Optimal Design of Layered Periodic Composites for Mitigation of Impact-Induced Elastic Waves

A systematic method for optimal design of layered periodic composites for mitigation of impact-induced shock waves is presented. Frequency spectrum of a pulse with a sharp rise-time is analyzed and the frequency range that carries most of the pulse energy is identified. A genetic algorithm is used to maximize the stop bands of a layered periodic composite over the target frequency range. Due to reflection of the pulse over the stop bands, the maximum stress and the energy of transmitted pulse become minimal. To verify the theoretical calculation a sample is fabricated and Hopkinson bar experiments are performed. It is observed that only 9.7% of energy of the incident pulse gets transmitted through the sample. In addition, the wave speed in the composite is measured to be 45.4% less than the wave speed in its constituent material with the lowest wave speed.