Adhesion is ubiquitous in a wide spectrum of artificial and natural systems, e.g. bacterial adhesion, stiction NEMS / MEMS and nano-structures, drug-eluting stents, and robotic grippers. The Johnson-Kendall-Roberts (JKR) theory has been the standard model for solid-solid adhesion. &nbsp;The basic JKR model was modified and extended to accommodate a wide spectrum of intrinsic surface forces, surface undulation and roughness, and environments, etc.&nbsp; One interesting area that is rarely addressed is the adhesion of shells, despite the voluminous literature in thin shell deformation.&nbsp; The most discussed geometry is thin cylindrical, hemispherical dome, and spherical shells based on small elastic strain.&nbsp;In this paper, we focus on a hyperelastic shell with spherical cap geometry that is compressed on its curved surface onto a rigid planar substrate. &nbsp;In our preliminary work, we investigated a linear elastic spherical shell with a thickness much smaller than the shell radius as well as the contact radius.&nbsp; Here we construct a model for large deformation in a hyperelastic thick shell. &nbsp;Since a full analytical solution is quite mathematically forbidden, we resort to a numerical approach for shells with specific dimensions.&nbsp; Using Maugis’ graphical method and a numerical approach, we determine the quasi-static adhesion-detachment process, the interrelation between applied load, approach distance and contact radius, and the critical pull-off parameters for shells with a range of materials stiffness with Young’s modulus E ranging from 0.1MPa to 3MPa, shell thickness t ranging from 0.5% to 100% of the shell radius R, shell depth ranging from 50% to 100% of R, and interfacial adhesion energy gamma ranging from 0.1J.m-2 to 30J.m-2. Contrasting JKR, the pull-off force P* depends predominantly on&nbsp;E and t. &nbsp;We note that P* follows quite the JKR prediction quite in initial loading, but once the contact radius exceeds the shell thickness, a significant deviation is inevitable.&nbsp; The same statement applies to a diminishing shell depth.&nbsp; Variation of adhesion strength leads to a linear P*(gamma) though the slope is different from the JKR prediction. &nbsp;These trends are particularly useful when the shell is made of nonlinear materials and subject to large deformation where an analytical solution is unachievable.We will demonstrate a few applications based on the new numerical scheme:&nbsp; (i) manipulation of objects by compliant flat-ended pillars based on dynamically tunable dry adhesion via subsurface stiffness modulation, (ii) locomotion based on dynamic friction modulation using soft materials of composite-pad geometry, (iii) design of new generation of soft grippers and haptic devices, (iv) bacterial adhesion in water filtration, and (v) contact lenses.&nbsp; The new numerical routines can help to estimate the behavior due to convoluted intersurface interactions such as the interplay of van der Waals attraction and electrostatic double-layer repulsion.&nbsp;&nbsp;&nbsp;

Adherence of a Hyperelastic Shell on a Rigid Planar Substrate

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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