Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session I02: Spall Nucleation IRecordings Available
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Chair: George Gray, Los Alamos Natl Lab Room: Anaheim Marriott Platinum 6 |
Tuesday, July 12, 2022 9:15AM - 9:30AM |
I02.00001: Shock Compression Response of a Single-Crystal Austenitic Stainless Steel Nathan Brown, Christopher R. Johnson, Paul E Specht Austenitic stainless steels are easily machined and exhibit high strength and corrosion resistance, making them ideal materials for a large variety of engineering applications. Mesoscale models of polycrystalline austenitic stainless steels require knowledge of the orientation-dependent properties of the constituent grains. In this work, we provide preliminary dynamic material property results from shock compression experiments of a single-crystal austenitic stainless steel (FeCr18Ni12.5). Samples oriented in the [100], [110], and [111] directions were compressed to peak stresses up to 12 GPa via plate impact using the single-stage air gun at the Shock Thermodynamics and Applied Research (STAR) facility at Sandia National Laboratories (SNL). Free surface velocity measurements provided by photonic Doppler velocimetry (PDV) and the velocity interferometry system for any reflector (VISAR) were used to compare the Hugoniot, Hugoniot elastic limit, and spall strength along the three principal crystallographic directions. |
Tuesday, July 12, 2022 9:30AM - 9:45AM |
I02.00002: Measurements of the Strain-Rate Dependence of Spallation Strength in 304L Stainless Steel Paul E Specht, Scott Alexander, Bill D Reinhart The spallation strength of a metal is known to be highly dependent on the material properties and the loading history. One of the most influential loading variables on the spallation strength is the tensile strain-rate. We present a series of experiments that probe the influence of tensile strain-rate and duration under tension on the spallation strength of 304L stainless steel. Two experimental configurations were utilized in this work. The first contained five individual impactor-sample pairs of differing thickness contained on a single projectile/target. This provided spallation strength measurements at five unique tensile strain-rates but identical peak compressive stress. The second experimental configuration used a wedge-shaped impactor to generate a continuously varying spall plane location along the sample, changing the duration under tension while the strain-rate and peak compressive stress remained constant. In each experiment, the 304L stainless steel samples were recovered and post-mortem computed tomography (CT) and scanning electron microscopy (SEM) was conducted to provide insight on the mechanisms of void nucleation and growth. |
Tuesday, July 12, 2022 9:45AM - 10:00AM |
I02.00003: Spall behavior in iron: microstructural effects on strength, failure, and phase transitions Gaia Righi, Richard J Briggs, Camelia V Stan, Orlando R Deluigi, Eduardo M Bringa, Samantha M Clarke, Raymond F Smith, Hye-Sook Park, Marc A Meyers Spall response of pure iron was studied using high power pulsed laser experiments at the Jupiter Laser Facility and Dynamic Compression Sector. Thin iron foils of varying initial microstructures were subjected to peak pressures of 60 GPa and strain rates ranging from 106 s-1 – 107 s-1. Simultaneous time-resolved free surface velocity measurements, diffraction, and recovery techniques were used to investigate spall strength, failure mechanisms, and phase transitions. These uniaxial strain experiments yielded strengths between 5 and 10 GPa for nanocrystalline and single crystal iron, respectively. Post-shock characterization and Molecular Dynamics simulations verify that this difference is due to void initiation sites. Grain boundaries in nano and polycrystalline iron are favorable sites for voids nucleation and will consequently cause failure to occur along grain boundaries perpendicular to the shock direction. In contrast, the formation and interaction of twin boundaries in single crystal iron are the cause for void initiation, growth, and coalescence that ultimately cause ductile failure. The complete α-ϵ phase transition during compression was observed, followed by a rapid transformation back to α-Fe. The grain structure during compression and release/spall failure was found to show strong single crystalline character. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. |
Tuesday, July 12, 2022 10:00AM - 10:15AM |
I02.00004: Grain structure dependence of spall dynamics in shock loaded tantalum Kory Beach, Jeremy Horwitz, Minta C Akin, Fady M Najjar, Ryan S Crum, Elida White, Dane C Ramos, Alyssa Maich We perform a gas gun experiment with shock loaded tantalum samples of varying grain structures to assess the suitability of a numerical model for simulating spall behavior. The observed differences in spall strength, as well spallation and re-compression history, are not captured in uncalibrated hydrodynamic simulations. An optimization is performed on the Johnson spall model to determine the best parameters that fit the observed trends. Linear stability analysis is used to motivate bounds on those parameters. Overall, optimized simulations agree well with the experimental results, reproducing pullback depth and recompression timescales across the different samples tested. The findings demonstrate the model is suitable for reproducing spall-induced free surface behavior across various microstructures, but also points to caution in using model coefficients for unvalidated microstructures. The experimental evidence also suggests that microstructure orientation may play less of a role in spall strength than grain size. |
Tuesday, July 12, 2022 10:15AM - 10:30AM |
I02.00005: Micro-spall investigation in Sn targets using velocity and multi-time X-ray diagnostics in plate impact experiments Laurianne Pillon, Camille Chauvin, Yulrick Philippe, Julien Tailleur, Pascal Hereil When a material is subjected to a Taylor (triangular) shock wave of sufficently high-level to induce its melting under shock or release, the spall strength reduces to a very small value and a volumic damage occurs called micro-spall. An expanding cloud of high-density particles is generated in the bulk. Experimental quantitative observations of this physical phenomenon are complex. In this work, a recent experimental set up is presented. It is dedicated to the investigation of an expanding microspall in Sn targets. |
Tuesday, July 12, 2022 10:30AM - 10:45AM |
I02.00006: Expanding the envelope for spall modeling using porosity mechanics incorporating microinertia Sayyad B Qamar, Nathan R Barton, John A Moore Spall response and its connection to material microstructure are of significant interest across a range of loading conditions, including those produced by impact, explosives, or lasers. In this study, spall failure is simulated for conditions that access a range of characteristic time scales. Material failure is simulated using a Cocks-Ashby based damage model [1,2], in a large-deformation hydrocode (ALE3D) [3]. Differences in the macroscopic response and in the corresponding microscopic stress conditions are observed, with the loading conditions having a strong influence on the porosity growth associated with spall. Results for simulated free-surface velocities confirm the value of complementary post-mortem analysis in experiments. The model accounts for microinertial effects and provides information about potential discrepancies between microscopic stress states and the nominal spall strength inferred from velocimetry. The observations including microinertia suggest a route to improved spall performance in specially engineered materials. |
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