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Thin supported elastic nano- or micrometric films are everywhere in our everyday life, and it is often of outmost importance for the quality of their function in a given application to be able to characterize precisely their mechanical properties. We show in the present review that this is however a quite difficult mechanical problem. We briefly present the successive contact mechanics models which have been elaborated to take into account the observed apparent increased rigidity of those elastic films when they are confined between the supporting solid and another solid (the indenter) used to squeeze them and deduce their mechanical properties from load versus deformation curves. We discuss the limitations of these models and put a special emphasis on the more recent one, by E. Barthel, which, based on a semi-analytical resolution of the contact mechanics equations, seems to correctly account for series of systematic experiments where micrometric elastomer films supported by a silicon wafer are characterized in a JKR test with microlenses of the same elastomer. We discuss in details why an important drawback of essentially all indentation type tests is the fact that they usually do not give access to the actual size of the contact between the probe and the tested film. A consequence is that adhesion contributions can hardly be incorporated in a correct manner. We then propose a new soft liquid probe test, in which the supported films are mechanically solicited not by a direct contact with another solid, but by the adjustable stress field resulting from the oscillating flow of a liquid intercalated between the films to be tested and a sphere which can be approached from the film down to a fraction of nanometers. We analyze the potentialities of this new test and show that it presents two main advantages compared to conventional solid–solid contact tests. First, the adhesion terms do not change during the test, as the solids are immersed into the liquid, and second, the amplitude of the stress field can be varied and perfectly controlled in an impressive wide range; thanks to the well-known validity of the Reynolds equations down to a few molecular sizes. [ABSTRACT FROM AUTHOR]

Axisymmetric contact problem about bending of a plate lying on inhomogeneous foundation with complicated structure is considered. The plate is bent under the action of distributed load and elastic response from a foundation. The foundation consists of elastic inhomogeneous soft interlayer and elastic homogeneous half-space. Lamé parameters of interlayer vary with depth by arbitrary law. Both continuously inhomogeneous and stratified interlayers are considered. Also case when layer is significantly softer than an underlying half-space is considered. Bilateral asymptotic method was used to construct an analytical solution of the problem. Analytical expressions for contact stresses and deflection of the plate are provided. The obtained solution is bilaterally asymptotically exact both for large and small ratio of layer thickness to plate radius. Both flexible and stiff plates can be modeled. Numerical results are given which shows that found approximations for kernel transform of integral equation of the problem allow us to construct analytical solution that is effective in the whole range of values of inhomogeneous layer thickness and plate stiffness. [ABSTRACT FROM AUTHOR]

With the scientific and technological accurate trend with diminish gradually of orientation, it has become increasingly important to study the surface phenomena. When surface touch each other, contact friction is predominantly made at the summits of surface roughness and particle. The particle effect and its manifestation in friction still attracts considerable debate as to its likely causes. Analysis had been conducted to study the important contribution that the formation of friction debris can have on the progression of friction. Based on the contact mechanics and friction theory, this work establishes a new three-body friction model with considering the surface friction and deformation friction of particles. It is proposed in order to understand the effects of particles between surfaces on contact characteristics for rough surface with different particle size. The results show that the particle size and plasticity index dominates the friction value for low mean separation between rough surfaces. Beyond the critical value of mean separation, the important factor in affecting total friction value is surface friction partition of total friction. The critical value have the sequence for the different particle sizes: (d/σ)Cn=500 > (d/σ)Cx=100 > (d/σ)Cx=20 at the same ratio x/Rq. The larger the wear particle size, the higher friction value and critical separation value for silicon under the same roughness parameters. [ABSTRACT FROM AUTHOR]