An Experimental Investigation on Metallic Plates Dynamic Cracking

Abstract

Metallic pressure vessels are of common use in the industrial field. They can contain either gases or liquefied gases. If a sudden pressure rise happens inside one of these vessels for any reason (human mistake, uncontrolled chemical reaction, BLEVE, rise in mass, explosion...), it can result in the bursting of the vessel. Though a pressure rise is relatively frequent, the response of the vessel to that sort of load cannot be easily forecasted, since the phenomenon is dynamic. Moreover, except from statistical studies, few experimental data are available on the topic. Therefore, an experimental study can help to understand the behavior of a pressurized enclosure in relation to such a solicitation. This paper analyzes the results of a set of experiments, that have been achieved in order to identify the mechanisms of a vessel rupture. The experimental device consists in a two-parts shock tube between which the sample, viz. a metallic plate, is set. This shock tube is fitted out with pressure gages. The plates are equipped out with strain and crack propagation gages. These sensors, in addition to a high velocity camera make possible the study of dynamic crack formation and fracture propagation on samples submitted to an explosion. Various classes of material with different ductilities have been tested. Moreover, the plate thickness influence has also been investigated. Flaws have been machined as external axial surface notches to produce and control cracking. Various solicitations have also been browsed: the loads were different kinds of explosions produced by the deflagration or the detonation of a stoichiometric hydrogen-oxygen mixture. Preliminary tests have shown a good reproducibility of the experiments. The loading amplitude (the pressure curves) and the shape of the plates after the operation, and especially the crack opening, are almost identical. These experiments have allowed to have a first overview of the role of the different input parameters on the plate behavior under load, and the way cracking occurs. The input parameters that have been monitored are the material ductility, the thickness of the samples and the kind of loading that is applied to them (i.e. different velocities deflagrations, detonations and so on). Output parameters are the strain rate of the plates and their cracking. Cracking is characterized by the size and the shape of the crack, its fracture facies and propagation velocity. In this paper, fracture behavior has been discussed with regard to the above mentioned parameters.