An approximate model for the adhesive contact of rough viscoelastic surfaces

Surface roughness is known to easily suppress the adhesion of elastic surfaces. Here a simple model for the contact of \emph{viscoelastic} rough surfaces with significant levels of adhesion is presented. This approach is derived from our previous model [E. Barthel and G. Haiat {\em Langmuir}, 18 9362 2002] for the adhesive contact of viscoelastic spheres. For simplicity a simple loading/unloading history (infinitely fast loading and constant pull-out velocity) is assumed. The model provides approximate analytical expressions for the asperity response and exhibits the full viscoelastic adhesive contact phenomenology such as stress relaxation inside the contact zone and creep at the contact edges. Combining this model with a Greenwood-Williamson statistical modeling of rough surfaces, we propose a quantitative assessment of the adhesion to rough viscoelastic surfaces. We show that moderate viscoelasticity efficiently restores adhesion on rough surfaces over a wide dynamic range

Elastic contact to nearly incompressible coatings -- Stiffness enhancement and elastic pile-up

We have recently proposed an efficient computation method for the frictionless linear elastic axisymmetric contact of coated bodies [A. Perriot and E. Barthel, J. Mat. Res. 19 (2004) 600]. Here we give a brief description of the approach. We also discuss implications of the results for the instrumented indentation data analysis of coated materials. Emphasis is laid on incompressible or nearly incompressible materials (Poisson ratio $\nu>0.4$): we show that the contact stiffness rises much more steeply with contact radius than for more compressible materials and significant elastic pile-up is evidenced. In addition the dependence of the penetration upon contact radius increasingly deviates from the homogeneous reference case when the Poisson ratio increases. As a result, this algorithm may be helpful in instrumented indentation data analysis on soft and nearly incompressible layers

Observation directe et analyse de la morphologie d'un front de fracture piégé dans une interface hétérogène

Nous avons étudié le piégeage d’une fissure par une interface hétérogène lors d’un test de clivage. Pour différentes structurations macroscopiques simples, nous montrons que la morphologie du front de fissure peut être décrite par une approche perturbative du premier ordre. Cette description nous a permis de déterminer les ténacités locales dans les zones de piégeage ainsi que le taux de renforcement de l’interface. Ainsi, on obtient une mesure locale d'adhésion entre deux couches structurées

Nano Imprint 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

On the plastic deformation of soda-lime glass - a Cr3+ luminescence study of densification

International audienceSilicate glasses are known to experience an anomalous plastic behavior at micron-scale: 1) they exhibit densification when flowing plastically and 2) hydrostatic pressure affects the yield point. We have previously shown (A. Perriot et al. J. Am. Ceram. Soc. 89 (2006) 596) that densification maps are useful to infer a reliable constitutive law for the plastic response of silicate glasses. It is shown here that for soda-lime glass Cr3+ luminescence microspectroscopy may be used for that purpose. We also show that the constitutive law we have previously developed for amorphous silica provides a qualitative description of normal glasses although it is unable to account for the finer details. More work is needed to quantitatively model normal-glass plasticity at the continuum length-scale

Plastic flow and structural heterogeneities in silicate glasses - A high throughput investigation

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Density hardening plasticity and mechanical aging of silica glass under pressure: A Raman spectroscopic study

In addition of 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 aging effect, we propose that the glass structure could be labelled by 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