Impact Test Condition Research Of Equivalence And Its Transformation Method

Abstract: Generally there are two test conditions for the shock test of aerospace products, i.e. the time-history condition which is in the form of half-sine wave, it usually used for component shock test. The other is frequency domain condition which is in the form of shock response spectrum, it can be used for produce time-history excite signal by vibration control device, this condition is usually used for the shock test of single or complete machine. Shock response spectrum test technology refers to use SRS as reference, synthesize the transient waveform which satisfies the SRS test condition to simulate shock environment in real world. As we can see from the definition of SRS, the conversion from frequency domain to time-history is non-unique, i.e. there could be infinite time-history waveforms have the same SRS. This passage will introduce the conversion method from SRS to half-sine waveform shock test condition based on the fact mentioned above.1) Synthesize plenty of time-history waveforms which satisfy SRS test condition using wavelet synthesis method.2) Take these waveforms as the shock test pulse signals, using finite element method simulate the responses of the tested product under these signals.3) Pick the peak response of each signal, we could get the probability density function. The peak response is also the shock load to the components in the tested product. And because using different shock signals there will be different peak responses, which means when simulate the shock test all these different peak response could have the probability to occur. Therefore we could choose a threshold value in the probability density function, take the peak response which related to the threshold value probability as the amplitude of the half-sine signal which used in shock test on components.4) Analyzing the relationship between the duration of half-sine signal and the shock response of component, we could get the duration of half-sine signal. Then we finish the conversion from SRS test condition to half-sine shock test signal.5) Compare durations when using mode superposition method which programed by author, NASTRAN direct method and NASTRAN Modal method to compute response of single shock excitation, find the quickest way to compute shock responses. Analysis values of selected parameters when sample number changes, find the minimum sample which can results a correct probability density function. It can improve the efficiency when consider the two way mentioned above.