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Mohammed A. Zikry - One of the best experts on this subject based on the ideXlab platform.

  • Coupled infrared laser-thermo-mechanical response of RDX-PCTFE energetic aggregates
    Computational Mechanics, 2016
    Co-Authors: Judith A. Brown, Mohammed A. Zikry
    Abstract:

    A computational approach is developed to investigate the coupled phenomena of high frequency electromagnetic (EM) wave propagation, laser heat absorption, thermal conduction, and inelastic dynamic thermo-mechanical deFormation in heterogeneous energetic materials. The method is used to study Hot Spot Formation in RDX-PCTFE aggregates subjected to high strain rate loads and infrared laser irradiation. The approach couples Maxwell’s equations with a dislocation density-based crystal plasticity formulation within a nonlinear finite-element approach to predict and understand thermo-mechanical response due to the interrelated effects of dielectric heating, adiabatic heating, thermal decomposition, and heat conduction. RDX crystalline interfaces and orientations, polymer binder, inelastic strains, dislocation-density evolution, and voids significantly affected the coupled EM-thermo-mechanical response. EM and thermo-mechanical mismatches at interfaces between RDX crystals, binder, and voids resulted in localized regions with high electric field and laser heat generation rates, which subsequently led to Hot Spot Formation. It is predicted that incident laser intensity and plastic shear strain localization are the dominant mechanisms that lead to Hot Spot Formation.

  • heterogeneous thermo mechanical behavior and Hot Spot Formation in rdx estane energetic aggregates
    International Journal of Solids and Structures, 2015
    Co-Authors: D. A. Labarbera, Mohammed A. Zikry
    Abstract:

    Abstract Hot Spot Formation has been investigated in energetic aggregates with a viscoelastic binder and crystalline grains that has been subjected to dynamic thermo-mechanical loading conditions. A dislocation-density based crystalline plasticity, finite viscoelasticity, and specialized finite-element formulations were used to predict Hot Spot Formation due to dynamic thermo-mechanical loading conditions in RDX–estane energetic aggregates. The interrelated effects of grain boundary (GB) misorientations, porosity, grain morphology, dislocation densities, polymer binder relaxation, and crystal–binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, viscous dissipation heating, and thermal conduction to analyze aggregate behavior and Hot Spot Formation. The predictions indicate that Hot Spot Formation occurs when temperatures become unbounded in localized regions at the peripheries of RDX crystals where RDX–estane interfacial incompatibilities result in crystal sliding and localized plastic deFormation at RDX crystal edges and interfaces.

  • Heterogeneous thermo-mechanical behavior and Hot Spot Formation in RDX–estane energetic aggregates
    International Journal of Solids and Structures, 2015
    Co-Authors: D. A. Labarbera, Mohammed A. Zikry
    Abstract:

    Abstract Hot Spot Formation has been investigated in energetic aggregates with a viscoelastic binder and crystalline grains that has been subjected to dynamic thermo-mechanical loading conditions. A dislocation-density based crystalline plasticity, finite viscoelasticity, and specialized finite-element formulations were used to predict Hot Spot Formation due to dynamic thermo-mechanical loading conditions in RDX–estane energetic aggregates. The interrelated effects of grain boundary (GB) misorientations, porosity, grain morphology, dislocation densities, polymer binder relaxation, and crystal–binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, viscous dissipation heating, and thermal conduction to analyze aggregate behavior and Hot Spot Formation. The predictions indicate that Hot Spot Formation occurs when temperatures become unbounded in localized regions at the peripheries of RDX crystals where RDX–estane interfacial incompatibilities result in crystal sliding and localized plastic deFormation at RDX crystal edges and interfaces.

  • Laser interaction effects of electromagnetic absorption and microstructural defects on Hot-Spot Formation in RDX-PCTFE energetic aggregates
    Modelling and Simulation in Materials Science and Engineering, 2014
    Co-Authors: Judith A. Brown, D. A. Labarbera, Mohammed A. Zikry
    Abstract:

    Hot-Spot Formation in energetic aggregates subjected to dynamic pressure loading and laser irradiation has been investigated. Specialized finite-element techniques with a dislocation-density-based crystalline plasticity constitutive formulation and thermo-mechanical coupling of heat conduction, adiabatic heating, laser heating and thermal decomposition were used to predict Hot-Spot Formation in RDX–polymer aggregates subjected to dynamic pressures and laser energies. The effects of the electromagnetic absorption coefficient coupled with void distribution and spacing, grain morphology, crystal–binder interactions and dislocation densities were analyzed to determine their influence on the time, location and mechanisms of Hot-Spot Formation. Four different mechanisms for Hot-Spot initiation under dynamic laser and pressure loads were identified, which depend on the localization of plastic shear strain and laser heat absorption within the aggregate. The predictions indicate that Hot-Spot Formation is accelerated by higher absorption coefficients and by localized plastic deFormations that occur in areas of significant laser heating.

  • The effects of microstructural defects on Hot Spot Formation in cyclotrimethylenetrinitramine-polychlorotrifluoroethylene energetic aggregates
    Journal of Applied Physics, 2013
    Co-Authors: D. A. Labarbera, Mohammed A. Zikry
    Abstract:

    Shock initiation due to Hot Spot Formation has been investigated in energetic aggregates subjected to dynamic thermo-mechanical loading conditions. A dislocation-density based crystalline plasticity and specialized finite-element formulations were used to predict Hot Spot Formation due to dynamic thermo-mechanical loading conditions in cyclotrimethylenetrinitramine-polymer energetic aggregates. The effects of grain boundary misorientations, porosity, grain morphology, dislocation densities, and crystal-binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, and dissipated heat to analyze Hot Spot Formation. The predictions indicate that Hot Spot Formation occurs when temperatures become unbounded in localized regions between voids. The time to Hot Spot Formation decreases with increases in dynamic pressure loads, which is consistent with experimental results.

Edson L. Meyer - One of the best experts on this subject based on the ideXlab platform.

  • an outdoor investigation of the absorption degradation of single junction amorphous silicon pHotovoltaic module due to localized heat Hot Spot Formation
    Pramana, 2016
    Co-Authors: G O Osayemwenre, Edson L. Meyer, Sampson Mamphweli
    Abstract:

    This paper investigates the absorbance degradation of single-junction amorphous silicon (a-Si:H) pHotovoltaic (PV) module, due to the presence of localized heat. The decrease in optical density is a huge challenge due to the long-term degradation of PV modules. The reduction in solar cell optical density causes a decline in its conversion efficiency. This decreases the pHotogenerating current, hence reduces the effective efficiency of the PV device. An infrared thermography was used for mapping the module temperature profile. Fourier transform infrared spectroscopy (FTIR) was used for the absorption characterization. The rationale behind the outdoor deployment was to deduce a practical effect of Hot Spot Formation on the module’s absorption ability. The results show a direct correlation between localized heat and the absorption degradation.

  • An outdoor investigation of the absorption degradation of single-junction amorphous silicon pHotovoltaic module due to localized heat/Hot Spot Formation
    Pramana, 2016
    Co-Authors: G O Osayemwenre, Edson L. Meyer, Sampson Mamphweli
    Abstract:

    This paper investigates the absorbance degradation of single-junction amorphous silicon (a-Si:H) pHotovoltaic (PV) module, due to the presence of localized heat. The decrease in optical density is a huge challenge due to the long-term degradation of PV modules. The reduction in solar cell optical density causes a decline in its conversion efficiency. This decreases the pHotogenerating current, hence reduces the effective efficiency of the PV device. An infrared thermography was used for mapping the module temperature profile. Fourier transform infrared spectroscopy (FTIR) was used for the absorption characterization. The rationale behind the outdoor deployment was to deduce a practical effect of Hot Spot Formation on the module’s absorption ability. The results show a direct correlation between localized heat and the absorption degradation.

  • Detection and analysis of Hot-Spot Formation in solar cells
    Solar Energy Materials and Solar Cells, 2010
    Co-Authors: Michael Simon, Edson L. Meyer
    Abstract:

    In this study, infrared thermography (IR) was used to map the surface temperature distribution of solar cells while in the reverse bias mode. It was observed that some cells exhibited an inhomogeneity of the surface temperature resulting in localized heating (Hot-Spot). Using the scanning electron microscopy (SEM), the structural images of Hot-Spot areas revealed that Hot-Spot heating causes irreversible destruction of the solar cell structure. Different techniques were later used to analyze the elemental composition of the different regions of the solar cells. It was revealed that a direct correlation exists between areas of high impurity contaminants and Hot-Spot heating. Areas with high concentration of transition metals resulted in Hot-Spot Formation. The results of all the samples are presented in detail in this paper.

P. Choi - One of the best experts on this subject based on the ideXlab platform.

  • beam and Hot Spot Formation in a low impedance line driven vacuum spark discharge
    Journal of Applied Physics, 1992
    Co-Authors: E. S. Wyndham, H. Chuaqui, Mario Favre, Leopoldo Soto, P. Choi
    Abstract:

    Observations of a vacuum spark discharge are presented using a coaxial line driver. A 120 ns, 1.5 Ω coaxial line is used to give peak discharges of 90 kA. The usual line spark gap is shorted out giving a new mode of operation. The discharge is initiated once the rising sinusoidal voltage is applied by focusing a Nd:YAG laser onto the cathode front surface, peak current is reached at 250 ns after this. Reproducible Hot Spot Formation is observed at this time. Holographic interferometry combined with time and space resolved x‐ray observations show emission from a dense anode plasma as well as from the dense plasma column in which Hot Spot forms at peak current.

  • Beam and Hot‐Spot Formation in a low impedance line driven vacuum spark discharge
    Journal of Applied Physics, 1992
    Co-Authors: E. S. Wyndham, H. Chuaqui, Mario Favre, Leopoldo Soto, P. Choi
    Abstract:

    Observations of a vacuum spark discharge are presented using a coaxial line driver. A 120 ns, 1.5 Ω coaxial line is used to give peak discharges of 90 kA. The usual line spark gap is shorted out giving a new mode of operation. The discharge is initiated once the rising sinusoidal voltage is applied by focusing a Nd:YAG laser onto the cathode front surface, peak current is reached at 250 ns after this. Reproducible Hot Spot Formation is observed at this time. Holographic interferometry combined with time and space resolved x‐ray observations show emission from a dense anode plasma as well as from the dense plasma column in which Hot Spot forms at peak current.

D. A. Labarbera - One of the best experts on this subject based on the ideXlab platform.

  • heterogeneous thermo mechanical behavior and Hot Spot Formation in rdx estane energetic aggregates
    International Journal of Solids and Structures, 2015
    Co-Authors: D. A. Labarbera, Mohammed A. Zikry
    Abstract:

    Abstract Hot Spot Formation has been investigated in energetic aggregates with a viscoelastic binder and crystalline grains that has been subjected to dynamic thermo-mechanical loading conditions. A dislocation-density based crystalline plasticity, finite viscoelasticity, and specialized finite-element formulations were used to predict Hot Spot Formation due to dynamic thermo-mechanical loading conditions in RDX–estane energetic aggregates. The interrelated effects of grain boundary (GB) misorientations, porosity, grain morphology, dislocation densities, polymer binder relaxation, and crystal–binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, viscous dissipation heating, and thermal conduction to analyze aggregate behavior and Hot Spot Formation. The predictions indicate that Hot Spot Formation occurs when temperatures become unbounded in localized regions at the peripheries of RDX crystals where RDX–estane interfacial incompatibilities result in crystal sliding and localized plastic deFormation at RDX crystal edges and interfaces.

  • Heterogeneous thermo-mechanical behavior and Hot Spot Formation in RDX–estane energetic aggregates
    International Journal of Solids and Structures, 2015
    Co-Authors: D. A. Labarbera, Mohammed A. Zikry
    Abstract:

    Abstract Hot Spot Formation has been investigated in energetic aggregates with a viscoelastic binder and crystalline grains that has been subjected to dynamic thermo-mechanical loading conditions. A dislocation-density based crystalline plasticity, finite viscoelasticity, and specialized finite-element formulations were used to predict Hot Spot Formation due to dynamic thermo-mechanical loading conditions in RDX–estane energetic aggregates. The interrelated effects of grain boundary (GB) misorientations, porosity, grain morphology, dislocation densities, polymer binder relaxation, and crystal–binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, viscous dissipation heating, and thermal conduction to analyze aggregate behavior and Hot Spot Formation. The predictions indicate that Hot Spot Formation occurs when temperatures become unbounded in localized regions at the peripheries of RDX crystals where RDX–estane interfacial incompatibilities result in crystal sliding and localized plastic deFormation at RDX crystal edges and interfaces.

  • Microstructural Modeling of Hot Spot and Failure Mechanisms in RDX Energetic Aggregates.
    2014
    Co-Authors: D. A. Labarbera
    Abstract:

    Abstract : Hot Spot Formation and failure mechanisms, such as dynamic fracture and shear strain localization, for RDX (cyclotrimethylene trinitramine)-polymer binder aggregates were investigated for dynamic thermo-mechanical loading conditions. A formulation based on a dislocation-density based crystalline plasticity and a finite viscoelasticity framework was coupled to a microstructurally-based dynamic fracture nucleation and propagation method, and it was used to investigate interrelated high strain-rate failure modes in RDX-polymer binder energetic aggregates. The effects of grain boundary (GB) misorientations, porosity, grain morphologies, dislocation densities, and crystal-binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, thermal conduction, and dissipated heat to predict and understand Hot Spot Formation for a PCTFE (Polychlorotrifluoroethylene) polymer binder. The validated predictions indicate that Hot Spots were induced by inelastic deFormation modes, which resulted in unbounded temperatures due to localized plasticity and thermal decomposition at the peripheries of the voids. Viscous dissipation, due to the estane polymer binder, where the operating temperatures were above the glass transition temperature, resulted in RDX crystal interactions due to hydrostatic compression of the polymer binder. This hydrostatic compression constrained the polymer binder interfaces, which enhanced RDX inelastic deFormation modes and resulted in and accelerated Hot Spot Formation at the RDX crystal peripheries in the interfacial regions between the estane binder and the RDX crystals. The effects of dynamic crack nucleation and propagation were also investigated in energetic aggregates subjected to high strain rate loading conditions.

  • Laser interaction effects of electromagnetic absorption and microstructural defects on Hot-Spot Formation in RDX-PCTFE energetic aggregates
    Modelling and Simulation in Materials Science and Engineering, 2014
    Co-Authors: Judith A. Brown, D. A. Labarbera, Mohammed A. Zikry
    Abstract:

    Hot-Spot Formation in energetic aggregates subjected to dynamic pressure loading and laser irradiation has been investigated. Specialized finite-element techniques with a dislocation-density-based crystalline plasticity constitutive formulation and thermo-mechanical coupling of heat conduction, adiabatic heating, laser heating and thermal decomposition were used to predict Hot-Spot Formation in RDX–polymer aggregates subjected to dynamic pressures and laser energies. The effects of the electromagnetic absorption coefficient coupled with void distribution and spacing, grain morphology, crystal–binder interactions and dislocation densities were analyzed to determine their influence on the time, location and mechanisms of Hot-Spot Formation. Four different mechanisms for Hot-Spot initiation under dynamic laser and pressure loads were identified, which depend on the localization of plastic shear strain and laser heat absorption within the aggregate. The predictions indicate that Hot-Spot Formation is accelerated by higher absorption coefficients and by localized plastic deFormations that occur in areas of significant laser heating.

  • The effects of microstructural defects on Hot Spot Formation in cyclotrimethylenetrinitramine-polychlorotrifluoroethylene energetic aggregates
    Journal of Applied Physics, 2013
    Co-Authors: D. A. Labarbera, Mohammed A. Zikry
    Abstract:

    Shock initiation due to Hot Spot Formation has been investigated in energetic aggregates subjected to dynamic thermo-mechanical loading conditions. A dislocation-density based crystalline plasticity and specialized finite-element formulations were used to predict Hot Spot Formation due to dynamic thermo-mechanical loading conditions in cyclotrimethylenetrinitramine-polymer energetic aggregates. The effects of grain boundary misorientations, porosity, grain morphology, dislocation densities, and crystal-binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, and dissipated heat to analyze Hot Spot Formation. The predictions indicate that Hot Spot Formation occurs when temperatures become unbounded in localized regions between voids. The time to Hot Spot Formation decreases with increases in dynamic pressure loads, which is consistent with experimental results.

E. S. Wyndham - One of the best experts on this subject based on the ideXlab platform.

  • beam and Hot Spot Formation in a low impedance line driven vacuum spark discharge
    Journal of Applied Physics, 1992
    Co-Authors: E. S. Wyndham, H. Chuaqui, Mario Favre, Leopoldo Soto, P. Choi
    Abstract:

    Observations of a vacuum spark discharge are presented using a coaxial line driver. A 120 ns, 1.5 Ω coaxial line is used to give peak discharges of 90 kA. The usual line spark gap is shorted out giving a new mode of operation. The discharge is initiated once the rising sinusoidal voltage is applied by focusing a Nd:YAG laser onto the cathode front surface, peak current is reached at 250 ns after this. Reproducible Hot Spot Formation is observed at this time. Holographic interferometry combined with time and space resolved x‐ray observations show emission from a dense anode plasma as well as from the dense plasma column in which Hot Spot forms at peak current.

  • Beam and Hot‐Spot Formation in a low impedance line driven vacuum spark discharge
    Journal of Applied Physics, 1992
    Co-Authors: E. S. Wyndham, H. Chuaqui, Mario Favre, Leopoldo Soto, P. Choi
    Abstract:

    Observations of a vacuum spark discharge are presented using a coaxial line driver. A 120 ns, 1.5 Ω coaxial line is used to give peak discharges of 90 kA. The usual line spark gap is shorted out giving a new mode of operation. The discharge is initiated once the rising sinusoidal voltage is applied by focusing a Nd:YAG laser onto the cathode front surface, peak current is reached at 250 ns after this. Reproducible Hot Spot Formation is observed at this time. Holographic interferometry combined with time and space resolved x‐ray observations show emission from a dense anode plasma as well as from the dense plasma column in which Hot Spot forms at peak current.