A5050326739- Advanced ceramic materials synthesis
- High-Velocity Impact and Material Behavior
- Boron and Carbon Nanomaterials Research
- Metal and Thin Film Mechanics
- High-pressure geophysics and materials
- Diamond and Carbon-based Materials Research
- Advanced materials and composites
- Energetic Materials and Combustion
- Intermetallics and Advanced Alloy Properties
- Semiconductor materials and devices
- Aluminum Alloys Composites Properties
- MXene and MAX Phase Materials
- Electromagnetic Launch and Propulsion Technology
- Microwave Dielectric Ceramics Synthesis
- Inorganic Chemistry and Materials
- Ion-surface interactions and analysis
- Rock Mechanics and Modeling
- Ultrasonics and Acoustic Wave Propagation
- Suicide and Self-Harm Studies
- Thermal and Kinetic Analysis
- Advanced Surface Polishing Techniques
- Child and Adolescent Psychosocial and Emotional Development
- Resilience and Mental Health
- Nuclear materials and radiation effects
- Chemical Synthesis and Characterization
DEVCOM Army Research Laboratory
2009-2023
Johns Hopkins University
2015-2023
Hopkins Extreme Materials Institute
2020-2023
Johns Hopkins University Applied Physics Laboratory
2023
Seton Hall University
2019
CECOM Software Engineering Center
2005-2010
United States Army
1986-2008
Rutgers, The State University of New Jersey
2008
Alfred University
2008
American Ceramic Society
1978-2005
High-resolution electron microscope observations of shock-loaded boron carbide have revealed the formation nanoscale intragranular amorphous bands that occur parallel to specific crystallographic planes and contiguously with apparent cleaved fracture surfaces. This damage mechanism explains measured, but not previously understood, decrease in ballistic performance at high impact rates pressures. The these is also an example how shock loading can result synthesis novel structures materials...
A new isobaric, condensed phase diagram in the region of stability cubic aluminum oxynitride spinel (ALON) along pseudobinary AI 2 O 3 ‐AIN composition join is presented, deduced primarily from various analytical measurements and microstructural observations. It shown that melts incongruently at ≊2050°C compositionally centered ≊35.7 mol% AIN, which equivalent to following stoichiometric composition: 23 27 N 5 or 5AIN·9AI . Single‐phase ALON material sintered nearly full density exhibits...
We report depressurization amorphization of single-crystal boron carbide (B4C) investigated by in situ high-pressure Raman spectroscopy. It was found that localized B4C takes place during unloading from high pressures, and nonhydrostatic stresses play a critical role the phase transition. First-principles molecular dynamics simulations reveal results pressure-induced irreversible bending C-B-C atomic chains cross-linking 12 atom icosahedra at rhombohedral vertices.
Gibbs free-energy calculations based on density functional theory have been used to determine the possible source of failure boron carbide just above Hugoniot elastic limit (HEL). A range B4C polytypes is found be stable at room pressure. The energetic barrier for shock amorphization by far lowest B12(CCC) polytype, requiring only 6 GPa approximately = P(HEL) collapse under hydrostatic conditions. results clearly demonstrate that phase leads segregation B12 and amorphous carbon in form 2-3...
Two commercial hot‐pressed boron carbide ceramics were investigated by transmission electron microscopy. Atomic‐scale observations suggest that the grain boundaries of two materials are free grain‐boundary films. triple‐junction phases found and characterized to be rhombohedral Fe 2 B 103 orthorhombic Ti 3 4 . In addition, intra‐granular precipitates, AlN, Mo (C, B) graphite, identified have coherent relationships with matrix. Micron‐scale inclusions also observed most them determined...
High‐speed photography has been used to observe the dynamic failure of uncoated and Cr‐coated transparent polycrystalline aluminum oxynitride (AlON) material, undergoing uniaxial, high‐strain rate compression with a modified Kolsky bar technique. The high‐speed photographs are correlated in time measurements stresses specimen. In fully samples, activation, growth, coalescence cracks resulting damage zones from spatially separated internal defects have directly observed macroscopic loss...
The effects of stoichiometry on the atomic structure and related mechanical properties boron carbide (B4C) have been studied using density functional theory quantum molecular dynamics simulations. Computational cells containing up to 960 atoms spanning compositions ranging from 6.7% 26.7% carbon were used determine structure, elastic properties, stress–strain response as a function hydrostatic, uniaxial, shear loading paths. It was found that different stoichiometries, well variable...
Recent observations of planar defects in boron carbide have been shown to deviate from perfect mirror symmetry and are referred as "asymmetric twins." Here, we demonstrate that these asymmetric twins really phase boundaries form stoichiometric B(4)C (i.e., B(12)C(3)) but not B(13)C(2). TEM ab initio simulations coupled show result an interplay stoichiometry, atomic positioning, icosahedral twinning, structural hierarchy. The composition icosahedra is B(11)C translation the carbon atom a...
An experimental technique is developed to impose a planar lateral confinement in prismatic specimen (with rectangular cross section); the setup enabled controlled and homogeneous stress state with high compressive stresses. A transparent polycrystalline aluminum oxynitride (AlON) was used for study. The statically precompressed then subjected axial dynamic loading using modified compression Kolsky bar setup. Experimental design performed 3D computational modeling. Initial exploratory...