Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Friction”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed2000

Surface and friction characterization by thermoelectric measurements during ultrasonic friction processes

Even though friction is one of the oldest problems in physics many aspects of friction processes are not clear today. We present an experimental setup, which permits the study of tribological systems by measuring the dissipated heat at the interface of two surfaces during a friction process with a time resolution of 1 ms. The apparatus is based on a standard ultrasonic wire-bond machine used in semiconductor industries to connect the internal semiconductor die to the external leads, but the standard bond wire is replaced by a thermocouple. To demonstrate the ability of the apparatus it will be shown that bond substrates used in semiconductor industries can be unequivocally characterized.

Journal Article↗
PubMed2004

Transition from stick-slip to continuous sliding in atomic friction: entering a new regime of ultralow friction.

A transition from stick-slip to continuous sliding is observed for atomically modulated friction by means of a friction force microscope. When the stick-slip instabilities cease to exist, a new regime of ultralow friction is encountered. The transition is described in the framework of the Tomlinson model using a parameter eta which relates the strength of the lateral atomic surface potential and the stiffness of the contact under study. Experimentally, this parameter can be tuned by varying the normal load on the contact. We compare our results to a recently discussed concept called superlubricity.

Journal Article↗
PubMed1989

[Study on frictional characteristics of KB horizontal brackets. A comparative study of kinetic frictional forces to be caused between various kinds of brackets and wires].

KB horizontal brackets were designed to tip no more than 6 degrees at the maximum. This tipping amount is based on the idea of reducing friction between a wire and brackets to allow the effective tooth movement of the Begg technique even with horizontally long brackets, and does not originate in the concept of carrying out tipping movement. Thereon, experimental measurements by use of Rheometer were conducted to review for comparison of the kinetic frictional forces caused between various wires and the following four types of brackets; KB horizontal brackets, Tip edge brackets, Straight edge brackets and Begg brackets. 1. In case of utilizing ribbon arch wires and rectangular wires, no significant difference was acknowledged among Tip edge, KB horizontal and Straight edge brackets. 2. There proved to be a reduction in the kinetic frictional forces by incorporating tip into the edgewise slots, when using smaller dimensions of the wires which call for the effective tooth movement, however, Begg brackets (in conjunction with Ordinary T-pins and/or Safety T-pins) showed the small value which is far less than that of the three kinds of brackets.

Orthodontic Appliances↗
PubMed2001

Friction studies of hydrogel contact lenses using AFM: non-crosslinked polymers of low friction at the surface.

The surface of soft contact lenses made of crosslinked poly(2-hydroxyethyl methacrylate). pHEMA, has been investigated with atomic force microscopy in contact mode. The friction force and adhesive force measurements were able to differentiate the non-crosslinked pHEMA chains from the surface of the crosslinked pHEMA networks. These non-crosslinked pHEMA chains at the surface were anchored to the crosslinked pHEMA network, most likely by entanglement and their surfaces were about 2-4nm higher than the surrounding surface in a dehydrated state. In saline solution, the surface friction and adhesive force of the contact lens were significantly reduced compared to those measured for the surface-dehydrated contact lens.

Adhesiveness↗
PubMedDate not supplied

Friction melanosis, friction amyloidosis, macular amyloidosis, towel melanosis: many names for the same clinical entity.

Macular or friction amyloidosis is a cutaneous entity characterized by a brownish pigmentation distributed on the skin over bony regions of the trunk and limbs after the use, for many years, of a nylon towel or scrub brush to clean the skin. Electron microscopy is necessary for the diagnosis of this dermatosis and reveals deposits of amyloid in the papillary dermis. This condition is relatively unknown in Western countries. In this report, we describe 24 Italian patients affected by friction amyloidosis which was caused by the use of cotton towels, horse-hair gloves or artificial and rough sponges to clean their skin.

Adult↗
PubMed2002

Acoustics of friction.

This article presents an overview of the acoustics of friction by covering friction sounds, friction-induced vibrations and waves in solids, and descriptions of other frictional phenomena related to acoustics. Friction, resulting from the sliding contact of solids, often gives rise to diverse forms of waves and oscillations within solids which frequently lead to radiation of sound to the surrounding media. Among the many everyday examples of friction sounds, violin music and brake noise in automobiles represent the two extremes in terms of the sounds they produce and the mechanisms by which they are generated. Of the multiple examples of friction sounds in nature, insect sounds are prominent. Friction also provides a means by which energy dissipation takes place at the interface of solids. Friction damping that develops between surfaces, such as joints and connections, in some cases requires only microscopic motion to dissipate energy. Modeling of friction-induced vibrations and friction damping in mechanical systems requires an accurate description of friction for which only approximations exist. While many of the components that contribute to friction can be modeled, computational requirements become prohibitive for their contemporaneous calculation. Furthermore, quantification of friction at the atomic scale still remains elusive. At the atomic scale, friction becomes a mechanism that converts the kinetic energy associated with the relative motion of surfaces to thermal energy. However, the description of the conversion to thermal energy represented by a disordered state of oscillations of atoms in a solid is still not well understood. At the macroscopic level, friction interacts with the vibrations and waves that it causes. Such interaction sets up a feedback between the friction force and waves at the surfaces, thereby making friction and surface motion interdependent. Such interdependence forms the basis for friction-induced motion as in the case of ultrasonic motors and other examples. Last, when considered phenomenologically, friction and boundary layer turbulence exhibit analogous properties and, when compared, each may provide clues to a better understanding of the other.

Journal Article↗
PubMed2002

[Study of friction and loosening in hip endoprostheses].

AIM: Like any other operative procedure, the implantation of hip prosthesis is associated with certain complications, which diminishes the value and purpose of such a procedure. One of the complications in artificial hip implantation is loosening of the alloplastic material. Therefore, the aim of this study was to examine the effect of lubrication on the torsional moment and its role in the loosening of the femoral component, using an experimental mechanical model. The following hypothesis was tested: the magnitude of torsional loading in the "bone-endoprosthesis-bone cement system" is similar to any other known loading. METHODS: The testing device was constructed with the possibility of simulation of positions similar to original performances in the implanted hip prosthesis. It refers primarily to the possibilities of achieving definite forces and velocities. The intention was to point quantitatively to the role of friction moment between the acetabular and femoral endoprosthesis part. Trials were conducted by combining 7 types of loading and 4 kinds of lubrication: dry, water, plasma, and light oil. The testing joint (Ring's prosthesis) was connected through tensometric measuring shaft upon the working forepart oscillating mechanism. Graded by the changeable static loading by means of the pendulum and via lever mechanism the testing joint was loaded by force from 610 to 7137 N. As the cause of friction resistance in the moving joint, torque deformaties of the measuring shaft occurred. The testing joint enabled oscillating movement using a four-part mechanism. In this way, it was possible to define not only the maximum values of the frictional moment (or the coefficient of friction) during one movement cycle but also to examine its relation to the kind of lubrication. Change in the measuring torsional moment were computer recorded. Before each trial, the gauging of the complete outfit was performed. Thereafter, cleaning of the frictional surfaces of the whole outfit was done. RESULTS: The results obtained in combination with lubrication showed a slight increase in the values of the frictional moment. With dry lubrication and greater loading, an extremely progressive gradient of change was recorded. The course of change in the coefficient of friction was essentially different from the course of change in the frictional moment. It was noted particularly during trials with lubrication. In trials without lubrication, a constant increase of loading (force) resulted in a progressive increase in the coefficient of friction, similar to the friction moment. Such a character of the friction moment increase in the observed loading field was explained by the presence of boundary friction in cases with lubrication and by dry friction in cases without lubrication. In dry friction, scratching occurs relatively early, at a loading of F = 1854 N. It occurs with substances of approximately the same hardness like Ring's prosthesis, where the acetabular and femoral prosthesis parts are of metal characteristics. CONCLUSION: The increase in the frictional moment within the observed loading range can be explained by the presence of bordering friction in cases with lubrication, and of dry friction in cases without lubrication. Contrary to this, dry friction relatively early leads to "scratching", especially when sparing materials of similar hardness are combined.

Arthroplasty, Replacement, Hip↗
PubMed2006

Studies of human hair by friction force microscopy with the hair-model-probe.

We employed a cantilever modified with a self-assembled monolayer (SAM) as a "hair-model-probe" for friction force microscopy (FFM) to measure friction acting between hair and hair-like surfaces. The "hair-model-probe" was prepared by forming a SAM of octadecanethiol on a gold-coated cantilever. We investigated frictional properties of human hair at both root and tip, and the dependency on applied load, influence of scanning direction, and local frictional distribution. The friction coefficient of the hair tip was greater than that of the hair root. Load dependency of friction at the hair tip was clearly observed, while friction at the hair root was less dependent on applied load. At the hair root, an anisotropic frictional property was observed: friction force along the long axis of the hair fiber was about 1.5-2 times larger than that along the short axis. Atomic force microscopy (AFM) images showed striations on the cuticle cells that have about 6 nm depth and their long axis oriented in the direction of the hair fiber. The frictional distribution images revealed that the local areas showing strong shear corresponded to striations. Since such distribution of friction was not observed at the hair tip, it is suggested that the anisotropic frictional property at the hair root was caused mainly by the striations. The frictional distribution in regions that excluded the striations also showed the anisotropic frictional property that friction parallel to the long axis of the hair fiber is greater than that along the short axis. This result suggests that the orientation of fatty acid molecules comprising the fat layer (F-layer) may also contribute to the anisotropic frictional property. We have concluded that loss of the F-layer is a dominant cause of strong friction detected at the hair tip, and at the striations of the hair root.

Friction↗
PubMed1998

Frictional forces related to self-ligating brackets.

Orthodontic tooth movement can be regarded as teeth sliding on a wire like pearls on a string, the force being supplied by springs or elastics. The movement implies friction between wire and bracket, taking up part of the force and leaving an uncontrolled amount to act on the teeth. The friction is likely to depend on bracket construction and wire material. Therefore, in this investigation the friction of self-ligating brackets and beta-titanium wires was evaluated, as opposed to more conventional configurations. Carried by low-friction linear ball bearings, a bracket was made to slide along an out-stretched archwire with minimal (and known) basic friction, either parallel or at an angle to the wire. Two self-ligating brackets were used in their closed position without any normal force. Friction was tested against four wires: stainless steel and beta-titanium, both in round and rectangular cross-sections. The force used to overcome friction and to move the bracket was measured on a testing machine at 10 mm/min, and the basic friction was subtracted. The results show that round wires had a lower friction than rectangular wires, the beta-titanium wires had a markedly higher friction than stainless steel wires, and friction increased with angulation for all bracket/wire combinations. The self-ligating brackets had a markedly lower friction than conventional brackets at all angulations, and self-ligating brackets, closed by the capping of a conventional design, exhibited a significantly lower friction than self-ligating brackets closed by a spring. The selection of bracket design, wire material, and wire cross-section significantly influences the forces acting in a continuous arch system.

Analog-Digital Conversion↗