Abstract :
[en] When used for space applications, electronic equipments are submitted to pyrotechnic shocks, for instance during the separation steps of the launcher vehicle stages or when the solar panels of a satellite are deployed. The pyrotechnical charges used for these events generate severe impulsive loads that can cause failures in electronic equipments. As the prediction of the mechanical behaviour of equipments, in regards of pyroshocks, is very difficult by calculation, the projects must rely on testing to validate the design. Thales Alenia Space ETCA has developed, some years ago, a pyroshock test facility dedicated to the testing of electronic units. The facility uses a resonant test fixture assembly which is excited by a detonating charge (for high acceleration levels) or a mechanical impact (pneumatic jack) for lower levels. The device under test, screwed to the fixture, is submitted to the direct shock wave and to the resonant response of the test fixture, simulating the required shock. To reach the specified levels, the set-up is checked, by using a dummy test item, and tuned in modifying some significant parameters: quantity of explosive (or pressure of pneumatic jack), type of test fixture (steel or aluminium plate, interfaces between the plates, explosive location,...). When the desired pyroshock is achieved, the nominal tests are performed on the test item. The choice of an adequate test fixture is the most important parameter in this trial-and-error process. Since the test facility building, more than 3000 firings have been performed. All the recorded results make up a pyroshocks data base. At the beginning of a new test campaign, a computer program scans the data base and looks for the test results closest to the specified spectra. A new interest is to minimise the number of trial real shocks before to be able to achieve the nominal test. For that, the different set-up used by ETCA are modelled with ANSYS FEA software and used as a new help in the performing of a pyroshock qualification process. The objective of this paper is to describe the way to reach a high specification (in terms of shock response spectrum) along two axes simultaneously. At first, the notion of pyroshock is explained in a general way and the mechanical tools used to compare severities of shocks are presented. Then, the pyroshock test facilities of TAS ETCA are described and the main steps of a test campaign are presented to do understand the difficulty to achieve a request nominal level. A new help is now used by ETCA to reduce the time necessary to perform calibration phases. Numerical simulations are realised to give a good idea of the influence of some parameters of the different possible configurations of the facilities. For that, an approach by equivalent mechanical shock is presented and is used to perform mechanical transitional analyses. The excitation is modelled by a triangular impulsion. The parameters of amplitude and duration can be optimised to minimise the difference between simulated and experimental results. First experimental shocks are realised to have a data base of possibilities to reach the imposed specification. Then, the numerical tools described are used to perform parametrical analysis and develop a new configuration of the test facilities. At last, results obtained with the new set-up are presented and show the capability of Thales Alenia Space ETCA pyroshock test facilities to cover a large range of specifications in terms of SRS.
