A Numerical Simulation of Interfacial Slip and its Role in Friction

2012 ◽  
Author(s):  
Jeffrey L. Streator
Keyword(s):  
Friction Coefficient ◽  
Friction Force ◽  
Lateral Displacement ◽  
Reaction Force ◽  
Static Friction ◽  
Constant Load ◽  
Interfacial Slip ◽  
Stick Slip ◽  
Elastic Slab ◽  
Static Coefficient Of Friction

The transition from static friction to kinetic friction results from the attainment of a point of instability, whereby interfacial slip becomes more energetically favorable than sticking. Such an instability is explored in this work via a plane-strain elastostatic analysis. A rigid pin of prescribed geometry is placed in contact with an elastic slab and translated horizontally under conditions of constant load. An intrinsic static coefficient of friction is prescribed, which limits the ratio of shear stress to contact pressure at each location within the interface. Additionally, the surface of the elastic slab is given a desired undulation to simulate the effects of surface roughness. As the pin is translated horizontally, a lateral reaction force (i.e., friction force) is developed and is observed to grow nearly linearly with increasing lateral displacement. At a critical point, a substantial portion of the interface experiences slip, leading to a large decrease in the friction force and thereby revealing a stick-slip behavior. It is found that the overall (macroscopic) static friction coefficient can be significantly less than the intrinsic friction coefficient and that the presence of even a small amount of roughness can have a large effect on the friction force.

Uncertainty Analysis of CNC Machine Tools Based on Monte Carlo Method

2020 ◽  
Vol 900 ◽  
pp. 9-13
Author(s):  
Yunn Lin Hwang ◽  
Thi Na Ta
Keyword(s):  
Monte Carlo ◽  
Friction Coefficient ◽  
Numerical Simulations ◽  
Friction Force ◽  
System Performance ◽  
Numerical Control ◽  
Machining Accuracy ◽  
Force Model ◽  
Stick Slip ◽  
System Components

The uncertainty of mechanical system performance is strongly influenced by the properties of system components such as mass, stiffness-damping coefficient, and friction coefficient. Based on computational simulations, the system performance under uncertainty conditions can be estimated. However, the nonlinear dynamic behavior of friction is difficult to simulate in numerical simulations, this research is therefore employed a smooth stick-slip friction force model instead of the Coulomb friction force model. Monte Carlo simulation (MCS) combined with multibody dynamic (MBD) simulation is proposed to evaluate the uncertainty characteristics of the system components and stick-slip friction force between two contacting bodies. Numerical simulations applied the proposed method were performed to consider the effects of uncertainty of friction coefficient on the machining accuracy of a three axes CNC (Computer Numerical Control) machine tool.

scholarly journals Anisotropy of Graphene Nanoflake Diamond Interface Frictional Properties

Materials ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1425 ◽  
Author(s):  
Ji Zhang ◽  
Ehsan Osloub ◽  
Fatima Siddiqui ◽  
Weixiang Zhang ◽  
Tarek Ragab ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Friction Force ◽  
Md Simulations ◽  
Equilibrium Distance ◽  
Sliding Angle ◽  
Stick Slip ◽  
Single Crystalline ◽  
Frictional Properties ◽  
Diamond Substrate ◽  
Graphene Nanoflake

Using molecular dynamics (MD) simulations, the frictional properties of the interface between graphene nanoflake and single crystalline diamond substrate have been investigated. The equilibrium distance between the graphene nanoflake and the diamond substrate has been evaluated at different temperatures. This study considered the effects of temperature and relative sliding angle between graphene and diamond. The equilibrium distance between graphene and the diamond substrate was between 3.34 Å at 0 K and 3.42 Å at 600 K, and it was close to the interlayer distance of graphite which was 3.35 Å. The friction force between graphene nanoflakes and the diamond substrate exhibited periodic stick-slip motion which is similar to the friction force within a graphene–Au interface. The friction coefficient of the graphene–single crystalline diamond interface was between 0.0042 and 0.0244, depending on the sliding direction and the temperature. Generally, the friction coefficient was lowest when a graphene flake was sliding along its armchair direction and the highest when it was sliding along its zigzag direction. The friction coefficient increased by up to 20% when the temperature rose from 300 K to 600 K, hence a contribution from temperature cannot be neglected. The findings in this study validate the super-lubricity between graphene and diamond and will shed light on understanding the mechanical behavior of graphene nanodevices when using single crystalline diamond as the substrate.

Static Friction and Initiation of Slip at Magnetic Head-Disk Interfaces

1999 ◽  
Vol 122 (1) ◽  
pp. 246-256 ◽  
Author(s):  
S. Wang ◽  
K. Komvopoulos
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Film Thickness ◽  
Contact Resistance ◽  
Friction Force ◽  
Static Friction ◽  
Electric Contact ◽  
Magnetic Head ◽  
Friction Coefficients ◽  
Lubricant Films

The apparent friction force and electric contact resistance at the magnetic head-disk interface were measured simultaneously for textured and untextured disks lubricated with perfluoropolyether films of different thicknesses. The initial stick time, representing the time between the application of a driving torque and the initiation of interfacial slip, was determined based on the initial rise of the apparent friction force and the abrupt increase of the electric contact resistance. Relatively thin lubricant films yielded very short initial stick times and low static friction coefficients. However, for a film thickness comparable to the equivalent surface roughness, relatively long initial stick times and high static friction coefficients were observed. The peak value of the apparent friction coefficient was low for thin lubricant films and increased gradually with the film thickness. The variations of the initial stick time, static friction coefficient, and peak friction coefficient with the lubricant film thickness and surface roughness are interpreted in the context of a new physical model of the lubricated interface. The model accounts for the lubricant coverage, effective shear area, saturation of interfacial cavities, limited meniscus effects, and the increase of the critical shear stress of thin liquid films due to the solid-like behavior exhibited at a state of increased molecular ordering. [S0742-4787(00)03101-5]

Compensation of Stick-Slip Phenomenon in an Electrical Actuator

2003 ◽  
Vol 15 (4) ◽  
pp. 398-405 ◽  
Author(s):  
R. Merzouki ◽  
◽  
J. C. Cadiou ◽  
N. K. M'Sirdi
Keyword(s):  
Friction Force ◽  
Static Friction ◽  
Adaptive Controller ◽  
Nonlinear Observer ◽  
Convergence To Equilibrium ◽  
Dynamic Friction ◽  
Slip Effect ◽  
Stick Slip ◽  
Electrical Actuator ◽  
Slip Phenomenon

In mechanical systems involving low-speed motion, consisting of a succession of jumps and stops, as in trained wagons or manipulated robots, control usually exhibits error when the static friction force exceeds the dynamic friction force in what is known as the stick-slip effect. We developed a nonlinear observer to determine the friction force of contact during motion and to compensate for its effect. Simulation and experimental results show global convergence to equilibrium and good performance by the adaptive controller.

STATIC FRICTION OF REVERSE STEEL–ELASTOMER SLIDING PAIRS

Tribologia ◽  
2018 ◽  
Vol 279 (3) ◽  
pp. 147-151
Author(s):  
Wojciech WIELEBA ◽  
Mariusz OPAŁKA
Keyword(s):  
Friction Coefficient ◽  
Friction Force ◽  
Polymeric Materials ◽  
Static Friction ◽  
Steel Sample ◽  
Thermoplastic Elastomers ◽  
Wear Process ◽  
Polymer Metal ◽  
Deformation Component ◽  
Deformation Area

Sliding cooperation of materials with different hardness (deformability), e.g., a polymeric material cooperating with metallic materials, occurs in machine elements in one of the following two variants: a conventional pair or a reverse pair. In the case of the conventional sliding pair, the deformation area (contact area) of the sliding materials does not move on the surface of the polymer element during their cooperation. In the case of reverse pairs, the contact surface changes its position when moving on the surface of the polymer element. Depending on the variant of the sliding pair, the differences in the friction and wear process of polymer material can be observed. Tribological investigations of chosen sliding pairs (elastomer on steel or steel on elastomer) in the static friction were carried out on the rig. The polymeric materials selected for the tests were thermoplastic elastomers TPU, PUR, and silicone rubber SI. These materials co-operated with C45 steel in the different contact pressures (p = 0.1 – 0.26 MPa) under dry friction or mixed lubrication conditions (hydraulic oil Hipol HLP-68). Based on the recorded value of the friction force Ft, the values of static coefficients of friction μstat were determined. The test results showed a significant influence of the variant of the combination of materials (metal-polymer or polymer-metal) on the value of the friction coefficient. In all tested pairs in which steel sample (pin) slid against elastomeric plates, the friction coefficient was higher than in the case when the elastomeric sample (pins) cooperated with steel counterfaces (plates). The main reason is the considerable value of the deformation component of the friction force. This is probably due to the displacement of the elastomer deformation area in its surface layer and energy dissipation as a result of stress-strain hysteresis in the elastomeric material, as in the case with reversed pairs.

A Model for Study of Stick-Slip Vibrations in Caliper-Disc Brake Systems

2000 ◽  
Author(s):  
Glenn Meinhardt ◽  
Kambiz Farhang
Keyword(s):  
Friction Coefficient ◽  
Dynamic Properties ◽  
Equations Of Motion ◽  
Static Friction ◽  
Friction Material ◽  
Theoretical Treatment ◽  
Disc Brake ◽  
Vehicle Speed ◽  
Coupling Effects ◽  
Stick Slip

Abstract Friction-induced vibration in caliper-disc brake systems is examined using mathematical formulations based on the lumped-parameter approach. The theoretical treatment of the system considers the kinematic and dynamic properties of the caliper motion, accounting for the slider translation and flexure as well as rotational stiffness of the caliper assembly. In addition, compressive and shear properties of the friction material is included in the derivation of the model. The geometric and material/friction coupling effects are also included in the model. The geometric coupling effects arise from the kinematic nature of the caliper-disc brake system. The material/friction coupling effects are due to the compressive properties of the pad friction material leading to the determination of instantaneous pad/rotor average pressure and, thereby, its influence on the transmitted braking torque due to frictional contact. The coefficients of friction of the pad are represented by an exponential function (Larsson and Farhang, 1997) that describes the decay from the static friction coefficient to the kinetic friction coefficient as the relative velocity between the pad and rotor is increased. The resulting equations of motion are a set of second-order ordinary differential equations. Results are presented using an initial vehicle speed of 55 miles per hour.

A Model for Contact and Static Friction of Nominally Flat Rough Surfaces Under Full Stick Contact Condition

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
D. Cohen ◽  
Y. Kligerman ◽  
I. Etsion
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Friction Force ◽  
Contact Area ◽  
Rough Surfaces ◽  
Normal Load ◽  
Static Friction ◽  
Contact Condition ◽  
Maximum Friction ◽  
Static Friction Coefficient

A model for elastic-plastic nominally flat contacting rough surfaces under combined normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of junction growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results.

Robust Nonlinear Stick-Slip Friction Compensation

1991 ◽  
Vol 113 (4) ◽  
pp. 639-645 ◽  
Author(s):  
S. C. Southward ◽  
C. J. Radcliffe ◽  
C. R. MacCluer
Keyword(s):  
Friction Force ◽  
Direct Method ◽  
Piecewise Linear ◽  
Static Friction ◽  
Force Term ◽  
Stick Slip ◽  
Servo Systems ◽  
Stability And Control ◽  
Nonlinear Compensation ◽  
And Control

A nonlinear compensation force for stick-slip friction is developed to supplement a proportional + derivative control law applied to a one-degree-of-freedom mechanical system. Inertial control objects acted on by stick-slip friction are common mechanical components in mechanical servo systems and the conceptual model chosen for this investigation is a mass sliding on a rough surface. The choice of a discontinuous compensation force is motivated by the requirement that the desired reference be a unique equilibrium point of the system. The stick-slip friction force, modelled with a sticking force term and a slipping force term, generates discontinuous state derivatives. A Lyapunov function is introduced to prove global asymptotic stability of the desired reference using a modification of the direct method for discontinuous systems. Stability is verified numerically as well as experimentally. The nonlinear compensation force is robust with respect to the character of the slipping force which is assumed to lie within a piecewise linear band. Exact knowledge of the static friction force levels is not required, only upper bounds for these levels. Stability and control effectiveness is verified analytically, numerically and experimentally on a laboratory test stand.

scholarly journals Effect of Stick - Slip Phenomena between Human Skin and UHMW Polyethylene

2021 ◽  
Vol 29 (3) ◽  
Author(s):  
Emad Kamil Hussein ◽  
Kussay Ahmed Subhi ◽  
Tayser Sumer Gaaz
Keyword(s):  
Friction Coefficient ◽  
Human Skin ◽  
Coefficient Of Friction ◽  
Normal Load ◽  
Static Friction ◽  
Time Interval ◽  
Dynamic Friction ◽  
Sliding Velocity ◽  
Stick Slip ◽  
The Coefficient Of Friction

The present paper investigates experimentally effect of applied load and different velocity on the coefficient of friction between two interacting surfaces (human skin and Ultra-high-molecular-weight polyethylene (UHMW- polyethylene) at static and dynamic friction. It is possible to conclude specific point based on the above practical part and frictional analysis of this investigation as the most important mechanical phenomenon was creep has been observed a stick time interval where the static friction force is significantly increased during this stroke. The analytical model for stick-slip of skin and UHMWPE is proposed. The difference between static and kinetic friction defines the amplitude of stick-slip phenomena. The contact pressure, the sliding velocity, and rigidity of system determine the stability conditions of the movement between skin and UHMWPE. Experiments were carried out by developing a device (friction measurement). Variations of friction coefficient during the time at different normal load 4.6 and 9.2 N and low sliding velocity 4, 5, 6 and 7 mm/min were experimentally investigated. The results showed that the friction coefficient varied with the normal load and low sliding velocity. At static friction, the coefficient of friction decreased when the time increases, whereas, at dynamic friction, the coefficient of friction decreased when the time increased at normal load 4.6 and 9.2 N.

scholarly journals Fracture mechanics implications for apparent static friction coefficient in contact problems involving slip-weakening laws

2015 ◽  
Vol 471 (2180) ◽  
pp. 20150271 ◽  
Author(s):  
A. Papangelo ◽  
M. Ciavarella ◽  
J. R. Barber
Keyword(s):  
Friction Coefficient ◽  
Static Friction ◽  
Contact Problems ◽  
Adhesive Contact ◽  
Small Scale ◽  
Force Measurements ◽  
Scale Yielding ◽  
Static Coefficient Of Friction ◽  
Dynamic Slip ◽  
Slip Distance

We consider the effect of differing coefficients of static and dynamic friction coefficients on the behaviour of contacts involving microslip. The classic solutions of Cattaneo and Mindlin are unchanged if the transition in coefficients is abrupt, but if it occurs over some small slip distance, the solution has some mathematical similarities with those governing the normal tractions in adhesive contact problems. In particular, if the transition to dynamic slip occurs over a sufficiently small area, we can identify a ‘JKR’ approximation, where the transition region is condensed to a line. A local singularity in shear traction is then predicted, with a stress-intensity factor that is proportional to the square root of the local contact pressure and to a certain integral of the friction coefficient–slip distance relation. We can also define an equivalent of the ‘small-scale yielding’ criterion, which enables us to assess when the singular solution provides a good approximation. One consequence of the results is that the static coefficient of friction determined from force measurements in experiments is significantly smaller than the value that holds at the microscale.

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