Atomic-Scale Friction Measurements Using Friction Force Microscopy: Part II—Application to Magnetic Media

1994 ◽  
Vol 116 (2) ◽  
pp. 389-396 ◽  
Author(s):  
Bharat Bhushan ◽  
Ju-Ai Ruan
Keyword(s):  
Surface Roughness ◽  
Friction Force ◽  
Coefficient Of Friction ◽  
Natural Diamond ◽  
Local Variation ◽  
Atomic Scale ◽  
Poor Correlation ◽  
Magnetic Media ◽  
Micro Scale ◽  
Friction Measurements

Atomic Force/Friction Force Microscopes (AFM/FFM) were used to study tribological properties of metal-particle tapes with two roughnesses, Co-γFe2O3 tapes (unwiped and wiped), and unlubricated and lubricated thin-film magnetic rigid disks (as-polished and standard textured). Nanoindentation studies showed that the hardness of the tapes through the magnetic coating is not uniform. These results are consistent with the fact that the tape surface is a composite and is not homogeneous. Nanoscratch experiments performed on magnetic tapes using silicon nitride tips revealed that deformation and displacement of tape surface material occurred after one pass under light loads (~ 100 nN). A comparison between friction force profiles and the corresponding surface roughness profiles of all samples tested shows a poor correlation between localized values of friction and surface roughness. Detailed studies of friction and surface profiles demonstrate an excellent correlation between localized variation of the slope of the surface roughness along the sliding direction and the localized variation of friction. Micro-scale friction in magnetic media and natural diamond appears to be due to adhesive and ratchet (roughness) mechanisms. Directionality in the local variation of micro-scale friction data was observed as the samples were scanned in either direction, resulting from the scanning direction and the anisotropy in the surface topography. Micro-scale coefficient of friction is generally found to be smaller than the macro coefficient of friction as there may be less ploughing contribution in micro-scale measurements.

Micro/nanotribology using atomic force microscopy/friction force microscopy: State of the art

1998 ◽  
Vol 212 (1) ◽  
pp. 1-18 ◽  
Author(s):  
B Bhushan
Keyword(s):  
Surface Roughness ◽  
Atomic Force Microscopy ◽  
Friction Force ◽  
Boundary Lubrication ◽  
Normal Load ◽  
Atomic Scale ◽  
Friction Force Microscopy ◽  
Material Transfer ◽  
Force Microscopy ◽  
Atomic Force

Atomic force microscopy/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales ranging from atomic and molecular to microscales. These techniques have been used to study surface roughness, adhesion, friction, scratching/wear, indentation, detection of material transfer and boundary lubrication and for nanofabrication/nanomachining purposes. Micro/nanotribological studies of materials of scientific and engineering interest have been conducted. Commonly measured roughness parameters are found to be scale dependent, requiring the need of scale-independent fractal parameters to characterize surface roughness. Measurement of atomic-scale friction of a freshly cleaved highly orientated pyrolytic graphite exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography were displaced relative to each other. Variations in atomic-scale friction and the observed displacement have been explained by the variations in interatomic forces in the normal and lateral directions. Local variation in microscale friction is found to correspond to the local slope, suggesting that a ratchet mechanism is responsible for this variation. Directionality in the friction is observed on both micro- and macroscales which results from the surface preparation and anisotropy in surface roughness. Microscale friction is generally found to be smaller than macroscale friction as there is less ploughing contribution in microscale measurements. Microscale friction is load dependent and friction values increase with an increase in the normal load, approaching the macrofriction at contact stresses higher than the hardness of the softer material. The wear rate for single-crystal silicon is negligible below 20 μN and is much higher and remains approximately constant at higher loads. Elastic deformation at low loads is responsible for negligible wear. The mechanism of material removal on a microscale is studied. At the loads used in the study, material is removed by the ploughing mode in a brittle manner without much plastic deformation. Most of the wear debris is loose. Evolution of the wear has also been studied using AFM. Wear is found to be initiated at nanoscratches. AFM has been modified to obtain load-displacement curves and for measurement of nanoindentation hardness and Young's modulus of elasticity, with the depth of indentation as low as 1 nm. Hardness of ceramics on the nanoscale is found to be higher than that on the microscale. Ceramics exhibit significant plasticity and creep on the nanoscale. Scratching and indentation on nanoscales are powerful ways to screen for adhesion and resistance to deformation of ultra-thin films. Detection of material transfer on the nanoscale is possible with AFM. Boundary lubrication studies and measurement of lubricant-film thickness with a lateral resolution on a nanoscale have been conducted using AFM. Self-assembled monolayers and chemically bonded lubricant films with a mobile fraction are superior in wear resistance. Friction and wear on micro- and nanoscales at low loads have been found to be generally smaller compared to that at macroscales. Therefore, micro/nanotribological studies may help define the regimes for ultra-low friction and near-zero wear.

Atomic-Scale Friction Measurements Using Friction Force Microscopy: Part I—General Principles and New Measurement Techniques

1994 ◽  
Vol 116 (2) ◽  
pp. 378-388 ◽  
Author(s):  
Ju-Ai Ruan ◽  
Bharat Bhushan
Keyword(s):  
Friction Force ◽  
Microelectromechanical Systems ◽  
Atomic Scale ◽  
Magnetic Storage ◽  
Basic Operation ◽  
Friction Force Microscopy ◽  
Force Measurements ◽  
Friction Forces ◽  
Force Microscopy ◽  
Friction Measurements

Friction force measurements using modified atomic force microscopy, called here Friction Force Microscopy (FFM), are becoming increasingly important in the understanding of fundamental mechanisms of friction, wear, and lubrication, and to study interfacial phenomena in micro- and nanostructures used in magnetic storage systems and Microelectromechanical Systems (MEMS). FFMs can be used to study engineering surfaces in dry or wet conditions. A review of existing designs of FFMs and methods of friction force measurements is presented. In terms of friction force measurements, there are important issues related to the basic operation and calibration of these instruments which have not been fully studied. A new method of measuring friction fore using a commercial FFM and a calibration procedure for conversion of measured data to normal and friction forces are presented. Microscale friction data of selected materials are presented and discussed in light of macro-friction measurements.

Friction Force and Stresses Analysis for Contact of Assembled Details

2006 ◽  
Vol 113 ◽  
pp. 334-338
Author(s):  
Z. Dreija ◽  
O. Liniņš ◽  
Fr. Sudnieks ◽  
N. Mozga
Keyword(s):  
Mechanical Properties ◽  
Surface Roughness ◽  
Plastic Deformation ◽  
Friction Force ◽  
Sliding Friction ◽  
Friction Model ◽  
Contact Interface ◽  
Finite Element Program ◽  
Elastic Plastic ◽  
Element Program

The present work deals with the computation of surface stresses and deformation in the presence of friction. The evaluation of the elastic-plastic contact is analyzed revealing three distinct stages that range from fully elastic through elastic-plastic to fully plastic contact interface. Several factors of sliding friction model are discussed: surface roughness, mechanical properties and contact load and areas that have strong effect on the friction force. The critical interference that marks the transition from elastic to elastic- plastic and plastic deformation is found out and its connection with plasticity index. A finite element program for determination contact analysis of the assembled details and due to details of deformation that arose a normal and tangencial stress is used.

Effect of scan size and surface roughness on microscale friction measurements

1997 ◽  
Vol 81 (6) ◽  
pp. 2472-2479 ◽  
Author(s):  
Vilas N. Koinkar ◽  
Bharat Bhushan
Keyword(s):  
Surface Roughness ◽  
Friction Measurements

Enhancement of tribological properties and characteristic of polymer matrix composite (UHMWPE reinforced with short fibres of polyester) for Total Disc Replacement (TDR)

2020 ◽  
Vol 2 (102) ◽  
pp. 55-65
Author(s):  
M.N. Obaid ◽  
S.H. Radhi
Keyword(s):  
Surface Roughness ◽  
Contact Angle ◽  
Wear Resistance ◽  
Composite Material ◽  
Thermal Properties ◽  
Coefficient Of Friction ◽  
Tribological Properties ◽  
Total Disc Replacement ◽  
Short Fibres ◽  
The Matrix

Purpose: The number of people suffering from Degenerative Disc Disease (DDD) is increasing. The disease causes heavy pain and restrict a number of day-to-day life activities. In extreme cases, the degraded disc is removed under total disc replacement which is usually made up of Ultra-High Molecular Weight Polyethylene (UHMWPE). The material has astounding biocompatible characteristics mechanical properties and wear resistance. However, these characteristics are insufficient in arthroplasty application. Therefore, research investigations are ongoing to improve tribological properties through reinforcement that may result in a composite material of UHMWPE. Thus the current study is aimed at reinforcing UHMWPE with short fibres of polyesters to enhance the tribological properties and surface characteristic so as to improve wear resistance and nourish the fibroblast cells on synthetic disc. Design/methodology/approach: The researcher prepared UHMWPE composite material, reinforced with different weight fractions of short polyester fibres (2, 4, 6, 8 and 10% following hot press method. Further pin-on-disc device was used to study the tribological properties (coefficient of friction and volume of wear). The study tested surface roughness and surface characteristics by atomic force microscopy (AFM) device, hardness by shore D device, contact angle to study the effect of polyester short fibres on wettability of UHMWPE surface and tested the thermal properties and crystalline degree using Differential Scanning Calorimetry measurement (DSC) device. Findings: The results infer that the wear resistance got improved when using 2% w.t polyester though it got decreased initially. However, the value was still more than neat UHMWPE. There was a decrease observed in coefficient of friction, but after 4 w.t% polyester, the coefficient of friction got increased due to increasing percentage of fibres which make it harder and stiff compared to UHMWPE. There was a decline observed in surface roughness due to alignment of the fibres with smooth surface. The contact angle got increased in a moderate range while the roughness enhanced the growth of fibroblast cell. The hardness of composite material got increased, because the fibres turned stiffer and harder than the matrix. DSC results infer the improvements in thermal stability due to high thermal properties of polyester fibres compared to UHMWPE. The degree of crystallinity got increased which in turn enhanced wear resistance, especially at 6 w.t % polyester fibres. There was a mild increase observed in density since the density of polyester is higher than polymer. Research limitations/implications: The major challenge was the dispersion of fibres. Uniform distribution of fibres within the matrix (UHMWPE) was achieved through two steps of mixing processes such as mechanical mixture and twin extruder. In future studies, fatigue tests must be conducted to study the behaviour of prepared composite materials under fatigue cycle. Practical implications: A significant objective is how to connect among different properties to obtain good improvement in tribological and surface properties so as to enhance wear resistance and growth of fibrolase cells. Originality/value: In this study, polymeric short fibres were used as reinforcement with polymeric matrix to enhance the wettability of fibres with matrix. In this way, the bonding among them got increased which supports the tribological, surface, and crystalline behaviour.

scholarly journals The description of friction of silicon MEMS with surface roughness: virtues and limitations of a stochastic Prandtl–Tomlinson model and the simulation of vibration-induced friction reduction

2010 ◽  
Vol 1 ◽  
pp. 163-171 ◽  
Author(s):  
W Merlijn van Spengen ◽  
Viviane Turq ◽  
Joost W M Frenken
Keyword(s):  
Surface Roughness ◽  
Critical Role ◽  
Measurement Data ◽  
Friction Model ◽  
Friction Reduction ◽  
Atomic Scale ◽  
Mems Devices ◽  
Tomlinson Model ◽  
Atomic Force ◽  
On Chip

We have replaced the periodic Prandtl–Tomlinson model with an atomic-scale friction model with a random roughness term describing the surface roughness of micro-electromechanical systems (MEMS) devices with sliding surfaces. This new model is shown to exhibit the same features as previously reported experimental MEMS friction loop data. The correlation function of the surface roughness is shown to play a critical role in the modelling. It is experimentally obtained by probing the sidewall surfaces of a MEMS device flipped upright in on-chip hinges with an AFM (atomic force microscope). The addition of a modulation term to the model allows us to also simulate the effect of vibration-induced friction reduction (normal-force modulation), as a function of both vibration amplitude and frequency. The results obtained agree very well with measurement data reported previously.

Floor Slipperiness Measurement in a Food Factory

2013 ◽  
Vol 303-306 ◽  
pp. 769-772
Author(s):  
Kai Way Li ◽  
Ching Chung Chen ◽  
Li Wen Liu ◽  
Chih Yong Chen
Keyword(s):  
Coefficient Of Friction ◽  
Safety Standard ◽  
The Usa ◽  
The Coefficient Of Friction ◽  
Friction Measurements ◽  
Ergonomic Interventions ◽  
Northern Taiwan

Floor slipperiness assessment was conducted in a food factory in northern Taiwan. Three areas in the popcorn sector of the factory were measured. The friction measurements were conducted using the Brungraber Mark II slipmeter. A total of 96 measurements of the coefficient of friction on the floor were conducted. In addition, six employees were interviewed concerning their experiences of slipping and falling in the sector and their perception of floor slipperiness. The results showed that all the readings in the measurement areas were lower than 0.5, a safety standard commonly adopted in the USA. All the interviewees reported that they had the experiences of slipping without falling in the sector. All of them reported the floor in the popping area was “extremely slipperiness.” Ergonomic interventions are required and in this sector.

Deformation mechanisms of polytetrafluoroethylene at the nano- and microscales

2019 ◽  
Vol 21 (1) ◽  
pp. 490-503 ◽  
Author(s):  
Matthew Brownell ◽  
Arun K. Nair
Keyword(s):  
Surface Roughness ◽  
Coefficient Of Friction ◽  
Deformation Mechanisms

Polytetrafluoroethylene (PTFE) coefficient of friction is dependent on a particles density and surface roughness.

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