Planar shock wave amplification by logarithmic spiral ducts within polymethyl methacrylate (PMMA)

High-speed quantitative schlieren photography was used to quantified the effective shock wave amplification within arrays of internal logarithmic spiral ducts in polymethyl methacrylate (PMMA) coupons. The PMMA coupons were adhered to a steel plate that was impacted with a projectile from a propellant-driven gas gun to impart a planar shock to the PMMA. The log spirals were subtractive cut into the PMMA with a laser to introduce an airgap within the material. The spirals were arranged in various geometries to determine the shock wave amplification on one side of the spiral and the shock wave transmission to subsequently stacked log spirals. The spirals were also tested at orientations perpendicular to and reverse of the incoming planar shock to analyze the effect of the log spirals with alternate shock impingement locations. The high-speed videos with quantitative schlieren were used to determine the density changes within PMMA coupons and create streak images showing shock wave propagations. Photon Doppler velocimetry (PDV) was used to determine the particle velocity on the opposite surface of the shock initiation to compare to the results of the high-speed video and analyze the shockwave attenuation from passing through the log spiral arrays.