Characterization of blast waves using solid and gaseous explosives: application to dynamic buckling of cylindrical shells

A launcher’s engine and in particular its nozzle are subjected to several loads during the rocket launch. Most of these loads are dynamic, such as the external pressure pulse caused by the blast wave bouncing back from the floor and engulfing the nozzle. Nevertheless, they usually are considered as quasi-static in buckling computations as conservative design methods. Few studies have been investigated on dynamic buckling of thin shells subjected to external pressure pulse. Thus, a large program including experimental tests and numerical simulations have been conducted by the CNES, the French Space Agency. The main objectives are a better understanding of dynamic buckling and establishing a robust design methodology. In this context, two experimental means used for producing dynamic pulses are here considered and investigated, to explore the dynamic buckling of such structures. In one case, the shock wave is produced using a solid explosive, in the shape of a stick in which a nitrate ammonium/sodium nitrate mix is encapsulated. In another setup, the shock wave is produced using a commercial apparatus named DaisyBell. A hydrogen/oxygen mixture is detonated within a conical shock tube, producing a directional free-air-like blast. Both apparatuses are designed to be hanged above snowpack for avalanche preventive release, thus can be held at the desired height using a crane. The pulse intensity measured at the tested sample level can be tuned by moving the explosive up or down. A simplified model of the nozzle, in the form of a cylindrical shell, is proposed for the analysis. This study aims at showing how both apparatuses can be used to simulate free-air-like blasts and can cause the dynamical buckling of a steel cylindrical shell structure.