Understanding and Predicting Dynamic Behavior of Materials : Equation of State
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

Wednesday 2:00 PM
February 26, 2020
Room: 5A
Location: San Diego Convention Ctr

Session Chair: Nitin Daphalapurkar, Los Alamos National Laboratory


2:00 PM  
Low-stress Shock Hugoniot of Additively Manufactured 304L Stainless Steel: Sarah Thomas1; M. Cameron Hawkins1; Robert Hixson1; 1MSTS
     As additive manufacturing becomes more prevalent in scientific and industrial applications, more information is needed about the properties of materials formed this way. The shock behavior of additively manufactured materials is of particular importance to applications that are dynamic in nature. Additively manufactured 304L stainless steel was grown and tested for strength characteristics by our collaborators at Los Alamos National Laboratory. As an extension of their work, we have conducted experiments to measure low-stress Hugoniot properties of additively manufactured 304L stainless steel in both the normal and transverse directions with respect to the direction of growth. We have also conducted forged metal control experiments to provide a direct comparison of time-resolved results. We will present the results of our shock Hugoniot work.This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy. DOE/NV/03624--0554.

2:20 PM  Invited
Meso-scale Topology Effects on the Shock Compression Response of Reactive Powder Mixtures: Manny Gonzales1; Lauren Poole2; Austin Gerlt3; Zachary Cordero4; 1U.S. Air Force Research Laboratory; 2University of California, Santa Barbara; 3UES, Inc.; 4Rice University
    Dynamic loading conditions are fascinating since unique thermodynamic states are achieved extremely rapidly. Heterogeneous materials in particular can behave quite differently under shock compression in contrast with quasi-static loading. Waves propagate information under extreme dynamic loading events, and the local microstructure can be a major determinant of subsequent behavior. The matter is further complicated by the lack of both spatial and time-resolved measurements of the dynamic event, although major advancements have been made with synchrotron-based phase contrast imaging. This talk presents current efforts at AFRL to address how meso-level heterogeneity can affect bulk dynamic response. Two-point correlation functions and their evolution during shock compression are presented for reactive powder mixtures, and the role that microstructural topology plays on bulk shock response is explored. Mechanical dissipation and its relation to meso-scale wave mechanics is probed with microstructure-based hydrocode simulations.

2:40 PM  
Determination of Equation of State in Polyurea Elastomers via Reverberation and Hydrodynamic Instability Experiments: Tyler Eastmond1; Elizabeth Fortin1; Zak Wilde2; Kirk Bohlen1; Jay Oswald1; Pedro Peralta1; 1Arizona State University; 2Los Alamos National Laboratory/Arizona State University
    Polyurea has shown potential as a protective coating in body and vehicle armor, serving to reduce damage and fragmentation when a coated armor is exposed to blasts and ballistic impacts. Hence, the behavior of polyurea at pressures above 20 GPa and strain rates of 105-106 s-1 needs to be better understood and quantified to design polyurea coatings. Experiments to quantify the equation of state of polyurea at high pressures were performed using a shock reverberation in a single stage gas gun, where a thin polyurea film was sandwiched between tungsten plates and impacted with a tungsten flyer, while the free surface velocity history on the back tungsten plate was recorded using laser velocimetry. In addition, laser-driven experiments to monitor the evolution of perturbed shock fronts were used to reach pressures ≈ 60 GPa. Results were used to validate molecular dynamic simulations of the high-pressure behavior of polyurea.

3:00 PM  
Observation of Metal Particle Deformation inside a Shock Compressed Polymer: David Bober1; Moono Rhee1; Nathan Barton1; Mukul Kumar1; 1Lawrence Livermore National Laboratory
     The shock compression of particulate composites is affected by matrix-particle interactions, which are in turn affected by particle size, shape and distribution, i.e. microstructure. With applications ranging from structural to reactive materials, we wish to understand how these microstructural properties evolve during dynamic compression. To that end, high speed radiography was used to provide in situ images of shock induced deformation in a model polymer-metal composite. The entrained metal microparticles (50-100 µm) were seen to remain approximately spherical for relative polymer velocities up to 1.7 km/s, but above 3.2 km/s the particles experienced large plastic deformation. The strength of the metal particles, the shear resistance of the polymer, and interfacial stresses were considered using finite element simulations. The effect of changing the polymer/metal combination will also be 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.

3:20 PM  
Mechanical Behavior and Deformation Mechanisms of Mg in Shear Using In-situ Synchrotron Radiation X-Ray Diffraction: Christopher Meredith1; Jeffrey Lloyd1; Daniel Magagnosc1; 1Army Research Laboratory
    A fundamental understanding of magnesium during high rate, large deformation processes that occur during impact and penetration are not well known. This metal possesses a limited number of deformation mechanisms, each with disparate strengths, strain hardening, and strain rate sensitivity. Thus, an understanding of material behavior undergoing large shears at dynamic rates is required. A specimen geometry was utilized that induces shear localization, called the compact forced simple shear (CFSS) specimen. The deformation occurs on a 2D plane in the specimen, which is oriented with respect to directional aspects of the material’s microstructure and deformation modes. We performed experiments at dynamic strain rates at the Dynamic Compression Sector using in-situ synchrotron x-ray diffraction, in order to probe the microstructural evolution during shear-induced localization. We also perform FEA simulations using a reduced-order crystal plasticity model and correlate the mechanical response at different orientations to identify key deformation mechanisms responsible for localization.

3:40 PM Break

4:00 PM  
Effect of Heat Treatment on Adiabatic Shear Band Microstructures and Internal Strains using HR-EBSD in Segmented Ti-6Al-4V Chips from Turning: Jiawei Lu1; Thomas Bieler1; Patrick Kwon1; 1Michigan State University
    The relationship between the hardness of primary alpha grains in Ti-6Al-4V (wt.%) segmented chips obtained from a rolled rod turned at cutting speeds of 61 and 122 m/min, was investigated. More twinning and a lower hardness of chips was observed at 122 m/s, suggesting that less deformation occurred in regions between adiabatic shear bands at this higher cutting speed, such that strain was more concentrated in the adiabatic shear bands. To examine the nature of deformation in the adiabatic shear bands, heat treatments at different temperatures were done to examine how recovery and recrystallization provide indications of the strain state in the adiabatic shear bands. High resolution EBSD measurements in as-recovered chips from 61 and 122 m/min cutting speeds as well as on heat treated chips are used to gain insight into the internal strain states in segmented chip deformation mechanisms operating in cutting conditions.

4:20 PM  
On the Evolution of Adiabatic Shear Bands in the Beta Titanium Alloy Ti-10V-2Fe-3Al: Mario Scholze1; Philipp Frint1; Sven Winter2; Martin Wagner1; 1Institute of Materials Science and Engineering, Technische Universität Chemnitz; 2Fraunhofer Institute for Machine Tools and Forming Technology
    We investigate the evolution of (quasi-)adiabatic shear bands in a Ti-10V-2Fe-3Al alloy with different initial microstructures: solution-annealed β-titanium, β-titanium with primary α precipitates as well as a condition with primary and secondary α precipitates. Dynamic testing of cyclindrical shear-compression specimens with strain rates up to 103 s-1 is performed at room temperature. The nominal deformation is limited to predefined strains, which allows to investigate nucleation and propagation of the shear bands using electron microscopy. Our post mortem observations show that the formation mechanisms of (quasi-)adiabatic shear bands differ considerably between the different material conditions. In β-titanium with primary α-phase, massive bands with a thickness of 5 μm are formed. In contrast, β-titanium with primary as well as secondary α precipitates exhibits many fine, branching shear bands. Our experimental observations contribute to an in-depth micromechanical understanding of the effect of microstructural features on the formation and growth of adiabatic shear bands.

4:40 PM  
Transient State Rheological Behavior of Poly(ethylene glycol) Diacrylate Hydrogels at High Shear Strain Rates: Ke Luo1; Kshitiz Upadhyay1; Ghatu Subhash1; Douglas Spearot1; 1University of Florida
    Transient rheological properties of poly(ethylene glycol) diacrylate (PEGDA) hydrogels under Couette flow conditions are determined via molecular dynamics simulations and validated by high strain rate shear experiments. The transient shear response is characterized via the introduction of dimensionless variables and the application of a self-similar solution to the power-law fluid model. This enables meaningful comparison across the disparate length and time scales between MD simulations and experiments. The momentum diffusion exponent is found to increase with a decrease in PEGDA concentration, which indicates higher shear-thickening behavior in lower PEGDA concentration hydrogels. Shear-thickening mechanisms in hydrogels are explained by computing the average mesh size and the distribution of junction separations. Two stages of deformation are observed under shear, where the first stage is associated with PEGDA chain conformational changes and the second stage is associated with bond length and angular deviations within PEGDA chains.