Application of tape-cast graded impedance impactors for light-gas gun experiments

Abstract

Fabrication of compositionally graded structures for use as light-gas gun impactors has been demonstrated using a tape casting technique. Mixtures of metal powders in the Mg-Cu system were cast into a series of 19 tapes with uniform compositions ranging from 100% Mg to 100% Cu. The individual compositions were fabricated into monolithic pellets for characterization of microstructure, density, and sound wave velocity. Graded impactors were fabricated by stacking layers of different compositions in a sequence calculated to yield a tailored acoustic impedance profile, and were characterized by ultrasonic C-scan and white light interferometry. The graded impactors were launched into stationary Al targets using a two-stage light-gas gun, and the resulting wave profiles were measured with either VISAR or Photonic Doppler Velocimetry. For an impactor using only seven compositions ranging from Mg to Cu, the composition steps are visible in the wave profiles. An impactor utilizing the full series of 19 compositions produces smoother compression with no visible manifestation of the discrete-layer structure. Hydrodynamic simulations of these impactors also suggest smooth compression profiles within the impactor.

Single-mode fiber, velocity interferometry

“…The target included a LiF tamper window adjacent to the back of an aluminum target [29]. The changing optical delays at the target include contributions due to compression of the tamping window that produces an apparent interface velocity that is higher than actual [18,21,22,[26][27][28].…”

“…We wished to examine the accuracy of the method at higher velocities by a direct comparison between SMV and another velocimetry technique. To perform this comparison we inserted a single SMV probe into an existing gas gun experiment to measure the mass velocities at the back surface of a target after projectile impact (for details related to the projectile, target and shock-wave physics, see reference [29]). …”

“…5, light returned from a single target probe was split and detected using an existing PDV detection channel [29] and the SMV velocimeter. We used a single 1550 nm laser to provide laser light for the probe (Fig.…”

Waves in periodic dissipative laminate metamaterial generated by plate impact

“…In these cases, the Hugoniot curve can't describe the state of the dynamically compressed laminates. For incoming pulses with short duration, experiments and numerical calculations [5][6][7][8][9] demonstrated the anomalous dependence of leading shock amplitude on the cell size (increase of stress amplitude with decrease of cell size) contradicting expectations based on the acoustic approximation [10]. A combination of dispersive properties and nonlinear elastic behavior of nondissipative laminates may result in the generation of solitary like stress waves, numerically investigated in [11][12][13][14][15][16][17].…”

Tailored ramp wave generation in gas gun experiments

“…A feasible method of generating a ramp wave under impact conditions is through the use of a flyer whose density is low at the leading face but increases with distance from that face. Previously this has been achieved through the use of a layered impactor consisting of multiple materials of varying density [3][4][5], using powder metallurgical or sedimentation techniques. These have produced good results but can be complex to manufacture, with layer thickness being a significant factor in the quality of the ramp profile.…”