Resonant plate and other resonant fixture shock techniques were developed in the 1980s at Sandia National Laboratories as flexible methods to simulate mid-field pyroshock for component qualification. Since that time, many high severity shocks have been specified that take considerable time and expertise to setup and validate. To aid in test setup and to verify the shock test is providing the intended shock loading, it is useful to visualize the resonant motion of the test hardware. Experimental modal analysis is a valuable tool for structural dynamics visualization and model validation. This chapter describes a method to perform experimental modal testing at pyroshock excitation levels, utilizing input forces calculated via the SWAT-TEEM (Sum of Weighted Accelerations Technique—Time Eliminated Elastic Motion) method and the measured acceleration responses. The calculated input force and the measured acceleration data are processed to estimate natural frequencies, damping, and scaled mode shapes of a resonant plate test system. The modal properties estimated from the pyroshock-level test environment are compared to a traditional low-level modal test. The differences between the two modal tests are examined to determine the nonlinearity of the resonant plate test system.
The resonant plate shock test is a dynamic test of a mid-field pyroshock environment where a projectile is struck against a plate. The structure undergoing the simulated field shock is mounted to the plate. The plate resonates when struck and provides a two sided shock that is representative of the shock observed in the field. This test environment shock simulates a shock in a single coordinate direction for components looking to provide evidence that they will survive a similar or less shock when deployed in their operating environment. However, testing in one axis at a time provides many challenges. The true environment is a multi-axis environment. The test environment exhibits strong off-axis motion when only motion in one axis is desired. Multiple fixtures are needed for a single test series. It would be advantageous if a single test could be developed that tests the multi-axis environment simultaneously. In order to design such a test, a model must be developed and validated. The model can be iterated in design and configuration until the specified multi-axis environment is met. The test can then execute the model driven test design. This report discusses the resonant plate model needed to design future tests and the steps and methods used to obtain the model. This report also details aspects of the resonant plate test discovered during the process of model development that aids in our understanding of the test.
Satellites and launch vehicles are subject to pyroshock events that come from the actuation of separation devices. The shocks are high frequency transients that decay quickly—within 5-20 ms—and can be damaging events for satellites and their components. The damage risk can be reduced by good design practice, taking advantage of the attenuating properties of structural features in the load path. NASA and MIL handbooks provide general guidelines for estimating the attenuating effects of distance, joints, and other structural features in the load path between the shock source and the shock sensitive component. One of the challenges is adequately modeling the dissipative mechanisms in structural features to better understand the risk to shock sensitive components. Previously, we examined the modeling of pyroshock attenuation in a cylindrical structure and used peak acceleration to evaluate how much shocks are attenuated by distance and structural features in a cylindrical structure. In this work, we investigated different quantities to gain more insight into how and why pyroshocks get attenuated by a bulkhead. We found that the bulkhead affects the SRS peak more than the SRS ramp and that approximately 30% of the structural intensity of the pyroshock flows into the bulkhead regardless of the thickness.