Silicone elastomers are commonly used in engineering designs, e.g. as actuators in soft robotics. However, these materials are viscoelastic, so their response to loading depends on the load rate. At pressures below the elastic critical buckling load, shells made of these viscoelastic materials can still buckle, following a delay period. Here, we show that viscoelastic creep deformation acts like a geometric defect, slowly lowering the critical load to cause delayed buckling in seemingly stable elastomer shells under a constant load. This work can offer a pathway to introduce tunable, time-controlled actuation to existing mechanical actuators.

L. Stein-Montalvo, D.P. Holmes, and G. Coupier. Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load. Proc. R. Soc. A, 477 (2021) doi: 10.1098/rspa.2021.0253 (Write-up)