Development of material strength and failure models for structural simulation of metallic shock tube diaphragms

Abstract

Rupture dynamics of thin metallic diaphragms significantly influence the development of radially uniform planar shocks in hypersonic impulse facilities and consequently have a significant influence on the operating conditions of such facilities. Little literature exists for predicting the rupture pressure and opening times of diaphragms in impulse facilities and therefore there is interest among researchers in this field to develop characteristic models that describe mechanical properties of diaphragms during deformation and rupture. This thesis investigates a novel procedure for developing material models that describe plastic yielding and ductile rupture of thin metallic diaphragms using tensile testing equipment. Johnson-Cook strength and damage model constants have been determined from raw tensile data produced from tensile specimens of notched and un-notched geometries tested at a range of strain rates. The validity of the model constants produced was shown by comparing simulated load-displacement plots of tensile tests to data taken directly from such experiments. It was found that the models produced accurate predictions for specimens with geometries that introduced high stress concentrations at quasi-static speeds. Simulations of specimens without stress concentrations had over-predicted extensions at failure, and high strain rate simulations were impeded by experimental uncertainty in the strain rate dependent constants. To continue previous work in this field at the University of Queensland, a finite element model of 1/8 th of the diaphragm region of the X3 impulse facility was created and simulations performed. Mesh convergent simulations predicted a rupture pressure of 11.88 which was similar to the experimentally determined rupture pressure of 15 − 18 . Disagreement in results was attributed to uncertainty in damage constants due to measurement techniques, uncertainty in strain rate dependent constants due to experimental variation and an uncertainty in the exact rupture pressure at the diaphragm location in the X3 impulse facility.