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Previous studies have demonstrated that skin vibration is an important factor affecting the roughness perception of fine textures. For coarse textures, the determining physical factor is much less clear and there are indications that this might be participant-dependent. In this paper, we focused on roughness perception of both coarse and fine textures of different materials (glass particle surfaces and sandpapers). We investigated the relationship between subjective roughness ratings and three physical parameters (skin vibration, friction coefficient, and particle size) within a group of 30 participants. Results of the glass particle surfaces showed both spatial information (particle size) and temporal information (skin vibration) had a high correlation with subjective roughness ratings. The former correlation was slightly but significantly higher than the latter. The results also indicated different weights of temporal information and spatial information for roughness ratings among participants. Roughness ratings of a different material (sandpaper versus glass particles) could be either larger, similar or smaller, indicating differences among individuals. The best way to describe our results is that in their perceptual evaluation of roughness, different individuals weight temporal information, spatial information, and other mechanical properties differently., Competing Interests: The authors have declared that no competing interests exist.

This study compares two methods for estimating static friction coefficients for skin. In the first method, referred to as the 'tilt method', a hand supporting a flat object is tilted until the object slides. The friction coefficient is estimated as the tangent of the angle of the object at the slip. The second method estimates the friction coefficient as the pull force required to begin moving a flat object over the surface of the hand, divided by object weight. Both methods were used to estimate friction coefficients for 12 subjects and three materials (cardboard, aluminium, rubber) against a flat hand and against fingertips. No differences in static friction coefficients were found between the two methods, except for that of rubber, where friction coefficient was 11% greater for the tilt method. As with previous studies, the friction coefficients varied with contact force and contact area. Static friction coefficient data are needed for analysis and design of objects that are grasped or manipulated with the hand. The tilt method described in this study can easily be used by ergonomic practitioners to estimate static friction coefficients in the field in a timely manner.

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). The normal force and the tangential force (i.e., the force due to the sensor motion) were recorded. The coefficient of friction (mu(d)) 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 the normal force (in a horizontal direction) and the tangential force (in the vertical direction). The slip 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) the skin-sandpaper coefficient of friction was the highest mu(d) =0.96+/-0.09 (for 4-N normal force) and the skin-rayon rayon coefficient of friction was the smallest mu(d) =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).

The coefficient of friction for different contacting materials against skin is mainly influenced by the nature of the materials (synthetic and natural fabrics), mechanical contact parameters (interfacial pressure and sliding velocities), and physiological skin conditions (ambient humidity and skin moisture content). In the present research work, seven different types of papers used in everyday life were analyzed. The physical properties of these materials were determined through tensile tests and friction tests. By comparing mechanical properties with coefficient of friction, it was possible to conclude that the coefficient of friction is strongly correlated with the mechanical properties. [ABSTRACT FROM AUTHOR]

Surface characterization is important and has many applications in the paper industry. Surface characterization requires both surface roughness and surface friction. The relationship between the two has not been fully established for paper and paperboard. It has been a common practice that only the average property and the standard deviation with the coefficient of variation (COV) are reported for surface roughness and friction measurements. This practice, however, provides few information on surface structure and can lead to wrong judgments because two samples having the same average and the COV can have different physical properties. To avoid such mistake, a new surface characterization method has been developed. To this end, surface roughness- and frictionprofiles have been obtained using a latest version of Kawabata surface tester (Model: KES-SESRU, Kato Tech, Kyoto Japan). This new version uses the same stylus for both measuring surface roughness and friction under the same operating conditions. It was found that a correlation between the surface roughness and surface friction was very low. This indicates that they should be independent of each other. Therefore, both should be determined for surface characterization.

This work deals the creasing characteristics of coated paperboard. It was not clarified to estimate the deformation behavior of creased line from the first peak bending moment Mp1 and the initial gradient C1 of bending moment. In this study, a new prototype testing apparatus has been developed for seeking the bending moment and the side view picture of creased part during repeated folding motion. The permanent (residual) deformation angles, the variance of residual stiffness and the hysteresis characteristics of bending moment were analyzed for the nominal shear strain (the scoring depth) γ . The obtained results were as follows: (1) C1 was characterized with γ, while the second term gradient C2 was characterized with γ and the inverse of tracking angle Θ-1. (2) By introducing the area of closed curve of second term hysteresis ACC, it is revealed that the gradient of ACC was remarkably varied with Θ at near the peak point Mp1.

The article experimentally investigates the properties of offset print friction and determines static and kinetic coeffi­cients of friction. Conventional and UV inks have been found to increase the static friction coefficient and re­duce the kinetic friction coefficient between paper and print. The roughness pro­perties of two different types of paper and prints using conventional and UV inks have been examined and compared thus determining that conventional inks strongly increase the roughness of print surface and that the influence of UV inks depend on the type of paper. Santrauka Nagrinėjamos popieriaus ofsetinių atspaudų trinties savybės ir nustatyti statinis bei kinetinis trinties koeficientai. Nustatyta, kad įprastiniai ir UV dažai didina atspaudo į popierių statitinio trinties koeficiento dydį ir mažina kinetinio koeficiento dydį. Atliktas dviejų rūšių popieriaus su įprastais ir UV dažais šiurkštumo palyginamasis tyrimas ir nustatyta, kad įprasti dažai atspaudų paviršiaus šiukštumą stipriai didina, o UV dažų poveikis priklauso nuo popieriaus rūšies. Reikšminiai žodžiai: atspaudai; įprasti dažai; popierius; šiurkštumas; trintis; UV dažai.

Materials sliding on a larger substrate age faster than the substrate itself, but no available model of friction takes into account this aspect. We developed a model based on the memory effect of both the mobile and the plane samples, separately, and characterized by macroscopic geometric measurements (e.g., sliding distances and samples sizes). We studied the contact between fresh paper samples and samples that have already underwent several slidings. Experimental and theoretical results are in good agreement. Finally, we used our model to demonstrate how the existing test methods can lead to differences in the measured forces of friction. The results allow both a better understanding and quantitative characterization of the dependence of friction with the history of the contact. [ABSTRACT FROM AUTHOR]

Different methods for measuring the friction forces are investigated in this paper. We consider the paper-on-paper contact as an example of application. We first underline several drawbacks for the two main standard methods, namely the inclined and horizontal plane methods. In particular, the horizontal plane test method often involves stick-slip oscillations that make the measurement of the friction force impossible. We then propose a method for characterizing these oscillations and removing their influence on the friction force measurement. The comparison of the proposed method to standards suggests that our proposed method delivers measurements that are much more accurate and repeatable. We finally discuss the validity of averaging the friction force measured during the sliding movement. [ABSTRACT FROM AUTHOR]

The article experimentally investigates the properties of offset print friction and determines static and kinetic coefficients of friction. Conventional and UV inks have been found to increase the static friction coefficient and reduce the kinetic friction coefficient between paper and print. The roughness properties of two different types of paper and prints using conventional and UV inks have been examined and compared thus determining that conventional inks strongly increase the roughness of print surface and that the influence of UV inks depend on the type of paper. [ABSTRACT FROM AUTHOR]

Friction between different papers, flexographic and laser prints were investigated experimentally and static (SCOF) and kinetic (KCOF) friction coefficients between paper and paper, paper and prints, prints and prints were determined. The dependence of the the SCOF and KCOF values on the paper PPS roughness, paper grammage and ink content on prints was investigated. The results showed that highest friction is between paper and prints and lowest is between two prints. It was found that SCOF and KCOF deacrease with pressure. Static friction coefficient increases with paper roughness and kinetic coefficient remains constant. [ABSTRACT FROM AUTHOR]

"WEB" is defined as a material that has micron level thickness and used in industries. Some important properties of web media include Co-efficient of friction, Stiffness of media, Absorbing capacity of media, tensile and compressive strength of media etc. Among these characteristics, Co-efficient of friction and Stiffness of web media have an inevitable impact in designing printing machines, textile industry, chemical filtration and refinery industries. This work is aimed towards designing a compact - portable instrument that readily portrays the Static and Dynamic Co-efficient of Friction between any two web media and stiffness of the particular web media under study. This work is particularly useful in newspaper printing presses where the properties of paper can be determined with the help of the machine and the safe stress that can be applied to the paper is determined. This instrument is fully automated and gives the output in digital form. These web media play a dominant role in the printing industries, chemical industries, manufacturing industries and automobile industries too. By this instrument, the industries relying on web media will be benefitted to a great extent. [ABSTRACT FROM AUTHOR]

Abstract: Finger friction measurements performed on a series of printing papers are evaluated to determine representativeness of a single individual. Results show occasionally large variations in friction coefficients. Noteworthy though is that the trends in friction coefficients are the same, where coated (smoother) papers display higher friction coefficients than uncoated (rougher) papers. The present study also examined the relationship between the measured friction coefficients and surface roughness to the perceived coarseness of the papers. It was found that both roughness and finger friction can be related to perceived coarseness, where group data show that perceived coarseness increases with increasing roughness. [Copyright &y& Elsevier]

In this paper a smoothing procedure is suggested for the 3D beam-to-beam contact. A smooth segment is defined basing on current position vectors of three nodes limiting two adjacent finite elements. The approximated fragment of a beam axis as a 3D curve spans between the centre points of these elements. The curve is described parametrically using three Hermite polynomials. The four boundary conditions necessary to determine the coefficients for each of these polynomials involve co-ordinates and slopes at the curve ends. The slopes are defined in terms of the element nodal co-ordinates, too. There is no dependence on nodal rotations so this formulation can be embedded in a beam analysis using any type of beam finite element. This geometric representation of the curve is incorporated into the 3D beam-to-beam frictional contact model with the penalty method used to enforce contact constraints. The residual vector and the corresponding tangent stiffness matrix are determined for the normal part of contact and for the stick or slip state of friction. A few numerical examples are presented to show the performance of the suggested smoothing procedure in the cases featuring large frictional sliding. [ABSTRACT FROM AUTHOR]

The purpose of this investigation was to characterize the dependence of paper-to-paper friction on the sliding direction of the previous slide for various paper grades. Static and kinetic friction forces and coefficients of friction were measured using a friction tester based on the horizontal plane principle. The papers were also characterized with respect to fiber-rising tendency and they were imaged by environmental scanning electron microscopy (ESEM).The results showed that uncoated papers exhibited a behavior where the coefficient of friction rapidly decreased to a low value with repeated slides over the same track in the same direction. When the sliding direction was reversed the coefficient of friction increased and maintained a high level. A term called friction hysteresis is defined to quantify these effects in order to relate the behavior of the coefficient of friction to various characteristics of the paper. ESEM imaging showed that sliding caused fiber ends to rise out of the plane of the paper surface and to align themselves in the sliding direction. A correlation was found between the magnitude of friction hysteresis of the different papers and the total area of the raised fibers. The results suggest that friction hysteresis is due to the interlocking of fiber ends on the paper surfaces and that the degree of interlocking is influenced by the orientation of fiber ends relative to the sliding direction. [Copyright &y& Elsevier]

Asperity flattening study plays an important role in predicting the friction behavior at the interface and the surface roughness transfer during sheet metal-forming process. This paper presents a comparison of asperity flattening activities under 1-wavelength, 2-wavelength and 3-wavelength finite-element models developed based on a power spectral density (PSD) analysis of measured data on steel sheet surfaces. First, a proper asperity thickness for the modeling has been determined by the investigation of plastic strain distribution along the depth of asperity. The comparison then examines the evolution of real contact area, surface roughness, contact pressure distribution and variation of friction force at the interface between a tool and a workpiece drawn from different wavelength simplification models under various friction conditions. It is concluded that 3-wavelength model has closer results to experimental measurements and introduces less contact area and more local pressure concentrations than those from the other two models. [Copyright &y& Elsevier]

In this paper, we use a prevalent finite element analysis software, MARC, to simulate the process for a subject material undergoing equal channel angular extrusion (ECAE), as well as calculating the strain conditions. For a single ECAE pass, the transversal strain distribution in the deformed body will be analyzed to investigate the influences from channel angle, friction between die and pressed material, and curved joining channels. Simulations involving double passes of the subject material were also conducted, something that has not been previously pursued much elsewhere. [Copyright &y& Elsevier]

This paper presents friction tests results of AISI 1006 low-carbon steel and an AISI 52100 bearing steel using a spiral pin-on-disk apparatus. 3 mm diameter pins on two average (0.06 or 0.20 mm) diameters glass particle coated abrasive paper were used. The normal force applied was 20 N, the tangential sliding speed was 0.08 m/s, and the radial pin movement was 20 mm/min. The micro-indentation hardness of the pins was measured before and after testing. In general, the higher the strain hardening, the higher was the friction coefficient. For AISI 1006, which wore in a severe regime, the strain hardening intensity depended on the abrasive particle size. For AISI 52100, which wore in a mild regime, the particle size had no effect. Tests on AISI 1006 exhibited paper loading, but tests on AISI 52100 exhibited abrasive particle fragmentation. [Copyright &y& Elsevier]