Etienne Barthel

Adhesive elastic contacts: JKR and more

Since the early 1990s, adhesive contact mechanics has emerged as an area of considerable interest in nano- and bio-sciences. Here we review the methods which have been developed in the past 75 years to account for adhesive interactions in elastic contact problems. Emphasis is given to the connection between the local, physical mechanism of adhesion and the macroscopic, mechanical loading. The discussion centres on the contact equations. In an attempt to provide a broad view of the field, we outline the key concepts and their progressive developments, starting from the approximate calculation by Derjaguin in 1934 and ending with recent results for coated systems and time dependent materials, through the well established DMT and JKR models.

The adhesive contact of viscoelastic spheres

Abstract We have formulated the restricted self-consistent model for the adhesive contact of linear viscoelastic spheres. This model is a generalization of both the Ting (J. Appl. Mech. 33 (1966) 845) approach to the viscoelastic contact of adhesionless spheres and the restricted self-consistent model for adhesive axisymmetric bodies. We also show how the model can be used in practice by giving a few examples of numerical solutions.

Nanoimprint Lithography on Silica Sol–Gels: A Simple Route to Sequential Patterning

Since the pioneering work of S.Y. Chou et al.[1] Nano Imprint Lithography (NIL) has emerged as a promising technique for surface patterning, opening for numerous applications ranging from nanophotonics[2] to microfluidics[3]. NIL basically consists in the stamping of deformable surfaces or films. Preferred materials are thermoplastics[4] and UV curable resists[5]. So far, most papers report on single imprinting methods for which the same surface is imprinted only once. In the present paper, we report the imprinting of square silica structures from simple line gratings and demonstrate how the specific thermo-rheological behavior of ICSG resists can be harnessed to form complex structures by sequential imprinting at low pressures.

Self-sustained etch masking: A general concept to initiate the formation of nanopatterns during ion erosion

A material allowing for rapid and reliable formation of nanopatterned surfaces is an important issue in many areas of science today. Self-organized pattern formation induced by ion erosion is a promising bottom-up approach. In the case of the III-V semiconductors, this method can lead to several remarkable structure types even if the formation mechanism has yet to be found. Through high resolution chemical scanning, transmission electron imaging, and x-ray photo emission, we show through an investigation of GaSb that the capacity of III-V semiconductors to pattern under ion erosion is linked to the phase diagram of these materials. We suggest an original scenario to explain the specific behavior of III-V semiconductors, where one species segregates and acts as a continuously resupplied etching shield. This concept is at variance with the standard Bradley–Harper model and opens interesting perspectives for bottom-up patterning of compound materials.

Density hardening plasticity and mechanical ageing of silica glass under pressure: a Raman spectroscopic study

In addition to a flow, plastic deformation of structural glasses (in particular amorphous silica) is characterized by a permanent densification. Raman spectroscopic estimators are shown to give a full account of the plastic behavior of silica under pressure. While the permanent densification of silica has been widely discussed in terms of amorphous–amorphous transition, from a plasticity point of view, the evolution of the residual densification with the maximum pressure of a pressure cycle can be discussed as a density hardening phenomenon. In the framework of such a mechanical ageing effect, we propose that the glass structure could be labeled with the maximum pressure experienced by the glass and that the saturation of densification could be associated with the densest packing of tetrahedra only linked by their vertices.

Assessment of Microelastic Properties of Bone Using Scanning Acoustic Microscopy: A Face-to-Face Comparison with Nanoindentation

The current work aimed at comparing, on site-matched cortical bone tissue, the micron-level elastic modulus Ea derived from 200 MHz-scanning acoustic microscopy (SAM) acoustic impedance (Z) combined with bone mineral density (assessed by synchrotron radiation microcomputed tomography, SR-µCT) to nanoindentation modulus En. A good correlation was observed between En and Z (R2=0.67, p<0.0001, root mean square error RMSE=1.9 GPa). The acoustical elastic modulus Ea derived from Z showed higher values of E compared to nanoindentation moduli. We assumed that the discrepancy between Ea and En values may likely be due to the fixed assumed value of Poissons ratio while values comprised between 0.15 and 0.45 have been reported in the literature. Despite these differences, a highly significant correlation between Ea and En was found (R2=0.66, p<0.001, RMSE=1.8 GPa) suggesting that SAM can reliably be used as a modality to quantitatively map the local variations of tissue-level bone elasticity.

Adhesive contact to a coated elastic substrate

We show how the quasi-analytic method developed to solve linear elastic contacts to coated substrates (Perriot and Barthel 2004 J. Mater. Res. 19 600) may be extended to adhesive contacts. Substrate inhomogeneity lifts accidental degeneracies and highlights the general structure of the adhesive contact theory. We explain the variation of the contact variables due to substrate inhomogeneity. The relation to other approaches based on finite element analysis is discussed.

Surface Pressure and Shear Stress Fields within a Frictional Contact on Rubber

This paper addresses the issue of the determination of the frictional stress distribution from the inversion of the measured surface displacement field for sliding interfaces between a glass lens and a rubber (poly(dimethylsiloxane)) substrate. Experimental results show that high lateral strains are achieved at the periphery of the sliding contacts. As a consequence, an accurate inversion of the displacement field requires that finite strains and non-linear response of the rubber substrate are taken into account. For that purpose, a Finite Element (FE) inversion procedure is implemented where the measured displacement field is applied as a boundary condition at the upper surface of a meshed body representing the rubber substrate. Normal pressure is also determined in the same way, if non-diverging values are assumed at the contact edge. This procedure is applied to linearly sliding contacts as well as on twisting contacts.

ADHESIVE CONTACT OF VISCOELASTIC SPHERES: A HAND-WAVING INTRODUCTION

We give an overview of the general features of the linear viscoelastic adhesive contact model. The two main features are (1) a delay between the contraction of the contact radius and the onset of the indenter retraction, and (2) the enhancement of the adherence force. We emphasize the role played by stress relaxation within the contact zone in these phenomena and give simple forms of the viscoelastic adhesive contact equations to account for it. Two characteristic timescales are identified, respectively associated with the crack tip and the contact zone. Their asymmetric roles in the growing and receding contact phases is evidenced. Energy release rates for both phases are calculated together with their irreversible components.

SIMULTANEOUS ATOMIC FORCE MICROSCOPY MEASUREMENT OF LONG RANGE FORCES AND ADHESION ENERGY BETWEEN TUNGSTEN AND OXIDE SURFACES UNDER AMBIENT ATMOSPHERE AND ULTRAHIGH VACUUM

In the field of metal/oxide adhesion, it is contended that long range interactions may contribute to the work of adhesion. The combination of dc and ac atomic force microscopy is shown to provide a quantitative answer to this question by the simultaneous measurement of the long range forces and the adherence force. Different systems are considered: W/MgO under ambient atmosphere, where we show that adhesion is completely accounted for by the capillary force, and W/TiO2 (stoichiometric and nonstoichiometric) under ultrahigh vacuum, where the results suggest that the van der Waals contribution has to be taken into account in the adhesion energy.