Dynamic Behavior of Materials IX: Modeling and Simulation II
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
Wednesday 2:00 PM
March 2, 2022
Room: 304D
Location: Anaheim Convention Center
Session Chair: Saryu Fensin, Los Alamos National Laboratory; Douglas Spearot, University of Florida
2:00 PM
Understanding the Implications of Finite Specimen Size on the Interpretation of Dynamic Experiments for Polycrystalline Metals through Direct Numerical Simulations: Bryan Zuanetti1; Darby Luscher1; Cynthia Bolme1; Kyle Ramos1; 1Los Alamos National Laboratory
Normal and Pressure-shear plate impact (NPI and PSPI) are popular techniques for studying the mean-field macroscopic behavior of polycrystalline metals under high rate loading. However, since both configurations rely upon geometry for imposing high rates, these experiments involve a limited specimen size. Moreover, because of inherent heterogeneities in polycrystalline metals, it is difficult to ascertain when the size is large enough for making representative inferences from point measurements. Presently, we quantify the expected variability in observable point measurements by performing direct numerical simulations of synthetic microstructures subjected to NPI and PSPI. Our analysis demonstrates that the grain size correlates directly with the variation in point measurements, showing a decrease in variation to zero (i.e. point measurements approach the mean-field value) with decreasing grain size. We discuss the reasoning and summarize the results into a framework for assessing the required number of grains per characteristic length for minimizing scatter in NPI/PSPI.
2:20 PM
Phase Transformation of Aluminum under Ramp Loading Compression; A Combined Atomistic Simulation and Experimental Study: Lijie He1; Danae Polsin1; Shuai Zhang1; Gilbert Collins1; Niaz Abdolrahim1; 1University of Rochester
In this study, we carried out a series of NEMD simulations to investigate the plastic deformation properties of Aluminum under ramp loading conditions where it fcc-hcp-bcc phase transitions. An excellent agreement is observed in stress-density response between previously published laser-driven ramp compression experiments and simulation results. The atomistic configurations and virtual diffraction analysis demonstrated a plastic deformation route of micro twin formation->stacking fault formation and thickening->phase transformation via Bain path. Furthermore, the virtual XRD patterns are compared with experimental in-situ XRD results and showed remarkable similarity in the fcc and bcc signature at comparable stresses. The proposed phase transformation path is also cross-examined with the experimental diffraction result and showed perfect agreement.
2:40 PM
Shockwave Propagation and Attenuation in Poly(ethylene glycol) Diacrylate Hydrogels: Ke Luo1; Ghatu Subhash1; Douglas Spearot1; 1University of Florida
The nonequilibrium molecular dynamics (NEMD) method is used to investigate one-dimensional shockwaves in poly(ethylene glycol) diacrylate (PEGDA) hydrogels. The role of PEGDA polymer concentration on shockwave velocity and the structure of the shock front is evaluated by constructing hydrogels with 20, 35, and 50 wt.% PEGDA concentrations with an idealized crosslinked network. The NEMD simulations provide data that is used to develop an analytical model to predict shockwave propagation and attenuation characteristics in hydrogels, by combining the classical method of shock characteristics and a solution for the shock front structure. The new model successfully captures salient features of shockwave attenuation, including shock pressure, the velocities of the shock and release waves, and the attenuation timeline. Hydrogels with higher polymer concentrations exhibit a shorter attenuation time at all particle velocities studied. This behavior is attributed to differences in bulk properties and shock front structure in hydrogels with different concentrations.
3:00 PM
Mechanisms Responsible for Kinking in Layered Crystalline Solids: Gabriel Plummer1; Xingyuan Zhao1; Leslie Lamberson1; Garritt Tucker1; 1Colorado School of Mines
Kinking is a deformation mode shared by many layered materials, ranging from geological formations to layered crystalline solids (LCSs). Observations of kinking in LCSs date back over 100 years, but the underlying mechanisms have remained elusive. Utilizing newly developed interatomic potentials, atomistic simulations provide the first dynamic demonstration of kinking in LCSs, with the MAX phases, ternary carbides and nitrides, as a model material. The results show that kinking occurs when elastic layer buckling couples with nucleation of basal dislocation dipoles. Notably, the resulting kink boundaries remain elastically strained with pronounced curvature over several nanometers, making the process reversible in many scenarios. An important consequence of this mechanism is that microstructures oriented favorably for kinking exhibit significant strengthening at high strain rates. These mechanistic insights should serve to help better design innovative structural materials which utilize the unique properties offered by kinking in LCSs.
3:20 PM Break
3:35 PM
Understanding the Phase Transformation Mechanisms of Fe-based Microstructures at the Atomic Scales: Avanish Mishra1; Jonathan Lind2; Mukul Kumar2; Avinash Dongare1; 1University of Connecticut; 2Lawrence Livermore National Laboratory
Large-scale molecular dynamics (MD) simulations are carried out to investigate the shock-induced evolution of single-crystal Fe and Cu/Fe alloy microstructures. The shock compression of Fe leads to BCC (α) → HCP (ε) phase transformation. The shock release causes reverse ε → α phase transformation-induced twinning. The microstructure is characterized using lattice orientation, misorientations, and rotation matrices to identify the variants of ε phases under shock compression and understand the mechanisms for the formation of twins during shock release. The simulations reveal that the α → ε → α transformation-induced twinning for shock loading along [110] direction is due to a dominant [0001] ε phase variant formed during compression that rotates with the arrival of the release wave followed by reverse phase transformation to twins in the α phase. The evolution of the ε phase variant and the twinning mechanism for Fe and Cu-Fe layered microstructures will be presented.
3:55 PM
Reduction of Richtmyer-Meshkov Instabilities via Layered Explosive Charge Design: Michael Hennessey1; H. Springer1; Jon Belof1; 1Lawrence Livermore National Lab
This study details the optimization of layered explosive charge geometries to reduce Richtmyer-Meshkov instability (RMI) in metal plates with sinusoidal surface features through numerical simulation. The impact of a detonation wave from a high explosive (HE) charge on a metal target results in shock refraction at the interface between the two materials. For a target with an unconfined surface opposite the HE-target interface, the shock refraction results in complex wave behavior related to Mach-stem interaction within the target ultimately leading to the formation of RMI at the unconfined surface of the target. The reduction of this instability is investigated in a two-fold manner: first by varying the charge design and composition, and second by varying the initial design of the unconfined surface of the target. Within a limited scope of this design space, a wide variety of behaviors related to the RMI growth (or suppression thereof) are observed and investigated.