Studying shock-driven interface sliding 50 ns at a time

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(Left): Dynamic Friction experiment schematic. The Trident laser beam is absorbed and ablates a thin coating layer on a sapphire window, which expands and accelerates a flyer plate. Surface dynamics are measured with TIDI (data in upper right) at the 50 ns increments of the “H-beam” probe laser.

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New models that include the effects of finite resistance to interface sliding (friction) between two materials under high strain rate or shock deformation are use in multi-physics hydrodynamics codes. With these modern interface treatments, modelers expect to obtain more reliable predictions of multi- material dynamic systems. Until recently, there was little to no experimental data to validate the interface friction models. New experiments at the Trident Laser have demonstrated the ability to provide this important data using a technique called Transient Imaging Displacement Interferometry (TIDI).

In Dynamic Friction experiments, Trident’s high energy, long pulse (1.2 microsecond) laser accelerated small copper flyer plates towards a two-metal target consisting of a central piece of beryllium pressed and diffusion bonded into the center of a 1 cm diameter copper disk. The impact created a shock propagating at different velocities in each material. This established a relative velocity difference at the interface and caused it to slide. Trident sent a series of probe laser pulses to the target surface as the shocks exited the rear surface. The TIDI diagnostic used these pulses to form displacement-sensitive interferometric fringes of the near interface region. Captured with fast optical framing cameras, the shifting of these fringes created a “movie” of surface deformation that researchers compared with friction model predictions. Preliminary comparisons to measured surface profiles show that simulations capture well the interface friction dynamics with bonded interfaces sliding using a three times greater resistance than unbonded.

Participants include: Eric Loomis, Tom Shimada, and Randall Johnson (Plasma Physics, P-24); James Hammerberg (Materials and Physical Data, XCP-5); Jason Cooley (Metallurgy, MST-6); Gerald Rivera, Jim Williams, and Deanna Capelli (Polymers and Coatings, MST-7); Darrin Byler and George T. Gray III (Materials Science in Radiation and Dynamics Extremes, MST-8); Curt Bronkhorst (Fluid Dynamics and Solid Mechanics, T-3); Aaron Koskelo (Verification and Analysis, XCP-8), Scott Greenfield (Chemical Diagnostics and Engineering, C-CDE); and Russ Olson (Neutron Science and Technology, P- 23).

NNSA Science Campaign 2 (LANL Program Manager, Rick Martineau) funded the work, which supports the Lab’s Nuclear Deterrence mission area and the Science of Signatures science pillar. Technical contact: Eric Loomis

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Displacement profiles from an unbonded Dynamic Friction target compared with predictions (thick curves) using a 0.25 kbar interface friction force. Profiles are taken at beryllium shock breakout time plus the time indicated in the figure.