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 649 records · Page 36Linked to original sources
PubMed2001

Frictional heating of total hip implants. Part 2: finite element study.

Due to higher friction artificial hip joints warm up more than natural joints during walking and other continuous activities. This could lead to thermal damage in the surrounding tissues and be a reason for long-term implant loosening, an effect which has not yet been investigated. In vivo measurements with instrumented implants showed temperatures inside the prosthetic head up to 43.1 degrees C (Part 1 of this work). Based on the experimental data a finite element model was developed to calculate the temperatures in the tissues surrounding the hip implant to determine whether these tissues can heat up to critical levels. Various parameters were investigated which could account for the variations in the measured temperatures in the patients, including the perfusion rate in tissues, the volume of synovial fluid, and different implant materials. We found that the synovial fluid is most endangered by thermal damage and consequent deterioration of lubricating properties. Implants with a cobalt-chromium head and a polyethylene cup are unfavourable as they can elevate the temperature in the synovia to more than 46 degrees C. With regard to thermal properties stems made from cobalt-chromium alloys are superior to titanium stems, by better conducting heat to the femur and minimizing the synovial fluid temperature. Factors determining the temperatures during walking are insufficiently known or cannot be determined in the individual patient. Therefore, the risk of a thermally induced implant loosening cannot currently be estimated. Under unfavourable conditions such a risk exists, however. General improvements of implant materials and clinical studies on the possibility of implant loosening due to high temperatures are therefore required.

Alloys↗
PubMed1997

Artifactual nonlinearity due to wear grooves and friction in four-point bending experiments of cortical bone.

Experiments and analyses were performed to determine the cause of a nonlinear force-deflection response observed in four-point flexural fatigue of beams of cortical bone machined from the mid-diaphysis of the equine third metacarpus. Observable grooves which formed on the beam surface at supports and load noses were found to be the primary cause of the nonlinearity. An additional geometric nonlinearity at large deflections revealed by finite element modeling may be minimized by using the smallest diameter supports and load noses recommended in ASTM 790. However, frictional constraint of the beams at the load noses and supports can occur at low load levels and should be avoided by using roller-bearing supports and load noses, or some equivalent method.

Animals↗
PubMed2003

Elastic friction drive of surface acoustic wave motor.

Importance of elastic deformation control to obtain large output force with a surface acoustic wave (SAW) motor is discussed in this paper. By adding pre-load to slider, stator and slider surfaces are deformed in a few tens nanometer. Appropriate deformation in normal direction against normal vibration displacement amplitude of SAW existed. By moderate deformation, the output force of the SAW motor was enlarged up to about 10 N and no-load speed was 0.7 m/s. To produce this performance, the transducer weight and slider size were only 4.2 g and 4 x 4 mm(2).By traveling wave propagation, surface particles of the SAW device move in elliptical motion. Due to the amplitude of the elliptical motion is 10 or 20 nm order, the contact condition of the slider is very critical. To control the contact condition, namely, the elastic deformation of the slider and stator surface in nanometer order, a lot of projections were fabricated on the slider surface. The projection diameter was 20 micro m. In static condition, the elastic deformation and stress were evaluated with the FEM analysis. From this calculation and the simulation result, it is consider that the wave crest is distorted, hence the elasticity has influence on the friction drive condition. Elastic deformation of the stator surface beneath the projection from the initial position were evaluated. In 4 x 4 mm(2) square area, the sliders had from 1089 to 23,409 projections. Depression was independent to the contact pressure. However, the output force depended on the depression although the projection density were different. From the view point of the output power of the motor, the proper depression was independent to the projection density. Around 25 nm depression, the output force and output power were maximized. This depression value was almost same as the vibration displacement amplitude of the stator transducer.

Acoustics↗
PubMed2001

Reconstruction of a full-thickness defect of the chest wall caused by friction burn using a combined myocutaneous flap of teres major and latissimus dorsi muscles.

This report describes the therapeutic course of a case of deep burns caused by friction heat generated over a long contact time by a rotating tractor wheel. The burn was accompanied by a full-thickness defect of the chest wall, which we treated with a combined myocutaneous flap of teres major and latissimus dorsi muscles with a large skin flap. Our therapeutic concept of this case is discussed. Based on the postoperative course of this case, we think a combined myocutaneous flap of teres major and latissimus dorsi muscles with two nourishing vessels as an alternative is a very useful, safe, and secure method for the treatment of cases with axillary damages which require one-stage and stable reconstruction, like our patient.

Accidents, Occupational↗
PubMed2000

Car-tyre friction injuries of the foot in children.

In a prospective study, 25 cases of car-tyre friction injuries of the foot in children were included. The mechanism of injury was similar in all patients: As the car-tyre impacted on the child's foot, the driver was usually trying to stop the car resulting in an injury of variable severity, depending on the amount of energy absorbed by the foot. The site of injury varied according to the position of the foot in relation to the tyre at the time of impact. Sixteen out of the 25 patients presented with acute injuries. The severity of foot injury was classified into five grades and the plan of management in these patients was guided by the grade of the acute injury. The remaining nine patients presented with secondary deformity and principles of secondary reconstruction were also demonstrated with clinical examples. Prevention of these injuries are discussed.

Accidents, Traffic↗
PubMed2000

Reduction of polyethylene wear by concave dimples on the frictional surface in artificial hip joints.

For the purpose of reduction of polyethylene wear generated in artificial hip joints, concave dimples were formed on the surface of the metal femoral head by electrical discharge etching with the constant diameter of 0.5 mm, pitch of 1.2 mm, and depth of 0.1 mm. Using a hip joint simulator, the total amount of polyethylene wear was 7.2 mg in the concave-patterned condition and 23.1 mg in the nonpatterned condition. The reasons for the reduction of polyethylene wear by the concave pattern may be i) a reduction of abrasive wear by providing escape dimples for wear particles and ii) an improvement in the lubricity on the frictional surface by the supply of lubricant that is stored in dimples.

Friction↗
PubMed2003

Force and repetition in cycling: possible implications for iliotibial band friction syndrome.

This study examined force and repetition during simulated distance cycling with regard to how they may possibly influence the on-set of the overuse injury at the knee called iliotibial band friction syndrome (ITBFS). A 3D motion analysis system was used to track lower limb kinematics during cycling. Forces between the pedal and foot were collected using a pressure-instrumented insole that slipped into the shoe. Ten recreational athletes (30.6+/-5.5 years) with no known history of ITBFS participated in the study. Foot-pedal force, knee flexion angle and crank angle were examined as they relate to the causes of ITBFS. Specifically, foot-pedal force, repetition and impingement time were calculated and compared with the same during running. A minimum knee flexion angle of approximately 33 degrees occurred at a crank angle of 170 degrees. The foot-pedal force at this point was 231 N. This minimum knee flexion angle falls near the edge of the impingement zone of the iliotibial band (ITB) and the femoral epicondyle, and is the point at which ITBFS is aggravated causing pain at the knee. The foot-pedal forces during cycling are only 18% of those occurring during running while the ITB is in the impingement zone. Thus, repetition of the knee in the impingement zone during cycling appears to play a more prominent role than force in the on-set of ITBFS. The results also suggest that ITBFS may be further aggravated by improper seat position (seat too high), anatomical differences, and training errors while cycling.

Adult↗
PubMed2004

The nonlinear nature of friction.

Tribology is the study of adhesion, friction, lubrication and wear of surfaces in relative motion. It remains as important today as it was in ancient times, arising in the fields of physics, chemistry, geology, biology and engineering. The more we learn about tribology the more complex it appears. Nevertheless, recent experiments coupled to theoretical modelling have made great advances in unifying apparently diverse phenomena and revealed many subtle and often non-intuitive aspects of matter in motion, which stem from the nonlinear nature of the problem.

Animals↗
PubMed2005

Friction and torque govern the relaxation of DNA supercoils by eukaryotic topoisomerase IB.

Topoisomerases relieve the torsional strain in DNA that is built up during replication and transcription. They are vital for cell proliferation and are a target for poisoning by anti-cancer drugs. Type IB topoisomerase (TopIB) forms a protein clamp around the DNA duplex and creates a transient nick that permits removal of supercoils. Using real-time single-molecule observation, we show that TopIB releases supercoils by a swivel mechanism that involves friction between the rotating DNA and the enzyme cavity: that is, the DNA does not freely rotate. Unlike a nicking enzyme, TopIB does not release all the supercoils at once, but it typically does so in multiple steps. The number of supercoils removed per step follows an exponential distribution. The enzyme is found to be torque-sensitive, as the mean number of supercoils per step increases with the torque stored in the DNA. We propose a model for topoisomerization in which the torque drives the DNA rotation over a rugged periodic energy landscape in which the topoisomerase has a small but quantifiable probability to religate the DNA once per turn.

DNA Topoisomerases, Type I↗
PubMed2004

Evaluation of the frictional resistance of conventional and self-ligating bracket designs using standardized archwires and dental typodonts.

The frictional behavior of four conventional and four self-ligating brackets were simulated using a mechanical testing machine. Analyses of the two-bracket types were completed by drawing samples of three standardized archwires through quadrants of typodont models in the dry/wet states. Pretreatment typodonts of an oral cavity featured progressively malocclused quadrants. As nominal dimensions of the archwires were increased, the drawing forces of all brackets increased at different rates. When coupled with a small wire, the self-ligating brackets performed better than the conventional brackets. For the 0.014-inch wires in the upper right quadrant, the maximum drawing forces averaged 125 and 810 cN for self-ligating and conventional brackets, respectively. When coupled with larger wires, various designs interchangeably displayed superior performance. For the 0.019- x 0.025-inch wires in the upper left quadrant, the maximum drawing forces averaged 1635 and 2080 cN for self-ligating and conventional brackets, respectively. As the malocclusion increased, the drawing forces increased. For example, in the least malocclused quadrant and with the smallest wire, maximum drawing forces for self-ligating and conventional brackets averaged 80 and 810 cN, respectively, whereas in the most malocclused quadrant tested with the same wire size, maximum drawing forces for self-ligating and conventional brackets averaged 870 and 1345 cN, respectively. For maximum values between the dry and wet states, significant differences between ambient states existed only for the In-Ovation brackets in the lower left quadrant. These test outcomes illustrated how bracket design, wire size, malocclusion, and ambient state influenced drawing forces.

Dental Alloys↗
PubMed2005

Frictional evaluations of dental typodont models using four self-ligating designs and a conventional design.

Abstract: After a previous study using typodonts and three standardized archwire (AW) sizes, the frictional evaluations of four self-ligating brackets were directed toward the optimal AW-bracket system. Four participating manufacturers suggested three AWs, which were a representation of the three stages of orthodontic treatment, to be coupled with their respective self-ligating design. Four replicated typodont models were mounted with a self-ligating design, and a fifth model was mounted with a conventional design that served as a control. The first experiment evaluated the manufacturer-suggested AWs against the respective self-ligating design. Because no third-stage AWs could engage their respective designs, a second experiment was implemented to gain more detailed analyses of the designs. This experiment included any successful manufacturer-suggested AWs from the first experiment against the four self-ligating designs and the control design. All self-ligating designs performed with the efficiency and reproducibility associated with expectations. Specifically, self-ligation outperformed the conventional brackets when coupled with up to 0.020- x 0.020-inch wires. The clearance of the various AW sizes and alloys changed with malocclusion. Furthermore, the parameter that best correlated with drawing forces was the bending stiffness of the AW, which was directly associated with the nominal dimension of each wire. The best AW-bracket system can be selected, when taking into account the stiffness (elastic modulus and size of the AW) along with the amount of malocclusion present, once the treatment plan is determined.

Dental Alloys↗
PubMed1993

Friction--slipping--traction.

The minimum translational traction requirements of outsoles for shoes used for walking, running, and activities involving lateral movements are presented. Since it will be shown that the classical friction relationships described by Coulomb do not always apply to the elastomeric materials used in modern day athletic footwear, empirical measures of the traction characteristics of candidate materials and designs must be made. A physical traction testing device has been developed to make measurements of the traction characteristics of shoe outsoles will be described. This device quantifies both translational and rotational traction characteristics. Examples of factors affecting both of these variables are presented. Combining a knowledge of the traction characteristics of materials and designs and the factors influencing traction with knowledge of the traction requirements of different activities permits the matching of appropriate outsoles to shoes used for specific activities.

Biomechanical Phenomena↗
PubMed2005

Quantum Brownian motion with large friction.

Quantum Brownian motion in the strong friction limit is studied based on the exact path integral formulation of dissipative systems. In this limit the time-nonlocal reduced dynamics can be cast into an effective equation of motion, the quantum Smoluchowski equation. For strongly condensed phase environments it plays a similar role as master equations in the weak coupling range. Applications for chemical, mesoscopic, and soft matter systems are discussed and reveal the substantial role of quantum fluctuations.

Computer Simulation↗
PubMed2006

Prediction of slips: an evaluation of utilized coefficient of friction and available slip resistance.

The purpose of this study was to investigate the relationship between measures of floor surface slip resistance and an individual's peak utilized coefficient of friction (COFU) on the probability of a slip occurring during level walking. Video, kinematic and ground reaction force data were recorded simultaneously as subjects walked at a self-selected speed during conditions of normal and reduced floor surface slip resistance. Peak COFU during weight acceptance was calculated and the available floor surface slip resistance was measured using the variable incidence tribometer (VIT). Separate logistic regression analyses identified that knowledge of the available slip resistance (as measured by the VIT) in combination with an individual's peak COFU allowed for greater accuracy in classifying slip outcomes (89.5%; p = 0.004), while knowledge of only the available slip resistance reduced the accuracy of categorization to 78.9% (p = 0.021).

Accidental Falls↗
PubMed2002

Interaction of wrestling shoe and competition surface: effects on coefficient of friction with implications for injury.

The purpose of this study was to determine whether there is a significant difference in the co-efficient of friction (Fc) between old versus new wrestling shoes and mats and to investigate the effect of perspiration. Fc was measured by dragging a weighted shoe over a wrestling mat surface and measuring the vertical and horizontal forces produced. Three different shoe conditions were assessed over two mat types for both wet and dry conditions for a total of 12 conditions. To simulate the wet condition, saline solution was smeared over the surface of the mat. There was a significant effect of shoe, mat, and wet/dry conditions. In addition, significant interactions of shoe by mat, shoe by dry/wet, and mat by dry/wet were observed. Overall, Fc was 36% higher for the new wrestling mat compared to the old wrestling mat. Application of the saline solution reduced Fc by 14% compared to the dry condition. Comparison of the mean Fc for all three shoe types revealed the Fc for the older design shoe was 23% to 28% lower than the brand new shoe and the worn newer design, respectively. A high Fc, such as in the new mat/new shoe combination, has the potential to increase the risk of knee and ankle injuries by fixing the foot more securely to the ground.

Athletic Injuries↗
PubMed2005

Psychophysically determined horizontal and vertical forces of dynamic pushing on high and low coefficient of friction floors for female industrial workers.

The purpose of this experiment was to investigate horizontal and vertical components of maximum acceptable initial and sustained forces while performing pushcart tasks on high and low coefficient of friction (COF) floors. Eleven female industrial workers performed two sessions of 120 pushcart tasks on a high COF (.68) floor and one session of 120 pushcart tasks on a low COF (.26) floor. Each pushcart task was 7.6 meters long and initiated once a minute. A psychophysical methodology was employed whereby the workers were asked to select a work load they could sustain for 8 hours without "straining themselves or without becoming unusually tired, weakened, overheated, or out of breath." The results revealed that maximum acceptable weights of the pushcart task on the low COF floor were significantly lower (20%) than the maximum acceptable weights on the high COF floor, which coincided with a significant reduction in the initial and sustained horizontal forces of push (28% and 29%, respectively) on a low COF floor. Push durations on the low COF floor were also significantly longer (36%) than on the high COF floor. Vertical forces and ratios of the vertical to horizontal forces were not significantly different comparing both floors. Calculated probabilities of slipping were supported by observations of repeated slipping by some workers during pushing on the low COF floor. Ergonomic strategies should include the maintenance of sufficient COF on floors to maximize the psychophysical pushing capabilities of the industrial worker.

Accidental Falls↗
PubMedDate not supplied

Treadmills: a preventable source of pediatric friction burn injuries.

Treadmills are a burn risk for children. A child's hand can get trapped in the conveyor belt, causing friction burns to the underlying tissue. The purpose of this retrospective study was to review the characteristics and treatment of treadmill-related burns in children from 1998 to 2002. Ten patients, at a mean age of 3.4 years, sustained injuries associated with treadmill use. Trapping of the hand between the conveyor belt and the base was the most frequent injury mechanism. Burn location was predominantly on fingers and palms. Four patients required operative intervention. All patients required specialized wound care as well as scar management and occupational therapy. Treadmills pose a danger to children. Current safety devices are ineffective for preventing serious hand injuries in children. New design modifications and public awareness are needed to improve child safety.

Accidents, Home↗