Finite element modelling of metallic diaphragm rupture in hypersonic shock tube

Abstract

This thesis investigates spontaneous rupture of the primary diaphragm used in hypersonic ground testing facilities. It is known that many non-ideal and complex flow fields arise as a result of the primary diaphragm, however it is currently not well modelled in the literature. These complex flow fields are known to effect the final flow conditions for the test, and therefore the ability to model them is of great importance to the use, and optimisation, of hypersonic ground testing facilities. A brief summary of these fluid effects has been provided. The overarching aim of this thesis was to provide a foundation of knowledge for numerical studies on the diaphragm rupture, and to provide estimates on the opening dynamics of the primary diaphragm in the X2 expansion tube at The University of Queensland. The primary method for achieving this aim was the use of the explicit finite element package LS-DYNA. The challenge in obtaining accurate estimates is in the large number of nonlinearities inherent to the problem. The model contains both material and geometric nonlinearities which must be appropriately modelled and verified. To verify the accuracy of the estimates provided, a series of benchmark experiments from the literature were identified and modelled in LS-DYNA, which allowed verification of the input parameters. These experiments provided information on various parts of the diaphragm rupture and provided insight into the mechanisms in the different parts of the failure. The information from these models was used to validate the final simulations of X2 since experimental measurements were not taken on this facility. Final simulations of X2 were only approximate, due to the lack of material and loading data available, however it is still expected that these estimates are in a reasonable range of the true values. Whilst the numerical answers are limited in their accuracy, the diaphragm rupture could still be qualitatively described.