A comprehensive kinetic meniscus model for prediction of long-term static friction

1999 ◽  
Vol 86 (8) ◽  
pp. 4649-4656 ◽  
Author(s):  
Sameera K. Chilamakuri ◽  
Bharat Bhushan
Keyword(s):  
Static Friction ◽  
Meniscus Model

Experimental Study of Long-Term Static Friction and Magnetic Slider/Disk Interplanar Separation

1996 ◽  
Vol 118 (1) ◽  
pp. 12-20 ◽  
Author(s):  
C. T. Gerber ◽  
B. Bhushan ◽  
N. V. Gitis
Keyword(s):  
Experimental Study ◽  
Parallel Plate ◽  
Static Friction ◽  
Lubricant Thickness

Capacitance between a slider and disk was measured to relate slider/disk interplanar separation to static friction. The parallel plate capacitance formula was used to convert the capacitance into separation with a resolution of less than 1 nm. Separation and coefficient of static friction (stiction) were measured using assorted lubricant thicknesses with and without bonding on polished and textured disks. Separation was measured during contact start/stop (CSS) and long term slider dwell times, after which static friction was measured. Polished disks had high stiction events with smaller separations during and after the stiction event, unlike textured disks. Long-term dwell studies showed the coefficient of static friction and slider micro descent (decrease in interplanar separation) to be greatest with greater lubricant thickness and polished disks. Static friction and separation with bonded and unlubricated disks were time independent.

The Role of Relative Humidity, Surface Roughness and Liquid Build-Up on Static Friction Behavior of the Head/Disk Interface

1993 ◽  
Vol 115 (1) ◽  
pp. 28-35 ◽  
Author(s):  
Hong Tian ◽  
Takeo Matsudaira
Keyword(s):  
Surface Roughness ◽  
Relative Humidity ◽  
Static Friction ◽  
Height Distribution ◽  
Head Disk Interface ◽  
Friction Behavior ◽  
Friction Forces ◽  
Disk Interface ◽  
Percent Relative Humidity

Stiction at the head/disk interface has become one of the major concerns as smoother surfaces are required to achieve lower flying heights of magnetic heads over magnetic disks. In this paper, static friction forces on three types of disk samples with different surface roughness values were measured at various relative humidities. It was found that static friction coefficients were well correlated with total thickness of liquid (lubricant and adsorbed water) at the head/disk interface. The experimental data also agreed fairly well with the calculated values based on a proposed stiction model. It is implied in the stiction model that the bearing ratio or the shape of asperity height distribution, especially the part of high asperities, determines the stiction force. Moreover, long-term stiction was investigated on the unlubricated disk surfaces at 80 percent relative humidity and on the lubricated disks at 5 percent relative humidity to separate the effects of water build-up and lubricant build-up at the head/disk interface. It appears that long-term stiction occurs only when enough mobile lubricant is present and the thickness of liquid at the head/disk interface is close to a critical thickness value which is related to surface roughness values.

Kinetic Meniscus Model for Prediction of Rest Stiction

1998 ◽  
Vol 120 (1) ◽  
pp. 42-50 ◽  
Author(s):  
B. Bhushan ◽  
C. A. Kotwal ◽  
S. K. Chilamakuri
Keyword(s):  
Static Friction ◽  
Disk Drives ◽  
Equilibrium Time ◽  
Smooth Disk ◽  
Asperity Contacts ◽  
Rest Time ◽  
First Time ◽  
Stationary Contact ◽  
Computer Disk ◽  
Meniscus Model

The time dependence of static friction is an important aspect of tribological studies whereby the static friction increases with an increase in the time of stationary contact (rest static friction or rest stiction). This effect is commonly observed in computer disk drives especially at high humidities, in which the static friction increases rapidly with an increase in rest time between some head slider and the disk surfaces. For the first time, a comprehensive kinetic meniscus model is proposed to explain this phenomenon, both for a single asperity and multiple asperity contacts at a liquid mediated interface. It is found that the static friction increases up to a certain equilibrium time with a power law relationship after which it remains constant. The equilibrium time is dependent on the liquid film thickness, the liquid viscosity and the contact geometry. The model developed is applied to a rough textured disk, a polished disk and a super smooth disk. To study the effect of the scan size on the meniscus force, the static friction is calculated by using roughness parameters obtained from measurements at different scan sizes.

Bridging Long- and Short-term Behavior Shows Fault Strength as a Strain-average

2020 ◽  
Author(s):  
Ylona van Dinther
Keyword(s):  
Subduction Zones ◽  
Large Scale ◽  
Dominant Role ◽  
Mechanical Energy ◽  
Fluid Pressure ◽  
Static Friction ◽  
Short Term ◽  
Friction Coefficients ◽  
Fault Strength

<p><span>The strength of faults is subject of an important debate throughout various Earth Scientific disciplines. Different scientific communities have different perspectives with respect to appropriate values for friction coefficients μ. Geodynamicists with a long-term perspective require very low effective strengths (μ<0.05), while at the same time realizing mountains need to be sustained as well. Geologists and seismologists typically start from Byerlee friction coefficients of 0.6<μ<0.85, whereas rock mechanics experiments at high seismic slip rates show short-term low dynamic friction values of 0.03<μ<0.3. Here I show that both long- and short-term approaches can be made more compatible through considering that a regional or global frictional strength should be approached as a strain-averaged quantity. Doing this accounts for large variations of strain in both time and space. What matters for large-scale models is that most deformation occurs over a very small space and time during which friction is exceptionally low, thus making the representative long-term strength low. This is supported by seismo-thermo-mechanical models that self-consistently simulate the dynamics of both long-term subduction and short-term seismogenesis. The latter sustain mountain building, while representative earthquake-like events occur on faults with pore fluid pressure-effective static friction coefficients between 0.125 and 0.005 (or 0.75<Pf/Ps<0.99). These low friction values suggest faults are weak and suggest the dominant role of fluid pressures in weakening faults in subduction zones. This is confirmed in analytical considerations based on mechanical energy dissipation, which provide an equation to calculate the long-term fault strength as a strain-average quantity. Constraining the four parameters in this equation by observations confirms that fluid weakening is more important for long-term weakening than dynamic frictional weakening and low static friction coefficients. From the short-term perspective of modeling earthquake rupture dynamics it is now also becoming evident that fluid overpressured faults are preferable. They namely facilitate the incorporation of laboratory-observed dynamic weakening (70-90%) by limiting the stress drop to reasonable values. In summary, this cross-scale perspective supports long-term effective friction values in the range of about 0.03 to 0.2.</span></p>

Static and Clinging Friction of Pivot Bearings

1944 ◽  
Vol 151 (1) ◽  
pp. 274-284
Author(s):  
M. C. Hunter
Keyword(s):  
Stainless Steel ◽  
Coefficient Of Friction ◽  
Rapid Growth ◽  
Static Friction ◽  
Clear Distinction ◽  
Special Apparatus ◽  
The Coefficient Of Friction

The author points out the clear distinction which has to be drawn between kinetic and static friction, and describes the special apparatus used in the investigation carried out to determine the static friction of various combinations of metals, including stainless steel and duralumin, under several conditions of dry and viscous lubrication. The paper stresses the effect of time, and gives data showing the rapid growth of the coefficient of friction during the first twenty-four hours at rest, and the subsequent increases over a period of five days. A series of long-term tests of thirty, sixty, and ninety days, on a selected number of specimens, provides a direct comparison from which the relative merits of the various combinations of materials is drawn. Evidence is provided suggesting advantages to be derived from the use of graphite as a preventative of clinging friction. In conclusion, an explanation is put forward as to the possible causes responsible for the building up of friction with the passage of time.

scholarly journals Wax-oil lubricants to reduce the shear between skin and PPE

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Kian Kun Yap ◽  
Manoj Murali ◽  
Zhengchu Tan ◽  
Xue Zhou ◽  
Luli Li ◽  
...  
Keyword(s):  
Olive Oil ◽  
Coefficient Of Friction ◽  
Static Friction ◽  
Mineral Oil ◽  
The Coefficient Of Friction ◽  
Friction Measurements ◽  
Lubricant Application ◽  
Static Coefficient Of Friction

AbstractProlonged use of tight-fitting PPE, e.g., by COVID-19 healthcare workers leads to skin injuries. An important contributor is the shear exerted on the skin due to static friction at the skin-PPE interface. This study aims to develop an optimised wax-oil lubricant that reduces the friction, or shear, in the skin-PPE contact for up to four hours. Lubricants with different wax-oil combinations were prepared using beeswax, paraffin wax, olive oil, and mineral oil. In-vivo friction measurements involving seven participants were conducted by sliding a polydimethylsiloxane ball against the volar forearms to simulate the skin-PPE interface. The maximum static coefficient of friction was measured immediately and four hours after lubricant application. It was found that the coefficient of friction of wax-oil lubricants is mainly governed by the ratio of wax to oil and the thermal stability and morphology of the wax. To maintain long-term lubricity, it is crucial to consider the absorption of oil into the PPE material. The best performing lubricant is a mixture of 20 wt% beeswax, 40 wt% olive oil, and 40 wt% mineral oil, which compared to unlubricated skin, provides 87% (P = 0.0006) and 59% (P = 0.0015) reduction in instantaneous and 4-h coefficient of friction, respectively.

scholarly journals Wax-Oil Lubricants to Reduce the Shear Between Skin and PPE

2021 ◽  
Author(s):  
Kian Kun Yap ◽  
Manoj Murali ◽  
Zhengchu Tan ◽  
Xue Zhou ◽  
Luli Li ◽  
...  
Keyword(s):  
Olive Oil ◽  
Coefficient Of Friction ◽  
Static Friction ◽  
Mineral Oil ◽  
The Coefficient Of Friction ◽  
Friction Measurements ◽  
Lubricant Application ◽  
Static Coefficient Of Friction

Abstract Prolonged use of tight-fitting PPE, e.g., by COVID-19 healthcare workers leads to skin injuries. An important contributor is the shear exerted on the skin due to static friction at the skin-PPE interface. This study aims to develop an optimised wax-oil lubricant that reduces the friction, or shear, in the skin-PPE contact for up to four hours. Lubricants with different wax-oil combinations were prepared using beeswax, paraffin wax, olive oil, and mineral oil. In-vivo friction measurements involving seven participants were conducted by sliding a polydimethylsiloxane ball against the volar forearms to simulate the skin-PPE interface. The maximum static coefficient of friction was measured immediately and four hours after lubricant application. It was found that the coefficient of friction of wax-oil lubricants is mainly governed by the ratio of wax to oil and the thermal stability and morphology of the wax. To maintain long-term lubricity, it is crucial to consider the absorption of oil into the PPE material. The best performing lubricant is a mixture of 20 wt% beeswax, 40 wt% olive oil, and 40 wt% mineral oil, which compared to unlubricated skin, provides 87% (P = 0.0006) and 59% (P = 0.0015) reduction in instantaneous and 4-hour coefficient of friction, respectively.

Therapy and prevention for mental health: What if mental diseases are mostly not brain disorders?

2019 ◽  
Vol 42 ◽  
Author(s):  
John P. A. Ioannidis
Keyword(s):  
Mental Health ◽  
Mental Disease ◽  
Brain Disorders ◽  
Social Stressors ◽  
Labor Education ◽  
Mental Diseases ◽  
Long Term Follow Up ◽  
Political Decisions

AbstractNeurobiology-based interventions for mental diseases and searches for useful biomarkers of treatment response have largely failed. Clinical trials should assess interventions related to environmental and social stressors, with long-term follow-up; social rather than biological endpoints; personalized outcomes; and suitable cluster, adaptive, and n-of-1 designs. Labor, education, financial, and other social/political decisions should be evaluated for their impacts on mental disease.

Conceptual short-term memory (CSTM) supports core claims of Christiansen and Chater

2016 ◽  
Vol 39 ◽  
Author(s):  
Mary C. Potter
Keyword(s):  
Working Memory ◽  
Rapid Serial Visual Presentation ◽  
Language Comprehension ◽  
Short Term Memory ◽  
Visual Presentation ◽  
Long Term Memory ◽  
Short Term ◽  
Term Memory ◽  
Use Of Knowledge

AbstractRapid serial visual presentation (RSVP) of words or pictured scenes provides evidence for a large-capacity conceptual short-term memory (CSTM) that momentarily provides rich associated material from long-term memory, permitting rapid chunking (Potter 1993; 2009; 2012). In perception of scenes as well as language comprehension, we make use of knowledge that briefly exceeds the supposed limits of working memory.

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