A Theoretical Analysis about the Driving Mechanism of Mild Detonating Fuse

Abstract

[a] 1IntroductionIn aerospace applications many devices utilizing explosive, propellant and pyrotechnic compositions play important roles to achieve various functions, such as severance/fracture, release, jettison, switching, and so on. Pyrotechnics are extensively applied because of their high efficiency including high energy delivered per unit weight, small volume and compact, long-term storable energy,a nd controllable initiation and output energies [ 1].T able 1l ists major past and current pyrotechnic applicationsi na stronautics.According to the source of the shock,t hese pyrotechnic devices could generally be classified as point, line, or combined source as shown in Ta ble 2[ 2].S ince internal structural deformationo ften occurredi ne ach firing, pyrotechnics normally are utilizedo nly once. The best assurance of successful operationi st hat the devices are designed with functional margins andh ave beena ccurately manufactured. Meanwhile the explosive, propellant and pyrotechnic-composition energy sources will burn completely and quickly no matter if the ignition input is intentional or inadvertent. Thus selecting the lowest-level energy input to ensure ignition is the main priority.M ild detonating fuse (MDF) can be processed with av arietyo fs pecifications and good consistency,s oi ti sc ommonly used in linear source pyrotechnic devices as actuator. Figure 1s howsa nexample [1].Althoughe xtensivelya pplied, pyrotechnics are used with reservations, because some rocket launchingm ission failAbstract:T wo theoretical models basedo nm omentum conservation, energyc onservation,a nd law of motion were constructed to predict the velocity of fragments driven by mild detonatingf use (MDF). In the models, it is assumed that the driven velocity includes two parts:i nstant velocity coming from the impact of metal sheath and velocity increment caused by detonation products. Twog roups of experiments were designed and carried out to validate the models. The experimentr esults show that the modelb ased on momentum methodb etter describes the fragments driving process. Furthermore, as eries of finite-element simulations using LS-DYNA3D were done to fully verify the model. The simulation results show that the assumption of the fragment velocity composed of instant velocity and velocity increment is reasonable.B oth theoreticalp redictions and simulation results all indicate that instant velocity coming from the impact of the metal sheath accounts for majority( average8 9%)o ft he final velocity,w hich shows that lead sheath playsakey role in the acceleratingp rogress of fragment drivenb yM DF.A saresult, ac ertain distance should bea llowedf or the lead sheath to be accelerated to make full use of the MDF.T his research may relate to the design of linear pyrotechnic separation device in aerospace engineering.

Influence of Weakening Groove on Cutting Results of Composites Subjected to Shaped Charge Jet

“…e separation shell is usually made of metal material, which needs to be slotted in three places. e separation principle can be summarized as follows: after the explosive is detonated, it is disconnected along the prefabricated weakening groove under the action of the generated shock wave, so as to achieve the separation function [5,6]. It can be seen that the weakening groove has an important application in the metal separation structure.…”