scholarly journals Effect of skin hydration on the dynamics of fingertip gripping contact

2011 ◽  
Vol 8 (64) ◽  
pp. 1574-1583 ◽  
Author(s):  
T. André ◽  
V. Lévesque ◽  
V. Hayward ◽  
P. Lefèvre ◽  
J.-L. Thonnard
Keyword(s):  
Coefficient Of Friction ◽  
Contact Region ◽  
Tangential Force ◽  
Normal Component ◽  
Specific Effect ◽  
Skin Hydration ◽  
Skin Area ◽  
Force Component ◽  
Dry Skin ◽  
The Coefficient Of Friction

The dynamics of fingertip contact manifest themselves in the complex skin movements observed during the transition from a stuck state to a fully developed slip. While investigating this transition, we found that it depended on skin hydration. To quantify this dependency, we asked subjects to slide their index fingertip on a glass surface while keeping the normal component of the interaction force constant with the help of visual feedback. Skin deformation inside the contact region was imaged with an optical apparatus that allowed us to quantify the relative sizes of the slipping and sticking regions. The ratio of the stuck skin area to the total contact area decreased linearly from 1 to 0 when the tangential force component increased from 0 to a maximum. The slope of this relationship was inversely correlated to the normal force component. The skin hydration level dramatically affected the dynamics of the contact encapsulated in the course of evolution from sticking to slipping. The specific effect was to reduce the tendency of a contact to slip, regardless of the variations of the coefficient of friction. Since grips were more unstable under dry skin conditions, our results suggest that the nervous system responds to dry skin by exaggerated grip forces that cannot be simply explained by a change in the coefficient of friction.

scholarly journals A Technique to Determine Friction at the Fingertips

2008 ◽  
Vol 24 (1) ◽  
pp. 43-50 ◽  
Author(s):  
Adriana V. Savescu ◽  
Mark L. Latash ◽  
Vladimir M. Zatsiorsky
Keyword(s):  
Coefficient Of Friction ◽  
Normal Force ◽  
Tangential Force ◽  
Vertical Direction ◽  
Force Sensor ◽  
Displacement Method ◽  
Significant Difference ◽  
The Coefficient Of Friction ◽  
Slip Method ◽  
Slip Force

This article proposes a technique to calculate the coefficient of friction for the fingertip– object interface. Twelve subjects (6 males and 6 females) participated in two experiments. During the first experiment (the imposed displacement method), a 3-D force sensor was moved horizontally while the subjects applied a specified normal force (4 N, 8 N, 12 N) on the surface of a sensor covered with different materials (sandpaper, cotton, rayon, polyester, and silk).Thenormal forceand thetangential force(i.e., the force due to the sensor motion) were recorded. Thecoefficient of friction(µd) was calculated as the ratio between the tangential force and the normal force. In the second experiment (the beginning slip method), a small instrumented object was gripped between the index finger and the thumb, held stationary in the air, and then allowed to drop. The weight (200 g, 500 g, and 1,000 g) and the surface (sandpaper, cotton, rayon, polyester, and silk) in contact with the digits varied across trials. The same sensor as in the first experiment was used to record thenormal force(in a horizontal direction) and thetangential force(in the vertical direction). Theslip force(i.e., the minimal normal force or grip force necessary to prevent slipping) was estimated as the force at the moment when the object just began to slip. The coefficient of friction was calculated as the ratio between the tangential force and the slip force. The results show that (1) the imposed displacement method is reliable; (2) except sandpaper, for all other materials the coefficient of friction did not depend on the normal force; (3) theskin–sandpapercoefficient of friction was the highest µd= 0.96 ± 0.09 (for 4-N normal force) and theskin–rayonrayon coefficient of friction was the smallest µd= 0.36 ± 0.10; (4) no significant difference between the coefficients of friction determined with the imposed displacement method and the beginning slip method was observed. We view the imposed displacement technique as having an advantage as compared with the beginning slip method, which is more cumbersome (e.g., dropped object should be protected from impacts) and prone to subjective errors owing to the uncertainty in determining the instance of the slip initiation (i.e., impeding sliding).

Simulating Torsional Slip in V-Band Clamp Joints

2015 ◽  
Vol 798 ◽  
pp. 53-58
Author(s):  
Salahaddin M. Sahboun ◽  
Simon M. Barrans
Keyword(s):  
Finite Element ◽  
Coefficient Of Friction ◽  
Load Capacity ◽  
Contact Region ◽  
Finite Element Technique ◽  
Torsional Load ◽  
V Band ◽  
The Coefficient Of Friction ◽  
Element Technique

In this paper a finite element technique to predict the torsional load capacity of V-band clamp joints is presented. The development of this complex, multi-step analysis is explained and the results compared with alternate theories which ignore or take account of transverse friction in the band to flange contact region. It is shown that accounting for transverse friction yields a better comparison with the finite element results for lower coefficients of friction whilst ignoring this component gives better results for higher coefficients of friction. Torsional load capacity is shown to increase with band diameter and T-bolt tension but to be less dependent on the coefficient of friction.

scholarly journals Sintered Hydroxyapatite Ceramic for Wear Studies

1978 ◽  
Vol 57 (7-8) ◽  
pp. 777-783 ◽  
Author(s):  
Hillar M. Rootare ◽  
John M. Powers ◽  
Robert G. Craig
Keyword(s):  
Coefficient Of Friction ◽  
Tricalcium Phosphate ◽  
Friction And Wear ◽  
Tangential Force ◽  
Hydroxyapatite Ceramic ◽  
Track Width ◽  
Failure Data ◽  
Surface Failure ◽  
Human Enamel ◽  
The Coefficient Of Friction

A sintered hydroxyapatite (HAP) ceramic for use in wear studies was prepared from a commerical tricalcium phosphate. The sintered HAP had physical properties close to those of human enamel. The coefficient of friction and wear of the sintered HAP ceramic as characterized by tangential force, track width, and surface failure data, approximated those of human enamel.

Fully Developed Sliding of Rough Surfaces

1989 ◽  
Vol 111 (3) ◽  
pp. 445-451 ◽  
Author(s):  
C. Liu ◽  
B. Paul
Keyword(s):  
Closed Form ◽  
Contact Region ◽  
Tangential Force ◽  
Normal Pressure ◽  
Shear Stresses ◽  
Closed Form Solutions ◽  
Pressure Distributions ◽  
The Coefficient Of Friction ◽  
Force Components ◽  
Instantaneous Center

Given the contact region between two bodies, the normal pressure distribution over the contact region, and the coefficient of friction, we seek to find all combinations of tangential forces and twisting moment (about the normal to the contact surface) for which fully developed sliding impends. As part of the solution we must determine the distribution of the surface tractions (shear stresses) and the location of the instantaneous center (IC) of the impending motion. New closed form solutions of the stated problem are found for circular contact patches with pressure distributions corresponding to (a): a flat stamp; and (b): elastic spheroids with Hertzian pressure distributions. For contact regions other than circular, no closed form solutions are known. We have developed numerical procedures to solve for arbitrary contact patches, with arbitrary distributions of normal pressure, and present carpet plots of tangential force components (Fx, Fy) and IC coordinates for the following cases: flat ellipsoidal stamps; ellipsoidal indenters (Hertzian pressure); and a non-Hertzian, nonelliptical contact of a rail and wheel. Level curves of twisting moment Mz versus tangential force components are provided. Given any two of the three quantities (Fx, Fy, Mz), the algorithms and the plots in this paper make it possible and convenient to find the remaining force or moment which will cause gross sliding to impend, for virtually arbitrary contact regions and arbitrary pressure distributions.

Shear and normal stresses measured on the Weissfluhjoch Snow Chute

2016 ◽  
Vol 53 (3) ◽  
pp. 445-454 ◽  
Author(s):  
Marius Schaefer
Keyword(s):  
Coefficient Of Friction ◽  
Normal Component ◽  
Flow Density ◽  
Shear Stresses ◽  
Normal Stresses ◽  
Flow Depth ◽  
Air Temperatures ◽  
Wet Snow ◽  
Before And After ◽  
The Coefficient Of Friction

Shear stresses on the running surface are believed to crucially determine the flow of snow avalanches. Measurements of shear and normal stresses on the running surface are presented as well as measurements of flow depth of snow flows down the Weissfluhjoch Snow Chute before and after a reduction of the chute’s inclination. In the measurements before the inclination change, maxima of measured normal stresses agreed with the maxima of the normal component of the column weight calculated using pre-release snow density. After the reduction of inclination, stresses increased considerably and the magnitude of the increase depended on the density of the flow. Using the measurements of normal stress and flow depth before the inclination change, a depth-averaged flow density was computed. The flow density was lower in the front and the tail of the avalanches and approached the pre-release density in the avalanche body. The ratio of measured shear to normal stresses, the coefficient of friction, was higher in wet snow flows than in dry snow flows. Upon analysis of the dependence of the coefficient of friction on parameters varying between the experiments, higher coefficients of friction for higher densities, snow and air temperatures, and average avalanche velocities were found. The total avalanche volume correlated negatively with the coefficient of friction. Measured coefficients of friction were generally lower as expected for flows of constant velocity, which might indicate the importance of other frictional processes such as friction at the snow–air interface, which is supported by the evolution of small dilute snow clouds on top of the flows that consisted of dry snow.

Junction growth in metallic friction: the role of combined stresses and surface contamination

1959 ◽  
Vol 251 (1266) ◽  
pp. 378-393 ◽  
Keyword(s):  
Shear Stress ◽  
Tangential Stress ◽  
Coefficient Of Friction ◽  
Tangential Force ◽  
Critical Shear Stress ◽  
Surface Contamination ◽  
Combined Stresses ◽  
The Coefficient Of Friction ◽  
True Contact ◽  
Metallic Friction

This paper extends earlier work on the adhesion mechanism of friction and considers in particular the growth in area of contact as the tangential force is increased to the point at which gross sliding occurs. The earlier studies assumed that the area of true contact A is the same as that produced under static loading so that A = W / p 0 where W is the normal load and p 0 the plastic yield pressure of the metal. If the junctions have a specific shear strength s , the friction F , that is the force to shear them, will be F = As and the coefficient of friction becomes μ = s / p 0 (Bowden & Tabor 1954). Recent studies, however, show that as the tangential stress is applied the area of true contact increases according to a relation of the type p 2 + αs 2 = p 2 0 where p is the normal and s the tangential stress in the contact region and α an appropriate constant. With thoroughly outgassed metals, junction growth generally proceeds until practically the whole of the geometric area is in contact and coefficients of friction of the order of 50 or more are observed (Bowden & Young 1951). If the interface is contaminated, the stresses transmitted through it cannot exceed the critical shear stress of the interface. The new point developed in this paper based on the work of Courtney-Pratt & Eisner (1957), is that until the shear stress reaches this value junction growth occurs as for clean metals. Beyond this point, however, further junction growth is impossible and gross sliding occurs within the interfacial layer itself. The analysis given here shows that if the interface is only 5% weaker than the bulk metal, junction growth ceases and gross sliding occurs when the coefficient of friction is of the order of unity. This corresponds to the experimental observation that minute amounts of oxygen or air reduce the friction of thoroughly clean metals from extremely high values to values of about 1. In the presence of a lubricant film the transmissible stresses are so small that little junction growth can occur before sliding takes place. The expression for the coefficient of friction now reduces to a form resembling that given by the earlier simpler theory, namely μ = s i / p 0 , where s i is the critical shear stress of the lubricant layer. The present treatment thus incorporates the effect of combined stresses and surface contamination into a more general theory of metallic friction.

The Nature of Static Friction in Elastomers

1961 ◽  
Vol 34 (2) ◽  
pp. 461-465 ◽  
Author(s):  
G. M. Bartenev ◽  
V. V. Lavrent'ev
Keyword(s):  
Coefficient Of Friction ◽  
Dry Friction ◽  
Tangential Force ◽  
Static Friction ◽  
Initial Moment ◽  
Elastomeric Materials ◽  
The Coefficient Of Friction ◽  
Accuracy Of Measurement

Abstract 1. A method free from the shortcomings of earlier work is proposed for the measurement of the friction of elastomeric materials in the initial moment of shear. 2. From results of measurement of friction of rubber on steel it follows that static friction, determined as the coefficient of friction in the initial moment of slip, is a conventional parameter, since it depends upon the accuracy of measurement of the movement and upon the rate of application of the tangential force. 3. The conventional coefficient of static friction of elastomeric materials is particularly evident at low rates of application of the tangential force, which fact is connected with the nature of dry friction of rubberlike polymers.

scholarly journals Determination of dynamic and statistical efforts in the construction elements of skid plate of the forest tractor

2018 ◽  
Author(s):  
Л.Л. Нгуен ◽  
Э.М. Гусейнов
Keyword(s):  
Mathematical Model ◽  
Coefficient Of Friction ◽  
Velocity Component ◽  
Normal Component ◽  
Normal Velocity ◽  
Shock Pulse ◽  
A Value ◽  
The Coefficient Of Friction ◽  
The Moment

Приведена математическая модель для исследования динамики колесного лесохозяйственного трактора с активным полуприцепом в процессе погрузки пачки деревьев. Установлены минимальные значения нормальной составляющей скорости и ударного импульса. Расчеты, проведенные на основе математической модели, показали, что при погрузке пакета с помощью четырехзвенного щита, минимальные значения нормальной составляющей скорости и ударного импульса соответствуют значению угла , определяющего положение щита в момент контакта с пакетом, равного 55. Величина ударного импульса при значении  = 55 практически не зависит от коэффициента трения f. Апробация модели выполнена применительно к лесохозяйственному трактору Т-40Л. The article presents a mathematical model for studying the dynamics of a wheeled forestry tractor with an active semitrailer in the process of loading a bundle of trees. As a result of the studies, the minimum values of the normal component of velocity and shock pulse. Calculations carried out on the basis of a mathematical model showed that when loading a bundle of trees using a four-link shield, the minimum values of the normal velocity component and the shock pulse correspond to the value of the angle  determining the position of the shield at the moment of contact with the packet equal to 55. The magnitude of the shock pulse at a value of  = 55 is practically independent of the coefficient of friction f. Approbation of the model was carried out with reference to the tractor T-40L.

Experimental Investigation of aluminum doping crumb rubber/epoxy composite in reciprocating motion

2015 ◽  
Vol 3 ◽  
pp. 1
Author(s):  
Goutam Chandra Karar ◽  
Nipu Modak
Keyword(s):  
Experimental Investigation ◽  
Coefficient Of Friction ◽  
Epoxy Composite ◽  
Normal Load ◽  
Crumb Rubber ◽  
The Other ◽  
Reciprocating Motion ◽  
Molding Process ◽  
Friction Tester ◽  
The Coefficient Of Friction

The experimental investigation of reciprocating motion between the aluminum doped crumb rubber /epoxy composite and the steel ball has been carried out under Reciprocating Friction Tester, TR-282 to study the wear and coefficient of frictions using different normal loads (0.4Kg, 0.7Kgand1Kg), differentfrequencies (10Hz, 25Hz and 40Hz).The wear is a function of normal load, reciprocating frequency, reciprocating duration and the composition of the material. The percentage of aluminum presents in the composite changesbut the other components remain the same.The four types of composites are fabricated by compression molding process having 0%, 10%, 20% and 30% Al. The effect of different parameters such as normal load, reciprocating frequency and percentage of aluminum has been studied. It is observed that the wear and coefficient of friction is influenced by the parameters. The tendency of wear goes on decreasing with the increase of normal load and it is minimum for a composite having 10%aluminum at a normal load of 0.7Kg and then goes on increasing at higher loads for all types of composite due to the adhesive nature of the composite. The coefficient of friction goes on decreasing with increasing normal loads due to the formation of thin film as an effect of heat generation with normal load.

Sign in / Sign up

Export Citation Format

Share Document