scholarly journals Linear frictional forces cause orbits to neither circularize nor precess

2008 ◽  
Vol 41 (23) ◽  
pp. 235205 ◽  
Author(s):  
B Hamilton ◽  
M Crescimanno
Keyword(s):  
Frictional Forces

Quantitative analysis of in situ straining experiments in the case of strong frictional forces

1978 ◽  
Vol 36 (1) ◽  
pp. 570-571
Author(s):  
F. Louchet ◽  
L.P. Kubin
Keyword(s):  
Strain Rate ◽  
Radiation Effects ◽  
Dislocation Line ◽  
Critical Length ◽  
Local Strain ◽  
Local Flow ◽  
Double Kink ◽  
Dislocation Densities ◽  
Frictional Forces ◽  
Local Strain Rate

Investigation of frictional forces -Experimental techniques and working conditions in the high voltage electron microscope have already been described (1). Care has been taken in order to minimize both surface and radiation effects under deformation conditions.Dislocation densities and velocities are measured on the records of the deformation. It can be noticed that mobile dislocation densities can be far below the total dislocation density in the operative system. The local strain-rate can be deduced from these measurements. The local flow stresses are deduced from the curvature radii of the dislocations when the local strain-rate reaches the values of ∿ 10-4 s-1.For a straight screw segment of length L moving by double-kink nucleation between two pinning points, the velocity is :where ΔG(τ) is the activation energy and lc the critical length for double-kink nucleation. The term L/lc takes into account the number of simultaneous attempts for double-kink nucleation on the dislocation line.

scholarly journals Comparative Evaluation of Frictional forces between different Archwire-bracket Combinations

2014 ◽  
Vol 4 (1) ◽  
pp. 22-28 ◽  
Author(s):  
Vinit Singh ◽  
Swati Acharya ◽  
Satyabrata Patnaik ◽  
Smruti Bhusan Nanda
Keyword(s):  
Stainless Steel ◽  
Tooth Movement ◽  
Testing Machine ◽  
Frictional Resistance ◽  
Nickel Titanium ◽  
Orthodontic Bracket ◽  
Fixed Appliance ◽  
Beta Titanium ◽  
Frictional Forces

Introduction: During sliding mechanics, frictional resistance is an important counterforce to orthodontic tooth movement; whichmust be controlled to allow application of light continuous forces.Objective: To investigate static and kinetic frictional resistance between three orthodontic brackets: ceramic, self-ligating, andstainless steel, and three 0.019×0.025” archwires: stainless steel, nickel-titanium, titanium-molybdenum.Materials & Method: The in vitro study compared the effects of stainless steel, nickel-titanium, and beta-titanium archwires onfrictional forces of three orthodontic bracket systems: ceramic, self-ligating, and stainless steel brackets. All brackets had 0.022”slots, and the wires were 0.019×0.025”. Friction was evaluated in a simulated half-arch fixed appliance on a testing machine. Thestatic and kinetic friction data were analyzed with 1-way analysis of variance (ANOVA) and post-hoc Duncan multiple rangetest.Result: Self-ligating (Damon) brackets generated significantly lower static and kinetic frictional forces than stainless steel (Gemini)and ceramic brackets (Clarity). Among the archwire materials, Beta-titanium showed the maximum amount of frictional forceand stainless steel archwires had the lowest frictional force.Conclusion: The static and kinetic frictional force for stainless steel bracket was lowest in every combination of wire.

The effect of the indenter elasticity on the Hertzian fracture of brittle materials

1973 ◽  
Vol 334 (1596) ◽  
pp. 95-117 ◽  
Keyword(s):  
Fracture Stress ◽  
Opposite Effect ◽  
Test Material ◽  
Test Surface ◽  
Dynamic Tests ◽  
Frictional Forces ◽  
Consistent Increase ◽  
Static And Dynamic Tests ◽  
Ring Crack ◽  
Ring Cracks

A spherical indenter loaded statically or dynamically into contact with the surface of a brittle material produces a well-defined ring crack. This phenomenon, when interpreted by the Hertz theory of elastic contact, provides a convenient test for the strength of the material. If the elastic modulus of the indenter is different from that of the test material, e. g. a steel indenter in contact with a glass surface, frictional forces are brought into play at the interface which modify the Hertz distribution of contact stress. This effect has been examined both theo­retically and experimentally. An indenter which is more rigid than the test surface is shown to lead to an apparent increase in fracture strength of the material, a less rigid indenter has the opposite effect. Static and dynamic tests of plate glass showed a consistent increase in apparent fracture stress of about 50 % using spherical steel indenters compared with glass indenters. This increase agrees well with the influence of friction upon the Hertzian stress calculated theoretically. The average radius of the ring cracks produced by steel indenters was observed to be greater than that produced by glass indenters, an effect of friction also predicted by the theory. Secondary ring cracks of smaller radius have frequently been observed during unloading of a steel indenter. These were not found when a glass indenter was used and an explanation is suggested in terms of the frictional effect which arises from a difference in elasticity between the indenter and the test surface.

An experimental study of the influence of heat storage and transportability of different lubricants on friction under transient elastohydrodynamic conditions

2003 ◽  
Vol 217 (1) ◽  
pp. 27-37 ◽  
Author(s):  
B-O Åhrström ◽  
C Penchinat ◽  
T Norrby
Keyword(s):  
Heat Storage ◽  
Improve Performance ◽  
Dynamic Simulations ◽  
Successful Model ◽  
Frictional Properties ◽  
Fast Fourier Transform Analysis ◽  
Propagating Waves ◽  
Frictional Forces ◽  
Observed Behaviour ◽  
Reduce Emissions

Lubricated transient elastohydrodynamic (EHD) conjunctions are extremely difficult to simulate numerically since lubricant properties such as temperature and viscosity vary significantly during the loading-unloading event. Nevertheless, industry has invested considerable time and effort in trying to create such models in order to improve performance and to reduce emissions and friction. One of the essential requirements for a successful model is accuracy in the implementation of frictional properties. The experimental method presented in this paper used an impact on the end surface of a beam to generate propagating waves that were subjected to fast Fourier transform analysis. The method yielded detailed information about the build-up and decay of normal and frictional forces as a function of time for various lubricants at three different initial temperatures (20, 40 and 80°C) and at relevant EHD pressures. A variety of lubricants were studied to a peak Hertzian pressure of 2.5GPa for loading-unloading times of 200-400 μs (typical for elastohydrodynamically lubricated conjunctions in ball bearings and gears). A qualitative study of the thermal properties of the lubricants and their influence on viscosity and friction coefficient was also undertaken and, finally, a plausible explanation of the observed behaviour is presented and parallels to dynamic simulations of polyatomic gases are drawn.

scholarly journals Intrinsic Friction of Monolayers Adsorbed on Solid Surfaces.

2003 ◽  
Vol 790 ◽  
Author(s):  
O. Bénichou ◽  
A.M. Cazabat ◽  
J. De Coninck ◽  
M. Moreau ◽  
G. Oshanin
Keyword(s):  
Density Distribution ◽  
Master Equation ◽  
Vapor Phase ◽  
Tracer Particle ◽  
Hard Core ◽  
Solid Surfaces ◽  
Equation Approach ◽  
Frictional Properties ◽  
Master Equation Approach ◽  
Frictional Forces

ABSTRACTWe review recent results on intrinsic frictional properties of adsorbed monolayers, composed of mobile hard-core particles undergoing continuous exchanges with a vapor phase. In terms of a dynamical master equation approach we determine the velocity of a biased impure molecule - the tracer particle (TP), constrained to move inside the adsorbed mono-layer probing its frictional properties, define the frictional forces exerted by the monolayer on the TP, as well as the particles density distribution in the monolayer.

Frictional forces and surface topography of a new ceramic bracket

1994 ◽  
Vol 106 (3) ◽  
pp. 273-278 ◽  
Author(s):  
Kazuo Tanne ◽  
Susumu Matsubara ◽  
Yoshihisa Hotei ◽  
Mamoru Sakuda ◽  
Masahiro Yoshida
Keyword(s):  
Surface Topography ◽  
Frictional Forces ◽  
Ceramic Bracket

scholarly journals In Vitro Frictional Forces Generated by Three Different Ligation Methods

2008 ◽  
Vol 78 (5) ◽  
pp. 917-921 ◽  
Author(s):  
Paola Gandini ◽  
Linda Orsi ◽  
Chiara Bertoncini ◽  
Sarah Massironi ◽  
Lorenzo Franchi
Keyword(s):  
Steel Wire ◽  
Testing Machine ◽  
Low Friction ◽  
Instron Testing Machine ◽  
Resistance To Sliding ◽  
Titanium Wire ◽  
Frictional Forces ◽  
Conventional Bracket ◽  
Wire Resistance

Abstract Objective: To test the hypothesis that there is no difference between the frictional forces produced by a passive self-ligating bracket (SLB) in vitro and a conventional bracket (CB) used with two types of elastomeric ligatures. Materials and Method: The brackets, wires and ligation methods used in vitro were a passive SLB and a CB used with two types of elastomeric ligatures (conventional elastomeric ligature [CEL] and unconventional elastomeric ligatures [UEL]). The bracket ligation systems were tested with two types of wires (0.014″ super elastic nickel titanium wire and 0.019″ × 0.025″ stainless steel wire). Resistance to sliding of the bracket/wire/ligature systems was measured with an experimental model mounted on the crosshead of an Instron testing machine with a 10 N load cell. Each sample was tested 10 consecutive times under a dry state. Results: Frictional forces close to 0 g were recorded in all tests with SLB and in all tests with UEL on CB with both wire types. Resistance to sliding increased significantly (87–177 g) (P < .05) when CEL on CB was used with both wires. Conclusion: UELs may represent a valid alternative to passive SLBs for low-friction biomechanics.

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