64,535 research outputs found
Hybridized polymer matrix composite
Under certain conditions of combined fire and impact, graphite fibers are released to the atmosphere by graphite fiber composites. The retention of graphite fibers in these situations is investigated. Hybrid combinations of graphite tape and cloth, glass cloth, and resin additives are studied with resin systems. Polyimide resins form the most resistant composites and resins based on simple novolac epoxies the least resistant of those tested. Great improvement in the containment of the fibers is obtained in using graphite/glass hybrids, and nearly complete prevention of individual fiber release is made possible by the use of resin additives
Hybridized polymer matrix composites
The extent to which graphite fibers are released from resin matrix composites that are exposed to fire and impact conditions was determined. Laboratory simulations of those conditions that could exist in the event of an aircraft crash and burn situation were evaluated. The effectiveness of various hybridizing concepts in preventing this release of graphite fibers were also evaluated. The baseline (i.e., unhybridized) laminates examined were prepared from commercially available graphite/epoxy, graphite/polyimide, and graphite/phenolic materials. Hybridizing concepts investigated included resin fillers, laminate coatings, resin blending, and mechanical interlocking of the graphite reinforcement. The baseline and hybridized laminates' mechanical properties, before and after isothermal and humidity aging, were also compared. It was found that a small amount of graphite fiber was released from the graphite/epoxy laminates during the burn and impact conditions used in this program. However, the extent to which the fibers were released is not considered a severe enough problem to preclude the use of graphite reinforced composites in civil aircraft structure. It also was found that several hybrid concepts eliminated this fiber release. Isothermal and humidity aging did not appear to alter the fiber release tendencies
Recommended from our members
Polymer Matrix Nanocomposites by Inkjet Printing
This paper describes work on a continuing project to form functional composites that contain
ceramic nanoparticles using a Solid Freeform Fabrication (SFF) inkjet printing method. The process
involves inkjet deposition of monomer/particle suspensions in layers followed by curing each layer in
sequence using UV radiation. The reactive monomer is hexanediol-diacrylate (HDODA); the polymer
forming reaction proceeds by a free radical mechanism. The liquid monomer containing nanoparticles
is essentially a printing ink formulation. Successfully suspending the particles in the monomer is
critical. We have developed a surface treatment method for forming stable suspensions of the
nanoparticles so that they remain discrete throughout the processing sequence.
The SFF process involves careful control of the polymer cure so that the interface between layers
is seamless and residual stresses in the composites are eliminated. An immediate use for such
composites is in optical applications as gradient refractive index lenses (GRIN). GRIN lenses have
planar surfaces, eliminating the need for costly grinding and polishing. The planar surfaces also
eliminate optical aberrations that result at the edges of spherical lenses and diminish the accuracy of
focus.
If the appropriate nanoparticles are fully dispersed they will modify the polymer's refractive index
without interfering with light transmission. The effect is additive with volume concentration. Using
'inks' of different compositions in a multiple nozzle inkjet printer allows the formation of composites
with precise composition gradients. Since an object is built one planar layer at a time, changes can be
made readily both within each layer and from layer to layer. Inkjet printing with picoliter resolution is
ideal for this task.
Working with SiC nanoparticles in HDODA as a model system for demonstrating the inkjet
deposition process, nanocomposite films with a linear concentration gradient varying from 0 to 4.5%
(wt) were fabricated on Silicon wafers. These composites are 30 layer films, which total 140µm in
thickness. Each layer in the composite is about 5 µm in thickness. Analytical methods for
characterizing the dispersion of the nanoparticles in the composite and some of the salient optical
properties of the composites also were established. The status of the program is reviewed in this
paper.Mechanical Engineerin
High-temperature polymer matrix composites
Polymers research at the NASA Lewis Research Center has produced high-temperature, easily processable resin systems, such as PMR-15. In addition, the Polymers Branch has investigated ways to improve the mechanical properties of polymers and the microcracking resistance of polymer matrix composites in response to industry need for new and improved aeropropulsion materials. Current and future research in the Polymers Branch is aimed at advancing the upper use temperature of polymer matrix composites to 700 F and beyond by developing new resins, by examining the use of fiber reinforcements other than graphite, and by developing coatings for polymer matrix composites to increase their oxidation resistance
Light weight polymer matrix composite material
A graphite fiber reinforced polymer matrix is layed up, cured, and thermally aged at about 750 F in the presence of an inert gas. The heat treatment improves the structural integrity and alters the electrical conductivity of the materials. In the preferred embodiment PMR-15 polyimides and Celion-6000 graphite fibers are used
Creep-rupture of polymer-matrix composites
An accelerated characterization method for resin matrix composites is reviewed. Methods for determining modulus and strength master curves are given. Creep rupture analytical models are discussed as applied to polymers and polymer matrix composites. Comparisons between creep rupture experiments and analytical models are presented. The time dependent creep rupture process in graphite epoxy laminates is examined as a function of temperature and stress level
Synthesis and characterization of hybrid organic-inorganic materials based on sulphonated polyamideimide and silica
The preparation of hybrid organic–inorganic
membrane materials based on a sulphonated polyamideimide
resin and silica filler has been studied. The method
allows the sol–gel process to proceed in the presence of a
high molecular weight polyamideimide, resulting in well
dispersed silica nanoparticles (<50 nm) within the polymer
matrix with chemical bonding between the organic and
inorganic phases. Tetraethoxysilane (TEOS) was used as
the silica precursor and the organosilicate networks were
bonded to the polymer matrix via a coupling agent
aminopropyltriethoxysilane (APTrEOS). The structure and
properties of these hybrid materials were characterized via a
range of techniques including FTIR, TGA, DSC, SEM and
contact angle analysis. It was found that the compatibility
between organic and inorganic phases has been greatly
enhanced by the incorporation of APTrEOS. The thermal
stability and hydrophilic properties of hybrid materials have
also been significantly improved
Fracture toughness testing of polymer matrix composites
A review of the interlaminar fracture indicates that a standard specimen geometry is needed to obtain consistent fracture toughness measurements in polymer matrix composites. In general, the variability of measured toughness values increases as the toughness of the material increases. This variability could be caused by incorrect sizing of test specimens and/or inconsistent data reduction procedures. A standard data reduction procedure is therefore needed as well, particularly for the tougher materials. Little work has been reported on the effects of fiber orientation, fiber architecture, fiber surface treatment or interlaminar fracture toughness, and the mechanisms by which the fibers increase fracture toughness are not well understood. The little data that is available indicates that woven fiber reinforcement and fiber sizings can significantly increase interlaminar fracture toughness
- …