Abstract :
[en] Nowadays, numerous pyrotechnic devices are used on satellites to seperate structural subsystems, deploy appendages and activate on-board operating subsystems. The firing of these pyrotechnic charges generates severe impulsive loads (so-called pyroshocks). Past experience has shown that the pyroshocks generated in the environment of satellites are the origin of numerous failures such as relay chatter and transfer. It is therefore becoming necessary to characterize the equipment response submitted to pyroshocks. For several years, Thales Alenia Space ETCA (Charleroi - Belgium) and the Faculte Polytechnique de Mons (FPMs) collaborate to develop some pyroshock test facilities to simulate pyrotechnic environments. These facilities use a resonant fixture that can be excited either by a mechanical impact or by an explosive charge. The resonant fixture can be a simple plate, a beam, a double plate assembly or a more complex structure. The test item, attached to the fixture, is subjected to the shock wave and to the resonant response of the test fixture so as to reproduce the operational pyroshock. A test campaign always begins by a trial and error experimental procedure in order to tune the operating parameters of the test facility to the specifications of the equipment manufacturers. When the desired pyroshock is achieved, the nominal tests are performed on the equipment. Of course, such a procedure is rather inefficient and expensive. For this reason, the interest to develop a computer modelling of pyroshocks is quickly appeared. Presently, there is a lack of computational techniques able to predict the dynamic behaviour of complex structures subjected to high frequency shock waves such as explosive loads. Pyroshock model requires an accurate dynamic model of the test facility, as well as a mathematical description of the excitation sources which are unknown because they cannot be directly measured. In our work, the test facilities are modeled by a FE Model which has been validated and updated until 1000 Hz from an experimental modal analysis. In the matter of the excitation sources, we have have considered an approach by Equivalent Mechanical Shock (EMS). This approach consists in replacing the actual excitation by a simple mechanical shock, such as a triangular shock, for which the amplitude and the duration are tuned so as to generate equivalent acceleration fields. For different configurations of the pyroshock test facility and for several excitation levels, the amplitude and the duration of the EMS have been identified. A parametric analysis of the different operating parameters has allowed to determine those that influences significantly the dynamic response of pyroshock test facility, and thus to orient the experimental procedure of the pyroshock testing. The different obtained results show that our pyroshock model allows to efficiently estimate the acceleration levels undergone by the electronic equipments during a pyroshock and, in this way, to predict some eventual electrical failures, such as the chatter of electromagnetic relays.
