Poking and buckling of pressurized spherical shells

Imperfection sensitivity in shell buckling makes it difficult to predict the critical buckling conditions of shells with realistic distributions of defects. Recently, a non-destructive technique has been proposed and successfully applied to cylindrical shells [1,2], to access their landscape of stability using a probing force. It is still debatable whether this technique can also be used for spherical shells. Here, we combine precision experiments, finite element simulations and shell theory to explore the ability of a poking technique to determine the critical buckling pressure of a spherical shell containing a dimple-like defect. We find that the critical point can indeed be probed when the force is applied at the defect. However, when the poking is done further away from the defect, this becomes invisible to the probing and the shell buckles prior to the cue provided by the poking. Specifically, we quantify a threshold angle for the location of the probing force, beyond which poking no longer seems to be applicable as a non-destructive testing technique. The basis of our analysis is the localized nature of the deformation of shells under point-load indentation.
[1] T Kreilos, TM Schneider, Proc.R.Soc. A 473, 2017
[2] E Virot, T Kreilos, TM Schneider, SM Rubinstein, PRL 119, 2017