Indentation and puncture of double-network tough hydrogel membranes

Hydrogel membranes are commonly used in soft devices and soft robotics, which are prone to puncture failure when penetrated by external spiny objects. In this work, the indentation and puncture of double-network hydrogel (DNH) membranes are experimentally and theoretically investigated by using cylindrical indenters with both flat and spherical tips of various sizes. It is found that when a hydrogel membrane contacts with the side surface of a cylindrical indenter with a large area, the puncture force increases dramatically due to the friction force from the side contact, leading to the critical puncture force insensitive to the geometry of indenter tip. In the theory, the stretch field of the DNH membrane in the indentation is obtained and the contribution of friction force to the puncture force on the indenter is quantified. This work reveals the puncture mechanism of hydrogel membranes under the influence of friction, especially for that from the side surface of indenter.