Kinetic Friction Force Research Articles

Friction between various self-ligating brackets and archwire couples during sliding mechanics

The aim of this study was to evaluate the frictional resistance between active and passive self-ligating brackets and 0.019 × 0.025-in stainless steel archwire during sliding mechanics by using an orthodontic sliding simulation device. Maxillary right first premolar active self-ligating brackets In-Ovation R, In-Ovation C (both, GAC International, Bohemia, NY), and SPEED (Strite Industries, Cambridge, Ontario, Canada), and passive self-ligating brackets SmartClip (3M Unitek, Monrovia, Calif), Synergy R (Rocky Mountain Orthodontics, Denver, Colo), and Damon 3mx (Ormco, Orange, Calif) with 0.022-in slots were used. Frictional force was measured by using an orthodontic sliding simulation device attached to a universal testing machine. Each bracket-archwire combination was tested 30 times at 0° angulation relative to the sliding direction. Statistical comparisons were performed with 1-way analysis of variance (ANOVA) followed by Dunn multiple comparisons. The level of statistical significance was set at P <0.05. The Damon 3mx brackets had significantly the lowest mean static frictional force (8.6 g). The highest mean static frictional force was shown by the SPEED brackets (83.1 g). The other brackets were ranked as follows, from highest to lowest, In-Ovation R, In-Ovation C, SmartClip, and Synergy R. The mean static frictional forces were all statistically different. The ranking of the kinetic frictional forces of bracket-archwire combinations was the same as that for static frictional forces. All bracket-archwire combinations showed significantly different kinetic frictional forces except SmartClip and In-Ovation C, which were not significantly different from each other. Passive self-ligating brackets have lower static and kinetic frictional resistance than do active self-ligating brackets with 0.019 × 0.025-in stainless steel wire.

A comparison of the friction associated with diamond-like carbon (DLC) or titanium nitride (TiN) plating metal brackets

The purpose of the present study was to compare the friction associated with DLC as compared to TiN coating brackets. A total of 270 metal brackets were divided into 3 groups: a blank control group, a DLC-coated group, and a TiN-coated group. Energy-dispersive spectroscopy was used to identify the elemental composition of bracket surfaces. After metal brackets were corroded by an electrochemical device in artificial saliva and mouthwash, static and kinetic friction were evaluated and recorded on an EZ-test machine. A randomized design (two-way) ANOVA was used to test for significant differences. The DLC-coated corrosion group in mouthwash exhibited the highest corrosion potential among all groups (p<0.0001). Static friction was higher in the mouthwash group for all test samples (p<0.0001). The kinetic friction of corrosion brackets in mouthwash was statistically different from the no coated and DLC- or TiN-coated groups (p<0.0001). However, in artificial saliva, corrosion brackets (DLC- or TiN-coated groups) were not statistically different from control (p=0.241>0.05). The DLC-coated groups exhibited lower static and kinetic friction forces than TiN-coated brackets. DLC-coated metal brackets can be applied to reduce metal bracket friction.

Comparative evaluation of frictional forces in active and passive self-ligating brackets with various archwire alloys

Self-ligating brackets are claimed to eliminate or minimize the force of ligation at the bracket-wire interface; therefore, it is imperative to evaluate the frictional features of contemporary self-ligating brackets with different archwire alloys. This in-vitro study compared the effects of stainless steel, nickel-titanium, and beta-titanium archwires on frictional forces of passive and active self-ligating brackets with a conventional bracket. All brackets had 0.022-in slots, and the wires were 0.019 x 0.025 in. Friction was evaluated in a simulated half-arch fixed appliance on a testing machine. The static and kinetic friction data were analyzed with 1-way analysis of variance (ANOVA) and the post-hoc Duncan multiple range test. Archwire alloy and bracket effects were evaluated with 2-way ANOVA. Static and kinetic frictional forces were lower for both the passive and active designs than for the conventional brackets. Maximum values were seen with the beta-titanium archwires, and significant differences were observed between nickel-titanium and stainless steel archwires. With the passive or active self-ligating brackets, stainless steel wire did not produce a significant difference, but differences were significant with nickel-titanium and beta-titanium wires. When nickel-titanium and beta-titanium wires are used for guided tooth movement, passive appliances can minimize frictional resistance.

In vitro evaluation of the frictional forces between brackets and archwire with three passive self-ligating brackets

The aim of this in vitro study was to evaluate the frictional forces between bracket and archwire that included three passive self-ligating brackets (Damon SL2 SDS). The brackets were individually bonded to a brass mount using a preformed 0.021 x 0.025 inch stainless steel wire jig in order to exclude adverse tipping or torsion. The central bracket was positioned 1 mm higher than the others, in order that the three brackets were vertically unaligned. Thirty-six similar set-ups including in total 108 brackets were investigated using the same wire: copper (nickel-titanium) 0.014 inches. A testing machine was designed and constructed to measure the frictional forces between the wire and the three-bracket set-up. Twelve set-ups were tested to measure kinetic frictional forces between the wire and unaligned passive self-ligating brackets used in the closed position. The frictional properties of two sets of 12 three-bracket set-ups (control) were tested and measured with an open slide and conventional ligation. A stainless steel ligature wire was used in the former, while elastomeric modules were employed in the latter. One-way analysis of variance showed a significant effect of ligation mode on the frictional properties of the three-bracket set-ups (P < 0.001). Post hoc pairwise comparison showed that the frictional forces arising from passive self-ligation were significantly lower (P < 0.01) than those resulting from elastic ligation. The same result was achieved when comparing self-ligation and metallic ligation (P < 0.01). No significant difference was found when comparing elastic and metallic ligation.

Adhesion Control between Resist and Photomask Blank

Most problems in photomask fabrication such as pattern collapse, haze, and cleaning damage are related to the behavior of surfaces and interfaces of resists, opaque layers, and quartz substrates. Therefore, it is important to control the corresponding surface and interface energies in photomask fabrication processes. In particular, adhesion analysis in microscopic regions is strongly desirable to optimize material and process designs in photomask fabrication. We applied the direct peeling (DP) method with a scanning probe microscope (SPM) tip and measured the adhesion of resist patterns on Cr and quartz surfaces for photomask process optimization. We also studied the effect of tip shape on the reproducibility of adhesion measurements and the dependence of collapse behavior on the resist profile. We measured lateral forces between the resulting collapsed resist pillar and the Cr or the quartz surface before and after the sliding and related these observed lateral forces to the static and kinetic frictional forces, respectively. We also studied the effect of surface modification of the Cr and quartz surfaces with silanization reagents on adhesion measured with the DP method. Resist adhesion could be controlled by surface modification using silanes. We also discuss the relationship between the adhesion observed with the DP method and the properties of the modified surfaces including water contact angles and local adhesive forces measured from force–distance curves with an SPM.

Intelligent desktop NC machine tool with compliant motion capability

In this paper, a new desktop NC machine tool with compliance control capability is presented for finishing metallic molds with small curved surface. The NC machine tool consists of three single-axis robots. Tools attached to the tip of the z-axis are ball-end abrasive tools. The control system of the NC machine tool is composed of a force feedback loop, position feedback loop and position feed-forward loop. The force feedback loop controls the polishing force consisting of tool contact force and kinetic friction force. The position feedback loop controls the position in pick feed direction. Further, the position feed-forward loop leads the tool tip along cutter location data. In order to first confirm the application limit of a conventional industrial robot to a finishing task, we evaluate the backlash that causes the position inaccuracy at the tip of an abrasive tool, through a simple position/force measurement. Through a similar measurement and a surface following control experiment along a lens mold, the basic position/force controllability with high resolutions is demonstrated.

Friction of Macroscopic Systems -From Paper and Rock to Earthquake-

The frictional phenomena appear in various systems. Their scales spread to extraordinary wide range. The frictional systems of large scale extend to landslide, glacier and earthquake, while those of small scale reach to sub-nanometer. There are universal behaviors in friction which are independent from the scale of the system. Typical examples are the maximum static frictional force, which is the threshold strength of the external force to cause the translational motion, and the kinetic frictional force, which results from energy dissipation accompanied by the caused motion. Besides these, stick-slip phenomena, memory effect of static frictional force, velocity dependence of kinetic frictional force and so on appear in various systems with wide range of scale. There are common mechanisms in these universal phenomena. Here we review frictional phenomena of various systems from a unified point of view.

Durable Anti-Smudge Materials for Display Terminals

This article describes an anti-smudge layer deposited on an antireflective (AR) film. Several kinds of fluorinated compounds were designed on the basis of hydrophilic and hydrophobic groups. Both the perfluoro polyether (PFPE) and an alkoxysilane in the molecule exhibit good anti-smudge properties and a good adhesion to SiO 2 , which is the outermost layer of the AR coating. A 2-nm film thickness is essential to decrease the surface energy, which does not affect the antireflection properties. The addition of an amine and mineral acids was found to produce a significant increase in the rate of the reaction, and the surface energy decreased to 10 mJ/m 2 within several hours. The material endcapped with two alkoxysilyl groups is designed to have a strong interaction with the surface. The kinetic friction force on the AR film is reduced by onehalf when compared to the one side-end PFPE, which also enhances the abrasion resistance.

Conversion of Surface Energy and Manipulation of a Single Droplet across Micropatterned Surfaces

To clarify a driving mechanism for the self-movement of a droplet across hydrophobic textured surfaces in series and to develop applications for a microfluidic device, we report a theoretical model, a microfabrication technique, and experimental measurements. The contact angle of a droplet on a composite surface, the stable surface energy level, and the energy barrier caused by hysteresis were investigated. With increasing patterned density of the microstructure, the contact angle and stable surface energy decreased gradually, but the energy barrier increased. Both the analytical results and the experimental measurements show that the surface energy for a suspended status is greater than that for a collapsed status, which produces increased energy to generate the movement of a droplet. An analysis of interactions between actuation force, resistive force, and viscous force during the motion of a droplet is based on the equilibrium between forces. From the perspective of energy conversion, the difference in surface energy between a higher state and a lower state would drive a single droplet and make it move spontaneously if it could overcome the static friction force resulting from hysteresis and the kinetic friction force under droplet movement. The mean velocity in the present device, measured to be 62.5 mm s (-1), agrees satisfactorily with the theoretical prediction. The model developed for the energy levels enables us to assess the contact mode of a droplet placed on the patterned surface. For a prediction of the transport capability of the designed devices, a theoretical interpretation of the conversion between the surface energy and the kinetic energy of the droplet establishes a criterion that the pattern density of a textured surface should be less than 0.76. The effective rate of energy conversion is estimated to be 20.6%.

Evaluation of frictional forces during dental alignment: An experimental model with 3 nonleveled brackets

The aim of this in-vitro study was to evaluate the frictional forces generated by various combinations of brackets and orthodontic wires by using an experimental model with 3 nonleveled brackets to gain a better understanding of the resistance to sliding during dental alignment and leveling. Two kinds of orthodontic brackets were tested: passive self-ligating brackets and conventional twin stainless steel brackets. The following wires were tested: 3 nickel-titanium (.014, .016, and .016 x .022 in), 2 stainless steel (multistranded .0155 and .016 in), and 1 beta-titanium alloy (.016 in). The ligatures used with conventional brackets were elastomeric modules (power 'O' 110) and preformed stainless steel ligature wire (.010). Each of the 10 bracket-archwire combinations was tested 10 times. Kinetic frictional forces were measured on a specially designed testing machine. The wires tested were pulled through a set of multiple nonleveled brackets at a speed of 4 mm per minute over a distance of 5 mm. All data were statistically analyzed. The sliding of the wire in the 3-bracket nonaligned system was significantly influenced by wire cross-section dimension (P < 0.001), wire material (P < 0.001), number of wire strands (P < 0.001), and type of ligation (P < 0.001). Frictional forces can be reduced during alignment by using self-ligating brackets, small dimensions, and less stiff wires, thereby inducing the wire to slide in the slots. Under such conditions, the force required by the orthodontic wire to overcome resistance to sliding is reduced. This allows the wire to exploit its mechanical characteristics more efficiently.

Comparison of frictional forces during the initial leveling stage in various combinations of self-ligating brackets and archwires with a custom-designed typodont system

The purpose of this study was to compare the frictional force (FF) generated by various combinations of self-ligating bracket (SLB) types, archwire sizes, and alloy types, and the amount of displacement during the initial leveling phase of orthodontic treatment, by using a custom-designed typodont system. Two passive SLBs (Damon 2 [D2] and Damon 3 [D3]), and 3 active SLBs (SPEED [SP], In-Ovation R [IO], Time 2 [T2]), and SmartClip (SM) were tested with 0.014-in and 0.016-in austenitic nickel-titanium (A-Ni-Ti) and copper-nickel-titanium (Cu-Ni-Ti) archwires. To simulate malocclusion status, the maxillary canines (MXCs) were displaced vertically, and the mandibular lateral incisors (MNLIs) horizontally from their ideal positions up to 3 mm with 1-mm intervals. Static and kinetic FFs were measured with a speed of 0.5 mm per minutes for 5 minutes with a testing machine (model 4466, Instron, Canton, Mass). Two conventional brackets (Mini-Diamond [MD] and Clarity [CL]) were used as controls. Analysis of variance and Duncan tests were used for statistical purposes. FF was increased in ascending order: D2, D3, IO, T2, SM, SP, CL, and MD in the maxillary typodont; and IO, D2, D3, T2, SP, CL, and MD in the mandibular typodont, regardless of archwire size and alloy type. The A-Ni-Ti wire showed significantly lower FF than did the Cu-Ni-Ti wire of the same size. As the amounts of vertical displacement of the MXCs and horizontal displacement of the MNLIs were increased, FF also increased. These findings suggest that combinations of the passive SLB and A-Ni-Ti archwire during the initial leveling stage can produce lower FF than other combinations of SLB and archwire in vitro.

Elementary Processes and Dynamical Control of Friction and Lubrication at the Nanoscale-A Theoretical Approach-

Nanoscale boundary lubrication and interfacial friction are studied using computer simulations based on extended Frenkel-Kontorova models. Several peculiar properties of static and kinetic frictional forces and the dynamics of lubrication are discussed. Some possible methods to control frictional forces and dynamics of lubrication are proposed and discussed in relation to the mechanism of nanomachines.

Dependence of maximum static friction on waiting time using dynamics of vortices in superconductors

Vortices in high-Tc superconductors were investigated in terms of the microscopic friction. The I-V characteristics and the transient response of driven vortices were measured in La2-xSrxCuO4 thin films with different Sr concentrations and samples with columnar defects. We found the remarkable dependence of the maximum static friction force on the waiting time at low temperatures. The result suggests that the competition between the flux creep by the thermal fluctuation and the pinning yields a characteristic time scale to stabilize vortices. This relaxation phenomenon is very similar to the so-called boundary lubrication, which occurs under the existence of a thin lubricant film between interfaces. Such a strong dependence changed into a weak logarithmic dependence at higher temperatures. These results imply that the dynamics of vortices can be used for the model not only of the dry friction but also of the lubricated friction. Also, the dependence of the kinetic friction force on the sliding velocity showed the non-Amontons-Coulomb-like behavior even for the lubricated friction. Thus, we confirmed that the Amontons-Coulomb's law does not realize when the thermal fluctuation is sufficiently large.

Numerical study of friction of flake and adsorbed monolayer on atomically clean substrate

Frictional behaviors of flake and adsorbed monolayer on substrate can be observed by Frictional force microscope and Quartz crystal microbalance experiments and are typical problems in nano-friction. Computer simulations had been played important roles in understanding those behaviors, but in most of them the driving direction coincides with one of the crystal axes of the substrate. Here we report our numerical results of direction dependence of friction of flake and adsorbed monolayer. We found a new kind of dynamical phase transition in which flake and adsorbed monlayer change their structure relative to the substrate and make incommensurae structure to reduce kinetic frictional force after certain transition time. When the driving velocity is decreased the transition time tends to diverge at certain critical velocity for the flake. For the adsorbed monlayer the transition time tends to diverge at certain critical magnitudes of the external force or the interaction strength between adsorbates when they are decreased.

Study of friction using driven vortices of superconductor as a model system

Dynamics of driven vortices in high-Tc superconductors was investigated in terms of the elementary process of the motion and the microscopic friction. The I-V characteristics and the transient response of driven vortices were measured in La2-xSrxCuO4 thin films and in Bi2Sr2CaCu2Oy bulk crystals. First, with an aid of a recently proposed scaling relation between the driving force and the velocity, we found that the non-Arrhenius process did exist for interacting vortices at low temperatures. With increasing magnetic field, Arrhenius process revived suddenly at the vortex-glass vs Bragg-glass transition, which shows that this approach is suitable as a new method to investigate the equilibrium phase diagram of vortices. After constructing an explicit formula connecting the motion of driven vortices to the physics of friction, the dependence of the kinetic friction force on the sliding velocity was investigated. Based on the experimental results, we propose that the non-Amontons-Coulomb behavior is regarded as the consequence of the broadened dynamic phase transition. We also found the remarkable dependence of the maximum static friction force on the waiting time at low temperatures. Such a strong dependence changed into a weak logarithmic dependence at higher temperatures. The strong time dependence suggests that a characteristic time scale to stabilize vortices exists at low temperatures. This relaxation phenomenon is very similar to the so-called boundary lubrication. These results imply that the dynamics of vortices can be used for a model not only of the dry friction but also of the lubricated friction.

Mechanism of electromagnetic emission in plastically deformed ionic crystals

Experiments on the plastic deformation of LiF ionic monocrystals under uniaxial compression are performed with simultaneous recording of acoustic (AE) and electromagnetic (EME) emissions. A strong correlation between AE and EME events has been found, which clearly demonstrates that the observed EME is caused by a dynamical interaction between moving dislocations and charged vacancies in the ionic lattice during work hardening. The mechanism proposed to explain EME is based on the assumption that gliding edge dislocations sweep up the vacancies of a preferable sign. As a result, when a dislocation pileup is formed, a certain nonequilibrium charge density is accumulated at its head, resulting in electric polarization of the deformed crystal. As the external loading increases, a locked dislocation pileup bursts through the stoppers and quickly loses its bounded charge. The relaxation of this charge produces an intrinsic polarization current generating an electric pulse. It is assumed that the relaxation current can be described as an athermic viscous motion of vacancies under the kinetic friction force $\ensuremath{\sim}Bv$ ($B$ is the friction coefficient and $v$ is the vacancy velocity) in a self-consistent electric field determined by the distribution of the total charge density. A nonlinear integro-differential equation of motion for the nonequilibrium charge density is derived. For a special form of the initial charge density distribution, an automodel solution of this equation describing the polarization current has been built. The electrical signal generated by an acting slip system has been calculated. By comparing the calculated and experimentally measured electric signal patterns, the friction coefficient for the linear chain of vacancies (the analog of an edge dislocation extra plane) in LiF has been estimated to be $B\ensuremath{\simeq}0.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}\mathrm{g}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. This value is in accordance with the corresponding coefficient for dislocations in ionic lattices.

CAD/CAM-based position/force controller for a mold polishing robot

Control of robotic mold polishing is considered in this paper. CAD/CAM-based position/force controller that simultaneously performs stable force control and exact pick feed control along curved surface is presented for a mold polishing robot. The force feedback loop controls the polishing force consisting of the contact and kinetic friction forces. During the mold polishing, the position feedback loop has a delicate contribution to the force feedback loop in Cartesian space so that the abrasive tool does not deviate from the desired trajectory and keeps a constant pick feed, e.g., 0.2 mm. When the robot with the CAD/CAM-based position/force controller runs, cutter location (CL) data with normal vectors, called multi-axis CL data, are used for not only a desired trajectory of tool translational motion but also desired contact directions given to a mold. The multi-axis CL data allow the mold polishing robot to realize a complete non-taught operation of the position and contact direction. The experimental results show that the CAD/CAM-based position/force control method achieves successful robotic mold polishing with curved surface.

Comparison of frictional resistance after immersion of metal brackets and orthodontic wires in a fluoride-containing prophylactic agent

In this study, we investigated and compared the levels of frictional resistance between metal brackets and orthodontic wires after immersion in an acidified phosphate fluoride (APF) agent. Three types of mandibular incisor stainless steel metal brackets with beta-titanium alloy wire (TMA), heat-activated nickel-titanium wire (Ni-Ti), and 2 sizes of stainless steel wires (SSW) were immersed in 0.2% APF and pH 6.75 artificial saliva solutions for 24 hours. The study included 480 bracket-wire specimens. The frictional resistance was measured on an EZ-test machine (Shimadazu, Tokyo, Japan) with a 5-N load cell. An Alastik (Quik-Stik Clear, A-1 Alastik, 3M Unitek, Monrovia, Calif) module ligated to the bracket was attached to the crosshead of the machine and pulled at a speed of 10 mm per minute for a distance of 5 mm. A completely randomized 1-way ANOVA was used to test for significant differences among the 3 bracket/wire specimens after immersion in 0.2% APF and pH 6.75 artificial saliva solutions. This was followed by the Student-Newman-Keuls multiple comparison of means ranking at P <.05 to determine differences between the groups. In the APF-immersed group, the static frictional force was greater than the kinetic frictional force. The frictional forces of the orthodontic wires had statistically significant differences (P <.05) in this progressive order: TMA, Ni-Ti, and SSW. Similar frictional force results were obtained in the pH 6.75 saliva group (P <.05). The frictional force values of the APF group were higher than those of the pH 6.75 saliva group (P <.05). This study demonstrates that the frictional forces of orthodontic brackets and wires are influenced by contact with fluoride-containing solutions.

Orthogonally-Oriented Nanotube Arrays: Theory

A novel surface involving ordered arrays of partially-embedded carbon nanotubes is developed theoretically. Analysis indicates it should exhibit ultra-low values for friction, adhesion and wear, and also possess superior thermal and electrical properties. The surface consists of orthogonally-oriented, self-assembling arrays of carbon nanotubes, partially embedded lengthwise in a solid substrate. Calculations indicate that stiction forces due to van der Waals interactions can be made small, perhaps more than an order of magnitude less than for Teflon and other advanced perfluorocarbons. Static and kinetic frictional forces could be three orders of magnitude less than for conventional solids.

Robotic sanding system for new designed furniture with free-formed surface

In this paper, a sanding system based on an industrial robot with a surface following controller is proposed for the sanding process of wooden materials constructing furniture. Handy air-driven tools can be easily attached to the tip of the robot arm via a compact force sensor. The robotic sanding system is called the 3D robot sander. The robot sander has two novel features. One is that the polishing force acting between the tool and wooden workpiece is delicately controlled to track a desired value, e.g., 2 kgf. The polishing force is defined as the resultant force of the contact force and kinetic friction force. The other is that no complicated teaching operation is required to obtain a desired trajectory of the tool. Cutter location (CL) data, which are tool paths generated by a CAD/CAM system, are directly used for the basic trajectory of the handy tool attached to the robot arm. The robot sander can be applied to the sanding task of free-formed curved surface with which conventional sanding machines have not been able to cope. The effectiveness and promise are shown and discussed through a few experiments.