Investigation of the Buckling Instability in Free Thin-Shell Domes*

Shell buckling presents numerous opportunities to program fast and reversible reconfigurations into multifunctional devices. Applications such as soft actuators, locomotion systems, and biomedical instruments can leverage the diverse deformation properties of shell buckling mode shapes. Here, we investigate the buckling behavior of soft, thin-shell domes with free boundary conditions to facilitate a novel gripper design. Tuning the buckling mode and pressure could enhance the gripper's actuation speed and energy input characteristics. We will present analytical and numerical models used to find the dome's buckling pressure as a function of its material and geometric properties, such as its slenderness ratio and spherical cap angle. We analyze the shell's quasi-static response during pressurization with finite element methods (FEM), and we discuss good agreement between the two models. For experimental validation, we investigate a hemispherical soft shell with a thin film covering the leading edge to create an isolated fluid cavity. Using similar FEM, we model the fluid cavity to compare to the experimental results. Our research aims to advance knowledge about the buckling of soft, thin-shell domes and to inform the usage of hemispherical shells as soft grippers. This investigation also has the potential to pave a path forward for future research into soft devices with buckling controlled actuation.