Achieving enhanced adhesion through optimal stress distributions

Abstract Dry adhesives that rely on surface force mediated adhesion, such as van der Waals forces, are important in applications ranging from robotics to manufacturing. The maximum theoretical adhesion strength of a contact is achieved when the stress is uniformly distributed over the entire contact area as the full potential of all the bonds at the interface is realized in this scenario. Most dry adhesive structures are composed of a tip layer that forms contact and a support structure that transfers load from the far field to this tip structure. Here, we determine the displacement distribution that must be applied on the tip layer to generate an optimum interfacial stress distribution. We realize this through a linear, closed-form optimization framework that uses data obtained from finite element analysis for a few basis cases. It was found that adhesion can be maximized by applying an optimum displacement on the tip layer that consists of uniform tension in the center, a peak tension between the center and the edge, and compression near the edge. The displacement applied on the tip layer of a mushroom-shaped, composite, and novel segmented composite structures are then analyzed and compared with the optimal case to guide the design of dry adhesives.