Mitigation of impact vibrations using impedance mismatch in cylindrical structures

The focus of this work is to study the phenomenon of material impedance mismatch to determine its effect on the mitigation of high frequency accelerations in projectile and long bar structures within linear ranges of materials. In this study, the acceleration responses of structures with various materials and material combinations were studied experimentally, numerically and by the Finite Element Analysis (FEA). Air-gun tests conducted by the US Army Research Laboratory were modeled using FEA to simulate the acceleration pulse and shock waves experienced by artillery components during a launch. After the prototype of projectile was selected, further studies were conducted experimentally and computationally using wave tracing techniques to understand the effect of impedance mismatch on the high frequency axial acceleration response to an impact loading.;Electronic devices for sensing, control and actuation have become standard components of "smart" structural systems to enhance their structural response adaptively and effectively. Such devices are being incorporated in military vehicles and weapon systems. The reliability of these sensing devices under extreme loading conditions need much improvement since they are sensitive to high frequency vibrations.;Experimental results suggest that high frequency accelerations in layered cylindrical structures could be reduced compared either in frequency, magnitude or both to those in homogeneous cylinders if a reflected wave from the end of the projectile does not interfere with the applied impact force. Computational studies using FEA verified the experimental results of our interference hypothesis. Further, wave tracing results obtained using equations of wave propagations in a layered structure supported both computational and experimental results.;Our research was extended in two directions. One is the potential usage of new material types known as material foams in projectiles. Results show that mitigation can be obtained using metal foams if they do not get crushed completely under impact loads. Similarly, impedance mismatch concepts were considered using steel, concrete and wood for potential civil engineering applications. The results showed that the potential to reduce accelerations in hybrid building exists through the use of impedance mismatch if steel covers or joints are placed at the end of concrete beams.