Investigating the Frictional Characteristics of Tire‐Asphalt Pavement Interactions Under Complex Conditions

The friction force is one of the important influence factors on tire slip, overturning, and rollover characteristics of tractors. The maximum static friction forces of three different tractors were measured on paved roads under various loading conditions. The prediction models of the previous study were improved through regression analysis for the measured data. The model that uses the front and rear axle's reaction forces as variables showed the highest prediction accuracy. The overturning and rollover safety of a tractor located on a slope is decreased by tire slip, which is affected by static friction force. Existing regression models for predicting the static friction force of tractors demonstrate inadequate accuracy, necessitating further refinement. Therefore, this study was conducted to improve the accuracy of the maximum static friction force prediction model developed in a previous study for tractors with a front-end loader. As a result of measuring the maximum static friction, it tended to increase as the rear ballast weight increased and to decrease as the payload increased. The accuracy of the regression models in this study was significantly improved compared to that in previous studies. The regression model that used the reaction forces of the front and rear axles as variables exhibited the highest accuracy, followed by the model using the rear axle reaction only. The reaction force of the rear axle had a greater effect on the maximum static friction than that of the front axle. The developed regression model will predict the maximum static friction force of a tractor with a front-end loader on paved roads with high accuracy using the reaction forces of the front and rear axles. Future studies will focus on extending these predictions to various soil types and under dynamic conditions.

Abstract

Stick-slip friction is one of the material removal mechanisms in tribology. It occurs when the static friction force is larger than the dynamic friction force, and make the friction curve fluctuated. In the friction monitoring of chemical mechanical polishing(CMP), the friction force also vibrates just as stick-slip friction. In this paper, an attempt to show the similarity between stick-slip friction and the friction of CMP was conducted. The prepared hard pa(IC1000/Suba400 stacked/sup TM/) and soft pad(Suba400/sup TM/) were tested with SiO₂ slurry. The friction force was measured by piezoelectric sensor. According to this experiment, it was shown that as the head and table velocity became faster, the stick-slip time shortened because of the change of real contact area. And, the gradient of stick-slip period as a function of head and table speed in soft pad was more precipitous than that of hard one. From these results, it seems that the fluctuating friction force in CMP is stick-slip friction caused by viscoelastic behavior of the pad and the change of real contact area.

Friction, and in particular stick-slip friction, occurs on every length scale, from the movement of atomic force microscope tips at the nanoscale to the movement of tectonic plates of the Earth’s crust. Even with this ubiquity, there still appears to be outstanding fundamental questions, especially on the way that frictional motion varies generally with the mechanical parameters of a system. In this study, the frictional dynamics of the hook-and-loop system of Velcro® in shear is explored by varying the typical parameters of driving velocity, applied load, and apparent contact area. It is demonstrated that in Velcro® both the maximum static frictional force and the average kinetic frictional force vary linearly with apparent contact area (hook number), and moreover, in the kinetic regime, stick-slip dynamics are evident. Surprisingly, the average kinetic friction force is independent of velocity over nearly two-and-a-half orders of magnitude (~2 × 10−4 to ~6 × 10−2 m/s). The frictional force varies as a power law on the applied load with an exponent of 0.28 and 0.24 for the maximum static and kinetic frictional forces, respectively. Furthermore, the evolution of stick-slip friction to more smooth sliding, as controlled by contact area, is demonstrated by both a decrease in the spread of the kinetic friction and the spread of the fluctuations of the average kinetic friction when normalized to the average kinetic friction; these decreases follow power-law behaviors with respect to the increasing contact area with exponents of approximately −0.3 and −0.8, respectively. Lastly, we note that the coefficients of friction μs and μk are not constant with applied load but rather decrease monotonically with power-law behavior with an exponent of nearly −0.8. Phenomenologically, this system exhibits interesting physics whereby in some instances it follows classical Amontons–Coulomb (AC) behavior and in others lies in stark contrast and hopefully will assist in the understanding of the friction behavior in dry surfaces.

Introduction: Friction at the bracket-archwire interface has been observed as one of the most important factors affecting tooth movement. Hence it is importance to assess the friction generated during tooth movement to bring about optimal treatment results.Objective: To compare the frictional resistance of various ceramic brackets using different archwires, and to compare the static and kinetic frictional force of various ceramic brackets using different archwires.Materials & Method: The present study evaluated and compared the friction generated at the bracket archwire interface when 0.018” and 0.019”x0.025” stainless steel archwires and 0.019”x0.025” teflon coated stainless steel archwires were moved through conventionally ligated, passive self-ligating and interactive self-ligating ceramic brackets. The static and kinetic frictional forces were also evaluated and compared.Result: Highly significant differences in kinetic (p<0.001) and static (p<0.001) frictional forces were observed in all three groups when used with the different archwires. On comparing the static and kinetic frictional forces significant differences were observed among all three groups (p<0.05).Conclusion: The passive self-ligating brackets produce the least frictional forces when compared to interactive self-ligating and conventionally ligated brackets. Also, the static frictional forces were found to be more as compared to kinetic frictional forces.Orthodontic Journal of Nepal, Vol. 6 No. 1, June 2016, pp.18-22

This study evaluated the static and kinetic frictional forces produced between different combination of orthodontic archwires and brackets. Three types of archwires were examined: (1) stainless steel, (2) conventional NiTi alloy, and (3) improved superelastic NiTi alloy. Two types of brackets were tested: (1) stainless steel and (2) plastic. Both static and kinetic frictional forces were measured on a customdesigned apparatus under elastic ligature in the dry state. Each archwire-bracket combination was subjected to 20 independent evaluations. All data were statistically analyzed using two-way analysis of variance and Duncan’s test. The experimental results indicated that the static frictional force was significantly higher than the kinetic frictional force in all archwire-bracket combinations. The frictional force was lower for the stainless steel bracket than for the plastic bracket with stainless steel wire and the improved superelastic NiTi-alloy wire. The frictional force was lower for the improved superelastic NiTi-alloy wire than for NiTi wire with the stainless steel bracket, but higher for NiTi wire with the plastic bracket. The frictional force was lowest for stainless steel wire for both two types of bracket. This study demonstrates that the frictional forces of brackets are influenced by different combinations of bracket and archwire, and that the improved superelastic NiTi-alloy wire does not exhibit “low friction” (as claimed by the manufacturers) in all cases.KeywordsFrictional forceNiTi-alloy wireimproved superelastic NiTi-alloy wirestainless steel bracketplastic bracket

The Surface Forces Apparatus technique was used to measure the normal (perpendicular) and lateral forces between variously prepared surfaces under both dry and lubricated conditions. 'Normal' forces include the force vs distance functions, F(D), for surfaces separated by thin liquid films as well as the adhesion forces and energies, γ, for two surfaces in adhesional contact. 'Lateral' forces include the static and kinetic friction forces F of the surfaces as they slide past each other at a given separation, D. The results show that very thin liquid films confined between two solid surfaces can sustain both normal and shear forces or stresses. The results further indicate that the normal force, F(D) or γ, may be directly related to the static friction force, Fs, and simple equations are proposed that relate these forces (by 'static' friction force is meant the lateral force that must be applied to initiate motion, but not necessarily to maintain this motion). In contrast, the kinetic friction force, Fk, which is the force that must be continually applied to maintain motion at a given velocity, was found to be related, not to the equilibrium or reversible interaction but to the dissipative or irreversible part of the adhesion or interaction energy during a loading-unloading cycle. There is a high degree of correlation in the way that normal forces and friction forces are affected by changes in applied load or pressure, sliding velocity, loading-unloading rates and temperature. These systematic correlations can be conveniently represented by non-equilibrium 'adhesion' and 'friction' phase diagrams.

In orthodontic treatment, the efficiency of tooth movement is affected by the frictional force between the archwire and bracket slot. This study evaluated the static and kinetic frictional forces produced in different combinations of orthodontic archwires and brackets. Three types of archwires [stainless steel, nickel-titanium (NiTi) alloy, and beta-titanium (TMA) alloy] and two types of brackets (stainless steel and self-ligating) were tested. Both static and kinetic frictional forces of each archwire–bracket combination were measured 25 times using a custom-designed apparatus. The surface topography and hardness of the archwires were also evaluated. All data were statistically analyzed using two-way analysis of variance and Tukey's test. The experiments indicated that the static frictional force was significantly higher than the kinetic frictional force in all archwire–bracket combinations not involving TMA wire. TMA wire had the highest friction, followed by NiTi wire, and then stainless steel wire when using the stainless steel bracket. However, there was no difference between NiTi and stainless steel archwires when using the self-ligating bracket. For TMA wire, the friction was higher when using the stainless steel bracket than when using the self-ligating bracket. Scanning electron microscopy indicated that stainless steel wire exhibited the smoothest surface topography. The hardness decreased in the order of stainless steel wire > TMA wire > NiTi wire. This study demonstrates that the frictional forces of brackets are influenced by different combinations of bracket and archwire. The reported data will be useful to orthodontists.

This paper presents three methods of input voltage signals that allow low voltage operation of an electrovibration display while preserving the perceptual feel and strength of electrovibration stimuli. The first method uses the amplitude modulation of a high-frequency carrier-signal. The second method uses a dc-offset, and the third method uses a combination of the two methods. The performance of the three methods was evaluated by a physical experiment that measured and analyzed static (dc-component) and dynamic (vibratory component) friction forces and two subsequent psychophysical studies. The physical experiment showed that only the dc -offset method enabled a statistically significant increase in the static friction force between the fingertip and the surface of the electrovibration display. The static friction increase was closely related to the root mean square of input voltage level. In contrast, all of the three methods increased the dynamic friction force significantly, which was deemed to be related to the high frequency effect validated in the previous literature. The first psychophysical study showed that the three proposed methods can significantly reduce the peak-to-peak (p-p) amplitude of an input voltage signal while generating perceptually equally strong electrovibrations to that produced by the conventional method. Using lower p-p voltage has the merits of a simpler electrical circuit and less electromagnetic noise, saving the overall system cost. Further, the perceived intensity of electrovibration was more correlated to the dynamic friction force than the static friction force. The second psychophysical study was a discrimination experiment, and it demonstrated that all the three proposed methods and the conventional method can provide perceptually similar stimuli despite their different signal forms and voltage amplitudes. Our experimental investigation allowed us to conclude that the dc-offset method is the best way to lower the driving voltage of an electrovibration display while providing perceptually equivalent electrovibrations.

Analysis of static friction and elastic forces in a nanowire bent on a flat surface: A comparative study

In this study, the effect of adhesion on evolution of friction during the transition of the contact from pre-sliding into full sliding was investigated. In order to achieve the objectives, a micro optical friction (MOF) apparatus was developed to conduct dry sliding friction experiments and to allow for in situ visualization of the contact area for a sphere-on-flat configuration. MOF apparatus was used to measure friction under various load and speed combinations. The friction results exhibit the commonly observed behavior in friction (i.e., static friction is larger than dynamic friction). The results also demonstrated that the difference between static and dynamic friction forces increased with an increase in the applied normal load. We hypothesize and demonstrate that the difference between the measured maximum friction force commonly referred to as static friction force and the steady state or dynamic friction force divided by the dynamic coefficient of friction is the force of adhesion. The adhesion force results obtained from our experimental investigation corroborate well with the force of adhesion described by the DMT model. The reduction in friction force is attributed to the diminishing of adhesion force during full sliding of the contact.

To analyze the coatings covering esthetic orthodontic wires and the influence of such coatings on bending and frictional properties. Four commercially available, coated esthetic archwires were evaluated for their cross-sectional dimensions, surface roughness (Ra), nanomechanical properties (nanohardness, nanoelastic modulus), three-point bending, and static frictional force. Matched, noncoated control wires were also assessed. One of the coated wires had a similar inner core dimension and elasticity compared to the noncoated control wire, and no significant differences between their static frictional forces were observed. The other coated wires had significantly smaller inner cores and lower elasticity compared to the noncoated wires, and one of them showed less static frictional force than the noncoated wire, while the other two coated wires had greater static frictional force compared to their noncoated controls. The dimension and elastic modulus of the inner cores were positively correlated (r = 0.640), as were frictional force and total cross-sectional (r = 0.761) or inner core (r = 0.709) dimension, elastic modulus (r = 0.777), nanohardness (r = 0.802), and nanoelastic modulus (r = 0.926). The external surfaces of the coated wires were rougher than those of their matched controls, and the Ra and frictional force were negatively correlated (r = -0.333). Orthodontic coated wires with small inner alloy cores withstand less force than expected and may be unsuitable for establishing sufficient tooth movement. The frictional force of coated wires is influenced by total cross-section diameter, inner core diameter, nanohardness, nanoelastic modulus, and elastic modulus.

This article reviews the state of the knowledge and technology in the field of friction-loss measurements in internal combustion piston engines. The dependencies that describe the loss of energy in combustion engines and injection apparatus are presented. Currently, very little can be found in the literature on the study of frictional forces in injection apparatus, but mainly in the piston–cylinder group, so this work significantly fills that gap. The aim of this article is to construct a device and to develop a method for assessing the technical state of injector nozzles to minimize friction losses in internal combustion engines at the stages of evaluation, design, production and operation. This article presents a stand for determining the maximum friction forces due to gravity loading by water-jet control. This article also presents test results on the maximum friction force between a needle and a body of injector nozzles in piston combustion engines on a designed and purpose-built stand outside of the combustion engine. Various designs and injector nozzles are made from various types of alloy steel for marine and automotive piston internal combustion engines fueled with distillation or residual fuels, and are tested. The research concerned conventional elements for the injection apparatus as well as electronically controlled subsystems. Precision pairs of injection equipment are selected for the tests: new ones are employed after the storage period and operated in natural conditions. The elements dismantled from the internal combustion engines are tested in the presence of fuel or calibration oil of similar properties. The maximum static frictional forces under the hydrostatic loading are measured, alongside the parameters for the dynamic movement of the nozzle needles from bodies of the injector nozzle as time, speed, acceleration and dynamic force. The influence of the angular position of the needle in relation to the bodies of the precision pairs conventional internal combustion engines, the diametral clearance between the nozzle body and needle, and the surface conditions on the values of the maximum friction force are also presented. Errors in shape and position result in the uniqueness of the friction force at the mutual angular position of the needle in relation to the nozzle body, and the decrease in diametral clearance and deterioration of the surface state increase the friction losses. A model was elaborated of the influence of various factors on the value of the maximum friction force.

In this work a mathematical model of the motion of a cylinder moving on a plane is deduced using screw theory. The linear Coulomb friction equations are applicable for the maximum static and kinetic friction forces. In the case of the rolling motion of a cylinder, the friction forces are not necessarily maxima. This paper describes the dynamic states of motion of a cylindrical part moving in three separate scenarios by the Euler dual equation. The first scenario is when the cylinder is moving on a horizontal static plane due to an external harmonic force proportional to the mass of the part. For this case, the sliding conditions are expressed as a function of the vibration parameters and generalized based on a harmonic dimensionless variable. The second and third scenarios are when the cylinder is moving by translational displacements on a horizontal and inclined plane.

Particle morphology of pharmaceutical solids has practical importance for several reasons. In particular, surface roughness can influence formulation development and pharmaceutical performance for a wide range of delivery types including oral tablets and dry powder formulations for inhalation. For instance, the surface roughness can influence dissolution, friability, and adhesion of coatings and films for bare tablets (1–5). To illustrate, surface roughness correlated strongly with tablet friability for erythromycin acistrate tablets (3). The surface roughness has also been related to gloss and permeability, such that the reflectivity and surface texture of coated tablets were directly correlated (6,7). The surface roughness of particles also has been correlated to powder flow and powder packing (8), where the smoother particles led to an improvement of powder packing and flow properties. The adhesion of particles to surfaces or other particles can also be greatly affected by surface roughness. This is of particular concern for dry powder inhalation (DPI) formulation development. Dry powder formulations are often composed of small drug particles and inert larger carrier particles. Interactions between these particles can be dominated by physico-chemical properties of the particle, such as size, shape, morphology, contact area, and hygroscopicity (9,10). In particular, it has been shown that the surface roughness of the carrier particles has a significant impact on the adhesion and friction forces between the carrier and drug particles (11,12). Adhesion, blend homogeneity, and stability have been directly related to the surface roughness of the carrier particle (13). The ultimate performance properties of DPI blends as determined by in vitro testing has also been correlated to the primary particle surface roughness (13–15). There is an important balance between the relative scaling in the roughness of the particles and the relative size of the carrier and drug particles when considering the effects of surface roughness on particle–particle adhesion. This was previously described (16) and is illustrated by the schematic in Fig. 1. Assuming no other changes in particle properties (i.e., surface energy, particle size, amorphous content, hygroscopicity, etc.), the rank order of drug-carrier adhesion would obey the following trend in roughness of the larger carrier particle: macro-rough surface (Fig. 1a) > smooth surface (Fig. 1b) > micro-rough surface (Fig. 1c). This trend is strictly dependent on the contact area between drug and carrier. If adhesion is too weak, the active drug may be released during inhalation before the particles reach the deep lung. On the contrary, if adhesion is too strong, the active may not be released at all. This phenomenon has been observed and described in detail for several DPI studies (15–19). Fig. 1 Illustration of macro-roughness (a), smooth surface (b), and micro-roughness (c) affects on particle–particle contact and adhesion In this study, we focus on the measurement of micro-scale roughness using fractal dimensions determined from sorption isotherms with different adsorbates.