Lubricant Performance in Magnetic Thin Film Disks With Carbon Overcoat—Part I: Dynamic and Static Friction

1991 ◽  
Vol 113 (1) ◽  
pp. 22-31 ◽  
Author(s):  
J. L. Streator ◽  
B. Bhushan ◽  
D. B. Bogy
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Static Friction ◽  
Disk Surface ◽  
Stick Slip ◽  
Sliding Speed ◽  
Friction Coefficients ◽  
Friction Forces ◽  
Strong Adhesion ◽  
Lubricant Viscosity

Static and dynamic friction coefficients are presented for an Al2O3·TiC slider in contact with 130 mm carbon-coated rigid thin film disks lubricated with several different perfluoropolyether lubricants. The lubricants tested include three nonpolar liquid lubricants and one polar liquid lubricant with dihydroxyl end groups. The effects of lubricant film thickness, disk surface topography, sliding speed and lubricant viscosity are investigated. In many cases, the interfaces exhibited a sharp increase in the dynamic and static friction coefficients after a certain film thickness was reached, due to strong adhesion in the interface. In most cases, the lubricant thickness for the onset of high friction forces was found to increase with increasing disk surface roughness, lubricant viscosity and sliding speed. Under certain conditions stick/slip of the slider occurred during which the static friction increased with time of contact. The various data suggest that the rate at which strong adhesion develops depends on the lubricant viscosity.

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]

scholarly journals Tribological Behavior of Very Thin Confined Films

2000 ◽  
Vol 651 ◽  
Author(s):  
M. H. Müser
Keyword(s):  
Thin Film ◽  
Thermal Diffusion ◽  
Tribological Properties ◽  
Tribological Behavior ◽  
Static Friction ◽  
Generic Model ◽  
Stick Slip ◽  
Normal Contact ◽  
Flat Surfaces ◽  
Contact Pressures

AbstractThe tribological properties of two smooth surfaces in the presence of a thin confined film are investigated with a generic model for the interaction between two surfaces and with computer sim- ulations. It is shown that at large normal contact pressures, an ultra thin film automatically leads to static friction between two flat surfaces - even if the surfaces are incommensurate. Commen- surability is nevertheless the key quantity to understand the tribological behavior of the contact. Qualitative differences between commensurate and incommensurate contacts remain even in the presence of a thin film. The differences mainly concern the thermal diffusion of the contact and the transition between smooth sliding and stick-slip.

Friction of Different Surface Layer of Pavements in Contact With a Rubber

2005 ◽  
Author(s):  
F. Hammoum ◽  
S. Hamlat ◽  
P. Y. Hicher
Keyword(s):  
Surface Layer ◽  
Friction Velocity ◽  
Static Friction ◽  
Dynamical Behaviour ◽  
Experimental Investigations ◽  
Stick Slip ◽  
Friction Forces ◽  
Physical Mechanisms ◽  
Stick Slip Motion ◽  
Rubber Block

We analyse the physical mechanisms taking place in unlubricated friction between surface layer of pavements and a piece of rubber at low sliding speeds < 200 mm/s. This analysis is based on extensive experimental investigations of the load and velocity dependences of dynamic friction forces. The dynamical behaviour caused by dry friction is studied for a rubber-block system pulled with constant velocity over a surface layer of pavements. The dynamical consequences of a general type of phenomenological friction law (stick-time dependent static friction, velocity-dependent kinetic friction) are investigated. Three types of motion are possible: stick-slip motion, continuous sliding, and oscillations without sticking events. In the last case, we propose values of friction coefficient of different surface layer of pavements.

scholarly journals Nonlinear Dynamics of Torsional Waves in a Drill-string Model with Spatial Extent

2010 ◽  
Vol 16 (7-8) ◽  
pp. 1049-1065 ◽  
Author(s):  
David A.W. Barton ◽  
Bernd Krauskopf ◽  
R. Eddie Wilson
Keyword(s):  
String Model ◽  
Static Friction ◽  
Drill String ◽  
Numerical Continuation ◽  
Oil Well ◽  
Neutral Delay ◽  
Torsional Mode ◽  
Stick Slip ◽  
Friction Forces ◽  
Torsional Waves

In this paper we investigate the dynamics and bifurcations of an oil-well drill-string model that takes the form of a neutral delay differential equation. We consider the torsional mode of the drill-string and investigate the associated stick-slip motion. To analyze the model we develop numerical continuation routines based on Fourier methods since existing routines based on polynomial approximations are unable to cope with the presence of arbitrarily weakly damped modes. We find “resonance peaks” in the dynamics where a high-frequency mode is superimposed on the underlying periodic behavior, causing large torsional waves in the drill-string. We show that the resonance peaks are robust to small perturbations in the friction parameters but disappear if static friction forces are neglected completely.

Lubricant Performance in Magnetic Thin Film Disks With Carbon Overcoat—Part II: Durability

1991 ◽  
Vol 113 (1) ◽  
pp. 32-37 ◽  
Author(s):  
J. L. Streator ◽  
B. Bhushan ◽  
D. B. Bogy
Keyword(s):  
Thin Film ◽  
Disk Surface ◽  
Low Friction ◽  
Carbon Overcoat ◽  
Liquid Lubricant ◽  
Carbon Coated ◽  
Friction Measurements ◽  
Lubricant Performance ◽  
Lubricant Viscosity ◽  
Pfpe Lubricants

Several perfluoropolyether (PFPE) lubricants are evaluated in terms of their ability to maintain low friction and resist wear. The lubricants tested include three nonpolar liquid lubricants and one polar liquid lubricant. Dynamic friction measurements are presented for an IBM 3380-type slider in contact with 130 mm carbon-coated thin film disks. Disk surface run-in and disk durability are evaluated by monitoring the friction force during constant speed sliding. Disk run-in is presented as a function of lubricant thickness and sliding speed, while disk durability is determined for different disk topographies and lubricant thicknesses. It was found that lubricant viscosity was well correlated with the amount of disk run-in and the number of sliding cycles until disk failure. It is proposed that the greater wear durability of the less viscous lubricants can be attributed to their greater mobility on the disk surface.

Static Friction Modeling in the Presence of Soft Thin Metallic Films

2001 ◽  
Vol 124 (1) ◽  
pp. 27-35 ◽  
Author(s):  
Zhiqiang Liu ◽  
Anne Neville ◽  
R. L. Reuben
Keyword(s):  
Thin Film ◽  
Surface Roughness ◽  
Friction Coefficient ◽  
Film Thickness ◽  
Rough Surfaces ◽  
Contact Stiffness ◽  
Surface Film ◽  
Static Friction ◽  
Static Friction Coefficient ◽  
Light Load

A numerical model is presented for computing the static friction coefficient of rough surfaces with a soft thin film. In the calculation, an improved model, based on that due to Derjaguin et al., is used in conjunction with an elastic-plastic contact model for contact with a soft coating. The effects of the film thickness and surface roughness on the static friction coefficient and contact are investigated. The numerical results reflect published experimental observations and show the static friction coefficient depends strongly on surface film thickness, external force and surface roughness. The static friction coefficient (μ) increases with the surface film thickness when the plasticity index ψ⩾0.5 whilst μ increases with decreasing film thickness in the very thin film regime when ψ=0.25 and F/AnE<10−4. For real rough surfaces, contact and friction behavior is probably heavily influenced by the existence of such soft, thin surface films, which increase the contact area due to plastic deformation of the film and the contact stiffness of the surface in the case of thin film and light load.

Friction Induced Lateral Vibrations of a Tape Moving in Contact With a Slewing Head

2013 ◽  
Author(s):  
Hankang Yang ◽  
Sinan Müftü
Keyword(s):  
Dynamic Systems ◽  
Static Friction ◽  
Stick Slip ◽  
Friction Forces ◽  
Dynamic Motion ◽  
Lateral Vibrations ◽  
Head Assembly ◽  
Restoring Forces ◽  
Sudden Release ◽  
Friction Induced Vibration

In dynamic systems, motion transfer due to frictional effects could result in quasi-harmonic oscillations and stick-slip, with potentially undesirable effects. The track-following motion of a read/write (RW) head-assembly transfers frictional forced onto the translating tape. This, in turn, has the potential to introduce unwanted dynamic motion into the system, and to affect the track following operation. In extreme cases the tape could stick onto the head-assembly, which could then create the potential for sudden release (slip) of the tape, if the restoring forces exceed the static friction forces. Due to longitudinal tape motion, stick is only a possibility during start-stop operations. However, with increasingly smoother tape, the effects of friction induced vibration (FrIV) could become problematic for the next generation of tape drives.

scholarly journals Slipping–rolling transitions of a body with two contact points

2021 ◽  
Author(s):  
Mate Antali ◽  
Gabor Stepan
Keyword(s):  
Rigid Body ◽  
Contact Point ◽  
Static Friction ◽  
Rigid Body Dynamics ◽  
Contact Forces ◽  
Friction Forces ◽  
Contact Points ◽  
Body Dynamics ◽  
Coulomb Model ◽  
Rigid Surfaces

AbstractIn this paper, the general kinematics and dynamics of a rigid body is analysed, which is in contact with two rigid surfaces in the presence of dry friction. Due to the rolling or slipping state at each contact point, four kinematic scenarios occur. In the two-point rolling case, the contact forces are undetermined; consequently, the condition of the static friction forces cannot be checked from the Coulomb model to decide whether two-point rolling is possible. However, this issue can be resolved within the scope of rigid body dynamics by analysing the nonsmooth vector field of the system at the possible transitions between slipping and rolling. Based on the concept of limit directions of codimension-2 discontinuities, a method is presented to determine the conditions when the two-point rolling is realizable without slipping.

Organic thin film thickness-dependent photocurrents polarity in graphene heterojunction phototransistor

Carbon ◽  
2021 ◽  
Vol 178 ◽  
pp. 506-514
Author(s):  
Meiyu He ◽  
Jiayue Han ◽  
Xingwei Han ◽  
Jun Gou ◽  
Ming Yang ◽  
...  
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Organic Thin Film ◽  
Thin Film Thickness
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