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Weapons and Materials Research Directorate Research Areas

Polymers and Composites

Computational Mechanics for Composite Materials

Advisor: BP Burns             

Key words: dynamic loads, interior ballistics, laminates, structural composites

This research focuses on developing novel solution techniques for problems in dynamic structural analysis of composite material configurations for interior ballistics use. Applications that involve dynamic linear/nonlinear response and wave propagation in 3D thick-section composite laminates are of current interest.

Research opportunities include:

  • developing and incorporating, into an advanced structural analyzer, codes of appropriate 3D constitutive and failure models for composites
  • developing and implementing novel and efficient interactive graphics pre- and post-processing codes for treating thick-section ply-by-ply data
  • investigating the high-dynamic loading response of composites, including delamination phenomena, bulk energy dissipation processes, and dynamic cracking behavior
  • efficient coupling of composite structural analysis tools with optimal design procedures for ballistic components.

Structure/Property/Utility Relationships in Advanced Polymeric Systems

Advisor:  SH McKnight     

Key words: polymers, polymerization processes, textiles and fabrics, adhesion (polymers), coatings, chemical sensors, protective equipment

Research involves the design, synthesis, and characterization of novel polymeric systems with promise for improved ballistic and chemical/biological protection performance. Emphasis is placed on the use of structure developed through unique molecular architecture, controlled phase separation, novel processing schemes, or self-assembly to tailor macroscale properties and to create multifunctional or “smart” polymer technologies. Materials of interest include dendritic polymers, block copolymers, polymer blends, multilayered laminates, polymer nano-composites, and metallo-organics.

This research focuses on:

  • the analysis of structure on the nano- to microscale
  • the relationship between structure and macroscale polymer properties
  • the relationship between macroscale properties and the materials’ ultimate utility.

Facilities are available for the design and characterization of polymer systems and their properties including small-angle x-ray scattering, wide-angle x-ray scattering and diffraction, reflectometry and grazing incidence x-ray diffraction, thermal analysis, ion-beam analysis (Rutherford backscattering, FRES), x-ray photoelectron spectroscopy, environmental scanning electron microscopy, transmission electron microscopy, AFM, chromatography (GPC, SEC, high-performance liquid chromatography), spectroscopy (Fourier-transform infrared, ultraviolet-visible), and fully equipped mechanical testing laboratories.

Computational facilities are also available, including commercial modeling software and access to supercomputers. Potential applications for the polymers and polymer systems developed include flexible, transparent armor materials; lightweight textile membranes; smart fibers and coatings; reversible adhesives; and chemical sensors.

Emerging Materials and Advanced Characterization Techniques

Advisor:  AJ Hsieh                             

Key words: surface cracks, crystals and crystallography, micromechanics, polymers, advanced materials, adhesion (polymers), surfaces, fracture mechanics, thin films

Research will focus on structural characterization, morphological analysis, and measurement of micromechanical properties of various materials, and material surfaces and interfaces. Material systems of interest include high-performance transparent polymers, polymer blends, co-extruded micro/nanolayered composites, and emerging nanocomposites. Inorganic hardcoatings and multilayers of thin films including diamond-like carbon are also among our interests as barrier materials for various polymeric substrates.

This research will address the aspects of chemical miscibility and mechanical compatibility of the hybrid material systems, and residual stresses resulted from processing. Phenomena of interest include dynamic mechanical relaxation, enthalpy relaxation, interaction mechanisms of polymers with liquids, crystallization, adhesion, high-speed impact response, and fracture morphology.

Characterization techniques will include differential scanning calorimetry, dynamic mechanical analysis, dielectric analysis, small- and wide-angle x-ray scattering, environmental scanning electron microscopy, scanning probe microscopy, and nanoindentation. Our goals are to establish structural/processing/property relationships of hybrid material systems, and to better understand micromechanical properties at the material surfaces and interfaces.

Dynamic Deformation, Damage Mechanisms and Failure in Ceramics

Advisor:  JW McCauley    

Key words: ceramics, high strain rate, deformation and damage mechanisms, dynamic failure, alumina, A1ON, aluminum nitride, boron carbide, silicon carbide, glass

Over the last 25 years, much has been learned concerning the failure and life prediction of advanced structural ceramics, in particular silicon nitride, in high-temperature, high stress environments. Moreover, mathematically robust algorithms have been developed that reliably predict the probability of failure in these environments. However, the same cannot be said for understanding the deformation/failure mechanisms of advanced structural ceramics in very high strain rate (ballistic) and high-pressure applications.

Testing and evaluation of B4C, SiC, Al2O3, AlN, ALON, glass and other ceramics as armor against various threats has generated results which are contradictory and variable enough to suggest that the deformation and damage  mechanisms and failure of  these ceramics in the ballistic event are not well understood or quantified. Further, state-of-the-art computer models are not yet able to predict the ballistic performance of these materials. Recent work on these materials strongly suggests that the ballistic performance of these materials is strongly influenced by their microstructural characteristics and processing defects. In particular, dynamic “effective plasticity” seems to be a very important deformation mechanism, but its’ origin and control remain illusive, as well as capturing this affect in the ballistic codes.

Systematic studies of these materials should result in a clearer understanding of the quantitative relationship of crystallographic deformation mechanisms (e.g., anisotropic elasticity, twinning, cleavage, and slip), microstructure (e.g., grain size, preferred orientation-texture, and grain boundary characteristics) and processing defects to the high strain rate failure mechanisms.

The work could involve processing, characterization, non-destructive evaluation, mechanical property testing, computer code development, as well as ballistic evaluation. The results of this work would lead the way towards being able to design optimized armor ceramics at the microstructural level and refining computational models to better predict the performance of these materials in actual ballistic applications.

Polymer Adhesion and Interface Science

Advisor:  SH McKnight     

Key words: polymers, adhesion, surfaces, interfaces, composites, nanotechnology

Research opportunities exist in many areas of polymer adhesion and interphase science. Polymer-solid adhesion often controls the properties of composite materials, adhesive bonds, and protective organic coatings that are used in Army applications. Adhesively bonded multi-material assemblies comprised of combinations of metals, ceramics, polymers, or composites have already found significant use in Army weapon systems and are projected for emerging and future applications. These multifunctional hybrid structures will require strong, tough, ballistic-resistant, and durable bonds among the constituent materials.

Research has shown that the behavior of both thermoset and thermoplastic polymers can be significantly perturbed in the vicinity of solid surfaces resulting in material property variations in those regions. Our research focuses on understanding the origin of these interactions and exploiting them to achieve optimum composite/adhesive bond performance.

ARL conducts ongoing research on thermoset resins, polymer-solid adhesion, and fiber-matrix interphase science in a multidisciplinary environment. Different research topics involve novel adhesives synthesis (formulation), alternative curing technologies, theoretical modeling of polymer-substrate interactions, mechanical performance, environmental durability, and experimental characterization of surface and interfacial phenomena.

We have excellent facilities to study adhesion phenomena. Formulation and processing laboratories include full-scale polymer synthesis, formulation capabilities, lab-scale surface preparation lines, processing, and manufacturing equipment. We also have facilities to perform nondestructive evaluation, mechanical testing and modeling, and environmental conditioning.  

In addition, research may include characterization of surfaces and interfaces using surface spectroscopy techniques (x-ray photoelectron spectroscopy, Auger, secondary ion mass spectrometry, Rutherford backscattering, FES, and Fourier-transform infrared), microscopy methods (atomic force microscopy, scanning electron microcopy, ESEM, and transmission electron microscopy), and the development of in-house developed techniques to study adhesion phenomena.

Multifunctional Materials

Advisor: MS Bratcher                       

Key words: polymers, electronic materials, carbon nanotubes, biomaterials, hybrid materials, synthesis

This project focuses on the design, synthesis, and characterization of multifunctional materials, which include but are not limited to dendritic polymers, organic light emitting diodes, nonlinear optical materials, carbon nanotubes, ferroelectrics, and polypeptides. Synthesis and integration of these materials often lead to unexpected structured-property relationships that can be exploited in military applications.

Important characterization tools include spectroscopic methods (ultraviolet/visible, infrared, and x-ray photoelectron), microscopy (optical, near field, scanning electron microscopy, and transmission electron microscopy), scattering (light, x ray, and neutron), and thermal analysis (differential scanning calorimetry, thermal gravimetric analysis, and dynamic mechanical analysis).

Key areas for application of this research include conductive fiber networks, sensors, batteries, fuel cells, flat panel displays, electromagnetic shielding, signature management, ballistic protection, highly efficient biocides, and phase array antennas. Collaborations with the Army Research Office (MURI and SBIR programs), Natick Solider Center, and Edgewood Chemical and Biological Command among others are established to enhance our in-house research efforts.

Selectively Permeable Elastomeric Membranes for Protective Clothing

Advisor:  JM Sloan                             

Key words: Fourier-transform infrared spectroscopy, polymer membranes, diffusion

The object of this research is to characterize polymeric materials to be utilized in chemical protective clothing, fuel cell membranes, and separation membranes that demonstrates flexibility, durability, and selectively permeable properties utilizing a relatively thin (1-4 mil), nonlaminated elastomeric membrane. To address these multiple requirements, we have developed a series of sulfonated tri-block copolymers. The novel block copolymers exhibit flexibility over a broad temperature range and selectively permeable “membrane-like” characteristics.

This research opportunity will include calculation of the transport rates of various liquids and vapors through these new polymers using the Fourier-transform infrared (FTIR) permeation method. Time-evolved IR spectra for diffusion experiments will be obtained using a commercial FTIR spectrometer with a horizontal attenuated total reflectance (ATR) cell and a trapezoidal ATR crystal or IRE. Our specific goals include:

  1. Determine transport mechanisms for associating penetrants in polymers. The diffusion of liquid mixtures in sulfonated tri-block copolymers will be studied at different vapor activities. Many investigators have postulated a variety of structures that could be competing with the equilibrium between clusters varying in size. Can spectroscopic techniques determine small molecule structures and their individual transport rates among associating penetrants?
  2. Determine transport mechanisms in polymers for two penetrants capable of solvating with each other. The diffusion of methyl ethyl ketone (MEK)/methanol mixtures will be examined from the liquid phase. At what methanol concentration does solvation alone end and combined solvation and association begin? How do solvated clusters affect the overall transport rate?
  3. Determine transport mechanisms for penetrants that solvate with groups in the polymer. The diffusion of MEK in a series of sulfonated tri-block copolymers will be studied at various concentrations. How does solvation to the hydroxyl groups in this polymer impact the diffusion process?
  4. Determine the effect of polymer morphology on transport rates. Diffusion of various alcohols in sulfonated tri-block copolymers will be studied with varying morphologies that appear in the sulfonated tri-block copolymers when the sulphonation levels are increased. Can a penetrant be used to probe polymer morphology even when microscopic techniques fail? How does the polymer morphology affect the transport rate?

Nano- and Micro-scale Characterization Using Contact Probes

Advisor:  MR VanLandingham                         

Key words: nanoindentation, nanocomposites, thin films, AFM, polymers, coatings, viscoelasticity, micromechanics, rheology

In this research program, measurement capabilities are being developed and applied to study structure-properties-performance relationships of materials using instrumented nanoindentation and scanning probe microscopy (SPM). Material systems of interest include polymers and polymer composites (fiber-reinforced, particulate filled, and nanocomposites), as well as metallic, ceramic, and semiconducting materials, particularly those used as thin films or thin section components in multicomponent systems. This effort includes a combination of experimental development, modeling (e.g., finite element analysis), and theoretical development.

Research focuses on

  • viscoelasticity of polymeric materials at micrometer and nanometer scales with an emphasis on rate-dependent behavior under dynamic loading conditions
  • micromechanical characterization of heterogeneous materials, including filled polymers, metal blends, and multilayered materials
  • measurement of stress-strain response from indentation measurements.

We are also interested in SPM techniques that allow measurements and/or imaging of polymers and other materials at the nanoscale based on chemical, thermal, and electrical interactions between the probe tip and sample surface. These high-resolution measurement methods are utilized in a variety of basic and applied Army research programs. Attempts to moves these techniques towards high-throughput characterization and/or sensor technology are also being considered.

Reference
VanLandingham MR: Journal of Research in the National Institute of Standards and Technology 108(4): 249, 2003