Dynamic Behavior of Materials IX: X-ray, Spectroscopy and Imaging 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

Tuesday 2:30 PM
March 1, 2022
Room: 304D
Location: Anaheim Convention Center

Session Chair: Cyril Williams, Army Research Laboratory; Christopher Dimarco, Johns Hopkins University


2:30 PM  
Observation of Shear Band Localization in Ti-64 through In-situ Imaging under Dynamic Compression Conditions: Jonathan Lind1; Matthew Nelms1; Alison Kubota1; Mukul Kumar1; Nathan Barton1; 1Lawrence Livermore Laboratory
     Severe deformation of materials can lead to inhomogeneous intense zones of localized strain, called shear bands, serving as the precursor to failure. It has been observed Ti-64 readily shear bands under dynamic compression conditions. A series of plate-impact hole closure experiments with in-situ X-ray radiographic imaging were performed visualizing the inhomogeneous response. Observed regions of sharp discontinuity indicate formation of shear banding. The addition of a low-density filler material in the hole produces a more homogeneous closure response indicating inhibition of shear banding. Post-mortem characterization is performed on the recovered, fully intact samples with results discussed. ---This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, by the Dynamic Compression Sector supported by National Nuclear Security Administration under Award Number DE-NA0002442, used resources of the Advanced Photon Source at Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

2:50 PM  
NOW ON-DEMAND ONLY - Modified Reflective Digital Gradient Sensing (R-DGS) for Impact Applications: Pinkesh Malhotra1; Chengyun Miao1; Justin Moreno1; Matt Shaeffer1; Kaliat Ramesh1; 1Johns Hopkins University
    A modified Reflective Digital Gradient Sensing (R-DGS) method is used for the first time to measure rear surface displacements of plates subjected to spherical projectile impact. R-DGS offers a unique capability to measure full-field out-of-plane displacements with a sensitivity <0.1 um which makes it very valuable for dynamic applications involving small out-of-plane displacements. The method was employed for one such application, i.e., the study of brittle ceramics such as Boron Carbide which are hard to study using conventional full-field measurement techniques such as Digital Image Correlation. R-DGS enabled the measurement of material response prior to fragmentation and the measurement of surface transients at the same time. A rich dataset results from such measurements which can be utilized to calibrate material models for Boron Carbide and study the kinematics associated with spherical impact.

3:10 PM  
Using Full-field Strain and Temperature Measurements to Determine the Taylor-Quinney Coefficient in Tensile Split Hopkinson Bar Tests: Amos Gilat1; Jarrod Smith; Jermy Seidt1; 1Ohio State Univ
    Plastic deformation generates heat and the Taylor-Quinney coefficient (Beta) is the ratio between the energy dissipated as heat and the overall work invested in producing the deformation. Knowing the value of Beta is important for accurate modeling of plastic deformation since temperature rise may offset increase in stress due to strain hardening and may affect strain rate sensitivity. New tensile testing for determining the value of Beta is presented. Full field strain measurements (DIC) and temperature (IR) throughout the test (including in the necking region) are used to determine Beta as a function of strain at various strain rates, including high strain rates (split Hopkinson bar). Results from tests of Inconel 718 specimens show strains in the necking region exceeding 0.4 and temperature rises of about 200C, The value of the Beta increases with strain and reaches a plateau value of about 0.85 at strain of about 0.3.

3:30 PM  
Amorphization of Covalently-bonded Materials: A Generalized Deformation Mechanism under Extreme Conditions: Boya Li1; Shiteng Zhao2; Bruce Remington3; Christopher Wehrenberg3; Hye-Sook Park3; Eric Hahn1; Marc Meyers1; 1University of California San Diego; 2Beihang University ; 3Lawrence Livermore National Laboratory
    Laser shock compression subjects materials to an extreme regime of high quasi-hydrostatic pressure and coupled shear stresses for durations of 1-10 nanoseconds. The mechanisms of plastic deformation in metals whereby dislocations, twins, and phase transitions nucleate and propagate at velocities near the sound speed. Covalently bonded materials, however, have great difficulty in responding by conventional plastic deformation to this extreme regime of shock compression due to the directionality of their bonds. We propose that the shear from shock compression induces amorphization, as observed in Si, Ge, B4C, SiC, and olivine ((Mg, Fe)2SiO4) and that this is a general deformation mechanism in a broad class of covalently bonded materials. The crystalline structure transforms to amorphous along regions of maximum shear stress, forming nanoscale shear bands, and thereby relaxing the shear component of the imposed shock stress. This process is preceded by the emission and propagation of a critical concentration of dislocations.

3:50 PM Break

4:05 PM  
Twinning-assisted Dynamic Recrystallization: A New Mechanism Revealed by Single Microparticle Supersonic Impact: Ahmed Alade Tiamiyu1; Edward Pang1; Christopher Schuh1; 1MIT
    Grain refinement by dynamic recrystallization during deformation of FCC metals is usually explained by dislocation-mediated mechanisms. However, dynamic recrystallization remains mysterious in the high strain rate (low temperature) regime where twinning is a dominant plastic deformation mechanism. In this work, we employ single copper microparticle impact experiments at varying velocities to systematically shift the deformation conditions into this regime. Post mortem impacts have been characterized using transmission electron microscopy and dictionary indexing electron backscatter diffraction, which reveal a twin-assisted dynamic recrystallization mechanism. In the twin-mediated mechanism, nanotwins first form and are then partitioned by dislocation activity to form nano-grains smaller than what conventional dislocation-mediated recrystallization mechanisms produce. This finding fills in the gaps at high strains and strain rates in a deformation mechanism map for FCC copper.

4:25 PM  
Quasi-static to Dynamic Transition in Strengthening Effects of Helium Bubbles in Copper: Calvin Lear1; David Jones1; Jonathan Gigax1; Daniel Martinez1; Rachel Flanagan1; Minh Hoang1; Jeremy Payton1; Michael Prime1; Saryu Fensin1; 1Los Alamos National Laboratory
    The development of advanced modeling tools and cutting edge, in-situ techniques now allows for investigation, understanding, and prediction of dynamic behavior of materials. Of particular interest, both for civilian and defense applications, is the interaction of dislocations with various classes of defects. In this study, high purity copper samples were implanted with helium ions of varying energy to create a ~10 μm thick surface layer rich in helium bubbles. While nano-mechanical testing of this surface layer revealed increasing hardness and yield strength with helium dose, Richtmyer-Meshkov instability (RMI) experiments carried out on identically implanted copper targets indicated no significant trends in material strength. Molecular dynamics (MD) simulations were preformed to observe (1) helium bubble evolution during dynamic loading and (2) dislocation interactions with pressurized helium bubbles versus dispersed helium atoms. Findings will be discussed both in terms of the discrepancy in copper behaviors and for potential applicability to other materials.