Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session B4: Inelastic Deformations, Fracture and Spall I |
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Chair: Jeffrey Lloyd, Army Research Laboratory Room: Regency Ballroom A |
Monday, July 10, 2017 9:15AM - 9:30AM |
B4.00001: Investigating Deformation and Mesoscale Void Creation in HMX Based Composites using Tomography Based Grain Scale Finite Element Modeling David J. Walters, Darby J. Luscher, Virginia Manner, John D. Yeager, Brian M. Patterson The microstructure of plastic bonded explosives (PBXs) significantly affects their macroscale mechanical characteristics. Imaging and modeling of the mesoscale constituents allows for a detailed examination of the deformation of mechanically loaded PBXs. In this study, explosive composites, formulated with HMX crystals and various HTPB based polymer binders have been imaged using micro Computed Tomography ($\mu$CT). Cohesive parameters for simulation of the crystal/binder interface are determined by comparing numerical and experimental results of the delamination of a polymer bound bi-crystal system. Similarly, polycrystalline samples are discretized into a finite element mesh using the mesoscale geometry captured by in-situ $\mu$CT imaging. Experimentally, increasing the stiffness of the HTPB binder in the polycrystalline system resulted in a transition from ductile flow with little crystal/binder delamination to brittle behavior with increased void creation along the interfaces. Simulating the macroscale compression of these samples demonstrates the effects that the mesoscale geometry, cohesive properties, and binder stiffness have on the creation and distribution of interfacial voids. Understanding void nucleation is critical for modeling damage in these complex materials. [Preview Abstract] |
Monday, July 10, 2017 9:30AM - 9:45AM |
B4.00002: Numerical Representation and Modeling of Adiabatic Shear Banding in Metals Tao Jin, Hashem Mourad, Curt Bronkhorst, Veronica Livescu We will present an enriched element technique to represent the adiabatic shear banding process within a traditional Lagrangian finite element framework. A rate-dependent onset criterion for the initiation of a band is defined based upon a rate and temperature dependent material model. Once the bifurcation condition is met, the location and orientation of the embedded zone is computed and inserted at that Gauss point. Once embedded the boundary conditions between the localized and unlocalized regions of the element are enforced and the composite sub-grid element follows a weighted average representation of both regions. The material inside the band is able to be represented with a constitutive model independent from the outside material and the thickness of the band can be assigned by any appropriate method. In the finite strain formulation, rotation of the formed band is tracked with deformation. The process of dynamic recrystallization as an additional softening mechanism during the dynamic loading process is critical for some materials and a simple physically based representation of the structural recovery process is discussed. Both the initiation and growth of adiabatic shear banding is believed to be influenced by local structural features of a material and this talk will discuss the influence of the microstructure on this process. Experiments have been performed on 304L and 316L stainless steels and will be compared against numerical simulations to validate the performance of both the material model and computational approach. Remaining challenges will also be discussed. [Preview Abstract] |
Monday, July 10, 2017 9:45AM - 10:00AM |
B4.00003: Modeling perturbed shock wave decay in granular materials with intra-granular fracture Masoud Behzadinasab, Tracy Vogler, John Foster Shock wave perturbation decay experiments have recently been explored as a tool to probe the high-rate shear response of granular materials. This dynamic behavior involves complex intra- and inter-granular phenomena. Mesoscale simulations can give insight into this complexity by explicitly resolving the deformations and interactions of individual grains. Peridynamics, a nonlocal continuum thoery, provides a suitable framework for modeling dynamic problems involving fracture. Previous research has focused mostly on the continuum, bulk response, neglecting any localized material failure, of granular materials. A systematic investigation on the effects of frictional contact forces and grain fracture on the continuum behavior of granular materials is carried out by peridynamic simulations of shock wave perturbation decay experiments. Sensitivity assessment of dominant factors indicates that intra-granular fracture, a phenomenon ignored in most computational investigations of granular materials, plays a large role in the bulk dynamic response. [Preview Abstract] |
Monday, July 10, 2017 10:00AM - 10:15AM |
B4.00004: Hypervelocity impact and dynamic fragmentation of brittle materials Vinamra Agrawal, Alejandro Ortega, Daniel Meiron The process of hypervelocity impact and dynamic fragmentation finds application in planetary formation, satellite design for micrometeorite impact damage mitigation, armor design and crater formations. In this work, we study high velocity impact induced dynamic fragmentation processes of brittle materials. We implement ideas of Continuum Damage Mechanics (CDM) to perform fragmentation simulations on brittle materials in various geometries. The damage formulation was implemented on an existing computational framework capable of adaptive mesh refinement that operates on an Eulerian grid, thereby avoiding problems associated with grid entanglement in large deformation processes. A damage sensitive equation of state is developed for hyperelastic materials that depends on a damage variable D, the volume fraction of micro-cracks in the brittle material. The evolution of D is governed by a modified, thermodynamically consistent Grady-Kipp model that evolves damage at points of tensile eigenvalue stresses. We simulate sphere-on-sphere and sphere-on-plate impact events with ductile and brittle materials and study the resulting damage propagation. We validate our calculations with existing literature and comment on energy dissipation and optimal design. [Preview Abstract] |
Monday, July 10, 2017 10:15AM - 10:30AM |
B4.00005: Phase Contrast Imaging of Damage Initiation During Ballistic Impact of Boron Carbide Brian Schuster, Andrew Tonge, Kyle Ramos, Paulo Rigg, Adam Iverson, Adam Schuman, Nicholas Lorenzo For several decades, flash X-ray imaging has been used to perform time-resolved investigations of the response of ceramics under ballistic impact. Traditional absorption based contrast offers little insight into the early initiation of inelastic deformation mechanisms and instead typically only shows the gross deformation and fracture behavior. In the present work, we employed phase contrast imaging (PCI) at the Dynamic Compression Sector (DCS) at the Advanced Photon Source, Argonne National Laboratory, to investigate crack initiation and propagation following the impact of copper penetrators into boron carbide targets. These experiments employed a single-stage propellant gun to launch small-scale (0.6 mm diameter by 3 mm long) pure copper impactors at velocities ranging from 0.9 to 1.9 km/s into commercially available boron carbide targets that were 8 mm on a side. At the lowest striking velocities the penetrator undergoes dwell or interface defeat and the target response is consistent with the cone crack formation at the impact site. At higher striking velocities there is a distinct transition to massive fragmentation leading to the onset of penetration. [Preview Abstract] |
Monday, July 10, 2017 10:30AM - 10:45AM |
B4.00006: Boron carbide: hydrocode simulation of plate-impact experiments with an improved failure model Sergey Dyachkov, Anatoly Parshikov, Vasily Zhakhovsky Unique strength properties of boron carbide make it useful for numerous applications. However, shock compression accompanied by high strains rates involves material into the process of failure what significantly reduces its strength. In this research we compare simulation results for two sets of plate-impact experiments where samples were manufactured using different technology. Simulations are performed using our 3D SPH hydrocode and the improved Johnson-Holmquist failure model. Complex wave profiles obtained via VISAR are properly reproduced in our modeling. However, it was found that the failed boron carbide strength have a strong effect on the wave profiles and should be different for the each set of experiments. Moreover, heterogeneous distribution of failed boron carbide is shown to affect wave propagation to the rear surface of sample what results in spatial velocity profile variations obtained via line-VISAR system. [Preview Abstract] |
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