Effective Data Validation Methodology for Pyrotechnic Shock Testing

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Valid test data from explosively or ordnance-initiated pyrotechnic shock tests are difficult to acquire. Measurement of these frequency-rich acceleration time histories, a prerequisite to calculation of a valid shock response spectrum, drives the measurement system to its performance limits. Successful acquisition of demonstrably valid acceleration time histories requires a series of performance compromises that must be made with a depth of measurements expertise. Such expertise may not be available from vendors of the various data acquisition systems sold for these tests. All measurement system performance characteristics (transducer mount dynamics, gain, frequency response, phase response, linearity, lead wire effects, sampling rate, etc.) require compromise. It takes professional-level knowledge and experience to make the proper compromises to assure data validity for the measured wave shape. These measurements should never be taken for granted, as often and unfortunately happens. Data validation methods should be used by a test organization to prove the validity of the experimental shock wave shapes and subsequent shock response spectra (SRS). Recent events in the explosively driven, pyrotechnic shock test community show that methods for effective data validation are not in general use. This situation can lead to the problem of invalid shock test acceleration time histories causing invalid shock response spectra with both entering the design verification cycle. This paper defines the requirements for the measurement of valid shock wave shapes. It then defines an ordered series of validity tests that will both identify and quantify a number of detrimental effects in the acquisition of these frequency rich time histories, and resultant shock response spectra. Use of this set of validity checking methods assures the objective identification of invalid shock data to customers of pyrotechnic shock tests.