Real Area of Contact in a Soft Transparent Interface by Particle Exclusion Microscopy

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Kyle D. Schulze ◽  
Alex I. Bennett ◽  
Samantha Marshall ◽  
Kyle G. Rowe ◽  
Alison C. Dunn
Keyword(s):  
Flexible Electronics ◽  
Soft Matter ◽  
Colloidal Particles ◽  
Contact Region ◽  
Real Contact Area ◽  
The Real ◽  
Real Area Of Contact ◽  
Static Indentation ◽  
Real Area

Soft matter mechanics are characterized by high strains and time-dependent elastic properties, which complicate contact mechanics for emerging applications in biomedical surfaces and flexible electronics. In addition, hydrated soft matter precludes using interferometry to observe real areas of contact. In this work, we present a method for measuring the real area of contact in a soft, hydrated, and transparent interface by excluding colloidal particles from the contact region. We confirm the technique by presenting a Hertz-like quasi-static indentation (loading time > 1.4 hrs) by a polyacrylamide probe into a stiff flat surface in a submerged environment. The real contact area and width were calculated from in situ images of the interface processed to reduce image noise and thresholded to define the perimeter of contact. This simple technique of in situ particle exclusion microscopy (PEM) may be widely applicable for determining real areas of contact of soft, transparent interfaces.

A New Three-Dimensional Numerical Model of Rough Contact: Influence of Mode of Surface Deformation on Real Area of Contact and Pressure Distribution

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
A. Jourani
Keyword(s):  
Pressure Distribution ◽  
Pressure Field ◽  
Surface Deformation ◽  
Three Dimensional ◽  
Real Contact Area ◽  
Geometrical Approach ◽  
Deterministic Models ◽  
The Real ◽  
Real Area Of Contact ◽  
Real Area

Surface roughness causes contact to occur only at discrete spots called microcontacts. In the deterministic models real area of contact and pressure field are widely evaluated using Flamant and Boussinesq equations for two-dimensional (2D) and three-dimensional (3D), respectively. In this paper, a new 3D geometrical contact approach is developed. It models the roughness by cones and uses the concept of representative strain at each asperity. To discuss the validity of this model, a numerical solution is introduced by using the spectral method and another 3D geometrical approach which models the roughness by spheres. The real area of contact and the pressure field given by these approaches show that the conical model is almost insensitive to the degree of isotropy of the rough surfaces, which is not the case for the spherical model that is only valid for quasi-isotropic surfaces. The comparison between elastic and elastoplastic models reveals that for a surface with a low roughness, the elastic approach is sufficient to model the rough contact. However, for surfaces having a great roughness, the elastoplastic approach is more appropriate to determine the real area of contact and pressure distribution. The results of this study show also that the roughness scale modifies the real contact area and pressure distribution. The surfaces characterized by high frequencies are less resistant in contact and present the lowest real area of contact and the most important mean pressure.

Real Area of Contact between a Rough Surface and a Softer Optically Flat Surface

1970 ◽  
Vol 12 (4) ◽  
pp. 259-267 ◽  
Author(s):  
P. W. O'Callaghan ◽  
S. D. Probert
Keyword(s):  
Applied Pressure ◽  
Real Contact Area ◽  
Recent Theory ◽  
Micro Hardness ◽  
Normal Loading ◽  
The Real ◽  
Flat Interface ◽  
Contact Points ◽  
Real Area Of Contact ◽  
Real Area

The mean number of contact spots per unit area and their mean radius were measured and hence the real area of contact deduced for a rough-to-flat interface under normal loading. The contact pressure was varied from zero to half the micro-hardness of the softer material. The resulting experimental evidence did not endorse the predictions from the recent theory of Tzukizoe and Hisakado, which incorrectly assumes that the real contact area is given by the applied pressure P divided by the micro-hardness M of the softer material. It was found that this area equalled K( P/ M) n, where the coefficient K and index n depend upon the applied pressure range. A maximum number of contact points was encountered at a dimensionless loading ( P/ M) approximately equal to 7·5 × 10-3.

Analysis of the Real Area of Contact Between a Polymeric Magnetic Medium and a Rigid Surface

1984 ◽  
Vol 106 (1) ◽  
pp. 26-34 ◽  
Author(s):  
Bharat Bhushan
Keyword(s):  
Complex Modulus ◽  
Critical Value ◽  
Computer Applications ◽  
Hard Material ◽  
Rigid Surface ◽  
Magnetic Medium ◽  
The Real ◽  
Real Area Of Contact ◽  
The Mean ◽  
Real Area

The statistical analysis of the real area of contact proposed by Greenwood and Williamson is revisited. General and simplified equations for the mean asperity real area of contact, number of contacts, total real area of contact, and mean real pressure as a function of apparent pressure for the case of elastic junctions are presented. The critical value of the mean asperity pressure at which plastic flow starts when a polymer contacts a hard material is derived. Based on this, conditions of elastic and plastic junctions for polymers are defined by a “polymer” plasticity index, Ψp which depends on the complex modulus, Poisson’s ratio, yield strength, and surface topography. Calculations show that most dynamic contacts that occur in a computer-magnetic tape are elastic, and the predictions are supported by experimental evidence. Tape wear in computer applications is small and decreases Ψp by less than 10 percent. The theory presented here can also be applied to rigid and floppy disks.

A Relationship Between Autocorrelation Length and Adhesive Friction Behavior of Rough Surfaces

2005 ◽  
Author(s):  
Yilei Zhang ◽  
Sriram Sundararajan
Keyword(s):  
Rough Surface ◽  
Spatial Information ◽  
Roughness Parameter ◽  
Hertzian Contact ◽  
Root Mean Square Roughness ◽  
Friction Behavior ◽  
The Real ◽  
Real Area Of Contact ◽  
Autocorrelation Length ◽  
Real Area

Autocorrelation Length (ACL) is a surface roughness parameter that provides spatial information of surface topography that is not included in amplitude parameters such as Root Mean Square roughness. This paper presents a statistical relation between ACL and the real area of contact, which is used to study the adhesive friction behavior of a rough surface. The influence of ACL on profile peak distribution is studied based on Whitehouse and Archard’s classical analysis, and their results are extended to compare profiles from different surfaces. With the knowledge of peak distribution, the real area of contact of a rough surface with a flat surface can be calculated using Hertzian contact mechanics. Numerical calculation shows that real area of contact increases with decreasing of ACL under the same normal load. Since adhesive friction force is proportional to real area of contact, this suggests that the adhesive friction behavior of a surface will be inversely proportional to its ACL. Results from microscale friction experiments on polished and etched silicon surfaces are presented to verify the analysis.

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