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NASA NTRS1998

Low-Cost Manufacturing of High- Temperature Polymer Composites

Major goals of NASA and the Integrated High Performance Turbine Engine Technology (IHPTET) initiative include improvements in the affordability of propulsion systems, significant increases in the thrust/weight ratio, and increases in the temperature capability of components of gas turbine engines. Members of NASA Lewis Research Center's HITEMP project worked cooperatively with Allison Advanced Development Corporation to develop a manufacturing method to produce low-cost components for gas turbine engines. Affordability for these polymer composites is defined by the savings in acquisition and life-cycle costs associated with engine weight reduction. To lower engine component costs, the Lewis/Allison team focused on chopped graphite fiber/polyimide resin composites. The high-temperature polyimide resin chosen, PMR-II-50, was developed at NASA Lewis.

Sutter, James K.↗

NASA NTRS1993

Energy loss partitioning during ballistic impact of polymer composites

The objective of this study is to determine the energy dissipation processes in polymer-matrix composites during impact of ballistic projectiles. These processes include heat, fiber deformation and breakage, matrix deformation and fracture, and interfacial delamination. In this study, experimental measurements were made, using specialized specimen designs and test methods, to isolate the energy consumed by each of these processes during impact in the ballistic range. Using these experiments, relationships between material parameters and energy dissipation were examined. Composites with the same matrix but reinforced with Kevlar, PE, and graphite fabric were included in this study. These fibers were selected based on the differences in their intrinsic properties. Matrix cracking was found to be one of the most important energy absorption mechanisms during impact, especially in ductile samples such as Spectra-900 PE and Kevlar-49 reinforced polymer. On the contrary, delamination dominated the energy dissipation in brittle composites such as graphite reinforced materials. The contribution from frictional forces was also investigated and the energy partitioning among the different processes evaluated.

Zee, Ralph H.↗

NASA NTRS1990

Response of polymer composites to high and low velocity impact

The present investigation of fiber-reinforced polymer matrix composites' impact characteristics employed a drop tower for the low-velocity impact case and a novel, projectile instantaneous velocity-measuring sensor for high-velocity impact. Attention was given to the energy loss of projectiles in composites reinforced with polyethylene, kevlar, and graphite. Two distinct energy-loss mechanisms are noted, the first of which is due to the actual fracture process while the other is due to the generation of friction heat. The drop-tower impact-test results furnish the strain-rate dependence of the energy loss.

Hsieh, C. Y.↗

NASA NTRS2000

Erosion Coatings for High-Temperature Polymer Composites: A Collaborative Project With Allison Advanced Development Company

The advantages of replacing metals in aircraft turbine engines with high-temperature polymer matrix composites (PMC's) include weight savings accompanied by strength improvements, reduced part count, and lower manufacturing costs. Successfully integrating high-temperature PMC's into turbine engines requires several long-term characteristics. Resistance to surface erosion is one rarely reported property of PMC's in engine applications because PMC's are generally softer than metals and their erosion resistance suffers. Airflow rates in stationary turbine engine components typically exceed 2.3 kg/sec at elevated temperatures and pressures. In engine applications, as shown in the following photos, the survivability of PMC components is clearly a concern, especially when engine and component life-cycle requirements become longer. Although very few publications regarding the performance of erosion coatings on PMC's are available particularly in high-temperature applications the use of erosion-resistant coatings to significantly reduce wear on metallic substrates is well documented. In this study initiated by the NASA Glenn Research Center at Lewis Field, a low-cost (less than $140/kg) graphite-fiber-reinforced T650 35/PMR 15 sheet-molding compound was investigated with various coatings. This sheet-molding compound has been compression molded into many structurally complicated components, such as shrouds for gas turbine inlet housings and gearboxes. Erosion coatings developed for PMC s in this study consisted of a two-layered system: a bondcoat sprayed onto a cleaned PMC surface, followed by an erosion-resistant, hard topcoat sprayed onto the bondcoat as shown in following photomicrograph. Six erosion coating systems were evaluated for their ability to withstand harsh thermal cycles, erosion resistance (ASTM G76 83 "Standard Practice for Conducting Erosion Tests by Solid Particle Impingement Using Gas Jets") using Al2O3, and adhesion to the graphite fiber polyimide composite (ASTM D 4541 95 "Pull Off Strength of Coatings"). Glenn and Allison Advanced Development Company collaborated to optimize erosion coatings for gas turbine fan and compressor applications. All the coating systems survived aggressive thermal cycling without spalling. During erosion tests (see the final photo), the most promising coating systems tested had Cr3C2-NiCr and WC-Co as the hard topcoats. In all cases, these coating systems performed significantly better than that with a TiN hard topcoat. When material depth (thickness) loss is considered, the Cr3C2-NiCr and WC-Co coating systems provided, on average, an erosion resistance 8.5 times greater than that for the uncoated PMR 15/T650 35 composite. Similarly, Cr3C2-NiCr and WC-Co coating systems adhered to the PMC substrate during tensile tests significantly better than systems containing a TiN topcoat. Differences in topcoats of Cr3C2-NiCr and WC-Co were determined by considering issues such as cost and environmental impact. The preferred erosion-resistant coating system for PMR 15/T650 35 has WC-Co as the hard topcoat. This system provides the following benefits in comparison to the coating system with Cr3C2-NiCr topcoat: lower powder material cost (15 to 20 percent), environmentally friendly materials (Cr3C2-NiCr is hazardous), and higher deposition yield (10 to 15 percent), which results in less waste.

Sutter, James K.↗

NASA NTRS1990

Rate dependent constitutive models for fiber reinforced polymer composites

A literature survey was conducted to assess the state-of-the-art in rate dependent constitutive models for continuous fiber reinforced polymer matrix composite (PMC) materials. Several recent models which include formulations for describing plasticity, viscoelasticity, viscoplasticity, and rate-dependent phenomenon such as creep and stress relaxation are outlined and compared. When appropriate, these comparisons include brief descriptions of the mathematical formulations, the test procedures required for generating material constants, and details of available data comparing test results to analytical predictions.

Gates, Thomas S.↗

NASA NTRSDate not supplied

Polymer Composite Material Screening for a Cryotank Application

Composites↗

NASA NTRS2026

Polymer Composite Material Testing for a Cryotank Application

Composite cryotanks will play a key role in enabling the next generation of efficient aircraft. Carbon fiber reinforced polymer (CFRP) composites have the benefits of reduced weight and potentially higher structural strength compared to traditional metallic fuel tanks. A material screening study was conducted to inform material selection for liquid hydrogen (LH2) fuel storage. Three composite materials were considered because of their aerospace grade toughness, strength, and existing data to compare against. These materials were a thermoplastic low-melt polyaryletherketone (LM-PAEK)/carbon fiber (CF), thermoset/CF, and hybrid thermoset/thermoplastic polyurethane (TPU) veil/CF composite. Mechanical screening tests included tension, compression, in-plane shear (IPS), and tensile-tensile fatigue (TTF). Each material was tested at both a baseline (no liquid nitrogen/LN2 cycling) and 100 LN2-cycled conditions to determine the knockdown factor, if any, of each material when exposed to environmental loading effects in a cryotank. Results show minimal effects of the LN2-cycling compared against baseline values. The three materials behaved similarly in tension; however, the thermoplastic/CF had the highest IPS toughness. The hybrid thermoset/TPU/CF composite had the lowest IPS strength, compressive strength, and toughness. LN2-cycling had minimal effects on tensile-tensile fatigue performance of the thermoplastic/CF material. Mechanical data was captured to guide material down selection for future commercially viable hydrogen aircraft design. In its current state, there does not exist a consolidated, publicly available database for CFRP composite material performance data at cryogenic temperatures. The next step in this work is to test the thermoplastic and thermoset CFRP composites, as well as the neat resins, at LH2 relevant temperature (20 K) to capture this crucial material property data. These results are essential to inform cryotank design and modeling efforts. The process to start this next round of testing has begun. Planned mechanical tests include toughness (single-edge notched beam), tension (unidirectional and quasi-isotropic), thermal expansion, and thermal conductivity. Some tests will also be conducted at an intermediate temperature of 111 K relevant to liquid natural gas (LNG), another attractive fuel choice. The ultimate goal is to manufacture a sub-scale cryotank part that can pass relevant burst, fatigue, permeation, and thermal cycling tests. This work is a part of NASA’s Commercially viable Hydrogen Aircraft for Robust Growth in Efficiency (CHARGE) Project under the larger NASA Subsonic Vehicle Technologies and Tools (SVTT) Project.

composites↗

NASA NTRS1983

N-Butyl acrylate polymer composition for solar cell encapsulation and method

A polymer syrup for encapsulating solar cell assemblies. The syrup includes uncrosslinked poly(n-butyl)acrylate dissolved in n-butyl acrylate monomer. Preparation of the poly(n-butyl)acrylate and preparation of the polymer syrup is disclosed. Methods for applying the polymer syrup to solar cell assemblies as an encapsulating pottant are described. Also included is a method for solar cell construction utilizing the polymer syrup as a dual purpose adhesive and encapsulating material.

Gupta, Amitava↗

NASA NTRS1974

Polymer compositions suitable for use in enriched oxygen atmospheres

Three organic polymer systems are based on copolymer of chlorotrifluoroethylene, ethylene, and tin-based flame retardants. Fourth system is copolymer of chlorotrifluorethylene and tetrafluoroethylene. This system contains no stabilizers of flame retardant additives.

Schule, E. C.↗

NASA NTRS2001

Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites

Classical molecular dynamics (MD) simulations employing Brenner potential for intra-nanotube interactions and van der Waals forces for polymer-nanotube interface have been used to investigate thermal expansion and diffusion characteristics of carbon nanotube-polyethylene composites. Addition of carbon nanotubes to polymer matrix is found to significantly increase the glass transition temperature Tg, and thermal expansion and diffusion coefficients in the composite above Tg. The increase has been attributed to the temperature dependent increase of the excluded volume for the polymer chains, and the findings could have implications in the composite processing, coating and painting applications.

Wei, Chengyu↗

NASA NTRS2026

Influence of Processing Parameters on the Mechanical Properties of 3D Printed Borosilicate Particulate Reinforced Polymer Composites

Emerging composite materials are expanding the potential of additive manufacturing and enabling applications previously restricted by traditional manufacturing methods. The multi-phase nature of these composite materials combined with the complex in-ternal geometry of additively manufactured parts have enabled unique behavior, and potentially new applications. Additionally, these materials can be pyrolyzed to create dense metal, ceramic, and glass parts with geometries typically not achievable by tra-ditional processes. Additive manufacturing of borosilicate glass-based systems can open new applications in nuclear engineering, astronomy, and bone regrowth therapy. To elucidate the process-parameter relationship of borosilicate-polylactic acid (PLA) composites, mechanical testing was conducted and compared with a pure polylactic acid polymer baseline. Test specimens were fabricated by fused-filament fabrication with minimal post-processing. Yield strength, ultimate strength, and elastic modulus were calculated from stress-strain curves. Optical and scanning electron microscopy were conducted to observe the specimen microstructure before and after testing. The highest compressive yield strength for the composite was 28.22 MPa, and the highest compressive yield strength for PLA was 49.30 MPa. Print orientation was found to benefit the composite material but have a detrimental effect on the pure matrix material. An elastic modulus of 2.66 GPa was recorded for the borosilicate-PLA composite at 100% infill, 1 shell wall, and layer lines parallel to compression axis. Microscopy revealed that lower modulus composite specimens had the particulates re-distributed within the matrix. Tensile testing was done according to a polymer testing standard, which caused difficulties obtaining consistent fracture within the gauge length.

mechanical testing↗

NASA NTRS1991

Longitudinal splitting in epoxy and K-polymer composites - Shear lag analysis including the effect of fiber bridging

The shear-lag model used previously by Nairn (1988) to derive a fracture mechanics analysis of longitudinal splitting in double-edge notched unidirectional composites was used to investigate the effect of fibers bridging across the longitudinal split in these composites. Using the new analysis, the longitudinal splitting fracture toughness, G(Lc), was determined for Hercules AS4/3501-6 graphite/epoxy laminates and for K-polymer based laminates containing Magnamite IM-6 as the graphite reinforcing fiber. Results show that the inclusion of the fiber bridging in the fracture analysis significantly affects the reported fracture toughness.

Nairn, John A.↗

NASA NTRS1997

Metal oxide-polymer composites

A method of making metal oxide clusters in a single stage by reacting a metal oxide with a substoichiometric amount of an acid in the presence of an oxide particle growth terminator and solubilizer. A method of making a ceramer is also disclosed in which the metal oxide clusters are reacted with a functionalized polymer. The resultant metal oxide clusters and ceramers are also disclosed.

Wellinghoff, Stephen T.↗

NASA NTRS1994

Metal oxide-polymer composites

Wellinghoff, Stephen T.↗

NASA NTRS1972

Ultraviolet and thermally stable polymer compositions

Copolymers, produced from aromatic substituted aromatic azine-siloxane compositions, are thermally stable, solar ultraviolet light non-degradable by wavelengths shorter than those reaching earth surface.

Adamson, M. J.↗

NASA NTRS1987

Electrochemical studies of thin films of conducting polymers and conducting polymer composites deposited on metal and semiconductor electrodes

Electrochemical studies indicate that poly(Isothianaphthene) or PITN, can be p-doped only. Electrochemical properties of PITN and Nafion-PITN in acetonitrile solutions containing tetra-phenyl Phosphonium chloride as supporting electrolyte are compared. In both cases, the electrochemical behavior of thin films are different from that of thick films. In addition, Nafion does not seem to alter the electrochemical properties of PITN. Cyclic voltammetric and chronocoulometric measurements were made to compute the diffusion coefficient of the counter ions. Electrochemical behavior of both PITN and Nafion-PITN in acetonitrile solution containing different counter ions are described. PITN, when electrochemically deposited, apparently neither passivates surface states present nor forms ohmic contacts with p-Si or p(+)Si single-crystal electrodes.

Nagasubramanian, G.↗

NASA NTRS1988

Non-isothermal crystallization of poly(etheretherketone) aromatic polymer composite

The nonisothermal crystallization kinetics of PEEK APC-2 and of 450G neat resin PEEK material were compared using a differential scanning calorimeter to monitor heat flow during crystallization; the effects of cooling rate on the crystallization temperature, the degree of crystallinity, and the conversion rate were investigated. A modified Avrami (1940) analysis was used to describe nonisothermal crystallization kinetics. It was found that, compared with the 450G neat resin PEEK, the nonisothermal crystallization of the PEEK APC-2 composite is characterized by higher initiation temperature, higher heat flow maximum temperature, and greater relative conversion by primary processes.

Cebe, Peggy↗

NASA NTRS1990

Application of carbon-powder-polymer composite as a continuous crack-length sensor

This paper explores the application of carbon-powder-impregnated polymeric composites for measuring crack extensions. The strain sensitivity of the gage material is shown to be very small. In the first series of tests, the gage material is characterized by measuring the change in electrical resistance due to machined slits for various gage lengths. The measured responses is compared with the response predicted from a very simple electrical model. On the basis of good correlation and repeatability, the usefulness of such gages to measure crack extensions is assessed by a second series of tests. Further work to improve the gage response by optimizing the shape of the gage and making the gage and the adhesive layer thinner is proposed. The presented concept, with improvements, can result in a reliable, inexpensive crack gage requiring inexpensive instrumentation.

Prabhakaran, R.↗