Lubricated Friction of Rubber. V. Influence of Rubber Resilience and Hardness on Friction

1968 ◽  
Vol 41 (4) ◽  
pp. 870-880 ◽  
Author(s):  
E. P. Percarpio ◽  
E. M. Bevilacqua
Keyword(s):  
Measurement Error ◽  
Dry Friction ◽  
Road Surface ◽  
Relative Influence ◽  
Test Surface ◽  
Hard Surface ◽  
Wet Friction ◽  
Wide Range

Abstract The dominant importance of hysteresis in lubricated friction of rubber was first outlined by Tabor and has been extensively confirmed since. A number of workers have also shown that dry friction is correlated with hysteresis, but the mechanistic connection is still unclear. Rubber hardness has been less definitely correlated with friction. This may result in part from the choice of surface on which to test the rubber compositions studied. We have previously shown the importance of the test surface and recommended use of wavy glass to simulate actual slippery roads in lieu of a representative road surface. Carr reported our finding that the relative influence of rubber hardness depends on the texture of the hard surface on which it slides. Using the wavy glass and a slippery road surface, we have now studied a very wide range of compositions, both gum and filled, derived from commonly used tire rubbers, as well as others included to extend the range of properties studied. These results fully confirm the importance of hysteresis and more clearly define that of hardness. These two properties together almost completely determine wet friction on slippery roads. Most of the variance not accounted for is attributable to measurement error.

scholarly journals The motion of curling rocks: Experimental investigation and semi-phenomenological description

2004 ◽  
Vol 82 (10) ◽  
pp. 791-809 ◽  
Author(s):  
E T Jensen ◽  
Mark RA Shegelski
Keyword(s):  
Experimental Investigation ◽  
Liquid Film ◽  
Frictional Force ◽  
Dry Friction ◽  
Thin Liquid Film ◽  
Ice Surface ◽  
Wet Friction ◽  
Wide Range ◽  
Friction Models ◽  
Rule Out

A large number of curling shots using a wide range of rotational and translational velocities on two different ice surfaces have been recorded and analyzed. The observed curling-rock trajectories are described in terms of a semi-phenomenological model. The data are found to rule out "dry-friction" models for the observed motion, and to support the idea that the curling rock rides upon a thin liquid film created at the ice surface (i.e., "wet friction"). Evidence is found to support the hypothesis that the frictional force acting upon each segment of the curling rock is directed opposite to the motion relative to this thin liquid film and not relative to the underlying fixed ice surface. PACS No.: 01.80.+b

The Ascription of Attributes to Pupils by Experienced Teachers and Student Teachers: The Influence of Voice in this Process

1982 ◽  
Vol 26 (3) ◽  
pp. 305-326
Author(s):  
K. J. Eltis
Keyword(s):  
Student Teachers ◽  
Significant Influence ◽  
Physical Appearance ◽  
Teaching Experience ◽  
Experienced Teachers ◽  
Relative Influence ◽  
Cognitive Variables ◽  
Wide Range ◽  
Initial Impressions ◽  
Pupil Voice

This study was designed to gain substantial information about how teachers form initial impressions of pupils. The particular aim was to examine the relative influence of speech style, physical appearance, and written work on judgments about pupils on a wide range of classroom personality and cognitive variables. Teaching experience emerged as a key rater variable. The results indicated that, for raters in general, pupil voice was a strong discriminator on variables pertaining more narrowly to the child as a learner in the classroom, and was a significant influence on judgments about intelligence and likely success as a pupil.

Design of an FMCW Radar Altimeter for Wide-Range and Low Measurement Error

2015 ◽  
Vol 64 (12) ◽  
pp. 3517-3525 ◽  
Author(s):  
Jae-Hyun Choi ◽  
Jong-Hun Jang ◽  
Jin-Eep Roh
Keyword(s):  
Measurement Error ◽  
Radar Altimeter ◽  
Fmcw Radar ◽  
Wide Range

scholarly journals Testing repeatability, measurement error and species differentiation when using geometric morphometrics on complex shapes: a case study of Patagonian lizards of the genus Liolaemus (Squamata: Liolaemini)

2020 ◽  
Vol 130 (4) ◽  
pp. 800-812 ◽  
Author(s):  
Juan Vrdoljak ◽  
Kevin Imanol Sanchez ◽  
Roberto Arreola-Ramos ◽  
Emilce Guadalupe Diaz Huesa ◽  
Alejandro Villagra ◽  
...  
Keyword(s):  
Measurement Error ◽  
Geometric Morphometrics ◽  
Evolutionary Biology ◽  
Species Differentiation ◽  
Geometric Morphometric ◽  
Operator Error ◽  
Wide Range ◽  
Complex Shapes ◽  
Key Factor ◽  
Sources Of Variation

Abstract The repeatability of findings is the key factor behind scientific reliability, and the failure to reproduce scientific findings has been termed the ‘replication crisis’. Geometric morphometrics is an established tool in evolutionary biology. However, different operators (and/or different methods) could act as large sources of variation in the data obtained. Here, we investigated inter-operator error in geometric morphometric protocols on complex shapes of Liolaemus lizards, as well as measurement error in three taxa varying in their difficulty of digitalization. We also examined the potential for these protocols to discriminate among complex shapes in closely related species. We found a wide range of inter-operator error, contributing between 19.5% and 60% to the total variation. Moreover, measurement error increased with the complexity of the quantified shape. All protocols were able to discriminate between species, but the use of more landmarks did not imply better performance. We present evidence that complex shapes reduce repeatability, highlighting the need to explore different sources of variation that could lead to such low repeatability. Lastly, we suggest some recommendations to improve the repeatability and reliability of geometric morphometrics results.

Electromagnetic and thermal parameter identification method for best prediction of temperature distribution on transformer tank covers

2015 ◽  
Vol 34 (2) ◽  
pp. 485-495 ◽  
Author(s):  
Patricia Penabad Durán ◽  
Paolo Di Barba ◽  
Xose Lopez-Fernandez ◽  
Janusz Turowski
Keyword(s):  
Temperature Distribution ◽  
Measurement Error ◽  
Parameter Identification ◽  
Objective Function ◽  
Measurement Errors ◽  
Optimization Algorithms ◽  
Identification Problem ◽  
Content Type ◽  
Identification Method ◽  
Wide Range

Purpose – The purpose of this paper is to describe a parameter identification method based on multiobjective (MO) deterministic and non-deterministic optimization algorithms to compute the temperature distribution on transformer tank covers. Design/methodology/approach – The strategy for implementing the parameter identification process consists of three main steps. The first step is to define the most appropriate objective function and the identification problem is solved for the chosen parameters using single-objective (SO) optimization algorithms. Then sensitivity to measurement error of the computational model is assessed and finally it is included as an additional objective function, making the identification problem a MO one. Findings – Computations with identified/optimal parameters yield accurate results for a wide range of current values and different conductor arrangements. From the numerical solution of the temperature field, decisions on dimensions and materials can be taken to avoid overheating on transformer covers. Research limitations/implications – The accuracy of the model depends on its parameters, such as heat exchange coefficients and material properties, which are difficult to determine from formulae or from the literature. Thus the goal of the presented technique is to achieve the best possible agreement between measured and numerically calculated temperature values. Originality/value – Differing from previous works found in the literature, sensitivity to measurement error is considered in the parameter identification technique as an additional objective function. Thus, solutions less sensitive to measurement errors at the expenses of a degradation in accuracy are identified by means of MO optimization algorithms.

The Effect of Gravity and Rotor Configuration on Dry Friction Whip and Safe Rotor/Stator Clearance

2019 ◽  
Author(s):  
Rajiv Kumar Vashisht
Keyword(s):  
Mathematical Model ◽  
Fault Diagnosis ◽  
Dry Friction ◽  
Rotating Machinery ◽  
Degree Of Freedom ◽  
System Response ◽  
Rich Variety ◽  
Wide Range ◽  
Clearance Level ◽  
High Degree

Abstract A mathematical model is developed for a real rotor/stator system with high degrees-of-freedoms, multiple disks, flexible bearing supports and couplings. The safe clearance level for coasting up of the rotor is calculated for a general high degree-of-freedom rotor/stator system. The harmful phenomena of dry friction whip, which is generally observable for simple 2 degree-of-freedom Jeffcott rotors in the absence of gravity only, can be proved to exist (in real rotor/stator systems) even in the presence of gravity for a wide range of clearance levels. In case of Jeffcott rotors, by fixing the clearance and increasing the rotor spin frequency, the response of the system follows the pattern: No rub - Forward Annular Rub (FAR) - Partial Forward Whirl (PFW) - Partial Backward Whirl (PBW) - dry whip (WHIP). In case of a real rotor/stator system, at certain frequencies, the system directly jumps to dry whip. The simulated results show a rich variety of system dynamics including FAR, PFW and WHIP in case of vertical rotors where the effect of gravity is neglected. For horizontal rotors, under the effect of gravity, the system response contains multi-harmonics, chaotic responses and multi-period vibrations. Based on these responses, a robust fault diagnosis strategy can be designed to identify the rubbing action in rotating machinery.

Quantitation of measurement error with Optimal Segments: basis for adaptive time course smoothing

1993 ◽  
Vol 264 (6) ◽  
pp. E902-E911 ◽  
Author(s):  
D. C. Bradley ◽  
G. M. Steil ◽  
R. N. Bergman
Keyword(s):  
Measurement Error ◽  
Measurement Errors ◽  
Time Course ◽  
Smooth Curve ◽  
Random Group ◽  
Smooth Curves ◽  
Original Curve ◽  
Wide Range ◽  
Data Points ◽  
Time Courses

We introduce a novel technique for estimating measurement error in time courses and other continuous curves. This error estimate is used to reconstruct the original (error-free) curve. The measurement error of the data is initially assumed, and the data are smoothed with "Optimal Segments" such that the smooth curve misses the data points by an average amount consistent with the assumed measurement error. Thus the differences between the smooth curve and the data points (the residuals) are tentatively assumed to represent the measurement error. This assumption is checked by testing the residuals for randomness. If the residuals are nonrandom, it is concluded that they do not resemble measurement error, and a new measurement error is assumed. This process continues reiteratively until a satisfactory (i.e., random) group of residuals is obtained. In this case the corresponding smooth curve is taken to represent the original curve. Monte Carlo simulations of selected typical situations demonstrated that this new method ("OOPSEG") estimates measurement error accurately and consistently in 30- and 15-point time courses (r = 0.91 and 0.78, respectively). Moreover, smooth curves calculated by OOPSEG were shown to accurately recreate (predict) original, error-free curves for a wide range of measurement errors (2-20%). We suggest that the ability to calculate measurement error and reconstruct the error-free shape of data curves has wide applicability in data analysis and experimental design.

Second Paper: Studies on the Skidding Resistance of Passenger-Car Tyres on Wet Surfaces

1965 ◽  
Vol 180 (1) ◽  
pp. 122-157 ◽  
Author(s):  
G. Maycock
Keyword(s):  
Road Surface ◽  
Smooth Surfaces ◽  
Passenger Car ◽  
Force Coefficients ◽  
Potential Value ◽  
Lubricating Film ◽  
High Speeds ◽  
Wide Range ◽  
Road Surfaces ◽  
Braking Force

This paper reports investigations into the effect of tread pattern, pattern modifications, tread material and tyre casing construction, on the skidding resistance of passenger-car tyres at speeds between 25 and 80 mile/h on a range of wet road surfaces. The technique used was to brake the front wheels of a car until these wheels locked, and to record the resulting deceleration of the vehicle. From the deceleration record, both the peak and locked-wheel values of the braking force coefficients were obtained. The method is described and an assessment of the errors involved is given. The experiments showed the importance of adequate drainage of the region of contact between tyre and road, particularly at the higher speeds, in order to remove the lubricating film of water. Such drainage can be provided either by a tread pattern or a coarse road surface, and the present results indicate the importance of each and their inter-relation. The results of various modifications to a standard tread pattern are given; these show that on smooth surfaces worth-while increases in wet road adhesion at high speeds can be obtained by suitable design of tyre tread patterns. The magnitude of the increases in friction due to changes in tread material are given for both peak and locked-wheel coefficients. Ratios of peak to locked-wheel coefficients have been calculated over a wide range of surface and tyre combinations, and they show the potential value of devices enabling a vehicle to make use of these high coefficients.

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