Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session P1: Inelastic Deformation, Fracture, and Spall VII |
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Chair: Michael Greenfield, Army Research Laboratory Room: Grand Ballroom II-III |
Wednesday, June 29, 2011 2:00PM - 2:15PM |
P1.00001: Modeling ductile metals under large strain, pressure and high strain rates incorporating damage and microstructure evolution Gianluca Iannitti, Nicola Bonora, Andrew Ruggiero, Simone Dichiaro In this work, a constitutive modeling that couples plasticity, grain size evolution (due to plastic deformation and dynamic recrystallization) and ductile damage has been developed. The effect of grain size on the material yield stress (Hall-Petch) and on the melting temperature has been considered. The model has been used to investigate computationally the behaviour of high purity copper in dynamic tensile extrusion test (DTE). An extensive numerical simulation work, using implicit finite element code with direct integration, has been performed and the results have been compared with available experimental data. The major finding is that the proposed model is capable to predict most of the observed features such as the increase of material ductility with the decreasing average grain size, the overall number and size of fragments and the average grain size distribution in the fragment trapped into the dime [Preview Abstract] |
Wednesday, June 29, 2011 2:15PM - 2:30PM |
P1.00002: Spall Strength of Niobium and Molybdenum Matthew Cotton, Jeremy Millett, Glenn Whiteman, Nigel Park The shock response of niobium and molybdenum have been investigated as part of a wider programme on bcc metals. Previous work has studied shear strength development behind the shock front and related the observed behaviour to known deformation mechanisms. We now turn our attention to the dynamic tensile (spall) response of these materials. Although both are bcc in nature and adjacent to each other in the periodic table, they display very different behaviours. Niobium has been shown to be highly ductile, with a high spall strength. In contrast, molybdenum is brittle, with a low spall strength that reduces to near zero as stress amplitude increases. Results are discussed in terms of the deformation mechanisms. [Preview Abstract] |
Wednesday, June 29, 2011 2:30PM - 2:45PM |
P1.00003: A Mechanism Based Rate-Dependent Model for Ductile Fragmentation Justin Wilkerson, Kaliat Ramesh It is well known that a primary microscopic failure mechanism of ductile materials is the nucleation, growth, and coalescence of voids. These microscopic mechanisms govern the fracture and fragmentation of the bulk material at high strain rates. We present a numerical framework for investigating the fragmentation of ductile materials, accounting for the combined effects of dynamically growing voids in the microscale and localization in the macroscale. The macroscopic governing equations are integrated through the method of characteristics, thus restricting the propagation of macroscopic information to finite wave speeds. In order to account for the microscopic heterogeneous nature of materials, we assume a statistical distribution of nucleation properties. A self-consistent approach is employed to track the dynamics of each individual void and account for their interactions at all macroscopic material points. The full system of coupled integro-differential equations of the self-consistent void growth model are directly integrated at each macroscopic node, thus defining the continuously updated rate-dependent macroscopic constitutive response that drives localization and fragmentation. Fragment size distributions are predicted for a number of materials subjected to dynamic loading. [Preview Abstract] |
Wednesday, June 29, 2011 2:45PM - 3:00PM |
P1.00004: Advanced Plasticity Models Applied to Recent Shock Data on Beryllium Michael Prime, Chris Adams, Shuh-Rong Chen Recent plate impact experiments with pressures from 2 to 20 GPa have been performed on vacuum hot-pressed S-200F Beryllium. This hexagonal close-packed (HCP) metal shows significant plasticity effects. To examine the validity of advanced plasticity models in the shock regime, the plate impact experiments were modeled using a Lagrangian hydrocode. Two constitutive strength (plasticity) models, the Preston-Tonks-Wallace (PTW) and Mechanical Threshold Stress (MTS) models, were calibrated using the same extensive set of quasi-static and Hopkinson bar data taken at temperatures from 77K to 873K and strain rates from 0.001/sec to 4300/sec. In spite of being calibrated on the same data, the two models give noticeably different results when comparing with the experimentally measured wave profiles. Neither model is unequivocally superior, with each matching some aspects of the data better. The reasons for the differences are explored and discussed. Differences between the two models are particularly evident during reverse loading upon shock release, which is also examined. The performance of simpler plasticity models than PTW or MTS in simulating the impact tests is also presented for reference. [Preview Abstract] |
Wednesday, June 29, 2011 3:00PM - 3:30PM |
P1.00005: Mesoscale modeling of dynamic compressibility, shear strength, and fracture of ceramic polycrystals Invited Speaker: Fundamental understanding of dynamic behavior of polycrystalline ceramics is advanced via constitutive theory development and computational modeling. At the mesoscale, microstructures of silicon carbide grains (hexagonal polytypes) or aluminum oxynitride grains (cubic structure) are subjected to high rates of deformation with varying magnitudes of confining pressure. Each grain is resolved by numerous three-dimensional finite elements, and behavior of each grain is modeled using nonlinear anisotropic thermoelasticity. Cohesive fracture models and post-fracture contact are included. Failure statistics from many simulations are collected and analyzed. Results demonstrate possible effects of load directionality, confinement, dilatation, elastic anisotropy and elastic nonlinearity, and grain boundary strength on average (i.e., macroscopic) failure envelopes in stress space for loading conditions in the ballistic regime. Methods for informing macroscopic constitutive models of brittle and quasi-brittle material behavior incorporating microstructure- and size-dependent strength distributions are developed. [Preview Abstract] |
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