Effects of Dynamic Strength in the Velocity History of a Rippled ShockSebastian Garcia P, Mechanical Engineering

Mentor: Pedro Peralta, School for Engineering Matter, Transport and Energy

Research question: How does the dynamic strength of a material affect the velocity of particles at a perturbed shock front and can this be used to estimate dynamic strength in solids?

Abstract:This work investigates the relationship betweenthe evolution of particle velocity at differentlocations of a perturbed (rippled) shock front andthe dynamic strength of the material byperforming careful direct numerical simulations ofa several experimental configurations. The findingsof this research will further our understanding ofdynamic strength effects on the evolution ofhydrodynamic instabilities in solids and providethe basis for a potential new technique to evaluatedynamic strength of solids under extreme loadingconditions.

References:[1] Meyers, Marc A. 1994. Dynamic Behavior of Materials. New York: Wiley.[2] Peralta, P., Loomis, E., Chen, Y., Brown, A., McDonald, R., Krishnan, K. and Lim, H. (2015).Grain orientation effects on dynamic strength of FCC multicrystals at low shock pressures: ahydrodynamic instability study. Philosophical Magazine Letters, 95(2), pp.67-76.[3] Barnes, J.F., Blewett, P.J., McQueen, R.G., Meyer, K.A., and Venable, D., Taylor instability insolids, Journal of Applied Physics, 1974. 45(2): p. 727.[4] Park, H.-S., Remington, B.A., et al., Strong stabilization of the Rayleigh–Taylor instability bymaterial strength at megabar pressures, Phys. Plasmas, 2010. 17(5): p. 056314.[5] Opie, S., Gautam, S., Fortin, E., Lynch, J., Peralta, P. and Loomis, E. (2016). Behaviour ofrippled shocks from ablatively-driven Richtmyer-Meshkov in metals accounting for strength.Journal of Physics: Conference Series, 717, p.012075.[6] Opie, S., Loomis, E., Peralta, P., Shimada, T. and Johnson, R. (2017). Strength and ViscosityEffects on Perturbed Shock Front Stability in Metals. Physical Review Letters, 118(19).

Method:• 2-D, plane strain simulations were performed

using a specialized hydrocode.• The model simulated a stationary rippled

copper target, as shown in Fig. 1.• The target was impacted by a flat flyer plate,

made of Tungsten to increase the mean stress.• The impact occurred on the rippled side of the

target, which lead to a perturbed (rippled)shock front propagating towards the flat side ofthe sample.

• After the shock arrives at the flat surface, thedifference between particle velocities predictedat peaks and valleys of the perturbed shockfront was plotted versus time.

Results:• The amplitude of the shock front in the Tungsten to Copper setup was too large, and

theory states that large shock perturbation amplitudes are relatively insensitive to effects in strength.

• A setup to fix this insensitivity is to cover the perturbation with a different material [Fig. 2], like Tungsten or Nickel, this will produce a faster shockwave that lowers the amplitude of the rippled shock front, making in it more sensitive to strength effects.

• Simulations indicated that Nickel was a good choice to be the base material as Tungsten’s sound speed is too close to Copper’s so the shock arrives almost flat to the target. Nickel also has a faster wave speed than copper, which is also desirable.

Conclusion:

• Impact between Tungsten and Copper produces larger pressures in Copper than the Cu-Cu setup.

• A target thickness of 300 to 500 µm yields the largest velocity difference in the shockwave for the updated configuration. [Fig. 3]

• Fig. 3 and Fig. 4 show how sensitive the experiment is to changes in strength.

Acknowledgment:This work would not have been possible without contribution from the Fulton Undergraduate Research Initiative. Further thanks to Dr. Pedro Peralta for his mentorship.

Fig. 1 – (a) Solid Model of Copper target Target (b) Initial modeling geometry

Fig. 2 – Updated multimaterial setup

Fig. 3 – Velocity vs. Position plot at 550 µmof sample at 0Gpa.

Future Work:• Gas gun at Dr. Peralta’s Lab will be used to run

experiments with the updated setup, [Fig. 2]• Electroplate Nickel to Copper sample.• Develop a technique to evaluate dynamic strength of

solids with alternative methods.

Fig. 4 – Velocity vs. Position plot at 550 µmof sample at 2Gpa.