Axisymmetric adhesion tests of soft materials

Abstract

We describe a general, linearized fracture mechanics analysis for studying the adhesive properties of elastic, low modulus materials. Several adhesion tests are described, but all involve an elastic material which is brought into contact with a rigid surface along an axis of radial symmetry. Relationships between the load, displacement, and radius of the circular contact area between the two materials are described. These relationships involve the elastic modulus of the compliant material, the energy release rate (or adhesion energy) and various parameters which characterize the geometry of interest. The ratio of the contact radius to the thickness of the elastic material is shown to be a particularly important parameter. After reviewing some general concepts relevant to the adhesion of soft polymeric materials, we describe the fracture mechanics analysis, and provide examples from our own work on the adhesion of elastomers, thermoreversible gels and pressure sensitive adhesives.

Adhesive elastic contact between a symmetric indenter and an elastic film

“…Their analyses show that the deformation is confined to the surface layer, and the JKR model can be used by replacing the elastic properties of the half-space with those of the layer when considering a thick layer or small indentation (ratio a/h < 0.5). An overview of contact mechanics and adhesion of soft solids was presented in Shull (2002); he proposed approximate expressions for the indentation, compliance, and resultant pressure due to finite values of a/h (Shull et al, 1998). These semi-empirical expressions, suggested by experimental results and validated by finite element models, take a simplified form in the frequent special case a/h < 0.5, where the author assumed that the load is not significantly different from the Hertzian value.…”

“…An accuracy examination analysis and finite element (FE) examples will confirm the range of validity of the main hypothesis on the pressure distribution and show how the adhesion forces and the different film/substrate interface conditions affect the elastic solution. Furthermore, we will compare our results with those given by the semi-empirical Shull formula for soft film, obtaining a good agreement (Shull et al, 1998;see Eq. (30)).…”

Application of the bulk properties of a silicone PSA to peeling

“…The prediction of the compliance of a deformable layer sandwiched between two flat (most commonly circular) platens has been more latterly investigated by a number of workers both analytically and numerically [9][10][11][12][13]. The formulation of the last of these can be readily rearranged to provide the following equation:…”

Effects of thickness on the largely-deformed JKR (Johnson–Kendall–Roberts) test of soft elastic layers

“…For example, it cannot be applied to thin elastic lenses. Extension of the JKR theory to handle thin lenses has been addressed by Shull et al (1998). However, it should be noted that JKR theory assumes small strains and material linearity (Hui et al, 2000).…”