A lamb wave is a guided wave that propagates along a plate-like structures in various systems. Particularly, in space structures where weight saving is very important, various vibrations are often transmitted as Lamb waves; therefore, control and mitigation of Lamb waves are important issue. Since the high frequency components included in the pyroshock can be fatal to electronic devices, many engineers have studied shock isolators for mounting and protecting such electronic devices. Lamb waves, as with light, are refracted with a certain angle due to the difference in wave speed between the two media. Using the refraction of the lamb waves, shock response for selected region can be reduced by changing direction of the wave. Theoretically, this effect can be achieved by simply attaching a thin elastic material on the host plate to change flexural stiffness. Thus, it would be a very efficient solution to reduce shock response in a specific area behind the patch on the wavefront path by attaching one elastic patch on the path of the Lamb wave. In this study, we proposed elastic patches of various shapes for shock reduction, and the shock reduction characteristics of several patches were numerically and experimentally confirmed. The plane Lamb waves generated from the array of piezoelectric disk attached to the thin metal plate were refracted when passing through the elastic patch; as a result, the shock response was decreased in the area behind the patch.
Pyroshock or pyrotechnic shock generated by explosive events of pyrotechnic devices can induce fatal failures in electronic payloads. Therefore, understanding and estimation of pyroshock propagation through complex structures are necessary. However, an experimental approach using real pyrotechnic devices is quite burdensome because pyrotechnic devices can damage test structures and newly manufactured test structures are necessary for each experiment. Besides, pyrotechnic experiments are quite expensive, time-consuming, and dangerous. Consequently, nondestructive evaluation (NDE) of pyroshock propagation without using real pyrotechnic devices is necessary. In this study, nondestructive evaluation technique for pyroshock propagation estimation using hydrocodes is proposed. First, pyroshock propagation is numerically analyzed using AUTODYN, a commercial hydrocodes. Hydrocodes can handle stress wave propagation including elastic, plastic, and shock wave in the time domain. Test structures are modeled and pyroshock time history is applied to where the pyroshock propagation originates. Numerical NDE results of pyroshock propagation on test structures are analyzed in terms of acceleration time histories and acceleration shock response spectra (SRS) results. To verify the proposed numerical methodology, impact tests using airsoft gun are performed. The numerical analysis results for the impact tests are compared with experimental results and they show good agreements. The proposed numerical techniques enable us to nondestructively characterize pyroshock propagation.