Dynamic Behavior of Materials: Experiments and Molecular Dynamics Simulations: Dynamic Behavior of Materials: Experiments and Molecular Dynamics Simulations
Sponsored by: TMS: Computational Materials Science and Engineering Committee
Program Organizers: Ghatu Subhash, University of Florida; Douglas Spearot, University of Florida

Monday 8:00 AM
October 10, 2022
Room: 326
Location: David L. Lawrence Convention Center

Session Chair: Ghatu Subhash, University of Florida; Douglas Spearot, University of Florida

8:00 AM  Keynote
Structure / Property (Constitutive and Dynamic Strength / Damage) Characterization of Single-Phase FeAl: George Gray¹; Saryu Fensin¹; Carl Cady¹; H Wang²; Kenneth Vecchio²; ¹Los Alamos National Laboratory; ²University of California San Diego
    In this talk, the results of a study quantifying the constitutive behavior of two different B2-structured FeAl intermetallics, as well as an FeAl-based metallic-intermetallic laminate (MIL) composite is presented. One textured and layered polycrystalline FeAl was fabricated using an innovative “multiple-thin-foil” configuration and “two-stage reaction” strategy. Layers of metallic Al and Fe foils were alternating stacked and then processed utilizing a combination of a multiple pressure & temperature processing procedure to produce fully-dense single-phase FeAl samples. This same approach was used to fabricate the MIL composite. An equiaxed, random polycrystalline single-phase FeAl sample was fabricated from powders to be used as a reference material. In this talk, the influence of the constitutive behavior as a function of loading orientation, temperature, and strain rate, from quasi-static to dynamic rates, is presented. The dynamic damage evolution and failure response of the three materials was probed using flyer-plate impact driven spallation experiments.

8:40 AM
Shock-induced Spallation in Monocrystalline Boron Carbide: Ghatu Subhash¹; Amith Adoor Cheenady¹; ¹University of Florida
    Molecular dynamic simulations were used to investigate spall behavior in boron carbide (BC) along [111] and at 90° to [111] by propagating two tensile shock fronts of equal amplitude from opposite ends of a domain and meet at the center. In both cases, BC exhibited a linear-elastic axial stress-strain response up to the yield stress followed by non-linear behavior that differed significantly in the two orientations. Along [111], post-yield softening was followed by an almost perfectly plastic response. In contrast, a post-yield hardening was observed at 90° to [111] followed by an abrupt loss of strength. Spallation along [111] was accompanied by micro-crack initiation normal to the loading direction while at 90° to [111], spallation was preceded by crack formation at ~45° to the loading direction. These observations were explained by analyzing the deformation of the 41 bonds in the unit cell.

9:00 AM
Phase Transformation in Cu: Nilanjan Mitra¹; ¹Johns Hopkins University
    Cu is utilized as an impactor material in many plate impact experiments within the shock compression community, primarily because it is believed that there is no solid-solid phase transformation in the material. However, it has been reported that Cu based Hume-Rothery shape memory alloys exhibit body centric phase transformations at high temperatures. Thereby, the possibility of phase transitions of Cu under high temperature and/or high pressure cannot be completely ruled out. With that in perspective, atomistic simulations have been carried out to probe the phase transformation of Cu subjected to high temperature and high pressure in shock compression experiments and observance of BCT phase of Cu has been reported based on Gibbs free energy calculations within the quasiharmonic approximations, supporting previous postulation by Friedel. Interestingly, recent experimental investigations carried by Gupta group at WSU on polycrystalline Cu in 2020 also demonstrated presence of body centered phases (PRB (2020): 102, 020103(R)).

9:20 AM
Atomic Simulations of Shock Wave Propagation in Polymers and Their Interfaces: Nuwan Dewapriya¹; Ron Miller¹; ¹Simon Fraser University
    We conducted density functional theory (DFT) and molecular dynamics (MD) study of shock wave propagation through polymers and their interfaces with hard materials. First, we examined the fidelity of a non-reactive MD force field by comparing its predictions with available experimental data and DFT calculations. That study helped us establish the upper limits of the shock pressure that can be accurately modeled using the non-reactive MD force field. Subsequently, additional DFT calculations were performed to obtain accurate MD force field parameters to model the adhesive interactions of selected material interfaces. After that, we explicitly modeled the dynamic shock wave propagation and spallation of polymers as well as polymer/ceramic and polymer/metal multilayers.

9:40 AM
Shock Compression of Cu_xZr_100-x Metallic Glasses: Peng Wen¹; Brian Demaske²; Simon Phillpot³; Douglas Spearot³; ¹Nanjing University of Science and Technology ; ²Sandia National Laboratories; ³University of Florida
    The shock response of Cu_xZr_100-x (x = 30, 50 and 70) metallic glasses (MGs) is simulated using molecular dynamics simulations. Piston velocities from Up = 0.125 to 2.5 km/s are employed, corresponding to shock pressures from 3 to 130 GPa. Different shock wave propagation regimes are observed: (1) single elastic shock wave for Up < 0.25 km/s, (2) split elastic and plastic shock waves for 0.25 < Up < 0.75 km/s and (3) overdriven plastic shock wave for Up > 0.75 km/s. Hugoniot states are dependent on the Cu content with Cu₇₀Zr₃₀ exhibiting the highest resistance to plastic deformation than Cu₅₀Zr₅₀ or Cu₃₀Zr₇₀. Plastic deformation initiates via formation of shear transformation zones (STZs). At high shock pressures, STZ nucleation leads to shock-induced melting, which is identified via atomic diffusivity. Both the flow stress and the critical shock pressure associated with melting increase with increasing Cu content.

10:00 AM Break

10:20 AM
Exploring Thermal, Mechanical, and Electrical Shock via In-situ Electron Microscopy: Eric Lang¹; Ryan Schoell¹; Nathan Madden¹; Kathryn Small¹; Khalid Hattar¹; ¹Sandia National Laboratories
    The development of trusted models in extreme environments requires the direct correlation, refinement, and validation from experimental tests under similar conditions. This coupling is often difficult due to the engineering limitations associated with performing experiments on the associated length and time scales. This presentation will highlight some of the recent advancements made to enhance the extreme thermal, mechanical, and electrical shock conditions that can be achieved within a transmission electron microscope (TEM), as well as recent improvements in the temporal resolution. To highlight the potential of this approach, we will present the coupling of multi-scale modeling to experimental results in materials ranging from stainless steel to carbon fiber composites to additively manufactured refractory high entropy alloys. Finally, the presentation will conclude with recent in-situ extreme scanning electron microscopy (SEM) developments and the potential coupling to mesoscale modeling. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

10:40 AM
A Molecular Dynamics Study of the Effect of an Oxide Layer on the High Velocity Deposition of Tantalum Nanoparticles: Stephen Bierschenk¹; Michael Becker¹; Desiderio Kovar¹; ¹The University of Texas at Austin
    Micro-cold spray is the process of accelerating solid nanoparticles in a gas stream from ~1 atm through a nozzle and impacting them at high velocity onto a substrate in vacuum to deposit nanostructured films of metals and ceramics. Tantalum films deposited by micro-cold spray are desirable because they are non-reactive to certain molten metals. However, tantalum nanoparticles quickly form an oxide layer when exposed to air. Since micro-cold spray uses an order of magnitude smaller particle sizes than traditional cold spray, typically sub-500 nm, this oxide layer can inhibit film deposition. Nanoparticles impacted at velocities up to 1000 m/s can experience strain rates as high as 10^11 s^-1. The effect of this oxide layer on deformation and adherence to a substrate under these high strain rates is studied using molecular dynamics simulations. The effect of oxide layer thickness, particle diameter, and impact velocity will be examined.

11:00 AM
Micro Cold Spray of Zinc Oxide Films: Scott Burlison¹; Michael Becker¹; Desiderio Kovar¹; ¹University of Texas at Austin
    The micro cold spray (MCS) process utilizes high velocity impact of sub-micron ceramic particles to deposit thick films at room temperature. Although films from many ceramics have been successfully deposited, the mechanisms responsible for the sticking of particles upon impact remain poorly understood. In this study, the impact of wurtzite zinc oxide (ZnO) nanoparticles onto a zinc oxide substrate was studied as a function of particle diameter (size range) and particle impact velocity (velocity range) to determine the deformation mechanisms responsible for adhesion and film formation. Molecular dynamics (MD) simulations were conducted in the LAMMPS software package. Zinc oxide films were also produced experimentally using MCS and characterized to compare with the results from MD simulations.

11:20 AM
Scaling up Molecular Dynamics Simulations of High Velocity Particle Impacts: Aidan Moyers¹; Michael Becker¹; Desiderio Kovar¹; ¹The University of Texas at Austin
    Micro-cold spray (MCS) is a direct-write process that can produce patterned thick ceramic films (1-100 ľm) onto a wide variety of substrates through repeated high velocity impacts of sub-micron particles. These impact conditions and particle sizes result in extreme strain rates (1e9-1e12/s) that are very challenging to study in situ or with continuum mechanics models, but they are well suited to molecular dynamics (MD) simulations. Most MD simulations of particle impacts have been conducted with 10 nm or smaller particles, allowing them to accurately simulate the atomic-scale behaviors responsible for deformation, but not permitting the reproduction of continuum-scale behaviors observed for the 100 nm to 1 ľm particles used within physical experiments. This study seeks to bridge the gap between prior simulations and current experiments through with 3D MD simulations of 12-50 nm yttria (Y2O3) particles, as well as 2D simulations for particles up to 300 nm.

11:40 AM
Mechanical Properties in Thermally Processed Ag-Cu-Ni Nanoclusters: Effect of Surface Composition and Core-shell Morphology Using Hybrid Monte Carlo/Molecular Dynamics Simulations: Serzat Safaltin¹; Pamir Alpay¹; ¹University of Connecticut
    The aim of this study is to observe the effect of cooling rate and core-shell morphology on the mechanical properties of Ag-Cu-Ni based metallic systems using Hybrid Monte Carlo and Molecular Dynamics simulations. Model systems comprising mono (Ag, Cu, Ni), equiatomic binary (Ag-Cu, Ag-Ni, Cu-Ni) and ternary Ag-Cu-Ni metallic clusters were simulated under melting-quenching thermal process to get amorphous and polycrystalline core-shell structures. A theoretical treatment of the interatomic interactions was in good agreement with the phase transitions and melting temperatures. We used thermal process results in mechanical models that simulate similar conditions to compression and indentation processes to observe mechanical properties. By observing the deformed MD models and stress-strain relationships, we identified the effect of cooling rates, surface composition and core-shell morphology on mechanical properties and formability.