Blast Testing – Shock Tube Overview
Often times, researchers need to study the effect explosions will have on materials, devices, or even biological specimens. Because replicating a full-scale explosion is very dangerous and cost-prohibitive, shock tubes are used to simulate actual explosions and their effects in a controlled environment.
Shock waves, or blast waves, are the pressure impulse resulting from an explosion. The pressure impulse from an explosion can travel at supersonic speeds through air or water, and can be characterized by its rise time, positive and negative duration. The rise time is the time elapsed from ambient pressure to the maximum pressure of the shock wave and is usually in the order of microseconds. The positive duration is the amount of time that the pressure is above that of ambient conditions, and the negative duration is the amount of time that the pressure in the fluid is below that of ambient conditions. A theoretical shock wave is depicted below, showing the rise time as well as positive and negative duration.
In general, shock tubes can be blast-driven, where the shock wave is generated by a small explosive charge, or compression-driven, where the shock wave is generated by a quick release of pressure. The simplest type of blast-driven shock tube, the explosive charge is placed at the end of the tube, and the magnitude of the blast wave can be controlled by varying the amount of explosive material or diameter of the shock tube. In compression-driven shock tubes, the magnitude of the blast event is dictated by the selection of a diaphragm, which ruptures at a predetermined pressure, causing a rush of high-pressure fluid into a low-pressure medium. Similarly, blast-driven shock tubes can utilize diaphragms to create different types of explosive forces and shock events. Basic diagrams for each type of shock tube are shown below.
Advanced Materials and Devices, Inc (AMAD) has fabricated shock tubes for both in-air blast testing and underwater blast testing. Our shock tubes have been used to simulate explosions with peak pressures ranging from 50 to 500 psi. With our in-house fabrication facility and experience building custom testing setups, AMAD can develop tailored testing solutions across the defense, automotive, and industrial industries.