Pyrotechnic devices have been employed in satellite launch vehicle missions, generally for the separation of structural subsystems such as stage and satellite separation. Expanding tubes are linear explosives enclosed by an oval steel tube and have been widely used for pyrotechnic joint separation systems. A numerical model is proposed for the prediction of the proper load of an expanding tube using a nonlinear dynamic analysis code, AUTODYN 2D and 3D. To compute a proper core load, numerical models of the open-ended steel tube and mild detonating tube encasing a high explosive were developed and compared with experimental results. 2D and 3D computational results showed good correlation with ballistic test results. The model will provide more flexibility in expanding tube design, leading to economic benefits in the overall expanding tube development procedure. 1. Introduction Pyrotechnic devices are widely used in many space applications. They are used to perform releasing, cutting, pressurization, ignition, switching, and other mechanical work to initiate flight sequences during space missions, such as the separation of subsystems, boosters, fairings, stages, or payload satellites. Such explosive separation devices generate a shock environment that could have a destructive effect on the structure and hardware, especially on electromechanical and optical equipment. The environment is very complex, and studies have revealed that little information is available describing the basic mechanism of shock transmission and predicting shock response. Therefore, improved guidelines for pyrotechnic design, development, and qualification are clearly needed [1–3]. Pyrotechnic devices may generally be divided into point sources and line sources. Typical point sources include explosive bolts, separation nuts, pin pullers and pushers, and certain combinations of point sources for low explosive actuation. Typical linear sources include flexible linearly shaped charges, mild detonating fuses, and Super*Zip for high explosive actuation [4, 5]. An example of line sources is shown in Figure 1. The pyrotechnic device shown is a high-load-carrying separation system that must act without contamination of the payload and is called an expanding tube in this study. The device is one of the greatest shock producers in aerospace separation systems. The detailed components of the expanding tube are also represented in Figure 1, consisting of an MDF (mild detonating fuse), support, and a flattened steel tube. The MDF is a small diameter extruded tube containing a single strand of
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