Exploring structural instabilities in ridge-reinforced soft cylinders

Fluidic soft actuators capable of highly complex deformations have emerged as an ideal platform to realize active and adaptable robotic systems. More recently, structural instabilities have been utilized in the design of soft robots to unlock novel functionalities. In this context, we explore the mechanics of soft cylinders reinforced by helical ridges that twist and extend upon inflation. Remarkably, under certain geometrical conditions, the cylinders undergo a sudden twisting instability characterized by a heterogeneous deformation of the ridges. Guided by modeling and experiments, we describe the evolution of this instability and the transition between the different deformation regimes as a function of material properties, geometrical parameters, and input volume. This novel twisting instability may open new routes towards nonlinear textured soft actuators with increased performance.