Carbon nanotube structure
Macroscopic Nanotube Fabrication Process Control
A combination of magnetic and optical methods are applied to characterize the residual catalyst content, nanotube alignment and load transfer between individual nanotubes during the fabrication process. The techniques used in this method, which have been proven at the micro level, are applied so that scanning and mapping occurs at the macro level. These methods have been successfully used for nondestructive evaluation of large-format carbon nanotube-based structures, primarily yarns as well as sheets from several inches square to as large as 4ft. by 8ft.
materials and coatings
NASA Space Launch System concept drawing
Thermally Stable Nanocomposites with Aligned Carbon Nanotubes
Current state-of-the-art for lightweight and mechanically strong composites are graphite fiber composites. While graphite fibers have excellent mechanical properties, they do not have the desired thermal or electrical conductivities. Accordingly, when graphite fiber composites are to be used in high temperature environments, specialized high temperature or thermally conductive coatings are applied to the structure. These extra coatings add weight and cost to the ultimate structure. This invention, by way of nanocomposites with carbon nanotubes (CNTs), provides the lightweight mechanical strength of graphite fiber composites, but is also thermally stable and electrically conductive. The nanocomposite structure is a polymer in an extruded shape with carbon nanotubes (CNTs) longitudinally algined and dispersed in the extruded shape along a dimension. The polymer is characteristically defined as having a viscosity of at least approximately 100,000 poise at a temperature of 200 C.
crack testing
Method of Non-Destructive Evaluation of Composites
Guided wavefield techniques require excitation of guided waves in a specimen via contact or noncontact methods (such as attached piezoelectric transducers or laser generation). The resulting wavefield is recorded via noncontact methods such as laser Doppler vibrometry or air-coupled ultrasound. If the specimen contains damage, the waves will interact with that damage, resulting in an altered wavefield (compared to the pristine case). When guided wave modes enter into a delaminated region of a composite the energy is split above/below delaminations and travels through the material between delaminations. Some of the energy propagates beyond the delamination and re-emerges as the original guided wave modes. However, a portion of the wave energy is trapped as standing waves between delaminations. The trapped waves slowly leak from the delaminated region, but energy remains trapped for some time after the incident waves have propagated beyond the damage region. Simulation results show changes in the trapped energy at the composite surface when additional delaminations exist through the composite thickness. The results are a preliminary proof-of-concept for utilizing trapped energy measurements to identify the presence of hidden delaminations when only single-sided access is available to a component/vehicle. Currently, no other single-sided field-applicable NDT techniques exist for identifying hidden delamination damage.
power generation and storage
Thin film device for harvesting energy from wind
Compliant electrode and composite materials for piezoelectric wind and mechanical energy conversions
The NASA researchers integrated two innovations into this unique piezoelectric device. First, they combined polyvinylidene flouride (PVDF) with a metal oxide to improve conductance. Second, they designed a new carbon-electrode to improve durability (compliance) and reduce susceptibility to fatigue while retaining flexibility. Additionally, to integrate the carbon nanotube components, they use a polymer-to-polymer design that eliminates the need for adhesion layers. A prototype device generated 1 W power (at 15 mph wind) with a single layer of PVDF [4 inch by 12 inch and 50 um (micrometer) thick] sandwiched between two thin electrode films. A rectifier converts the AC signal into a DC signal and stores the charge in a capacitor. This electric power can be used for low power consuming devices, such an inaccessible sensors.
materials and coatings
Thermal Protection Systems
High Efficiency Tantalum-based Ceramic Composite (HETC) Structures
The various embodiments of this technology include insulating composites capable of surviving high heating rates and large thermal gradients in the aeroconvective heating environment that entry vehicles are exposed to characteristically. The tantalum-based ceramics contain tantalum disilicide, borosilicate glass and, optionally, molybdenum disilicide. The components are milled, along with a processing aid to facilitate sintering, then applied to a surface of a porous substrate, such as a fibrous or open-pored silica, carbon, aluminosilicate, silicon carbide or silicon oxycarbide substrate, as well as other substrates of silicon/carbon compositions. Following application, the coating is then sintered on the substrate. The composite structure is substantially impervious to hot gas penetration and capable of surviving high heat fluxes.
materials and coatings
Researcher looking into a microscope
Negative Dielectric Constant Material
Metamaterials or artificial Negative Index Materials (NIM) are specially designed to exhibit a negative index of refraction, which is a property not found in any known naturally occurring material. These artificially configured composites have a potential to fill voids in the electromagnetic spectrum where conventional material cannot access a response, and enable the construction of novel devices such as microwave circuits and antenna components. The negative effective dielectric constant is a very important key for creating materials with a negative refractive index. However, current methods to achieve a negative effective dielectric constant are difficult to produce, not readily applicable to producing commercial metamaterials, and can have limited tunabilty. This invention is for a novel method to produce a material with a negative dielectric constant by doping ions into polymers, such as with a protonated poly(benzimidazole) (PBI), without complex geometric structures. The doped PBI shows a negative dielectric constant at megahertz (MHz) frequencies due to its reduced plasma frequency and an induction effect. The magnitude of the negative dielectric constant and the resonance frequency are tunable by dopant type and doping concentration.
materials and coatings
hBN Dispersions
Exfoliated Hexagonal Boron Nitride
The invented method involves mechanical breakdown of large hBN particles followed by chemical functionalization to achieve exfoliation of the hBN sheets. The exfoliated h- nanosheets are of mono- or few atomic layers thick, and dispersible (or suspendable, soluble) in common organic solvents and/or water, depending upon the nature of the functionalities. The functionalities can be subsequently removed by thermal treatment, with the hBN nanostructures remaining intact and exfoliated.
materials and coatings
PICA being tested in Arcjet Facility
Creating Low Density Flexible Ablative Materials
The low density flexible ablator can be deployed by mechanical mechanisms or by inflation and is comparable in performance to its rigid counterparts of the same density and composition. Recent testing in excess of 400W/cm2 demonstrated that the TPS char has good structural integrity and retains similar flexibility to the virgin material, there by eliminating potential failure due to fluttering and internal stress buildup as a result of pyrolysis and shrinkage of the system. These flexible ablators can operate at heating regimes where state of the art flexible TPS (non-ablative) will not survive. Flexible ablators enable and improve many missions including (1) hypersonic inflatable aerodynamic decelerators or other deployed concepts delivering large payload to Mars and (2) replacing rigid TPS materials there by reducing design complexity associated with rigid TPS materials resulting in reduced TPS costs.
materials and coatings
Artist's concept of hypersonic inflatable aeroshell and technologies suitable for returning mass from the International Space Station.
A New Family of Low-Density, Flexible Ablators
The low-density, flexible ablators are comprised of a polymer resin embedded in a fibrous substrate, with a density range of 0.2g/cm cube-0.6 g/cm cube to date. The polymer resin thermally decomposes during ablation. The resin can be a thermo setting resin, athermoplastic polymer, or alternatively, a co-cured mixture. The fibrous substrate is flexible or conformable to a curved surface, with high thermal stability. The thickness of the fibrous substrate is between 1.3 and 7.6 cm, where the diameters of the fiber are between 7 and 25 micrometer. Embodiments of the fibrous substrates can include various woven, stitched or loosely packed carbon, polymer and ceramic felts as high-temperature substrates. One feature of this innovation is that it can withstand a range of heating rates with the upper limit approaching that of NASA rigid ablators. The amount and composition of polymer resin can be readily tailored to specific mission requirements. This technology offers a simple and versatile manufacturing approach to produce large areas of heat shields that can be relatively easily attached on the exterior of spacecraft.
materials and coatings
Reentry Vehicles
New Resin Systems for Thermal Protection Materials
This method produces a low density ablator similar to Phenolic Impregnated Carbon Ablator (PICA) using a cyanate ester and phthalonitrile resin system, rather than the heritage phenolic resin. Cyanate ester resin systems can be cured in a carbon matrix and generate high surface area structure within the carbon fibers. This helps to reduce the thermal conductivity of the material which is one of the key requirements of thermal protection system (TPS) materials. The material has densities ranging from 0.2 to .35 grams per cubic centimeter. NASA has successfully processed the cyanate ester and phthalonitrile resins with a morphology similar to that of the phenolic phase in PICA, but with more advanced properties such as high char stability, high char yield, and high thermal stability. This new generation of TPS materials has the same microstructure as heritage PICA, but improved characteristics of PICA such as increased char yield, increased char stability, increased thermal stability and increased glass transition temperature.
Stay up to date, follow NASA's Technology Transfer Program on:
facebook twitter linkedin youtube
Facebook Logo Twitter Logo Linkedin Logo Youtube Logo