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 U01: Statistical and Numerical Methods for Relating Microstructure to Continuum ResponseRecordings Available
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Chair: Marisol Koslowski, Purdue University Room: Anaheim Marriott Platinum 5 |
Thursday, July 14, 2022 11:00AM - 11:15AM |
U01.00001: Unraveling the Implications of Finite Specimen Size on the Interpretation of Dynamic Experiments for Polycrystalline Metals through Numerical Simulations Bryan Zuanetti, Darby J Luscher, Cynthia A Bolme, Kyle J Ramos Normal and Pressure-shear plate impact (NPI and PSPI) experiments 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 often involve a limited specimen size. Moreover, because of inherent heterogeneities present within polycrystalline metals, it is difficult to ascertain when the size of the sample is large enough for making representative inferences from free surface point velocity measurements. In the present study, we quantify the expected measurement variability on observable point measurements in NPI and PSPI experiments by carrying out direct numerical simulations (DNS) of statistically representative polycrystalline microstructures subjected to dynamic compression and compression-shear loading. In particular, we consider the role of specific material heterogeneities (e.g. grain size, morphology, the grain-to-grain difference in crystal orientation) on dispersion in the normal and transverse particle velocity records and on local fluctuations in key state variables (e.g. stress, temperature, accumulated plastic strain) by incorporating these effects directly into a synthetic microstructure geometry and crystalline description of a represetative FCC metal. 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 velocity measurements approach a mean-field value) with decreasing grain size. The reasoning for the scatter in particle velocity due to the heterogeneous microstructure is demonstrated to be dependent on the mechanisms for accommodating deformation and on the interaction of flow occurring at various length scales within the microstrcuture. Lastly, we summarize the results into a framework for assessing the required number of grains per characteristic length for minimizing scatter in NPI/PSPI. |
Thursday, July 14, 2022 11:15AM - 11:30AM |
U01.00002: Shock Compaction of Brittle Granular Media: Comminution Particle Size Statistics and the Localization of Thermal and Mechanical Dissipation Dennis E Grady A material response model is proposed that addresses the compaction of brittle granular media in the shock-wave environment. The model bridges deficiencies inherent to continuum compaction models on one hand and computational meso models on the other. Central to the model is assessment of the evolving particle size distribution as compaction comminution ensues. This aspect of the model relies on an extended history of crush and comminution of brittle solids and the bounded scale invariant fracture and resulting fractal character of the emerging particulate. Statistical features of the compaction process are inherent to the model and through this formulation the dynamics of energy localization emerge naturally. The model intentionally spans length scales from the mesoscopic to the continuum. Application results in transient local temperature intensities and persistence concurrent with and subsequent to the Hugoniot state shock compaction of the granular solids. Calculations address experimental shock compaction data for granular quartz sand and for nonreacting granular HMX. |
Thursday, July 14, 2022 11:30AM - 11:45AM |
U01.00003: Modeling tantatlum hole closure experiments to assess constitutive models at high strain rates and large strains Matt Nelms, Jonathan Lind, Mukul Kumar, Nathan R Barton We present numerical simulations and experimental results for tantalum hole closure experiments performed using the high-rate imaging systems within the Dynamic Compression Sector located at the Advanced Photon Source. The hole closure platform uses a cylindrically convergent geometry to produce large deformation at strain rates of 10^5/s and higher. In this study, we developed an updated configuration that uses a two-layer flyer and elongated target to mitigate the deleterious effects of porosity and anelasticity. The updated configuration allowed us to assess the capability of simpler constitutive models when materials are subjected to extreme conditions, such as strains that significantly larger than traditional plate impact experiments while achieving similar pressure and strain rates. Results from the updated experimental configuration are used to evaluate commonly-used strength models for tantalum. |
Thursday, July 14, 2022 11:45AM - 12:00PM |
U01.00004: Eulerian finite element implementation of a dislocation density-based continuum model with application to simulations of drop weight impact test Milovan Zecevic, Marc J Cawkwell, Roseanne M Cheng, Virginia W Manner, Darby J Luscher In Eulerian finite element simulations, the mesh moves relative to the material. After every change of position between the mesh and the material, the state variables are interpolated to the new mesh position, i.e., advection. Large strain crystal plasticity models are based on a multiplicative decomposition of the total deformation gradient. The stress is evaluated as a function of the thermoelastic strain, temperature, and other state variables. Advection of tensor quantities, e.g., strain, is coupled with possibly significant advection errors. In an effort to reduce the advection errors, we develop a rate form of a dislocation density-based continuum model by Luscher et al. in Abaqus. To that end, we replace the multiplicative decomposition of the deformation gradient with the additive decomposition of velocity gradient, and define the stress rate instead of the total stress. In a drop weight impact test, a sample sitting on an anvil is compressed to large strain by a falling weight. We use the Eulerian implementation to simulate the deformation and temperature evolution in the sample. Results for single crystal and polycrystal cyclotrimethylene trinitramine samples will be presented. |
Thursday, July 14, 2022 12:00PM - 12:15PM |
U01.00005: Evaluating microstructure features for shock sensitivity at the mesoscale Michael Sakano, Judith A Brown, Julia M Hartig, Dan S Bolintineanu, Mitchell A Wood Developing insight into the microstructure dependence on observed shock initiation sensitivity of energetic materials under a variety of mechanical stimuli and thermodynamic conditions will result in much needed capabilities towards predicting detonation performance. Current state-of-the-art experiments lack the connection between microstructure features and sensitivity, thus we turn to simulations for further investigation. To date, these high-fidelity computational efforts have often been limited to studying the criticality of single pore collapse; while interesting, it has not yet been feasible to predict the sensitivity of a more realistic multipore microstructure. Our work involves well-defined sets of simulations with increasing degrees of complexity to study materials behavior across a variety of shock conditions and length- and time-scales. These efforts define a suite of reaction progress metrics that better resolve the buildup of a deflagration wave, and we will discuss important computational details that impact their interpretation. Establishing connections between geometric relationship of pores, we can predict criticality thresholds built up from small scale tests. We conclude with compact, data-driven models to predict the response of the global metrics. |
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