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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Study of improved resins for advanced supersonic technology composites. Part 1: Heteroaromatic polymers containing ether groups. Part 2: Curing chemistry of aromatic polymers and composite studies

Fourteen ether-containing, aromatic dianhydrides have been synthesized from N-phenyl-3 or 4-nitrophthalimide and various bisphenols. The process involves nucleophilic displacement of activated nitro groups with bisphenolate ions. Ether-containing dianhydrides were indefinitely stable in the presence of atmospheric moisture. One-step, high temperature solution polymerization of the ether-containing dianhydrides with m-phenylene diamine, 4,4'-oxydianiline and 1, 3-bis(4-aminophenoxy)benzene afforded 42 polyetherimides. The polyetherimides were all soluble in m-cresol except two which were found to be crystalline. The glass transition temperatures of the polyetherimides ranged from 178 to 277 C. Soluble polybenzimidazopyrrolones containing ether groups were also prepared from the same ether-containing dianhydrides and aromatic tetraamines by one-step solution polymerization. Using low molecular weight polyetherimides, various thermoset resin systems were developed and tested as matrices for fiber-reinforced composites. The curing chemistry involving reaction of the phthalonitrile group and the o-diaminophenyl group was found to be generally applicable to crosslinking various aromatic polymers other than polyimides.

Takekoshi, T.↗
DOE OSTI2020

4D Printing via an Unconventional Fused Deposition Modeling Route to High-Performance Thermosets

An unprecedented four-dimensional (4D) printing process allowing high-performance and shape memory thermoset to be printed, for the first time, by fused deposition modeling (FDM) with isotropic properties has been achieved. Here, bisphenol A-based epoxy and benzoxazine were formulated to a low-temperature thermoplastic and high-temperature thermoset resin, which is melt-extrudable and can be postcured into covalently cross-linked material. Carbon nanotube (CNT) was added in the resin to work as both mechanical enhancement filler and rheology modifier to prevent shape deformation during postcuring process. The cross-layer reaction fuses individual layers into an integrity, thus eliminating layer delamination induced by FDM, offering isotropic mechanical properties regardless of the printing orientations. The highly cross-linked network provides outstanding mechanical strength and superb thermal stability. The excellent shape memory performance with fast recovery rate and large recovery degree is also obtained in the three-dimensional (3D) printed composites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Infusible Thermoplastic Composites for Wind Turbine Blade Manufacturing: Fatigue Life of Thermoplastic Laminates under Ambient and Low-Temperature Conditions

Traditionally, thermoset resins such as polyesters (PE) and epoxies are used as the polymer matrix for construction of wind turbine blades. However, concern about their end-of-life treatment garners interest to use thermoplastics for increased recyclability. However, the high viscosity of molten thermoplastics inhibits their use in manufacturing wind turbine blades with injection or compression molding. A recently developed, infusible, reactive thermoplastic resin overcomes this technological barrier. Toward verifying that this recyclable resin is suitable for use in wind turbine blades, a dataset of R?=?0.1 and R?=?10 fatigue data for glass fiber-reinforced acrylic composites is provided and equal fatigue life to industry standard epoxy and unsaturated PE resin systems is demonstrated. Specifically, R?=?0.1 fatigue data for acrylic composites at room temperature and -30?degrees C for verification of low-temperature performance are tabulated. To elucidate failure mechanisms, in situ mechanical testing with X-ray computed tomography demonstrates that damage accumulation occurs by crack propagation along the fiber-matrix interface under cyclic loading. Infrared (IR) thermography predicts failure points in composites specimens with porosity defects introduced from nonideal manufacturing processes. Furthermore, these manufacturing defects are shown to compromise the fatigue life of the acrylic laminates by an order of magnitude.

effect of defects↗
DOE OSTI2021

Optimal toolpath design of additive manufactured composite cylindrical structures

Structural design optimization for additive manufacturing is primarily focused on planar layer-by-layer processes and design of composite cylindrical structures does not often accommodate manufacturing constraints. In this study, we propose to optimize the toolpath trajectory of additively manufactured composite cylinders comprised of multiple thin cylindrical annuli. Additionally, our printing process is based on direct ink writing in which short carbon fibers in a thermoset resin are extruded through a moving nozzle to build up a structure. Since the fibers are primarily aligned in the flow direction of the extrudate, the printing trajectory influences the material properties of the composite structure. To accommodate this, we define the toolpaths as contours of parameterized level-set functions. This parameterization allows us to optimize the material properties and impose manufacturing constraints such as no-overlap, no-sag, minimum radius of curvature, and continuity of the toolpaths. Several examples illustrate the optimization procedure.

42 ENGINEERING↗
DOE OSTI2020

Comparison of semi-doped PANI/DBSA complex achieved by thermal doping and roll-mill process: A new perspective for application

Conductive polymers have garnered extensive attention over the last few decades owing to their vast applications and relative ease of production. One such polymer is PANI; with versatile thermo-mechanical, chemical, and electrical properties, has been researched for varied applications in the field of electronics, electrodes and corrosion protection. In this study, we focus on an alternative route to process semi-doped PANI/DBSA complexes with special focus on material properties for improved processability. This study investigates the influence of two different material preparation techniques: roll-milling and thermal-doping, on the formability and processability of such polymer-complex systems. Results confirm similar doping levels achieved in both processes and shear-thinning behavior was only observed for roll-milled samples. These results underline the formability of roll-milled PANI/DBSA with thermosetting resins. It essentially explains the production route and offers a perspective for commercial manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Increasing the Lifetime of Epoxy Components with Antioxidant Stabilizers

Epoxy thermoset resins are ubiquitous materials with extensive applications where they are used as encapsulants, composites, and adhesives/staking compounds used to secure sensitive components. Epoxy resins are inherently sensitive to thermo-oxidative aging, especially at elevated temperatures, which changes the bulk properties of the material and can lead to component failure for example by cracking due to embrittlement or by adhesion failure between the epoxy and filler material in a composite. This project investigated the effects of three commercial antioxidants (Irganox ® 1010 (I-102), butylated hydroxytoluene (BHT), or Chisorb ® 770 (HALS)) at two different loadings (2.5 and 5 wt%) on the mechanical and chemical aging of a model epoxy system (EPON TM 828 / Jeffamine ® T-403) under ambient conditions, 65, 95, and 110 °C. Additionally, synthetic routes towards an antioxidant capable of being covalently bound to the resin so as to prevent leaching were explored with one such molecule being successfully synthesized and purified. One commercial antioxidant (Irganox ® 1010) was found to reduce the degree of thermo-oxidatively induced damage in the system.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Imaging APO-BMI with Micro X-ray Computed Tomography (CT)

APO-BMI is a high-strength, high-temperature, and low-density foam comprised of 1,2-bis(2-aminophenylthio) ethane (APO-Link, formerly Apocure-601) and 4,4’-bismaleimidodiphenylmethane (BMI) that is used structural applications within the aerospace and weapons manufacturing sectors. APO-link is the diamine reagent used to synthesize BMI, a thermosetting resin. This resin can remain in a molten, flowing state for an extended period of time before crosslinking, allowing addition of glass or carbon microballoons to form its final structure. A portion of the current project was to observe the thermal effects on the structural integrity of the foam associated with exposure to an ion beam. Features within the foam were imaged using micro X-ray computed tomography (CT). The resulting imaging provided evidence that microballoon structure remained mostly intact at the points of failure, indicating that the failure of the material was occurring in the binder material.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Additively Manufactured, Lightweight, Low-Cost Composite Vessels for Compressed Natural Gas Fuel Storage

This project will develop a process to combine AM via direct ink writing (DIW) technology for CFC printing and to use design optimization tools pioneered at LLNL, with advances in resin/composite formulation enabled by chemical and nano-material modification to produce lightweight low-cost CNG tanks. Our approach will yield sub-scale prototype composite pressure tanks equivalent to Type-5 CNG vessel designs that demonstrate a potential cost-benefit advantage. Central to our vision is using agile AM and design based on computationally informed DIW of both short and continuous CF, further coupled with high-performance thermoset polymer matrixes modified by emergent nanomaterials. Our single-stage, multi-material AM technology, combined with a decreased volume fraction of CF and an increased proportion of economically advantaged short fiber, all together drive the reduction in manufacturing time and overall cost. Importantly, reductions in continuous fiber and overall fiber volume fraction will be achieved without detriment to the mechanical strength of the composite vessel. This will be achieved by employing a single process using multi materials grading involving a thermoset resin “ink” modified with aligned nanoplatelets to leverage the efficient tortuous-path gas barrier effect, printed as an inner flexible gas barrier as the initial stage in our manufacturing process before compositionally grading the AM feedstock in real-time to transition to a rigid, structural CF-filled resin. The proposed hybrid construction is projected to achieve pressure ratings at a service range of 2,900–3,600 psi with a 3× burst safety factor comparable to conventional filament-wound composite tanks with an estimated 30–50% reduction in total manufacturing cost.

03 NATURAL GAS↗
NASA NTRS1976

Integrally rigidized acoustic interior spacecraft panel

A sandwich panel concept is described which utilizes a monolithic I-beam design as the core. The core and skins are integrally bonded with thermosetting resin into a homogeneous structure. In addition to possessing a high strength to weight ratio, the panel resists combustion, delamination, aging due to fatigue, localized stresses, and exhibits good acoustic properties. Since the panel concept has definite potential as a high flame retardant and low smoke emission panel with excellent structural integrity, aerospace materials were used to optimize the construction for highly demanding space shuttle applications. The specific materials of construction were chosen for low flammability and off-gassing properties as well as for strength, light weight, and sound dampening.

Source record↗
NASA NTRS1981

A novel addition polyimide adhesive

An addition polyimide adhesive, LARC 13, was developed which shows promise for bonding both titanium and composites for applications which require service temperatures in excess of 533 K. The LARC 13 is based on an oligomeric bis nadimide containing a meta linked aromatic diamine. The adhesive melts prior to polymerization due to its oligomeric nature, thereby allowing it to be processed at 344 kPa or less. Therefore, LARC 13 is ideal for the bonding of honeycomb sandwich structures. After melting, the resin thermosets during the cure of the nadic endcaps to a highly crosslinked system. Few volatiles are evolved, thus allowing large enclosed structures to be bonded. Preparation of the adhesive as well as bonding, aging, and testing of lap shear and honeycomb samples are discussed.

St.clair, T. L.↗
NASA NTRS1985

Ultrasonic characterization of changes in viscoelastic properties of epoxy during cure

A technique for using the longitudinal velocity (LV) of an ultrasonic wave to monitor the extent of cross linking (CL) during the cure of thermosetting resins is described. The method was developed by monitoring the rate of change in LV during the cure of a bisphenol-A epoxy resin with an amine adduct. The experiment included variations in the temperature and stoichiometry in order to express the rate of change in terms of the reaction kinetics. The pulse-echo method was used with a single transducer operating at 20 MHz. Numerical models were defined to account for the acoustic response of a single layer, the attenuation and the reflection coefficient. A linear relationship was observed between the inverse of the temperature and the log of the rate of change in the velocity, supporting the theory that the velocity could be used to monitor the extent of the cross-linking reaction. An activation energy of 11.9 kcal/mole was calculated for the mixture being investigated.

Winfree, W. P.↗
NASA NTRS1988

Calculating Percent Gel For Process Control

Reaction state of thermosetting resin tracked to assure desired properties. Rate of gel determined as function of temperature by measuring time to gel of part of graphite fabric impregnated with Hexcel R120 (or equivalent) phenolic resin.

Webster, Charles Neal↗
NASA NTRS1987

Monitoring processing properties of high performance thermoplastics using frequency dependent electromagnetic sensing

An in situ NDE dielectric impedance measurement method has been developed for ascertaining the cure processing properties of high temperature advanced thermoplastic and thermosetting resins, using continuous frequency-dependent measurements and analyses of complex permittivity over 9 orders of magnitude and 6 decades of frequency at temperatures up to 400 C. Both ionic and Debye-like dipolar relaxation processes are monitored. Attention is given to LARC-TPI, PEEK, and poly(arylene ether) resins' viscosity, glass transition temperature, recrystallization, and residual solvent content and evolution properties.

Kranbuehl, D. E.↗
NASA NTRS1995

Multipurpose Prepregging Machine

Machine designed and built for variety of uses involving coating or impregnating ("prepregging") fibers, tows, yarns, or webs or tapes made of such fibrous materials with thermoplastic or thermosetting resins. Prepreg materials produced used to make matrix/fiber composite materials. Comprises modules operated individually, sequentially, or simultaneously, depending on nature of specific prepreg material and prepregging technique used. Machine incorporates number of safety features.

Johnston, N. J.↗
NASA NTRS2005

A Preliminary Investigation of the E-Beam Induced Polymerization of Maleimide and Norbornene End-capped Polyimides

A research area of high activity in connection with aerospace engineering has been the development of polymer thermosetting resins that can resist temperature as high as 300 C while maintaining adequate toughness, and providing ease of processing to enable low temperature and low cost composite fabrication methods. In order to meet such requirements, sequential interpenetrating polymer networks (IPNs) based on bismaleimide (BMI) and cyanate ester (CE) monomers were investigated. In these systems, a polycyanurate network is first formed in the presence of BMI and appropriate reactive diluent monomers and in a second step, a network based on the BMI is created in the presence of a fully formed polycyanurate network. The materials developed can be processed at relatively low temperature (less than 150 C) and with the aid of electron beam (EB) curing. Of major importance to the success of this work was the identification of a reactive diluent that improves ease of processing and has tailored reactivity to allow for the controlled synthesis of CE-BMI sequential IPNs. Based on solubility and reactivity of a number of reactive diluents, N-acryloylmorpholine (AMP) was selected as a comonomer for BMI copolymerization. A donor-acceptoreaction mechanism was suggested to explain the relative reactivity of a variety of reactive diluents towards maleimide functionality. The optimum processing parameters for the formation of the first network were determined through the study of metal catalyzed cure and hydrolysis of cyanate esters, whereas the reaction behavior for second network formation in terms of the influence of EB dose rate and temperature was elucidated through an in-situ kinetics study of maleimide and AMP copolymerization. Structure-property relationships were developed which allowed for the design of improved resin systems. In particular, appropriate network coupler possessing cyanate ester and maleimide functionality was synthesized to link the polycyanurate first network to the BMI/AMP second network and thus form linked sequential IPNs (LIPNs). Consequently, Tg as high as 370 C was achieved and a fracture toughness of 120 Joules per square meters was obtained for resin systems that possess adequately low viscosity for processing using liquid molding techniques at low temperature.

Palmese, Giuseppe R.↗
NASA NTRS2008

Self-Deploying Trusses Containing Shape-Memory Polymers

Composite truss structures are being developed that can be compacted for stowage and later deploy themselves to full size and shape. In the target applications, these smart structures will precisely self-deploy and support a large, lightweight space-based antenna. Self-deploying trusses offer a simple, light, and affordable alternative to articulated mechanisms or inflatable structures. The trusses may also be useful in such terrestrial applications as variable-geometry aircraft components or shelters that can be compacted, transported, and deployed quickly in hostile environments. The truss technology uses high-performance shape-memory-polymer (SMP) thermoset resin reinforced with fibers to form a helical composite structure. At normal operating temperatures, the truss material has the structural properties of a conventional composite. This enables truss designs with required torsion, bending, and compression stiffness. However, when heated to its designed glass transition temperature (Tg), the SMP matrix acquires the flexibility of an elastomer. In this state, the truss can be compressed telescopically to a configuration encompassing a fraction of its original volume. When cooled below Tg, the SMP reverts to a rigid state and holds the truss in the stowed configuration without external constraint. Heating the materials above Tg activates truss deployment as the composite material releases strain energy, driving the truss to its original memorized configuration without the need for further actuation. Laboratory prototype trusses have demonstrated repeatable self-deployment cycles following linear compaction exceeding an 11:1 ratio (see figure).

Schueler, Robert M.↗
NASA NTRSDate not supplied

Building and Breaking Carbon Composites with REACTER

Carbon composites have become indispensable for aerospace and other high-performance applications, and a detailed picture of their morphology and failure mechanisms remains difficult to obtain through experiment. REACTER is a versatile computational modeling tool for atomistic molecular dynamics designed to model chemical reactions at the speed and length scales of classical force fields.1 In this work, several recent features of REACTER were applied to the creation and subsequent mechanical testing of two classes of carbon composites, carbon-fiber reinforced polymers (CFRP) and carbon nanotube (CNT) composites. Carbon fiber core morphologies were created by the method of Desai et al.,2 but using the advanced reaction constraints framework of REACTER, their proposed multistep procedure was reduced to a single uninterrupted molecular dynamics simulation. The carbon fiber filler was embedded into a polymer matrix by simulated in situ polymerization of several thermosetting resins, including bismaleimide and polyarylacetylene, to obtain the final CFRP model. To generate the second class of carbon composite, CNT networks were grown dynamically using the new ‘create atoms’ feature of REACTER, and similarly infiltrated with resin to obtain CNT composites. The resulting models were compared directly to experiment using simulated high resolution transmission electron microscopy and x-ray diffraction. Failure mechanisms were elucidated by simulating mechanically induced bond breaking, as characterized by third-order DFT-based tight-binding (DFTB3) simulations, via a reaction constraint on the total potential energy of the involved atoms.

Molecular Dynamics↗
DOE OSTI2021

Thermoset composite having thermoplastic characteristics

A composite composition includes a thermoset resin and about 3 wt. % to about 35 wt. % of at least one material selected from the group consisting of cellulose nanofibrils (CNF), micro-sized cellulose fibers (MFC), and cellulose nanocrystals (CNC) dispersed therein as measured with respect to the overall weight of the composite composition. The cellulose nanofibrils and/or nanocrystals have an average diameter of about 5 nm to about 500 nm and an average aspect ratio in the range of about 5:1 to about 500:1. The cellulose micro-sized fibers have an average diameter of about 5 μm to about 100 μm and an average aspect ratio in the range of about 5:1 to about 250:1.

Ozcan, Soydan↗