scholarly journals Analysis of the Evolution of the Structure of a Surface With Pyramidal Asperities in Contact With a Hard and Smooth Plane

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Bensaad Bourassia ◽  
Bourouga Brahim
Keyword(s):  
Reference Model ◽  
Contact Point ◽  
Thermal Contact ◽  
Measurement Techniques ◽  
Theoretical Models ◽  
Real Area Of Contact ◽  
Smooth Plane ◽  
Contact Parameters ◽  
Real Area

Abstract This research deals with the evolution of the structure of the sapphire–brass interface due to the variation of contact pressure. This evolution primarily affects the essential parameters that govern the thermal contact resistance (TCR), namely, the contact point density N, the ratio of real area of contact S*, and the distance d separating the median contact planes. The combination of three measurement techniques, namely, profilometry, imaging, and mechanical characterization, was used for the purpose of investigating the structural variation of the interface. Alternatively, the TCR, which prevails at the interface, was estimated. Thus, the object of our study is to propose an original and new experimental approach allowing at the same time the precise measurement of the TCR and the estimate of the contact parameters of the interface studied constituting input data to the theoretical models of TCR. The estimated values given by these last are then compared with those measured. Through this approach, we try to open new ways of experimentation that would tend to reinforce the effort of TCR modeling. The results obtained showed that the roughness parameters Ra and Rq are independent of loading. The roughness Rp, which is considered equal to d, is sensitive to loading and has the same decreasing behavior under the effect of loading. The determination of S*, using the hardness testing, is even more relevant when the effective hardness Hc is considered. Analysis of data for the estimation of the TCR shows that the comparisons with the reference model (Bardon) attest to the relevance of our approach.

Determination of Adhesion Forces Between Smooth and Structured Solids

2012 ◽  
Author(s):  
Hartmut R. Fischer ◽  
Edwin R. M. Gelinck
Keyword(s):  
Adhesion Force ◽  
Smooth Surfaces ◽  
Adhesion Forces ◽  
Real Area Of Contact ◽  
Study Results ◽  
Colloidal Probes ◽  
Good Agreement ◽  
Real Area

The tendency of smooth surfaces to stick spontaneously to each other is becoming a serious problem, with: a) the increasing quality in surface finish for many components and systems, b) on miniaturization in mechanical components, and c) in demanded precision of positioning of parts in high-end equipment machines and systems. Surfaces tend to be made smoother in order to gain flatness or in order to fulfill the need for more precise and reproducible positioning of parts. Adhesion or even sticking of the surfaces is a major showstopper for these applications. There are several measures that can be taken in order to reduce spontaneous adhesion. Quantification of the effectiveness of the chosen solution is most often done using an AFM with probes varying from 1 nm to 8 micron of contact diameter. A serious disadvantage in measuring adhesion by sharp tips is the wear of the tips. Sharp tips wear easily, resulting in undefined contact areas. When the real area of contact is not well defined, the quantification of the adhesion force is not significant. In the current study results of AFM measurements from literature with different tip diameters of colloidal probes are compared with measurements we performed using AFM cantilevers with a plateau tip and using probes from large spheres using an alternative setup (UNAT). These methods give results that are in good agreement with values found in literature. Large contacting surface enhance the quality of the measured adhesion values. Another part of the study deals with a deliberately roughening of smooth surfaces to minimize (spontaneous) adhesion. Good agreement has been found with existing results. For the use of larger surfaces it is important that the surfaces to be tested are extremely clean. Particles on smooth surface do influence the measurements quite easily. Especially for larger areas, the possibility of encountering particles on the surface are more likely, when particles are present. For the measurements in this study a lot of care has been taken therefore to remove contamination: particles as well as contamination of organic origin.

Prediction of Thermal Contact Conductance by Surface Deformation Analysis

2001 ◽  
Author(s):  
Vishal Singhal ◽  
Suresh V. Garimella
Keyword(s):  
Surface Deformation ◽  
Thermal Contact ◽  
Thermal Contact Conductance ◽  
Deformation Analysis ◽  
Improved Method ◽  
Contact Conductance ◽  
The Real ◽  
Real Area Of Contact ◽  
Surface Profiles ◽  
Real Area

Abstract An improved method has been developed for the prediction of thermal contact conductance between two nominally flat metallic rough surfaces by analysis of the deformation of individual asperities in contact. The deformation of the asperities in contact has been taken into account by considering three different modes of deformation — elastic, elastic-plastic and plastic. The model uses an iterative procedure to determine the real area of contact between the deformed surfaces for a given load, nominal area of contact, surface profiles and material properties of the surfaces in contact. The contact conductance is then determined as a function of the ratio of the real area of contact to the apparent area of contact The predicted variation of contact conductance with load obtained from the model is compared to simplified analytical predictions in the literature as well as to experiments conducted as part of this work.

Review of Thermal Joint Resistance Models for Non-Conforming Rough Surfaces in a Vacuum

2003 ◽  
Author(s):  
M. Bahrami ◽  
J. R. Culham ◽  
M. M. Yovanovich ◽  
G. E. Schneider
Keyword(s):  
Experimental Data ◽  
Thermal Analysis ◽  
Flux Tube ◽  
Thermal Contact ◽  
Theoretical Models ◽  
Size Number ◽  
Data Points ◽  
Contact Models ◽  
The Mean ◽  
Contact Parameters

The thermal contact resistance (TCR) problem is categorized into three different problems: geometrical, mechanical, and thermal. Each problem includes a macro and micro scale sub-problem; existing theories and models for each part are reviewed. Empirical correlations for microhardness, and the equivalent (sum) rough surface approximation are discussed. Suggested correlations for estimating the mean absolute surface slope are summarized and compared with experimental data. The classical conforming rough contact models, i.e elastic and plastic, as well as elastoplastic models are reviewed. A set of scale (dimensionless) relationships are derived for the contact parameters, i.e. the mean microcontact size, number of micro-contacts, density of microcontacts, and the external load as functions of dimensionless separation, for the above models. These scale relationships are plotted; it is graphically shown that the behavior of these models, in terms of the contact parameters, are similar. The most common assumptions of existing thermal analysis are summarized. As basic elements of thermal analysis, spreading resistance of a circular heat source on a half-space and flux tube are reviewed, also existing flux tube correlations are compared. More than 400 TCR data points collected by different re-searchers during last forty years are grouped into two limiting cases: conforming rough, and elasto-constriction. Existing TCR models are reviewed and compared with the experimental data at these two limits. It is shown that the existing theoretical models do not cover both of the above-mentioned limiting cases.

A comparison of nanoscale measurements with the theoretical models of real and nominal contact areas

2020 ◽  
Vol 234 (11) ◽  
pp. 1735-1745 ◽  
Author(s):  
Yang Xu ◽  
Robert L Jackson ◽  
Yan Chen ◽  
Anqi Zhang ◽  
Barton C Prorok
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Contact Area ◽  
Theoretical Models ◽  
Real Area Of Contact ◽  
Contact Models ◽  
Nanoscale Measurements ◽  
Rough Surface Contact ◽  
Scanning Electron ◽  
Real Area

In this study, an experimental method is proposed to measure the real area of contact between an alumina sphere and an Al surface based on the adhesive transfer of the Au film and the scanning electron microscope in the back-scattered mode. A thin film of Au is sputtered on the alumina sphere before the indentation with the Al surface. After indentation, the interfaces of the alumina sphere and Al surface are observed by the scanning electron microscope. The contact area can be identified based on both the distributions of the alumina and Au on the alumina sphere and Al surface, respectively. The measured contact area at different nominal pressures are compared to predictions made by several popular theoretical elastic-plastic rough surface contact models.

Prediction of Thermal Conductance of Metallic Surfaces in Contact

1963 ◽  
Vol 85 (1) ◽  
pp. 15-24 ◽  
Author(s):  
H. Fenech ◽  
W. M. Rohsenow
Keyword(s):  
Contact Point ◽  
Thermal Contact ◽  
Thermal Conductance ◽  
Hardness Test ◽  
Knoop Hardness ◽  
Metallic Surfaces ◽  
Contact Points ◽  
Iron Aluminum ◽  
Good Agreement

A mathematical analysis of a thermal contact is first carried out on an idealized shape of contact point. The thermal conductance is expressed in terms of the thermal conductivities of the metals and of the fluid filling the voids, the real area in contact, the number of contact points per unit area, and the volume average thickness of the void gaps. A method is given for the determination of the above physical properties of a contact. To use this method the following measurements are needed: Two recorded profiles, perpendicular to one another; and a Knoop hardness test on the softer of the two metals making the contact. The last part of the paper is devoted to the experimental verification of the assumptions made in the theoretical analysis and to the application of the method outlined for the case of an iron-aluminum contact. Good agreement was found between the predicted and measured conductance over a range of pressures from 90 to 2600 psi.

Fully Coupled Frictional Contact Using Elastic Halfspace Theory

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
K. Willner
Keyword(s):  
Frictional Contact ◽  
Numerical Models ◽  
Normal Load ◽  
Friction Pair ◽  
Contact Problems ◽  
Elastic Halfspace ◽  
Real Area Of Contact ◽  
Fully Coupled ◽  
Real Area

The effect of dry metallic friction can be attributed to two major mechanisms: adhesion and ploughing. While ploughing is related to severe wear and degradation, adhesion can be connected to pure elastic deformations of the contacting bodies and is thus the predominant mechanism in a stable friction pair. The transmitted friction force is then proportional to the real area of contact. Therefore, a lot of effort has been put into the determination of the fraction of real area of contact under a given load. A broad spectrum of analytical and numerical models has been employed. However, it is quite common to employ the so-called Mindlin assumptions, where the contact area is determined by the normal load only, disregarding the influence of friction. In the subsequent tangential loading, usually the contact pressure distribution is kept fixed such that the coupling between the tangential and normal solutions is neglected. Here, a numerical solution scheme based on elastic halfspace theory for frictional contact problems is presented where full coupling between the normal and tangential tractions and displacements is taken into account. Several examples show the influence of the coupling effects, but also the limitations for the analysis of rough contacts.

Accurate Real Area of Contact Measurements on Polyurethane

1995 ◽  
Vol 117 (4) ◽  
pp. 607-611 ◽  
Author(s):  
C. P. Hendriks ◽  
M. Visscher
Keyword(s):  
Experimental Verification ◽  
Glass Plate ◽  
Theoretical Models ◽  
New Method ◽  
Contact Load ◽  
The Real ◽  
Real Area Of Contact ◽  
Contact Models ◽  
Better Than ◽  
Real Area

Theoretical models describing the contact of rough surfaces have been developed for at least three decades. Experimental verification, however, has not been straightforward up till now, since current measurements suffer from large inaccuracies, often 100 percent or worse. In this paper a new method, based on autofocus techniques, is applied with an accuracy better than 15 percent. Measurements are presented for the contact of a rough polyurethane specimen in contact with a smooth glass plate. It was not yet possible to conclude whether the real area of contact is proportional to the contact load, but the results show the forming of contact agglomerations, which becomes significant at 10 percent real area of contact. Asperity interaction appears to be important, even at low loads. However, one or both of these facts are often not considered in present contact models, questioning their reliability.

Sign in / Sign up

Export Citation Format

Share Document