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.

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.

Electron microscopy of niobium and tantalum hydrides

1978 ◽  
Vol 36 (1) ◽  
pp. 644-645
Author(s):  
T. Schober
Keyword(s):  
Electron Microscopy ◽  
Heat Storage ◽  
Measurement Techniques ◽  
Metal Hydrides ◽  
Detailed Understanding ◽  
Storage Devices ◽  
Unit Cells ◽  
Endothermic Reactions ◽  
Hydrogen Reactions ◽  
New Phase

Nb, Ta and V are prototype substances for the study of the endothermic reactions of H with metals. Such metal-hydrogen reactions have gained increased importance due to the application of metal-hydrides in hydrogen- und heat storage devices. Electron microscopy and diffraction were demonstrated to be excellent methods in the study of hydride morphologies and structures (1). - Figures 1 and 2 show the NbH and TaH phase diagrams (2,3,4). EM techniques have contributed substantially to the elucidation of the structures and domain configurations of phases β, ζ and ε (1,4). Precision length measurement techniques of distances in reciprocal space (5) recently led to a detailed understanding of the distortions of the unit cells of phases ζ and ε (4). In the same work (4) the existence of the new phase η was shown. It is stable near -68 °C. The sequence of transitions is thus below 70 %.

Replication of the Superstition and Performance Study by

2014 ◽  
Vol 45 (3) ◽  
pp. 239-245 ◽  
Author(s):  
Robert J. Calin-Jageman ◽  
Tracy L. Caldwell
Keyword(s):  
Task Difficulty ◽  
Statistical Power ◽  
Meta Analysis ◽  
A Priori ◽  
Significant Heterogeneity ◽  
Performance Study ◽  
Improve Performance ◽  
Research Designs ◽  
Series Of Experiments ◽  
And Performance

A recent series of experiments suggests that fostering superstitions can substantially improve performance on a variety of motor and cognitive tasks ( Damisch, Stoberock, & Mussweiler, 2010 ). We conducted two high-powered and precise replications of one of these experiments, examining if telling participants they had a lucky golf ball could improve their performance on a 10-shot golf task relative to controls. We found that the effect of superstition on performance is elusive: Participants told they had a lucky ball performed almost identically to controls. Our failure to replicate the target study was not due to lack of impact, lack of statistical power, differences in task difficulty, nor differences in participant belief in luck. A meta-analysis indicates significant heterogeneity in the effect of superstition on performance. This could be due to an unknown moderator, but no effect was observed among the studies with the strongest research designs (e.g., high power, a priori sampling plan).

Comparison of Rheumatological Diagnoses by a Bayesian Program and by Physicians

1991 ◽  
Vol 30 (03) ◽  
pp. 187-193 ◽  
Author(s):  
H. J. Moens ◽  
J. K. van der Korst
Keyword(s):  
Receiver Operating Characteristics ◽  
Bayesian Decision ◽  
Operating Characteristics ◽  
Likelihood Ratios ◽  
Improve Performance ◽  
Mathematical Basis ◽  
Human Expert ◽  
Test Population ◽  
Sensitivity Specificity ◽  
Diagnostic Outcome

AbstractA Bayesian decision support system was developed for the diagnosis of rheumatic disorders. Knowledge in this system is represented as evidential weights of findings. Simple weights were calculated as the logarithm of likelihood ratios on the basis of 1,000 consecutive patients from a rheumatological clinic. The effect of various methods to improve performance of the system by modification of the weights was studied. Three methods had a mathematical basis; a fourth consisted of weights adapted by a human expert, which allowed inclusion of diagnostic rules such as defined in widely accepted criteria sets. The system’s performance was measured in a test population of 570 different cases from the same clinic and compared with predictions of diagnostic outcome made by rheumatologists. The weights from a human expert gave optimal results (sensitivity 65% and specificity 96%), that were close to the physicians’ predictions (sensitivity 64% and specificity 98%). The methods to measure the performance of the various models used in this study emphasize sensitivity, specificity and the use of receiver operating characteristics.

Sign in / Sign up

Export Citation Format

Share Document