Advances in Shell Buckling: theory, experiments, localization and shock-sensitivity

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• Professor Mike Thompson - Dept of Applied Maths
• Friday 15 May 2015, 15:00-16:00
• Cambridge University Engineering Department, LR5.

If you have a question about this talk, please contact Lorna Everett.

This talk describes the static-dynamic analogy and its role in understanding the localized post-buckling of shell-like structures. We show, for example, the true significance of the Maxwell energy criterion load in predicting the sudden onset of “shock sensitivity” to lateral disturbances. For technically ‘non-integrable’ systems, such as thin compressed shells, we show how the emergence of spatial chaos generates a multiplicity of localized paths (and escape routes) with complex snaking and laddering phenomena. These are illustrated in the response and energy barriers of an axially compressed cylindrical shell. After surveying NASA ’s current shell-testing programme, we propose a new non-destructive technique to estimate the “shock sensitivity” of a laboratory specimen that is in a compressed metastable state before buckling. This uses a probe to measure the nonlinear load-deflection characteristic under a rigidly applied lateral displacement. Sensing the passive resisting force, it can be plotted in real time against the displacement, displaying an equilibrium path along which the force rises to a maximum and then decreases to zero: having reached the free state of the shell that forms a mountain-pass in the potential energy. The area under this graph gives the energy barrier against lateral shocks. The test is repeated at different levels of the overall compression. A symmetry-breaking bifurcation can be encountered on this path, and we show how this can be suppressed by a controlled secondary probe tuned to deliver zero force on the shell.

This talk is part of the Engineering Department Structures Research Seminars series.

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