Understanding and Predicting Dynamic Behavior of Materials : Materials in Extremes
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

Thursday 2:00 PM
February 27, 2020
Room: 5A
Location: San Diego Convention Ctr

Session Chair: Jie Chen, Los Alamos National Laboratory


2:00 PM  Invited
Dynamics of Necking and Fracture in Ductile Porous Materials: Ankit Srivastava1; 1Texas A&M University
    The onset of multiple localization/necking and fragmentation in expanding ductile structures is delayed due to the stabilizing effect of inertia, and with increasing expansion velocity, both the number of necks and fragments, increase. In general, neck retardation is expected to delay fragmentation as necking is often the precursor to fracture. However, in porous materials it is possible that fracture can occur without significant necking. Following this, we investigate the emergence of multiple necking in ductile porous materials subjected to dynamic stretching using finite element calculations and linear stability analysis. Our results reveal that, a heterogeneous distribution of defects (e.g. porosity) is needed to trigger the multiple necking pattern but it barely affects the average neck spacing, and low initial porosity levels favor necking before fracture while high initial porosity levels favor fracture before necking, at higher strain rates.

2:40 PM  
In-situ Measurement of Dynamic Stress due to Hyper-velocity Impact Using Nanosecond Resolved Raman Spectroscopy: Abhijeet Dhiman1; Hao Wang1; Vikas Tomar1; 1Purdue University
    Shock induced stress measurements in materials is important to design materials for hypersonic vehicles, accident tolerant nuclear materials, and energetic materials and structures. In this work, a novel experimental setup to measure in-situ dynamic stress induced by impact from a particle moving at hyper-velocity has been used. The stress measurement is performed based on a time resolved in-situ mechanical Raman spectroscopy to measure in-situ dynamic stress in a Hydroxyl-terminated polybutadiene (HTPB) sample. The hyper-velocity particle is accelerated by a pulse. After the impact, the shock propagates through sample inducing dynamic stresses. The high-speed in-situ mechanical Raman spectroscopy uses variation in Raman shift as a function of time to obtain stress induced due to impact for varying strain rates. The Raman spectroscopy is performed at the GHz frequencies with an integration time of a few nanosecond to capture stress-waves induced due to impact.

3:00 PM  
What Happens to a Microstructurally Stable Nanocrystalline Alloy after Undergoing Shock Loading?: Billy Hornbuckle1; Xuyang Zhou2; Cyril Williams1; Steven Dean1; Anit Giri1; Anthony Roberts1; Greg Thompson2; Kiran Solanki3; Kris Darling1; 1US Army Research Laboratory; 2The University of Alabama; 3Arizona State University
    The ability to evaluate a nanocrystalline material under extreme states of stress experienced in a shock experiment were once thought to be impossible. However, with the development of thermally and mechanically stable nanocrystalline alloys, this impossibility is now a reality. A nanocrystalline Cu-3Ta (At.%) alloy, that has been shown to be both thermally and mechanically stable, had shock recovery test performed on a 10 mm diameter specimen. This work reports the changes in hardness and microstructure of the Cu-3Ta alloy post mortem after undergoing shock compression up to 15 GPa. Scanning transmission electron microscopy (STEM) coupled with precession electron diffraction provide insight into the changes in grain size and texture of the initial microstructure as well as the dislocation density and other deformation mechanisms present.

3:20 PM Break

3:40 PM  
Investigating the Mesoscale Evolution of Microstructure during Cold Spray Single Particle Impact of BCC Metallic Powders: Sumit Suresh1; Seok-Woo Lee1; Mark Aindow1; Harold Brody1; Aaron Nardi2; Victor Champagne2; Avinash Dongare1; 1University of Connecticut; 2U.S. Army Research Laboratory
    Cold spray is a versatile powder deposition technique where supersonic impacts of metallic powders result in successful adhesion or bonding of the particle with a substrate. Quasi-Coarse-Grained Dynamics (QCGD) simulations are carried out to investigate the deformation behavior of tantalum powders onto tantalum substrates at the mesoscales. The QCGD method solves the equations of motion for a reduced number of representative atoms and uses scaling relationships for interatomic potentials as well as degrees of freedom to retain the evolution of microstructure, temperatures and pressures during single particle impact as predicted using molecular dynamics simulations. This work discusses the framework (scaling relationships) of the QCGD method and demonstrate the capability to model the dynamic evolution of microstructure (defect evolution, twinning, etc.) at the time and length scales of experiments, i.e., time scales on the order of tens of nanoseconds and length scales on the order of tens of microns.

4:00 PM  
Influence of Microstructure on The Dynamic Tensile Extrusion of Tantalum: Carl Trujillo1; Michael Burkett1; George Gray1; Saryu Fensin1; Shuh Rong Chen1; 1Los Alamos National Laboratory
    It is well known that processing can affect the resulting microstructure and eventually properties of materials. In this work, we aim to understand the tensile response of AM Tantalum in comparison to the wrought Ta especially when it is subjected to large strains at high strain rates. This is achieved through the use of the Dynamic Tensile Extrusion experimental technique. Specimens of wrought and AM Ta were accelerated up to 470 m/s and at temperatures of 275C through a high strength die and recovered. A combination of in-situ diagnostics: High Speed Imaging, Photon Doppler Velocimetry and High-Speed Infrared Camera, captured dynamic extruded material topologies, extrusion velocity history and specimen surface temperature. Post mortem microscopy measurements were used to assess the deformation process and the plastic strains realized during the process. Experimental data was used to evaluate hydrocode strength and damage evolution models. Quantitative examination of this work will be presented.