Abstract
The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces. In the past, the influence of roughness has been investigated thoroughly. However, even in the presence of perfectly smooth surfaces, geometry can come into play in form of the macroscopic shape of the contacting region. Here we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft, adhesive counterpart. When it is carefully pulled off, we find that in contrast to circular shapes, detachment occurs not instantaneously but detachment fronts start at pointed corners and travel inwards, until the final configuration is reached which for macroscopically isotropic shapes is almost circular. For elongated indenters, the final shape resembles the original one with rounded corners. We describe the influence of the shape of the stamp both experimentally and numerically.Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov. It is based on a local, mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of adhesion. The validation of the suggested method is made both by comparison with known analytical solutions and with experiments. The method is applied for simulating the detachment of flat-ended indenters with square, triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to “brushes”. The method is extended for describing power-law gradient media.
Highlights
Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov
As stated by Kendall [9], “solids are expected to adhere; the question is to explain why they do not, rather than why they do!” The reason for the obvious weakness of macroscopic adhesion in everyday-life is in most cases either a stress concentration on the boundary of a contact, a crack or the roughness of surfaces that hinders the intimate contact of the two bodies
Even in the presence of perfectly smooth surfaces, geometry can come into play in form of the macroscopic shape of the contacting region
Summary
“Adhesion” is a term which is used for describing different phenomena depending on the branch of science and technology [1]. In the present paper we understand under “adhesion” the relatively weak, so-called van der Waals interaction which acts between any electrically neutral bodies [2, 3] These forces cause “sticking together” of two solids when they are brought into a contact. They hold a lot better, so their sticking capability depends on the contour This influence of the macroscopic shape of the contact area remained till out of focus of the research of adhesion. In their paper from 1971 [13] —maybe the most famous paper on the theory of adhesive contacts—Johnson, Kendall and Roberts wrote: “the approach followed in this analysis, is similar to that used by Griffith in his criterion for the propagation of a brittle crack.” They realized that the adhesive contact is nothing but an “inverted crack”.
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