Stress Wave Attenuation in Noncollinear Structures Subjected to Impulsive Transient Loadings

This paper presents an exploration of noncollinear Timoshenko beam structures for attenuating the stress waves generated from impulsive transient loadings. Due to the existence of the noncollinear segments, flexural waves are generated in addition to the longitudinal waves. Furthermore, the resulting waves are dispersive and thus provide higher potential for the attenuation of the stress waves. Symmetric patterns are found to be more appropriate for increasing the stress-wave attenuation capacity, as these patterns can eliminate bending stress effects at the boundary of the structures. More generally, an adaptive optimization methodology is developed to find the most efficient layout of the noncollinear stress-wave attenuators (NSWAs). This methodology uses genetic algorithms (GA), coupled with an explicit finite-element (FE) method for analyzing the wave-propagation behavior of the structures. The developed methodology is capable of updating the FE model of each trial solution, as the geometric characteristics of the solutions are evolving during the optimization procedure. Through this evolutionary design process, the attenuation capacity of the noncollinear structures is observed to be a complex function of the number of noncollinear segments and the relative wavelength associated with the transient loading. In addition, the results show that the single-material noncollinear structures are not effective for attenuating the amplitudes of transient pulse loadings with longer durations, such as blast waves. Most interestingly, however, by incorporating geometric and material discontinuities, bimaterial NSWAs are found to provide impressive levels of attenuation within compact geometries. Although much analytical and experimental validation remains, designs along these lines could help to initiate a paradigm shift from hardening of structures for blast protection towards a protective systems design approach featuring creative management of stress wave propagation.