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).

Skin-skin contact: The normal-force dependence of the coefficient of friction between a bare finger and artificial skin changes randomly

2021 ◽  
Author(s):  
Koki Inoue ◽  
Shogo Okamoto ◽  
Yasuhiro Akiyama ◽  
Yoji Yamada
Keyword(s):  
Experimental Study ◽  
Coefficient Of Friction ◽  
Normal Force ◽  
Skin Surface ◽  
Artificial Skin ◽  
Skin Changes ◽  
Root Cause ◽  
Skin Contact ◽  
The Coefficient Of Friction ◽  
Frictional Forces

Abstract This study investigates the dependence of the coefficients of friction on the normal force produced by sliding a bare finger over different artificial skins with seven levels of hardness. The coefficient of friction was modeled as a power function of the normal force. An experimental study that involved sliding a finger over artificial skin surfaces was carried out under two conditions: the fingertip being wiped by a dry cloth or a cloth soaked in ethanol. Although the exponential term was assumed to be nearly constant for identical tribological conditions, we observed that the exponent varied randomly and could be negative, zero, or positive. This probabilistic behavior has not been explicitly analyzed in previous studies on human fingertips. The probability density function of the exponent depended on the moisture content of the finger. The exponent was either nearly zero or positive when the finger sliding on the skin surface was wiped with an alcohol-soaked cloth and dried. These findings play an important role in analyzing the frictional forces produced during skin–skin contact in terms of determining the root cause behind the random variations in the dependence of the coefficient of friction on the normal force.

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.

Comparison of Dry-Film and Zinc-Phosphate Lubricant for Tube Cold Forming

2011 ◽  
Vol 295-297 ◽  
pp. 2362-2365
Author(s):  
Zhi Yan Cheng
Keyword(s):  
Coefficient Of Friction ◽  
Zinc Phosphate ◽  
Test Results ◽  
Tube Surface ◽  
Cold Forming ◽  
Breakdown Time ◽  
Significant Difference ◽  
Potential Applications ◽  
The Coefficient Of Friction ◽  
Dry Film

Dry-film and zinc-phosphate (Zn-P) lubricants were compared for potential applications of dry-film lubricant in tube cold forming processes through the twist compression test. Test results showed that the coefficient of friction (m) had no significant difference between Zn-P soap lube and dry-film lube. The lube coating breakdown time is different between Zn-P soap and dry-film lube. A preliminary industrial trial with dry-film coated tube through the cold drawn over a mandrel showed that the tube surface quality is good and comparable with the Zn-P coated tubes.

Sensing characteristics of an optical three-axis tactile sensor under combined loading

Robotica ◽  
2004 ◽  
Vol 22 (2) ◽  
pp. 213-221 ◽  
Author(s):  
Masahiro Ohka ◽  
Yasunaga Mitsuya ◽  
Yasuaki Matsunaga ◽  
Shuichi Takeuchi
Keyword(s):  
Normal Force ◽  
Tangential Force ◽  
Testing Machine ◽  
Tactile Sensor ◽  
Combined Loading ◽  
Vertical Force ◽  
Load Testing ◽  
Brass Plate ◽  
The Coefficient Of Friction ◽  
Sensing Characteristics

This paper describes precision enhancement of an optical three-axis tactile sensor capable of detecting both normal force and tangential force. The sensor's single cell consists of a columnar feeler and 2-by-2 conical feelers. We have derived equations to precisely estimate the three-axis force from the area-sum and area-difference of the conical feelers' contact areas by taking into account wrench-length shrinkage caused by a vertical force. To evaluate the equations and determine constants included in the equations, we performed a series of calibration experiments using a manipulator-mounted tactile sensor and a combined load-testing machine. Subsequently. to evaluate the tactile sensor's practicality. it was mounted on the end of a robotic manipulator which rubbed flat specimens such as brass plates with step-heights of δ=0.05, 0.1, 0.2 mm and a brass plate with no step-height. We showed from the experimental data that the optical three-axis tactile sensor can detect not only the step-heights but also the distribution of the coefficient of friction, and that the sensor can detect fine plate inclination with accuracy to about ±0.4°.

scholarly journals Determination of the coefficient of friction in a screw joint loaded with a controlled torque

2021 ◽  
Vol 1199 (1) ◽  
pp. 012073
Author(s):  
J Mascenik
Keyword(s):  
Friction Coefficient ◽  
Coefficient Of Friction ◽  
Force Sensor ◽  
Surface Protection ◽  
Threaded Joint ◽  
Lubricating Film ◽  
Number Of Factors ◽  
Torque Wrench ◽  
The Coefficient Of Friction ◽  
Plastic Lubricants

Abstract The aim of this article is mechanism description for the measuring the friction coefficient in the threads of threaded joint and consecutive experimental measuring of friction coefficient. The coefficient of friction in the threads of a bolt and nut depends on a number of factors, in particular the roughness of the surfaces, the properties of the lubricating film and the angle of the side of the thread. The coefficient is a function of the heat treatment, the quality of the surface protection substance, the size of the screw load and the pitch angle of the thread. The principal parameters of the measuring was fastening torque, which was choose by the torque wrench, axial strength, measured by axial force sensor, and calculated friction coefficient. The friction coefficient was calculated through the use of exponential equation of the torque balance in the screw. The value of the friction coefficient was examined on the threaded joint of size M20 without the plastic lubricants and with the plastic lubricants. Measured values of friction coefficient was close to values listed in the norm and makes argument that plastic lubricants can decrease the friction coefficient in the threads of threaded joint.

scholarly journals Simulated Glacial Abrasion

1979 ◽  
Vol 23 (89) ◽  
pp. 51-56 ◽  
Author(s):  
W. H. Mathews
Keyword(s):  
Coefficient Of Friction ◽  
Low Temperatures ◽  
Normal Force ◽  
Tangential Force ◽  
Water Phase ◽  
Effective Coefficient ◽  
Normal Loading ◽  
Fine Grained

AbstractGlacial abrasion has been simulated by turning a grindstone made of ice and crushed quartz between two stone plates within a domestic deep-freeze. Within limits, the speed of rotation, the normal loading, and the temperature of operation can be controlled. The tangential force exerted on one of the stone plates can be measured. The ratio of tangential to normal force, the effective coefficient of friction, is found to vary with the “roughness” of the grindstone, to increase gradually as abrasion proceeds, and to increase with decreasing velocity. Even at very low temperatures (to −26°C), abrasion products accumulated in a pad of ice frozen to the tablet “down-stream” from the grindstone, indicating that a water phase at least momentarily exists. The abraded surface of a fine-grained limestone displays grain-from-grain plucking dominating over abrasion of individual crystals. The abraded surface of a granite, by contrast, shows striations of crystals and rupture of cleavage along individual striae.

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.

scholarly journals Simulated Glacial Abrasion

1979 ◽  
Vol 23 (89) ◽  
pp. 51-56 ◽  
Author(s):  
W. H. Mathews
Keyword(s):  
Coefficient Of Friction ◽  
Low Temperatures ◽  
Normal Force ◽  
Tangential Force ◽  
Water Phase ◽  
Effective Coefficient ◽  
Normal Loading ◽  
Fine Grained

Abstract Glacial abrasion has been simulated by turning a grindstone made of ice and crushed quartz between two stone plates within a domestic deep-freeze. Within limits, the speed of rotation, the normal loading, and the temperature of operation can be controlled. The tangential force exerted on one of the stone plates can be measured. The ratio of tangential to normal force, the effective coefficient of friction, is found to vary with the “roughness” of the grindstone, to increase gradually as abrasion proceeds, and to increase with decreasing velocity. Even at very low temperatures (to −26°C), abrasion products accumulated in a pad of ice frozen to the tablet “down-stream” from the grindstone, indicating that a water phase at least momentarily exists. The abraded surface of a fine-grained limestone displays grain-from-grain plucking dominating over abrasion of individual crystals. The abraded surface of a granite, by contrast, shows striations of crystals and rupture of cleavage along individual striae.

scholarly journals The Coefficient of Friction of Soccer Balls

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 92
Author(s):  
Adin Ming Tan ◽  
Yehuda Weizman ◽  
Firoz Alam ◽  
Franz Konstantin Fuss
Keyword(s):  
Coefficient Of Friction ◽  
Average Velocity ◽  
Normal Force ◽  
Force Plate ◽  
Average Coefficient ◽  
The Coefficient Of Friction

Nine soccer balls were tested for their friction against a leather sheet, using a force plate. An average normal force of 63.6 N was applied and the movement of the ball had an average velocity of 15 mm/s. Each test was repeated 15 times and the average Coefficient of Friction (COF) was reported. The following results were obtained: Jabulani (COF: 0.62 ± 0.05); Fracas (COF: 0.41 ± 0.01); Ordem 3 (COF: 0.63 ± 0.02); Teamgeist (COF: 0.38 ± 0.01); Brazuca (COF: 0.45 ± 0.01); Kopanya (COF: 0.39 ± 0.01); React (COF: 0.37 ± 0.01); Finale 15 (COF: 0.39 ± 0.06); Vintage T-panel leather ball (COF: 0.41 ± 0.02). Overall, the COF of all balls tested ranged between 0.37 and 0.62. The Finale 15 ball showed a decreasing COF trend with repeated trials and the React ball produced pronounced slip-stick phenomenon.

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.

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