Dynamic Behavior of Materials IX: Ejecta, RMI, RT & Jetting / Shear
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Eric Brown, Los Alamos National Laboratory; Saryu Fensin, Los Alamos National Laboratory; George Gray, Los Alamos National Laboratory; Marc Meyers, University of California-San Diego; Neil Bourne, University of Manchester; Avinash Dongare, University of Connecticut; Benjamin Morrow, Los Alamos National Laboratory; Cyril Williams, US Army Research Laboratory

Thursday 8:30 AM
March 3, 2022
Room: 263C
Location: Anaheim Convention Center

Session Chair: Arun Shukla, University of Rhode Island; Vikas Prakas, Washington State University


8:30 AM  
Experimental & Computational Development of Shallow Bubble Collapse as an Ejecta Production Mechanism: Garry Maskaly1; Fady Najjar1; Gerald Stevens2; William Turley2; Matthew Staska2; Brandon LaLone2; Thomas Hartsfield3; 1Lawrence Livermore National Lab; 2NNSS STL; 3Los Alamos National Lab
     Richtmyer-Meshkov Instability production has been extensively studied, but despite this, there are still experimental results that are not easily explained with RMI theory. In order to understand these physics, we began a campaign to model and validate a different ejecta source mechanism. We have identified Shallow Bubble Collapse (SBC) as an alternative production mechanism under certain drive conditions. In this work, we detail computational approaches and experimental methods used to develop an understanding of SBC. We demonstrate SBC in both tin and cerium, with some experiments showing temperatures exceeding 4000 K and areal masses exceeding 1 g/cm^2. Through computational modeling, we develop the theory of the creation of this high momentum ejecta cloud. This work demonstrates the conditions that impact SBC activation and production.LLNL-ABS-823993. Work performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC.

8:50 AM  
Ejecta and Melting Produced by High Velocity Impact of Steel Microparticles: Jasper Lienhard1; David Veysset2; Keith Nelson1; Christopher Schuh1; 1MIT; 2Stanford University
    Microparticles impacting metal substrates at supersonic velocity can cause a wide range of interesting ultra-high strain rate behavior, including impact-induced melting and rapid ejection of solid material from the impacted target. By using a laser system that can launch single metal microparticles to high speeds and a synchronized nanosecond-resolution imaging system, our recent experiments have enabled in situ observations of metal microparticle impacts at velocities in the range of 100 to 1500 m/s. By impacting relatively strong, rigid stainless steel particles on a softer metal target such as tin, we are able to isolate plastic deformation to the impacted target, enabling direct measurement of melt volumes and ejecta cloud volumes produced upon impact across a wide range of velocities. These experiments have revealed new details on the physics of impact cratering and the hardness properties of metals at strain rates as high as 10^8 s^-1.

9:10 AM  
3D Hydrodynamics Computations of High-areal Mass Ejecta Production from Shallow Bubble Collapse Mechanism: Fady Najjar1; Garry Maskaly1; Gerald Stevens2; W. Dale Turley2; Brandon LaLone2; Matthew Staska2; Ruben Valencia2; David Brantley1; 1Lawrence Livermore National Laboratory; 2MSTS-STL
     While extensive research of ejecta physics has been performed on Richtmyer-Meshkov Instability (RMI) production, recent experiments have demonstrated that, under certain conditions, Shallow Bubble Collapse (SBC) mechanism can produce substantial areal masses (>300 mg/cm2) at elevated temperatures (~2500K). Detailed 3D computations are performed using LLNL’s hydrodynamics code to understand the ejecta production and its evolution as activated by SBC. We will validate our computational analysis to recent experimental series campaign performed at STL for various metal samples. Our current experiments have explored the range of SBC activation, showing evidence of rapid vaporization of the ejected material. Experiments have shown that the SBC mechanism is agnostic to initial surface finish. This talk will provide highlights of our computational SBC effort.LLNL-ABS-823964. Work performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC.

9:30 AM  
In Situ X-ray Diffraction of Shock Driven Sn Microjets: David Bober1; Jonathan Lind1; Alison Saunders1; Minta Akin1; Fady Najjar1; 1Lawrence Livermore National Laboratory
     Synchrotron x-ray diffraction was used to identify the minimum pressure at which shock driven Sn microjets completely melt. This pressure was below the Hugoniot state from which a planar surface would melt upon the release of a normal shock. The difference in these states is a measure of the dissipation produced by the jetting process and is a useful benchmark for plasticity models. Regarding the solid jet material, the diffraction signal revealed extensive grain refinement had occurred; complete Debye-Scherrer rings were observed from an interaction volume that was smaller than the average initial grain volume. These results provide a new level of experimental constraint on the material state within Sn microjets. The jets were produced via parallel plate impact loading of polished Sn samples, each of which was cut with a single V-groove. Work performed under the auspices of the U.S. DOE by LLNL under contract DE-AC52-07NA27344. LLNL-ABS-823936

9:50 AM  
Determining Constitutive Properties of Metals under Extreme Deformation Conditions Using Cutting: Harshit Chawla1; Shwetabh Yadav2; Hrayer Aprahamian1; Dinakar Sagapuram1; 1Department of Industrial and Systems Engineering, Texas A&M University; 2Department of Civil Engineering, Indian Institute of Technology Hyderabad
    We demonstrate a novel application of cutting or “machining” as a high-throughput approach for determining the constitutive properties of metals under moderate-to-large plastic strains and high strain rates, deformation regimes that are difficult to access using conventional material testing methods. The constitutive parameters are obtained using in situ high-speed measurements of the plastic flow in the cutting deformation zone, coupled with an inverse scheme to estimate the parameters from full-field deformation data. The inverse algorithms are further tailored, based on the underlying structure of different constitutive laws, to ensure global optimality and unique parameter estimates. The approach is demonstrated using ductile metals with different constitutive models under conditions of large plastic strains up to ~ 10 and strain rates up to ~ 10^3 /s. Issues related to the effect of measurement uncertainties (e.g., noise) on parameter estimates and further extension of this approach to higher strain rates are also discussed.

10:10 AM Break

10:25 AM  
Dynamic Response of Polycrystalline Pure Magnesium under Pressure and Shear Plate Impact Loading at Elevated Temperatures: Vikas Prakash1; 1Washington State University
    Polycrystalline magnesium (Mg) and its alloys have been widely investigated to better understand and improve their mechanical properties including ductility, formability, yield anisotropy, elevated temperature performance, to name a few. However, significant questions remain as to how these materials behave under ultra-high strain-rate loading conditions, especially at elevated temperatures. In view of this, in the present study, elevated temperature combined pressure-and-shear plate impact experiments are employed to investigate the dynamic shearing resistance of polycrystalline commercially pure (99.9%) magnesium at strain-rates in excess of 105 s-1, temperatures up to 500˚C, and shear strains >100%. The results of the study provide important insights into the shearing resistance of polycrystalline pure Mg under extreme thermomechanical loading and its relationship to evolution of various inelastic deformation modes – dislocation-mediated slip, deformation twinning, and geometric strain softening -- with different mechanisms becoming dominant at different levels of inelastic strains and test temperatures.

10:45 AM  
In-situ SEM High Strain Rate Testing of Mg Micropillars with TEM Postmortem Analysis: Zhaowen Lin1; Daniel Magagnosc2; Jianguo Wen3; Chung-Seog Oh4; Sang-Min Kim5; Horacio Espinosa1; 1Northwestern University; 2The Army Research Laboratory; 3Argonne National Laboratory; 4Kumoh National Institute of Technology; 5Korea Institute of Machinery and Materials
    High strain rate mechanical characterization of materials, performed on micrometer scale, is attracting increasing interests as it provides a unique opportunity to understand rate effects on mechanical behavior of metals from nano to meso scales. Such experiments not only provide mechanistic understanding but also a means to close the gap between discrete dislocation dynamics and coarse grain atomistic modeling, which is done at high strain rates. Very few reports exist addressing the experimental challenges associated with the design of experiments that can simultaneously examine the effects of length and time scales. In this work, a suite of protocols ranging from sample microfabrication to instrumentation for testing and data analysis are presented. Moreover, the mechanical behavior and emergent defect organization, in micrometer scale single crystal magnesium subjected to high strain rate compression along the c-axis, are reported.

11:05 AM  
Understanding the Ejecta Dynamics in Gas Cells for Shallow Bubble Collapse Mechanism: Georges Akiki1; Garry Maskaly1; Fady Najjar1; Gerald Stevens2; William Turley2; Brandon La Lone2; Matthew Staska2; 1Lawrence Livermore National Laboratory; 2Special Technologies Laboratory
     We have recently observed that metal samples, subject to certain multi-shock conditions, generate substantially more ejecta compared to those produced from Richtmyer-Meshkov Instability (RMI). This mechanism activates due to bubbles forming near the surface of liquified metal, following a shock-and-release event. These bubbles collapse under an additional shock insult, thus releasing significant amounts of ejecta (~10X more than RMI) at very high temperatures (more than twice that expected without cavitation). We refer to this phenomenon as Shallow Bubble Collapse (SBC). Our study will present experimental measurements and numerical results of ejecta produced by SBC comparing ejection into gases and vacuum. We examine the impact of gas pressure on SBC ejecta transport and evolution. Numerical simulations using LLNL’s hydrodynamics code, ARES, will be used to examine these physics. Work performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. LLNL-ABS-823842.