Shock Model and Test Correlation for Structural Response Prediction

When defining hardware shock environments, it is typical to assume a reduction of shock levels through structural joints – nominally, a 30% reduction per joint up to a maximum of three joints. However, review of shock test data from a flight-like test article demonstrates that attenuation across interfaces is not always realized. Across a single joint, significant amplification is observed at various locations on the composite shell of the test article throughout the entire frequency range, with maximum amplification of ~12dB. Responses across a second joint still shows low frequency amplification coupled with mid- to high-frequency attenuation. While empirical scaling of shock inputs may be appropriate for most applications, its failure to account for potential amplification may result in an underestimate of a hardware’s shock environment. The effect of mass loading on hardware responses was also investigated, which demonstrated the complexities of mass attenuation, including frequency and location dependencies. This contrasts with the Barrett Method for mass scaling of vibroacoustic responses. An analytical framework for deriving shock environments and accurately predicting the degree of attentions and amplifications where structural modes are from system-level specifications would be beneficial to qualifying hardware for flight shock environments.