Understanding and Predicting Dynamic Behavior of Materials : Metals/HE Interactions -- ejecta and frag
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Saryu Fensin, Los Alamos National Laboratory; Avinash Dongare, University of Connecticut; Benjamin Morrow, Los Alamos National Laboratory; Marc Meyers, University of California-San Diego; George Gray, Los Alamos National Laboratory

Wednesday 8:30 AM
February 26, 2020
Room: 5A
Location: San Diego Convention Ctr

Session Chair: Benjamin Morrow, Los Alamos National Laboratory


8:30 AM  
A Non-RMI Source of Substantial Quantities of Ejecta Mass Due to Cavitation Bubble Collapse: Garry Maskaly1; Saryu Fensin1; Thomas Hartsfield1; Gerald Stevens2; Brandon La Lone2; Dale Turley2; 1Los Alamos National Laboratory; 2Mission Support and Test Services
    When shocked, materials can produce a spray of small ejecta particles ahead of the free surface. Richtmyer-Meshkov Instability growth of surface defects, such as machining marks, has been identified as a principal cause of ejecta. In this work, we identify another potential mechanism for ejecta production with computational and experimental studies. Here, if cavitation due to a first-shock release results in near-surface cavitation bubbles, a subsequent shock can collapse these bubbles resulting in substantially larger quantities of ejecta than RMI mechanism with temperatures well over 2000 K. This work covers sensitivities in experiment and computation on this phenomenon, in particular the impacts of shock history and previous RMI ejecta sourcing.

9:10 AM  
The Role of Heterogeneities in Ejecta Production via MD Simulations: Rachel Flanagan1; Timothy Germann2; Marc Meyers1; Saryu Fensin3; 1University of California, San Diego; 2T-1, Los Alamos National Laboratory; 3MST-8, Los Alamos National Laboratory
    We investigate the shock behavior of copper seeded with heterogeneities through molecular dynamics simulations. Specifically, we aim to understand the influence of heterogeneities such as atomic defects, grain boundaries, and bubbles on the ejecta production of copper. Since shock melting plays a major role in the production of ejecta, microstructure was previously thought to not matter, but recent results suggest that different microstructures alter the mechanism through which ejecta is produced. For example, the presence of helium bubbles near the free surface of copper has been shown to nearly triple ejecta production due to a loss of planarity at the shock front. We analyze the size and velocity distributions to understand the mechanisms of ejecta production and the influence of heterogeneities on material strength. The ultimate goal of this work is to inform and elucidate upon parallel experiments, where data collection presents a significant challenge. LA-UR-19-26660

9:30 AM  
Experimental and Computational Studies of Laser-driven Shocks through Metal Surface Perturbations and Planar Grooves: Fady Najjar1; Alison Saunders1; Camelia Stan1; Hye-Sook Park1; Suzanne Ali1; Jon Eggert1; 1Lawrence Livermore National Laboratory
     Understanding the mechanisms of ejecta-ejecta interactions and ejecta collisions has relevance to many applications including dynamic behavior of materials, spacecraft shielding, and planetary impacts. Much research work has examined the underlying physics of ejecta sourcing and transport; however, few examples of experiments that study the effects of ejecta-surface interactions exist. We extend ejecta interaction studies to laser facilities allowing us to take advantage of the higher repetition rates, the repeatability of drive conditions, and the advanced time-resolved diagnostics suites. This talk will present results from experiments being fielded on LLE’s OMEGA lasers and report on the development of platforms to study microjetting formation and interactions from planar divots. Further, we will describe our computational effort supporting this experimental campaign. Work performed under the auspices of the U.S. Department Of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and supported by LDRD Grant No. 18-ERD-060. LLNL-ABS-780377.

9:50 AM  
On Design Of High-throughput Compact High-explosive Ejecta Source Platform: Fady Najjar1; Jose Sinibaldi1; 1Lawrence Livermore National Laboratory
    Strong shocks in metals reflecting from free surfaces eject particles traveling at hypervelocities. These ejecta particles play a role in a wide range of phenomena from additive manufacturing, inertial confinement fusion, and meteorite impacts. Production, transport, and potential collisions of micron-sized ejecta traveling at velocities of exceeding 1 km/s are of interest. We have developed an ejecta platform using a Hydrodynamics ALE code. It utilizes less than one gram of high explosives (HE) in a cylindrical geometry, the HE pressure accelerates a thin aluminum flyer across a gap to sufficient speeds to generate >20GPa shock pressures in a tin coupon. This produces ejecta that can be either solid or melted upon release from the free surface. Our design methodology will be presented as well as results from recent experimental measurements. Work performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. LLNL-ABS-780220.

10:10 AM Break

10:30 AM  Invited
A Continuum Mesoscale Perspective of the Dynamic Response of Metals and Explosives: Darby Luscher1; Cindy Bolme1; Marc Cawkwell1; Saryu Fensin1; Abigail Hunter1; Nisha Mohan1; Thao Nguyen2; Kyle Ramos1; R Scharff3; Justin Wilkerson2; Milovan Zecevic1; 1Los Alamos National Laboratory; 2Texas A&M University; 3Nevada National Security Site
    The dynamic thermomechanical responses of polycrystalline materials under shock loading are often dominated by the interactions of defects and interfaces. Polymer-bonded explosives can be initiated under weak shock impacts that would be insufficient to drive a reaction if the material response were homogeneous. Within metals, a prescribed deformation associated with a shock wave may be accommodated by crystallographic slip, void nucleation and growth, and fracture; the competition amongst these processes is often influenced by the behavior of grain boundaries. Direct numerical simulation at the mesoscale offers insight into these physical processes that can be invaluable to the development of macroscale constitutive theories. However, this approach requires that the mesoscale models adequately represent the nonlinear thermomechanical response of individual crystals and their interfaces. Here, we highlight a mesoscale modeling approach and then discuss progress towards improving the underlying theory and models for each constituent based on experimental observation.

11:10 AM  
On the hcp-bcc Phase Transformation in Magnesium Shock Compressed up to 60 GPa: Cyril Williams1; Nicholas Lorenzo1; 1US Army Research Laboratory
     The phase diagram of magnesium was investigated by Stinton et al. [1] up to 221 GPa at 300 K and to 105 GPa at 4500 K respectively using DACs in combination with XRD, resistive and laser heating. Between 46-50 GPa at 300 K, they observed the onset of the hcp to bcc phase transformation. They found the bcc phase to be stable up to 221 GPa. However, the same was not true when AZ31B-H24 magnesium was shock compressed to approximately 60 GPa at the Dynamic Compression Sector (DCS). The XRD results did not reveal any hcp-bcc phase transformation when the AZ31B-H24 magnesium was shock compressed to approximately 60 GPa but the solid phase changes to liquid perhaps due to temperature rise in the material. [1] Stinton, G. W. et al. “Phase Diagram and Equation of State of Magnesium to High Pressures and High Temperatures.” Livermore, CA (United States), 2014.