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Weapons and Materials Research Directorate Research Areas

Material Behavior

Thin Films of Low Loss Dielectrics Research

Advisor: MW Cole            

Key words: thin films, ferroelectrics, processing science, materials characterization, dielectric characterization

This research focuses on synthesis and fabrication of thin-film ferroelectric materials for use in high-frequency devices, particularly antennas and sensors. Work efforts include (but are not limited to) process optimization of large area ferroelectric thin-film deposition by metallo-organic spin deposition, pulsed laser deposition, sputtering and rf-sputtering, electron beam evaporation, and organometallic chemical vapor deposition. Our laboratory offers research opportunities in thin-film materials development and processing science, including evaluation of electronic, dielectric, and materials thin-film properties as a function of deposition technique; chemical composition; and process parameters. The effects of substrate type, processing temperature, target composition, film stress, and electrode metallizations are strongly emphasized.

Our laboratory is fully equipped to perform all facets of thin-film deposition, electrical (I-V and C-V measurements) low frequency and microwave characterization, optical characterization (e.g., Fourier-transform infrared and micro-Raman spectroscopy), and possesses a state-of-the-art materials characterization facility (e.g., Rutherford backscattering, Auger emission spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, AFM, scanning electron microscopy, curvature-stress measurements, nanomechanical properties characterization, and high-resolution transmission electron microscopy).

Scientists currently working in the ferroelectrics thin-films group posses a broad spectrum of thin-films expertise, including heterostructure interface chemistry and physics, conduction mechanisms, film defect studies, modeling of dielectric loss factors, chemical and physical vapor film deposition, ferroelectric thin-film materials chemistry and physics, and electrode design and fabrication. Research efforts for transmission line design and modeling for high-frequency microwave applications also exist as a collaborative effort within ARL

Processing/Structure/Property Relations of Metals, Alloys, and Other Materials

Advisor:  MR Staker           

Key words: metals and metallurgy, alloys, metal solidification, metal matrix composites, uranium

Our goal is to understand basic mechanisms through experimental observations of physical properties, which are associated with a given structure at all levels: atomistic, nano, micro, macro, and full scale.  We process the materials using a variety of techniques in order to achieve the various structures.  Tools include metallography for optical and electron microscopy, x-ray and neutron diffraction, mechanical property testing, chemical analysis, and thermomechanical processing (e.g., forging/rolling, deformation, and solidification processing).

We also study the following types of phenomena: adiabatic shear at high strain rates, gas/metal eutectic reactions, behavior of uranium and tungsten alloys during ballistic penetration, uranium phase diagrams, high strength-high strain hardening alloys for armor applications (e.g., modified Hadfield steel), and the development of advanced metal matrix composites.

Processing and Characterization of Hybrid Metal Ceramic Composite Armor

Advisor: ESC Chin                             

Key words: ceramic matrix composites, metal matrix composites, composite materials, shock waves, terminal ballistics

Armor packages composed of multiple layers of ceramics and metals provide excellent ballistic protection. This research focuses on microstructural design, processing and integration of metals, ceramics and hybrid composites to provide optimal ballistic protection.

Research opportunities involve:

  • investigating the roles of microstructural morphologies in dynamic deformation.
  • exploring the effects of through property gradient on shock wave attenuation and failures.
  • determining the synergistic effects from grain boundary reactions and interfacial interactions associated with dynamic loading.
  • exploiting thermodynamic and kinetic fundamentals to process in situ hybrid metallic composites.
  • studying the correlation between static and dynamic properties as a function of microstructural constituents.

Computational Modeling of Transient Nonlinear Phenomena in Solids

Advisor: GA Gazonas                       

Key words: wave propagation, layered media, constitutive models, finite elements, computational mechanics, nonlinear optimization, dynamic fracture, localization, acoustics metamaterials, inverse methods

Research opportunities exist for analytical and computational modeling of transient wave propagation in layered media and complex structures comprised of materially and geometrically nonlinear solid media including cellular, composite, viscoplastic, micropolar, non-local, gradient, and inhomogeneous materials. Recent theoretical developments for periodic elastic media are focused on studying the mechanics of acoustic bandgap and metamaterials for shock wave mitigation and acoustic cloaking applications. Emphasis is placed on model validation against analytical solutions to transient boundary value problems involving wave propagation, dynamic fracture, fragmentation, and other localization phenomena, and the physics of nonlinear interfaces using cohesive zone modeling. Additional research opportunities exist in the area of transient structural optimization, utilizing nonlinear inverse methods and developing computational optimization tools (e.g., genetic algorithms, gradient search, pattern search, and computational geometric methods) for use in conjunction with large-scale finite element codes.

References

Wang X, Gazonas GA, Santare MH, International Journal of Fracture, 158: 27, 2009.
Velo AP, Gazonas GA, Ameya T, SIAM Journal on Applied Mathematics, 69: 762, 2009.Wildman RA, Gazonas GA, Geophysics, 74: 123, 2009.

 

Behavior of Materials under Extreme Pressures and Temperatures

Advisor: DP Dandekar and T Weerasooriya 

Key words: calorimetry, materials science, thermal conditions and measurements, pressure effects and measurements, shear forces, p orosity , c eramic matrix composites , m etal matrix composites , polymers, alloys

Research involves exploratory and advanced development leading to novel experimental techniques to determine the behavior of materials at high pressures and high temperatures achieved at a rapid rate (i.e., in less than a few microseconds or nanoseconds). Typical activities focus on elucidating the relationship between the structure and properties of materials. These materials include ceramics, heavy alloys, polymer, and metal matrix and ceramic composites.

Properties of interest include elastic constants at high pressures and temperatures, shock response of solids, stability of pore under high pressure, dispersion of sound waves in composites, shear strength of solids, phase transformations, equation of state, refractive index, electrical conductivity, sound speed in porous materials, dielectric constants of porous solids, compaction of powders for material synthesis under extreme pressures and temperatures.

Experimental facilities include single and two stage gas guns, piezoelectric and piezoresistive gages, and interferometer.

Effect of Structure on the Deformation/Failure Behavior of Materials under High Rates of Loading

Advisor: T Weerasooriya               

Key words: high rate, failure, deformation, hopkinson bar, shear localization, microstructure, failure mechanisms, tension, torsion, compression

Research focuses on understanding the effect of micro- and sub-structures on the deformation and failure behavior of materials at different strain-rates of loading, including high strain rates. Materials that are being studied include metallic alloys, ceramics, soft and hard polymers, and composites.  The effect of stress state on the failure behavior and failure mechanisms at high rates of loading is also being investigated.

We are especially interested in the relationship between structure and the failure that results from tensile and shear instability at high rates.  Tools being used for high-rate investigations include compression, tension, and torsion Hopkinson bars.

Experimental facilities also include Hopkinson bars that are designed for low-impedance soft material testing.  High speed photography (100 million frames per second) and digital image correlation techniques are also used to understand the deformation and failure process during experiments.  Optical/electron microscopes are used for pre- and post-mortem analysis of recovered with a known stress-strain history to relate the deformation and failure process/mechanisms to stress-state history.

Constitutive/Failure Models for High Strain Rate Loading Conditions

Advisor: SE Schoenfeld    

Key words: impact loads, shock waves, polymer matrix composites, metals and metallurgy, ceramics, numerical models and analyses, fatigue mechanics

Research focuses on:

  • developing material models to describe the impact behavior of metals, ceramics, and polymer composites.
  • conducting in-depth metallographical studies to determine the underlying deformation and failure mechanisms in advanced materials as a result of impact loading conditions.
  • proposing and developing physically based constitutive/damage equations.
  • developing appropriate numerical schemes to solve the governing equations and implementing the scheme in a general purpose shock-wave dynamics-based finite element computer code.
  • proposing quasi-static, high strain rate, and shock-propagation experiments to determine the material model parameters.
  • validating the applicability of the developed models in impact application problems.

Penetration Mechanics

Advisor: WP Walters                        

Key words: hydrodynamics, impact loads

The penetration of soils, metals, or liquids by high-pressure, transient-metallic, or liquid jets has several industrial applications including plate cutting and well drilling. Penetration phenomenon may be viewed as a solid-mechanics problem, especially in the low-velocity impact regime, or as a hydrodynamics problem in the hypervelocity regime where the strength of the penetrator and/or penetrated media may be of secondary importance.

Numerous models of the penetration process are available, but all of these models involve many simplifying assumptions. As a result, the application of these models is not universal.

The physical environment surrounding these processes is such that major technical contributions are possible involving innovative, experimental, and/or theoretical research studies.

The Formation and Breakup of Metallic Jets

Advisor: WP Walters                        

Key words: metals and metallurgy

Explosively driven metallic jets can be designed such that the metallic body coalesces to form a fast-moving jet, which then stretches and eventually breaks up into several particles. Metallic jets are useful for many applications including plate cutting and well drilling. The basic mechanisms (instability) or property of the jet that causes breakup is not known. However, the ability to predict and to control jet breakup is the key to future advances in shaped charge jet technology.

Dynamic Material Response

Advisor: TW Wright                         

Key words: pressure effects and measurements, ductility, brittleness, stress (mechanical), micromechanics, fatigue mechanics, shear forces, crack propagation

Research is needed to develop models of material response under high pressure, large strain, and high strain rate. Where possible, such models should be motivated by experiment and micromechanics, and include damage and failure mechanisms (e.g., void formation and shear banding in ductile materials, and microcracking in brittle materials). Models must be suitable for implementation in large-scale codes for either vector or massively parallel computations. Research may focus on some particular model or on the efficient implementation of the model for computing.

Material Behavior under Dynamic Conditions

Advisor: WP Walters                        

Key words: blast loads, dynamic loads, equations of state, pressure effects and measurements

Research in the material and mechanical properties of metals under dynamic loading conditions is necessary to predict the response of these metals to explosively induced loads resulting in extremely high pressures and temperatures. Fundamental research, both theoretical and experimental, is required to obtain the stress strain and stress-strain rate behavior of a variety of metals under transient pressure. Associated areas of fundamental research include equation-of-state modeling of metals under intense dynamic loading conditions and the determination of the viscosity of metals under dynamic conditions.

Modeling of materials under dynamic conditions is important to industry, especially in the areas of explosive welding, explosive cutting, and well drilling.

Computational Mechanics of Materials

Advisor: SE Schoenfeld    

Key words: computational mechanics. mechanics of materials, solid mechanics, material modeling, constitutive modeling, strength of materials

Computational Mechanics of Materials is an area of increasing importance in the conceptual development and design of engineering systems. High-performance systems are becoming more effective at lighter weight and increasingly dependent on subtle, yet significant (from a performance metric) material behavior that is truly rooted in the complex behavior of mesoscale material features and their interactions.

To complicate this issue, the small- (meso-) scale mechanical properties of materials are often severely anisotropic, governed by the kinematics of slip, twinning, and cleavage for many crystallographic species; and the extension and rearrangement of long complex molecular chains for many amorphous materials. Further, features such as relative volume fractions, phase morphology, and interface properties have become paramount in defining the bulk mechanical behavior of materials, and the efficiency and effectiveness engineering systems.

Research is needed in the development of both theoretical and computational models that account for mesoscale effects during large deformation and fracture of single and multiphase metals, ceramics, and polymers under high rates of loading.

Advanced Structural Analysis

Advisor: BP Burns                             

Key words: anisotropy (physics), composite materials, missile and rocket launching, plastic deformation, thrust loads

There is a continuing need for the development of sophisticated structural-analysis techniques to be able to study optimal configurations of structures subjected to launch forces. Opportunities exist for the study and refinement of existing three-dimensional finite-element code, which includes:

  • rate-dependent plastic deformation, gap-contact/slip interfaces, and anisotropic yielding.
  • the addition of the economical means for including dynamic effects (wave propagation) for problems involving “long” times and especially for determining the dynamic behavior of joints.
  • continuum modeling of structural features such as threads or driving grooves.
  • further improvements in modeling the response of anisotropic composite materials.

Although the scope of this effort is primarily analytical, experiments to investigate salient phenomena and methodologies are routinely conducted.

Corrosion Inhibition of Metals by Barrier and/or Electrochemical Approaches

Advisor: RPI Adler and JD Demaree              

Key words: corrosion, inhibition, cathodic, anodic, barriers, electrochemical, self-healing, surface treat, coatings, metals

Environmentally resistant treatments and barriers are required to ensure the reliability and long-term durability of metallic components used on Army materiel that must also survive harsh battlefield exposures. Although significant advances have been made in understanding some of the fundamental mechanisms of corrosion, more experimental details are needed to characterize the surface-protective properties and the effective lifetimes of a variety of prospective or novel barriers/coatings or surface treatments.

Specifically, any practical (cost-effective) system solution that may provide corrosion inhibition still will not be effective unless that system remains securely adhered to the metallic substrate and has self-healing mechanisms to survive defects created during processing/fabrication or as a result of in-service events.

This research provides an opportunity to scientifically investigate the utility and durability of candidate barrier systems (e.g., amorphous metallic macrocoats or other hard coatings) or electrochemical inhibition systems (e.g., improved sacrificial coatings or non-chromate alternates to self-healing conversion coatings based on oxyanion additions) on practical aluminum- and ferrous-based alloys.

To accomplish such goals, our modern laboratory has a full complement of directed beam and conventional surface analytic capabilities as well as accelerated corrosion facilities.

Process/Property Effects of Dynamic Behavior of Refractory-Metal Based Materials

Advisor: L Kecskes           

Key words: metallic glass alloys, phase transformations, mechanical property, crystallization kinetics, refractory alloys, failure behavior, deformation processing

This research opportunity focuses on refractory-metal-based composite materials, subjected to high temperatures and high pressures during ballistic loading. We are interested in materials with nanoscale and aperiodic structural features.

Our goal is to link processing changes of the material’s substructure to its failure behavior and mechanisms at all levels: atomistic, nano-, micro-, or macroscale. Materials processed by a variety of techniques, to achieve a certain substructure, are characterized pre- and post-ballistic strain-rate loading. Analytical tools include metallography for optical and electron microscopy, x-ray and neutron diffraction, thermal and mechanical property testing, and chemical analysis.

Conventional and non-conventional methods for composite fabrication include hot isostatic pressing, plasma pressure consolidation, mechanical alloying, arc melting, melt-spinning, extrusion, and explosive consolidation. Post-fabrication thermomechanical processing methodologies range from forging/rolling, severe plastic deformation, to solidification processing.

Experimental facilities also include access to compression, tension, and torsion Kolsky bar testing.

 

Static and Dynamic Response of Materials to Extreme Conditions

Advisor: JA Ciezak

Keywords: Pressure effects and measurements; Raman scattering; Crystallography; Temperature effects and measurement; Energetic materials; Phase transitions; Diamond anvil cell; Vibrational spectroscopy; Infrared spectroscopy.

Extensive experimental studies are needed to develop an understanding of the static and dynamic response of materials (e.g., energetic materials, ceramics) to extreme pressure/temperature conditions for use in model validation. Typical efforts focus on elucidating the relationship between the structure and properties of the materials under extreme conditions as it applies to detonation phenomena. Properties of interest under high-pressure/high-temperature conditions include the crystallographic structure, elastic constants, phase transitions, vibrational spectroscopy, equation-of-state, electrical conductivity, isentropic compression curves, and reaction phase diagrams. Work includes (1) conceiving and designing experiments on materials in high-pressure/high-temperature environments and (2) traveling to national laboratory facilities such as Brookhaven and Argonne National Laboratories to collect and analyze data.

Reference:
Ciezak JA, et al: Journal of Physical Chemistry A 111: 59, 2007