State and Rate Dependent Friction Laws for Modeling High-Speed Frictional Slip at Metal-on-Metal Interfaces

2006 ◽  
Vol 129 (1) ◽  
pp. 17-22 ◽  
Author(s):  
Hamid Ullah ◽  
M. A. Irfan ◽  
V. Prakash
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
High Speed ◽  
Friction Stress ◽  
Normal Pressure ◽  
Friction Model ◽  
Friction Laws ◽  
Rate Dependent ◽  
Applied Shear Stress ◽  
Slip Event

In the present paper the applicability of state and rate dependent friction laws in describing the phenomena of high speed slip at metal-on-metal interfaces is investigated. For the purpose of model validation, results of plate-impact pressure-shear friction experiments were conducted by Irfan in 1998 and Irfan and Prakash in 2000 using a Ti6Al4V and Carpenter Hampden tool-steel tribo pair are employed. In these experiments high normal pressures (1-3GPa) and slip speeds of approximately 50m∕s were attained during the high-speed slip event. Moreover, these experiments were designed to investigate the evolution of friction stress in response to step changes in normal pressure and also in the applied shear stress during the high-speed slip event. A step drop in normal pressure is observed to result in an exponential decay of the friction stress to a new steady-state characteristic of the current normal pressure and the current slip velocity. A step drop in applied shear stress is observed to lead to an initial drop in friction stress, which later increases toward a new steady-state friction stress level. In response to the step drop in applied shear stress the slip velocity initially increases and then decreases to a new steady-state level consistent with the new friction stress level. A modified rate and state dependent friction model that employs both velocity and normal stress dependent state variables is used to simulate the experimental results. A good correlation is found between the experimental results and the predictions of the proposed state and rate dependent friction model.

scholarly journals Effect of different rubber materials on husking dynamics of paddy rice

2012 ◽  
Vol 226 (6) ◽  
pp. 516-528
Author(s):  
A Baker ◽  
RS Dwyer-Joyce ◽  
C Briggs ◽  
M Brockfeld
Keyword(s):  
Shear Stress ◽  
High Speed ◽  
Sliding Friction ◽  
Normal Load ◽  
Normal Pressure ◽  
Applied Normal Load ◽  
Limiting Shear Stress ◽  
Governing Factor ◽  
The Coefficient Of Friction ◽  
Husk Rice

The conventional way to husk rice is to pass it between two rubber rollers that are rotating with a surface speed differential. The resulting normal pressure and shear stress causes the husk to be peeled away from the kernel. The process is suited to high-rice flow rates, but is energy intensive and can result in considerable wear to the surfaces of the rollers. The operating parameters for machines of this design are usually determined and set empirically. In this article, some experiments and calculations had been carried out in order to explore the mechanisms involved in husking rice grains using this method. A simple sliding friction rig with load cell and high-speed camera was used to observe the mechanisms that occur during husking. The husking performance of different rubbers was compared for changes in the applied normal load. It was found that grains rotate between the rubber counterfaces on initial motion before being husked. In addition, harder rubbers were found to husk a higher proportion of entrained grains at lower applied normal load. By measuring the coefficient of friction between rice and rubber samples, the shear force required to husk a given percentage of grains could be calculated and was shown to be constant regardless of rubber type. Based on the mechanism seen in the high-speed video, it was evident that there was a limiting shear stress that was the governing factor over the husked ratio.

Friction measurement and modelling in forward rod extrusion tests

2003 ◽  
Vol 217 (1) ◽  
pp. 71-82 ◽  
Author(s):  
X Tan ◽  
N Bay ◽  
W Zhang
Keyword(s):  
Steady State ◽  
Elastic Deformation ◽  
Low Carbon Steel ◽  
Friction Stress ◽  
Friction Model ◽  
Extrusion Pressure ◽  
Displacement Curve ◽  
Low Carbon ◽  
Molybdenum Disulphide ◽  
Forward Extrusion

Forward extrusion is one of the important processes in bulk metal forming. Friction stress can be estimated from the slope of the load-displacement curve at the steady state after the maximum load in a forward extrusion test. In this paper, forward rod extrusion tests are carried out to determine experimentally friction stress at various normal pressures, reductions in area, billet heights and lubrications. Tested materials include aluminium alloy, low carbon steel and stainless steel. Two lubrication methods are applied, conversion coating followed by either alkaline soap or molybdenum disulphide as the lubricant. Friction stresses are obtained from measurements of slopes of extrusion pressure-punch travel curves at the steady state stage. Normal pressures are evaluated by using Mohr's circle, in which shear flow stresses are estimated at the maximum elastic deformation points from the same extrusion pressure-punch travel curves. It is found that the relationship between normal pressure and friction stress appears linear, and therefore Coulomb's friction model fits the experimental data very well. Extrusion pressure-punch travel curves before the steady state can be divided into four stages: elastic deformation, filling container deformation, filling die aperture deformation and exiting inhomogeneous deformation.

Kinetics of elastic twinning in calcite

1962 ◽  
Vol 270 (1343) ◽  
pp. 525-537 ◽  
Keyword(s):  
Activation Energy ◽  
Shear Stress ◽  
Direct Observation ◽  
High Speed ◽  
High Speed Camera ◽  
Temperature Range ◽  
Applied Shear Stress ◽  
Velocity Of Propagation ◽  
Twin Propagation ◽  
Kinetics Of

An investigation of the effect of localized transient stresses on calcite is described. It is shown that twinning may or may not occur, depending on the duration of the stress pulse, the temperature and a factor related to the length of twin which may be formed. An hypothesis is suggested to explain the results and, from it, the velocity of propagation of twin lamellae is calculated in the temperature range from 20 to 300 °C. An activation energy for twin propagation is also calculated. Direct observation of the twinning process using a high-speed camera has confirmed the above hypothesis and results and has shown that the velocity of propagation of twin lamellae in calcite is not very dependent on the applied shear stress.

Quantitative Calculation of Dislocation Mobility

1998 ◽  
Vol 538 ◽  
Author(s):  
S. Swaminarayan ◽  
D. L. Preston
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Strain Rate ◽  
Applied Stress ◽  
New Method ◽  
Dislocation Mobility ◽  
Quantitative Calculation ◽  
Applied Shear Stress

AbstractWe present a new method to calculate the response of dislocations to applied stress. This new method, called the dislocation treadmill, can be used to study the effect of vacancies, interstitials, stresses, strain rate, temperature etc., on the steady state velocity of the dislocation. We demonstrate the use of the method by calculating the response of a dislocation to a constant applied shear stress.

scholarly journals Downdrag Loads Developed by a Floating Ice Cover: Field Experiments

1974 ◽  
Vol 11 (3) ◽  
pp. 339-347 ◽  
Author(s):  
R. Frederking
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Field Experiments ◽  
Ice Cover ◽  
Steady State Creep ◽  
Displacement Rate ◽  
Efficient Design ◽  
Shear Creep ◽  
Creep Characteristics ◽  
Applied Shear Stress

The first phase of an investigation of the vertical forces developed on a structure by a floating ice cover frozen to it is described. It is the objective of this work to develop the theoretical, experimental, and field aspects of vertically acting loads required for the more efficient design of structures subject to such loads. A load frame was constructed that would apply constant upward acting loads to wooden piles frozen into an ice cover composed mainly of snow ice. Load, ice temperatures, and movement of the pile in relation to the ice were measured.The time-dependent movement of the pile in relation to the ice exhibited creep characteristics, and these results were related to shear creep for grouted rod anchors in permafrost. Results of a previous study for WF steel H-beams in ice were also considered. The steady-state creep displacement rate for wooden piles in ice, rod anchors in permafrost, and WF steel H-beams in ice exhibited a comparable dependence on the constant applied shear stress. The steady-state creep displacement rate of a 100-mm wooden pile in snow ice at −3 °C and under a constant applied shear stress of 180 kN/m2 was about 1 mm/day.

Refined Friction Modeling for Simple Upsetting

1997 ◽  
Vol 119 (4A) ◽  
pp. 563-570 ◽  
Author(s):  
Tze-Chi Hsu ◽  
Chung-Hung Lee
Keyword(s):  
Friction Stress ◽  
Normal Pressure ◽  
Friction Model ◽  
Lubricant Film ◽  
Asperity Contact ◽  
Friction Modeling ◽  
Lubrication Regimes ◽  
Mixed Lubrication Regime ◽  
Boundary Model ◽  
Semi Empirical

A refined model for friction in lubricated simple upsetting processes which takes account of the different lubrication regimes which may occur at the workpiece/tooling interface is developed. The refined friction model considers not only the full film situation but also the mixed and boundary lubrication condition. The load carrying capacity of the lubricant in the mixed lubrication regime is evaluated by using the average flow model to treat the influence of surface roughness on lubricant flow. The mechanics of asperity contact is governed by a semi-empirical boundary model in which the plastic deformation of the workpiece is considered. The lubricant film thickness is then determined by using a shooting method to ensure that the interface pressure is partially supported by the asperity contact and partially supported by the lubricant film. The refined friction model is then combined with a rigid-plasticity finite element code to analyze the simple upsetting processes. Numerical results using the coupled codes such as the distribution of the friction stress and normal pressure, the geometry and surface topography of the deformed workpiece are compared with previous numerical and experimental investigation under different lubrication conditions. The simulation results are in good agreement with the experimental data.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

scholarly journals Direct Measurement of Stress at the Base of a Glacier

1979 ◽  
Vol 22 (86) ◽  
pp. 3-24 ◽  
Author(s):  
G. S. Boulton ◽  
E. M. Morris ◽  
A. A. Armstrong ◽  
A. Thomas
Keyword(s):  
Shear Stress ◽  
Volume Concentration ◽  
Normal Pressure ◽  
Spatial Average ◽  
Short Term ◽  
Overburden Pressure ◽  
Basal Ice ◽  
Debris Particles ◽  
Or Groups ◽  
Pressure Changes

AbstractContact stress transducers were placed in subglacial bedrock and used to monitor continuously shear stress and normal pressure changes at the contact with the overriding glacier sole 100 m beneath the surface of the Glacier d’Argentière during periods in summer 1973 and spring 1975. The measured fluctuations in normal pressure and shear stress do not appear to be related to changes in sliding velocity. Analysis of the data reveals short-term fluctuations in normal pressure and shear stress which appear to be related to the passage of individual large debris particles or groups of particles over the transducer. The shear stress appears to be a function of the volume concentration of debris in the ice. The volume concentration at any point appears to be partially dependent on a “streaming” process by which basal debris-rich ice tends to flow around the lateral flanks of hummocks on the glacier bed. Where sub-glacial cavities occur, this streaming effect appears to be dependent on the extent of cavitation and thus on ice overburden pressure and velocity. It is suggested that this process can account for an apparent lag between changes in normal pressure and shear stress.The maximum ratio between shear and normal stress averaged over a period of 10 min was 0.44. This is equivalent to a spatial average over 0.3 cm. Debris concentrations in basal ice of up to 43% by volume occurred. It is suggested that concentrations of this order are common at the base of temperate glaciers and thus that a significant part of the drag at the base of a glacier may be contributed by frictional interactions between the basal-debris load and the bed.

The Application of FEA in High-Speed Cutting

2011 ◽  
Vol 287-290 ◽  
pp. 104-107
Author(s):  
Lian Qing Ji ◽  
Kun Liu
Keyword(s):  
High Speed ◽  
Feeding Rate ◽  
Cutting Tools ◽  
Cutting Speed ◽  
Cutting Parameters ◽  
Material Model ◽  
Friction Model ◽  
Cutting Depth ◽  
High Speed Cutting ◽  
Key Technologies

The history and application of the FEA are briefly presented in this paper. Several key technologies such as the building of material model, the establishment of the chip - tool friction model as well as meshing are described. Taking the high-speed cutting of titanium alloy (Ti - 10V - 2Fe - 3Al) as an example , reasonable cutting tools and cutting parameters are determinted by simulating the influences of cutting speed, cutting depth and feeding rate on the cutting parameters using FEA.

scholarly journals Structural Damping with Friction Beams

2008 ◽  
Vol 15 (3-4) ◽  
pp. 291-298 ◽  
Author(s):  
L. Gaul ◽  
J. Roseira ◽  
J. Becker
Keyword(s):  
Linear Models ◽  
Natural Frequencies ◽  
Normal Force ◽  
Normal Pressure ◽  
Friction Model ◽  
Mode Shapes ◽  
Work Piece ◽  
Numerical Predictions ◽  
Double Beam ◽  
Excitation Force

In the last several years, there has been increasing interest in the use of friction joints for enhancing damping in structures. The joints themselves are responsible for the major part of the energy dissipation in assembled structures. The dissipated work in a joint depends on both the applied normal force and the excitation force. For the case of a constant amplitude excitation force, there is an optimal normal force which maximizes the damping. A ‘passive’ approach would be employed in this instance. In most cases however, the excitation force, as well as the interface parameters such as the friction coefficient, normal pressure distribution, etc., are not constant. In these cases, a ‘semi-active’ approach, which implements an active varying normal force, is necessary. For the ‘passive’ and ‘semi-active’ approaches, the normal force has to be measured. Interestingly, since the normal force in a friction joint influences the local stiffness, the natural frequencies of the assembled structure can be tuned by adjusting the normal force. Experiments and simulations are performed for a simple laboratory structure consisting of two superposed beams with friction in the interface. Numerical simulation of the friction interface requires non-linear models. The response of the double beam system is simulated using a numerical algorithm programmed inMATLABwhich models point-to-point friction with the Masing friction model. Numerical predictions and measurements of the double beam free vibration response are compared. A practical application is then described, in which a friction beam is used to damp the vibrations of the work piece table on a milling machine. The increased damping of the table reduces vibration amplitudes, which in turn results in enhanced surface quality of the machined parts, reduction in machine tool wear, and potentially higher feed rates. Optimal positioning of the friction beams is based on knowledge of the mode shapes, which are obtained from experimental modal analysis. The modal damping and the natural frequencies for the two dominant modes are measured for several combinations of excitation force and normal force.

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