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Designed pinning of peeling fronts in thin film adhesives
Thin film adhesives are ubiquitous in our daily life, and they have become increasingly important in various applications such as packaging and coating. Despite their apparent simplicity, these systems can reveal a wide range of behaviors resulting from the complex interplay between the deformations of the elastic thin film and the dissipative processes of failure at the substrate-film interface. Here, we show how to take advantage of this complexity by designing adhesives with specific periodic arrangements of defects or pinning sites - corresponding to zones of larger adhesion energy – that give rise to high variations of the adhesive strength with the peeling direction and its sense [1].
To go beyond strength asymmetry, we investigate systems with heterogeneous elastic properties. We show how arrangements of stiff and compliant stripes on the thin film can produce a dramatic increase of their effective resistance by controlling the rate of elastic energy released by the elastic film as peeled from a substrate [2].
The concepts explored in the context of thin film peeling are then applied to the brittle failure of threedimensional materials that is also governed by the interaction of the crack line with the material defects. We will focus on random spatial distribution of impurities and will show how microscale heterogeneities can control the overall macroscopic toughness [3]. Trough these experimental examples and their theoretical interpretation, we will illustrate how defects in materials, by controlling the motion of fronts during the process of peeling or fracture, can give rise to new and improved adhesion and failure properties.
[1] S. Xia, L. Ponson, G. Ravichandran and K. Bhatacharya, Toughening and asymmetry in peeling of heterogeneous adhesives, Phys. Rev. Lett. 108, 196101 (2012) and Adhesive tape with enhancement and directionality by material and adhesion heterogeneity, International Patent 79322 (2011).
[2] S. Xia, L. Ponson, G. Ravichandran and K. Bhatacharya, Adhesion of heterogeneous thin films : I Elastic heterogeneity, Submitted to J. Mech. Phys. Sol. 61, 838-851 (2013).
[3] V. Démery, A. Rosso and L. Ponson, From microstructural features to effective toughness in disordered brittle solids. arXiv:1212.1551 (in review).