Christopher Ibeh

Current Trends in Nanocomposite Foams

This article presents a brief but concise review of the current research efforts on polymeric nanocomposite foams production, characterization, and applications. Survey indicates that the emergence of nanocomposites has resulted in the development of a new group of materials regarded as nanocomposite foams. Nanocomposites result from the use of nano-sized (10-09 m) particles as fillers to modify and enhance the properties of polymers and other matrices. The combination of functional nanoparticles and foaming technologies such as supercritical fluid foaming, chemical foaming, syntactic foaming, aerogel foaming, phase inversion foaming etc. generate these new materials regarded as nanocomposite foams that have light weight, high specific strength, and multifunctional attributes. Enhanced thermo-mechanical properties of nanocomposite foams result from improved cell morphology that is mainly attributable to the role of nanoparticles as nucleation agents for bubble generation. High-specific mechanical properties and multifunctional characteristics of nanocomposite foams make them cost-effective and desirable in a multitude of application areas including structural, energy-dissipating/absorbing, acoustical insulation, flammability resistance, and others. Of particular importance in this study of nanocomposite foams is the flammability resistance effect of nanoparticles. The intumescent model (NIST, NMAB, and others) indicates that the flame barrier mechanism involves a high-performance carbonaceous-silicate char; this char build-up insulates the underlying material. Understanding this char build-up mechanism presents a challenge and area of research interest in the effort to develop new generation foams that are suitable in energy absorbing materials and structures.

Design and construction of a novel rotary magnetostrictive motor

Magnetostriction can be used to induce linear incremental motion, which is effective in giant magnetostrictive inchworm motors. Such motors possess the advantage of combining small step incremental motion with large force. However, continuous rotation may be preferred in practical applications. This paper describes a novel magnetostrictive rotary motor using terfenol-D (Tb0.3Dy0.7Fe1.9) material as the driving element. The motor is constructed of two giant magnetostrictive actuators with shell structured flexure-hinge and leaf springs. These two actuators are placed in a perpendicular position to minimize the coupling displacement of the two actuators. The principal design parameters of the actuators and strain amplifiers are optimally determined, and its static analysis is undertaken through finite element analysis software. The small movements of the magnetostrictive actuators are magnified by about three times using oval shell structured amplifiers. When two sinusoidal wave currents with 90° phase shif...

Thermal Viscoelastic Analysis of 3D Fabric Nanocomposites

Viscoelastic properties of 3D fabric reinforced Vinyl Ester composites were studied in different directions using Dynamic Mechanical Thermal Analysis (DMTA). Such materials filled by nanoparticles (silicon carbide) with different concentrations were also investigated. The increases of storage and loss moduli with addition of nanoparticles and with increase of their concentrations were observed. The maximal tangent of the angle of mechanical losses was especially compared at below and over glass transition temperature. Below glass transition temperature the presence of nanoparticles increases storage and loss moduli and loss tangent. These effects achieved maximum at glass transition temperature. Over glass transition, the loss modulus and loss tangent are decreased with increase of the concentration of nanoparticles.

Flammability Resistance of Nanocomposite Foams

The recent attention being given to blast mitigation research by government, industry and academia implies the need for flammability resistance studies of nanocomposite foams. Fire and smoke toxicity are typically associated with blasts, and some of the current designs for blast mitigation involve the use of nanocomposites and foams. The Center for Nanocomposites and Multifunctional Materials [CNCMM] employs a nanocomposite foam impregnated honeycomb as core for its energy dissipative designs. Preliminary results indicate that other than the enhancement of mechanical properties, well formulated nanocomposite foams provide improvement in flammability resistance. In this study, flammability resistance properties of syntactic nanocomposite foams are evaluated by cone calorimetry via such parameters as smoke density, mean heat release rate (MHRR), mass loss rate (MLR) and ignition time.Copyright

Flammability of polymer nanocomposite systems

Engineering and materials science face new challenges in more demanding space exploration and defense fields. The more severe req uisites concerning budget and safety have driven the focus of research toward a class of materials whose characteristics aim at satisfying various engineering requirements at the same time. In this picture, multifunctional materials seem to have a fundamental part. In this work the flammability behavior of a composite system made from epoxy, nanoparticles, and aramid fiber papers is studied using cone calorimetry. The heat release rate, effective heat of combustion, mass loss rate, and time of ignition are compared and discussed for dif ferent compositions; effect of nanofillers on flame retardance is verified and optimum solutio n suggested.

Aramid Papers Coated with Different Resin Systems as Excellent Gas Permeability Barrier

ठ** Present tests show that aramid papers coated with different resin systems have excellent gas barrier and impact resistance properties. This advantage can be used in composite sandwich structure wall design for liquid fuel tanks. Life-time durability requirements for cryogenic fuel tanks imply that the materials must safely carry pressure loads, external structural loads, resist leakage, and operate over an extremely wide temperature range. A number of aramid fiber paper sheets have been coated with polyester and epoxy resins in different procedures in order to obtain the best coating. Numerous samples were tested for helium permeability, stress distribution and flammability. Cryocycling and high velocity tests are scheduled in future in order to verify sandwich structure performance and durability.

Study of Synergistic Fire Retardancy of Nanoparticles in Polymer Matrix Composites

In this study, three kinds of carbon nanofiber sheets were made through a high-pressure filtration system: pure carbon nanofiber, carbon nanofiber with polyhedral oligomeric silsequioxane (PCNS) and carbon nanofiber with Cloisite Na+ clay (CCNS). Then these sheets were incorporated onto the surface of glass fiber reinforced polyester composites through resin transfer molding process. The samples were analyzed with scanning electron microscopy (SEM), thermal gravimetric analyses (TGA). The fire retardant performance of the laminates was evaluated with cone calorimeter test at an external radiated heat flux of 50kw/m2 . The results of laminates with PCNS indicated that the fire performance was impaired when comparing with the case of pure carbon nanofiber paper. However, in the case of CCNS, the primary results showed a pronounced improvement of the fire performance was observed. The possible mechanism was also discussed in the present study.Copyright

Flammability Resistance Properties of Epoxy Nanocomposites

Current aerospace and naval applications require blast and flammability resistance characteristics. Materials and formulations with flammability resistance properties are most suitable in these type applications since fire and smoke toxicity are inherently associated with blast situations. In this effort, VAHLUP fabricated epoxy nanocomposites are evaluated and characterized for flammability resistance properties such as effective heat of combustion, ignition time, rate of mass loss, rate of heat release and smoke density. The effects of nanoparticles on the mechanical properties of epoxy nanocomposites are also evaluated. Uncoated polyaramid papers (Kevlar, Nomex with heat release rates of 0.18, 0.175 MJ/m2 respectively) exhibit better flammability resistance properties than resin/nanocomposites coated polyaramid papers. VAHLUP fabricated epoxy nanocomposites exhibit better flammability resistance properties than cast epoxy nanocomposites. Kapton, polyimide film with ignition time of 90 seconds+] give the best overall flammability resistance properties. Mechanical properties of epoxy nanocomposites are enhanced by processing. The preliminary data of the influence of the post-curing protocol tend to suggest the 2.0% nanoclay level as the optimal clay content level with respect to mechanical properties.Copyright