Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

We performed dynamic pressure buckling experiments on defect-seeded spherical shells made of a common silicone elastomer. Unlike in quasi-static experiments, buckled at ostensibly subcritical pressures (i.e. below the experimentally-determined load which occurs elastically), often following significant time delay. While emphasizing close connections to elastic shell buckling, we rely viscoelasticity explain our observations. In particular, demonstrate that lower critical may be determined from material properties, is rationalized by simple analogy buckling. then introduce model centered empirical quantities show viscoelastic creep deformation lowers same predictable, quantifiable way growing defect would an shell. This allows us capture how both deflection and delay depend applied pressure, geometry. These are straightforward measure experiments. Thus, work not only provides intuition for behavior perspective, but also offers accessible pathway tunable, time-controlled actuation existing mechanical actuators, e.g. pneumatic grippers.