Imaging perturbed shock propagation in powders

Area of Science:

• Materials Science
• Shock Physics
• Powder Mechanics

Background:

• Understanding powder response under shock is crucial for applications like explosive welding and armor design.
• Deviatoric stresses, arising from irreversible processes like viscosity and strength, significantly influence shock wave propagation in granular materials.

Purpose of the Study:

• To develop and validate a novel experimental technique for characterizing the deviatoric response of powders under shock conditions.
• To investigate the shock damping behavior of various powders and mixtures, analyzing the influence of perturbation wavelength and initial shock strength.

Main Methods:

• A projectile-driven shock wave with a sinusoidal front was propagated through powders confined in a cylindrical wedge.
• High-speed imaging at 5 MHz captured shock wave propagation and damping via laser light reflection from a treated surface.
• Image analysis provided qualitative and quantitative data on shock wave perturbation and contrast loss.

Main Results:

• Observed damping of the perturbed shock wave front with increasing powder thickness, attributed to viscosity and strength.
• Presented new data on shock damping behavior for copper, tantalum, and tungsten carbide powders and their mixtures.
• Captured the first full-field images revealing spatial disturbances on the shock front, dependent on particle material and morphology.

Conclusions:

• The developed methodology effectively quantifies powder deviatoric response in shock regimes.
• Shock wave damping is a key phenomenon in powder shock compression, influenced by material properties and shock parameters.
• Particle-level details significantly impact shock front dynamics, offering avenues for future material design.