Seminar Schedule
Pradeep Guduru, Brown University
Recent discoveries in biological adhesion in animals such as geckos, flies, etc. have inspired attempts to develop practically useful surface engineering technologies to maximize reversible adhesion and frictional properties of a surface. These attempts have opened up a set of contact mechanics related problems, the solutions to which can potentially lead to practical benefits. As part of this effort, a theory of wavy surface adhesion and friction has been developed. It is shown that surface waviness causes the detachment process to proceed in alternating stable and unstable segments. Unstable segments dissipate mechanical energy and lead to apparent toughening and apparent strengthening. The instability induced toughening and strengthening have the potential to be exploited in designing surface topographies to enhance reversible adhesion of soft materials. The predictions of the theory have been verified experimentally. The work also presents an analysis of the effect of shape of a fiber tip in enhancing adhesion. The second aspect of this work is to create biologically inspired surface micro-scale architectures and investigate their adhesive and frictional properties. A film terminated tilted fiber architecture has been fabricated and its directional adhesion and sliding resistance behaviors have been investigated experimentally. The experiments show that such a surface displays a highly anisotropic sliding resistance. Also, sliding resistance in the fiber tilt direction shows a phase transformation-like behavior, with a sudden increase in magnitude with a small drop in the normal tensile force. Possible mechanisms responsible for such a response are discussed.