of the beam, provided that the bending stiffness and generalized elastic modulus remain the same. The calculated shear stresses in the equivalent beam are then converted to the stress values in the original composite beam from the equilibrium condition. The main equations and definitions of the method as well as the analytical equation for estimation of the transverse shear stress in a composite beam are presented. The method is verified by comparing the analytical solution and the results of the numerical solution of the problem by finite element method (FEM). It is shown that laminate stacking sequence has a significant impact both on the character and on the value of the transverse shear stress distribution. The limits of the applicability of the developed technique attributed to the conditions of the validity of the hypothesis of straight normal are considered. It is noted that under this hypothesis the shear stresses do not depend on the layer shear modulus, which explains the absence of this parameter in the obtained equation. The classical theory of laminate composites is based on the similar assumptions, which gives ground to use this equation for an approximate estimation of the transverse shear stresses in in a layered composite package.

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