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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Effects of Molecular Structure in Macroscopic Mechanical Properties of an Advanced Polymer (LARC(sup TM)-SI)

Mechanical testing of an advanced polymer resin with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The elastic properties, inelastic elongation behavior, and notched tensile strength all as a function of molecular weight and test temperature were determined. It was shown that notched tensile strength is a strong function of both temperature and molecular weight, whereas stiffness is only a strong function of temperature.

Nicholson, Lee M.↗
NASA NTRS2023

Thermomechanical Property Prediction of Amorphous and Crystal PEKK via Molecular Dynamics

Traditionally, advanced aerospace composites have been manufactured using thermoset resins. However, recently, thermoplastics have been investigated for use in the manufacturing of composite materials due to their unique manufacturing characteristics. Thermoplastic resins can be reshaped and formed, along with the added benefit of being recyclable, which thermoset resin cannot. Thermoplastic materials undergo a crystallization process during manufacturing which affects the percent crystallinity of the material. The crystallization needs to be understood better to maximize the potential of thermoplastic resins. PEKK is a thermoplastic material with good chemical, thermal, and mechanical loading resistance. PEKK is also a material NASA is interested in for developing new bonded joint technology. The crystalline microstructure of PEKK is at the micrometer length scale, and it is of interest to model the effects of the crystallinity structure on PEKK’s bulk properties. Molecular dynamics (MD) is a simulation tool that allows for property-structure relationships between atomistic structure and nanometer-length portions of a material. This makes MD a useful tool for developing the structure-property relationship of PEKK. However, the micrometer length scale of PEKK’s crystal structure is too large for MD. Thus, a hybrid approach to modeling PEKK’s microstructure is proposed in this work where MD models are built of both the amorphous and crystalline phases of PEKK. The engineering material properties can be obtained using MD at the nanometer length scale. A micromechanics approach can then generate the micrometer length scale of the crystallinity and the effective properties can be homogenized. The objective of this paper is to show the MD model workflow and the MD-predicted properties of PEKK. The properties can then be homogenized with different crystalline percentages to build design graphs that can be used to tailor PEKK for specific composite applications.

poly ether ketone ketone↗
NASA NTRS2005

Mechanical Properties of Nanostructured Materials Determined Through Molecular Modeling Techniques

The potential for gains in material properties over conventional materials has motivated an effort to develop novel nanostructured materials for aerospace applications. These novel materials typically consist of a polymer matrix reinforced with particles on the nanometer length scale. In this study, molecular modeling is used to construct fully atomistic models of a carbon nanotube embedded in an epoxy polymer matrix. Functionalization of the nanotube which consists of the introduction of direct chemical bonding between the polymer matrix and the nanotube, hence providing a load transfer mechanism, is systematically varied. The relative effectiveness of functionalization in a nanostructured material may depend on a variety of factors related to the details of the chemical bonding and the polymer structure at the nanotube-polymer interface. The objective of this modeling is to determine what influence the details of functionalization of the carbon nanotube with the polymer matrix has on the resulting mechanical properties. By considering a range of degree of functionalization, the structure-property relationships of these materials is examined and mechanical properties of these models are calculated using standard techniques.

Clancy, Thomas C.↗
NASA NTRS1983

Effects of high energy radiation on the mechanical properties of epoxy graphite fiber reinforced composites

The effects of high energy radiation on mechanical properties and on the molecular and structural properties of graphite fiber reinforced composites are assessed so that durability in space applications can be predicted. A listing of composite systems irradiated along with the maximum radiation dose applied and type of mechanical tests performed is shown. These samples were exposed to 1/2 MeV electrons.

Gilbert, R. D.↗
NASA NTRS1984

Effects of high energy radiation on the mechanical properties of epoxy-graphite fiber reinforced composites

The effects of high energy radiation on the mechanical properties and on the molecular and structural properties of graphite fiber reinforced composites were assessed so that the durability of such composites in space applications could be predicted. Investigative techniques including ESR and infrared spectroscopy, ESCA, contact angle measurements, and dynamic and static mechanical testing (3-point bending and interlaminar shear) were employed. The results using these different techniques are individually described, and the implications of the data are discussed. The proposed plan of work for the next fiscal year is outlined.

Fornes, R. E.↗
NASA NTRS2021

Molecular Dynamics Investigation of the Structural and Mechanical Properties of Off-Stoichiometric Epoxy Resins

Molecular dynamic (MD) simulations were performed to compute the mechanical properties of off-stoichiometric epoxy resins as a function of hardener/epoxy mixture ratio (r). Properties were characterized in relation to their microscopic structures. Such resins have been used recently for adhesive-free bonding of large-scale composite structures using the co-curing-ply method. In this process, two partially precured composite panels with hardener-poor (HP) off-stoichiometric resins are coupled with ply(ies) of complementary hardener-rich (HR) formulations and then cured simultaneously. This bonding process has the potential to produce reliable and certifiable composite joints without the need for additional fasteners, which are often required for many conventional bonding methods because even small amounts of contamination can cause a weak bond. The reflow and mixing of the HP/HR resin in this bonding process result in a joint with no discernable interface that should not be susceptible to surface contamination. However, incomplete mixing of the two offset resins may result in chemical heterogeneity of the cured polymeric joint. Thus, different r values may be obtained across the joint. Classical MD simulations were performed to compute the Young’s modulus of polymers with different r values and correlate their properties to network structures. High stiffness was associated with molecular packing due to chemical crosslinking, leading to a single network structure. Moreover, the networks became denser as the ratio approached the stoichiometric value r = 1. Thus, the r = 1 systems were single clusters, with high stiffness, high molecular weight, and a high degree of crosslinking. Structural properties such as radius of gyration and mean square displacement were determined to investigate the variation in the stiffness with respect to r. This MD simulation study was validated with experimental measurements.

Chang Woon Jang↗
NASA NTRS1997

The Effect of Molecular Weight on the Composite Properties of Cured Phenylethynyl Terminated Imide Oligomers

As part of a program to develop high temperature/high performance structural resins for aeronautical applications, imide oligomers containing terminal phenylethynyl groups with calculated number average molecular weights of 1250, 2500 and 5000 g/mol were prepared, characterized, and evaluated as adhesives and composite matrix resins. The goal of this work was to develop resin systems that are processable using conventional processing equipment into void free composites that exhibit high mechanical properties with long term high temperature durability, and are not affected by exposure to common aircraft fluids. The imide oligomers containing terminal phenylethynyl groups were fabricated into titanium adhesive specimens and IM-7 carbon fiber laminates under 0.1 - 1.4 MPa for 1 hr at 350-371 C. The lower molecular weight oligomers exhibited higher cured Tg, better processability, and better retention of mechanical properties at elevated temperature without significantly sacrificing toughness or damage tolerance than the higher molecular weight oligomer. The neat resin, adhesive and composite properties of the cured polymers will be presented.

Smith, J. G., Jr.↗
NASA NTRS2016

Molecular Dynamics Modeling of Carbon Nanotube Composite Fracture Using ReaxFF

Carbon nanotube (CNT) fiber reinforced composites with specific tensile strengths and moduli approaching those of aerospace grade carbon fiber composites have recently been reported. This achievement was enabled by the emerging availability of high N/tex yarns in kilometer-scale quantities. While the production of this yarn is an impressive advance, its strength is still much lower than that of the individual CNTs comprising the yarn. Closing this gap requires understanding load transfer between CNTs at the nanometer dimensional scale. This work uses reactive molecular dynamics simulations to gain an understanding at the nanometer scale of the key factors that determine CNT nanocomposite mechanical performance, and to place more realistic upper bounds on the target properties. While molecular dynamics simulations using conventional force fields can predict elastic properties, the ReaxFF reactive forcefield can also model fracture behavior because of its ability to accurately describe bond breaking and formation during a simulation. The upper and lower bounds of CNT composite properties are investigated by comparing systems composed of CNTs continuously connected across the periodic boundary with systems composed of finite length CNTs. These lengths, effectively infinite for the continuous tubes and an aspect ratio of 13 for the finite length case, result from practical limitations on the number of atoms that can be included in a simulation. Experimentally measured aspect ratios are typically on the order of 100,000, so the calculated results should represent upper and lower limits on experimental mechanical properties. Finally, the effect of various degrees of covalent crosslinking between the CNTs and amorphous carbon matrix is considered to identify the amount of CNT-matrix covalent bonding that maximizes overall composite properties.

Jensen, Benjamin D.↗
NASA NTRS1989

A 3D visualization system for molecular structures

The properties of molecules derive in part from their structures. Because of the importance of understanding molecular structures various methodologies, ranging from first principles to empirical technique, were developed for computing the structure of molecules. For large molecules such as polymer model compounds, the structural information is difficult to comprehend by examining tabulated data. Therefore, a molecular graphics display system, called MOLDS, was developed to help interpret the data. MOLDS is a menu-driven program developed to run on the LADC SNS computer systems. This program can read a data file generated by the modeling programs or data can be entered using the keyboard. MOLDS has the following capabilities: draws the 3-D representation of a molecule using stick, ball and ball, or space filled model from Cartesian coordinates, draws different perspective views of the molecule; rotates the molecule on the X, Y, Z axis or about some arbitrary line in space, zooms in on a small area of the molecule in order to obtain a better view of a specific region; and makes hard copy representation of molecules on a graphic printer. In addition, MOLDS can be easily updated and readily adapted to run on most computer systems.

Green, Terry J.↗
NASA NTRS1997

Machine Phase Fullerene Nanotechnology: 1996

NASA has used exotic materials for spacecraft and experimental aircraft to good effect for many decades. In spite of many advances, transportation to space still costs about $10,000 per pound. Drexler has proposed a hypothetical nanotechnology based on diamond and investigated the properties of such molecular systems. These studies and others suggest enormous potential for aerospace systems. Unfortunately, methods to realize diamonoid nanotechnology are at best highly speculative. Recent computational efforts at NASA Ames Research Center and computation and experiment elsewhere suggest that a nanotechnology of machine phase functionalized fullerenes may be synthetically relatively accessible and of great aerospace interest. Machine phase materials are (hypothetical) materials consisting entirely or in large part of microscopic machines. In a sense, most living matter fits this definition. To begin investigation of fullerene nanotechnology, we used molecular dynamics to study the properties of carbon nanotube based gears and gear/shaft configurations. Experiments on C60 and quantum calculations suggest that benzyne may react with carbon nanotubes to form gear teeth. Han has computationally demonstrated that molecular gears fashioned from (14,0) single-walled carbon nanotubes and benzyne teeth should operate well at 50-100 gigahertz. Results suggest that rotation can be converted to rotating or linear motion, and linear motion may be converted into rotation. Preliminary results suggest that these mechanical systems can be cooled by a helium atmosphere. Furthermore, Deepak has successfully simulated using helical electric fields generated by a laser to power fullerene gears once a positive and negative charge have been added to form a dipole. Even with mechanical motion, cooling, and power; creating a viable nanotechnology requires support structures, computer control, a system architecture, a variety of components, and some approach to manufacture. Additional information is contained within the original extended abstract.

Globus, Al↗
NASA NTRS1986

Observational constraints on the interaction of giant molecular clouds with the solar system

The properties of the molecular cloud distribution are summarized, with special emphasis on the solar neighborhood. It is shown that the mass density within molecular clouds is sufficiently low that passing or grazing encounters cannot be significant in the perturbation of cometary orbits at 40,000 AU. The mean time for the sun between penetrating encounters of GMCs is about 1.5 Gyr with a typical duration of 1 Myr. The long time interval between encounters rules out a link between short-term periodicities in the geologic record and molecular cloud passages.

Scoville, N. Z.↗
NASA NTRSDate not supplied

TPSAS-NF1676L-31622-DND

Electroactive polymers, especially electromechanically active polymers, have drawn extensive attention worldwide since the piezoelectricity and ferroelectricity of poly (vinylidene fluoride) (PVDF) was discovered in 1969. In the past three decades, several new classes of electroactive polymers that demonstrate promising electromechanical properties have been developed. Electrostrictive Graft Elastomers (G-elastomer) developed at NASA Langley Research Center have been recognized as one of the promising newly developed eletroactive polymers due to their large electric field-induced strain (~4%) and high mechanical modulus (~700 MPa). The combination of large induced strain and high mechanical modulus allows the electrostrictive graft elastomer to offer very promising electromechanical properties, in terms of output mechanical energy density, and plausible as a candidate for use in high performance and low mass actuation devices in various aerospace applications. In this presentation, the molecular structures, properties, processing and mechanisms of the electromechanical performance, as well as its applications in actuation devices for advanced aerospace technologies will be comprehensively reviewed and discussed.

Ji Su↗
NASA NTRSDate not supplied

TPSAS-NF1676L-31666-DND

Electroactive polymers, especially electromechanically active polymers, have drawn extensive attention worldwide since the piezoelectricity and ferroelectricity of poly (vinylidene fluoride) (PVDF) was discovered in 1969. In the past three decades, several new classes of electroactive polymers that demonstrate promising electromechanical properties have been developed. Electrostrictive Graft Elastomers (G-elastomer) developed at NASA Langley Research Center have been recognized as one of the promising newly developed eletroactive polymers due to their large electric field-induced strain (~4%) and high mechanical modulus (~700 MPa). The combination of large induced strain and high mechanical modulus allows the electrostrictive graft elastomer to offer very promising electromechanical properties, in terms of output mechanical energy density, and plausible as a candidate for use in high performance and low mass actuation devices in various aerospace applications. In this presentation, the molecular structures, properties, processing and mechanisms of the electromechanical performance, as well as its applications in actuation devices for advanced aerospace technologies will be comprehensively reviewed and discussed.

Ji Su↗
NASA NTRSDate not supplied

TPSAS-NF1676L-30019-DND

Electroactive polymers, especially electromechanically active polymers, have drawn extensive attention worldwide since the piezoelectricity and ferroelectricity of poly (vinylidene fluoride) (PVDF) was discovered in 1969. In the past three decades, several new classes of electroactive polymers that demonstrated promising electromechanical properties have been developed. Electrostrictive Graft Elastomers (G-elastomer) developed at NASA Langley Research Center have been recognized as one of the newly developed promising eletroactive polymers due to their large electric field-induced strain (~4%) and high mechanical modulus (~700 MPa). The combination of large induced strain and high mechanical modulus makes the electrostrictive graft elastomer offer very promising electromechanical properties, in terms of output mechanical energy density, and plausible as a candidate for use in high performance and low mass actuation devices in various aerospace applications. In this presentation, the molecular structures, properties, processing and mechanisms of the electromechanical performance, as well as its applications in actuation devices for advanced aerospace technologies will be comprehensively reviewed and discussed.

Ji Su↗
NASA NTRS1989

Molecular weight characterization of advanced thermoplastic resins

Analytical techniques including low angle laser light scattering photometry (LALLS), differential viscometry (DV), gel permeation chromatography (GPC), GPC-LALLS and GPC-DV, were used to characterize the molecular weight and molecular weight distribution of several advanced thermoplastics. A discussion is presented of various molecular-weight-related parameters obtained by these techniques on an experimental polyimide and poly(arylene ether ketone) and a commercially available polysulfone. Where possible, these parameters are correlated with processability and selected mechanical properties. The molecular weight was found to vary during the thermal conversion of poly(amic acid) to polyimide. However, no change in composition of the polysulfone was noted in response to various processing procedures.

Young, Philip R.↗
NASA NTRS1977

The energetics of molecular clouds. I - Methods of analysis and application to the S255 molecular cloud

Observations of the S255 molecular cloud in the radio lines of CO, (C-13)O, and H2O as well as in the IR region from 12 to 20 microns are presented. These results show that an extended molecular cloud is associated with the optically visible H II regions S255 - S257, both the kinetic temperature and molecular density are enhanced in an area centered on a compact near-IR source, this source is also coincident with an OH and an H2O maser (within the errors), and the IR source exhibits the silicon absorption feature. First-order techniques which allow physical properties of molecular clouds to be estimated and the energetics of the gas and dust in the clouds to be analyzed are developed and applied to S255. It is concluded that: (1) the gas cooling rate is much less than the dust cooling rate; (2) the primary energy flow is in the IR through dust emission over a range of temperatures; (3) the near-IR source is apparently responsible for the local peak in gas kinetic temperature; and (4) the exciting stars of nearby H II regions appear to be the primary heat sources for the overall molecular cloud.

Evans, N. J., II↗
NASA NTRS2021

Machine Learning the COSMO Model for Predicting Thermodynamics of Electrolyte Mixtures

Bottom-up design of electrolyte mixtures for battery systems requires predicting macro thermodynamic properties from molecular constituents. For instance, molten salt electrolyte batteries require conditions far above room temperature to operate. Therefore, discovering mixtures with increasingly lower eutectic melting points is desirable. A model that can approximate chemical activity is a valuable tool to search through the vast compositional design space. Machine learning can predict properties of materials such as vibrational free energies, electronic energy gaps, and thermal conductivities. Moreover, they can learn physical models such as interatomic potentials. The COSMO-SAC model uses theory and empirical parameterization to predict liquid-vapor and liquid-solid properties using first-principles calculations. However, obtaining activity coefficients required for parameterizing the COSMO-SAC model is costly and limited to a select chemical space. In this work, we explored if machine learning methods could improve the COSMO-SAC model and bridge density functional theory calculations to liquid phase thermodynamic properties. Our data-driven approach uses existing databases for sigma-profiles of organic solvents and reconciles their methodological differences via ensemble averaging. First, an optimal machine learning model is constructed for each dataset. Our machine learning algorithms use the sigma-profile as an input feature to predict binary mixtures' activity coefficients using multi-output regression. Each dataset uses different choices of functionals, methods, and basis sets. Therefore, our ensemble model attempts to predict corrected activity coefficients given the combination of all the model outputs. The activity coefficients used for training are generated using the COSMO-SAC model. This approach enables the extraction of meaningful information from the existing datasets to improve the COSMO-SAC model for obtaining thermodynamic properties of electrolyte mixtures. With the liquid phase activities, we can identify electrolyte mixtures that meet desired phase equilibria conditions.

Thermodynamics↗
NASA NTRS1987

Star formation in molecular clouds - Observation and theory

Star-formation (SF) processes occurring on the scale of giant molecular clouds (10 to the 6th solar masses and 10 to the 20th cm) or smaller are discussed, reviewing the results of recent theoretical and observational investigations. Topics examined include the origin of stellar masses; bimodal SF; initial mass functions; binary stars, bound clusters, and hierarchical fragmentation; and the efficiency of SF. The properties of molecular clouds and the origin of substructures in molecular clumps are explored in detail, and consideration is given to gravitational collapse and protostars, bipolar outflows from young stellar objects, visible young stellar objects, and the implications for binary-star and planetary-system formation.

Shu, Frank H.↗