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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Effect of thermal history on mechanical properties of polyetheretherketone below the glass transition temperature

The effect of thermal history on the tensile properties of polyetheretherketone neat resin films was investigated at different test temperatures (125, 25, and -100) using four samples: fast-quenched amorphous (Q); quenched, then crystallized at 180 C (C180); slowly cooled (for about 16 h) from the melt (SC); and air-cooled (2-3 h) from the melt (AC). It was found that thermal history significantly affects the tensile properties of the material below the glass transition. Fast quenched amorphous films were most tough, could be drawn to greatest strain before rupture, and undergo densification during necking; at the test temperature of -100 C, these films had the best ultimate mechanical properties. At higher temperatures, the semicrystalline films AC and C180 had properties that compared favorably with the Q films. The SC films exhibited poor mechanical properties at all test temperatures.

Cebe, Peggy↗
NASA NTRS1999

Low-Cost, High Glass-Transition Temperature, Thermosetting Polyimide Developed

PMR-15 polyimide, developed in the mid-1970's at the NASA Lewis Research Center, is recognized as a state-of-the-art high-temperature resin for composite applications in the temperature range of 500 to 550 F (260 to 288 C). PMR-15 offers easy processing and good property retention at a reasonable cost. For these reasons, it is widely used in both military and commercial aircraft engine components. Traditionally, polyimide composites have been designed for long-term use at 500 to 600 F over thousands of hours. However, new applications in reusable launch vehicles (RLV's) require lightweight materials that can perform for short times (tens of hours) at temperatures between 800 and 1000 F (425 and 538 C). Current efforts at Lewis are focused on raising the use temperature of polyimide composites by increasing the glass-transition temperature of the matrix resins. Achieving this dramatic increase in the upper use temperature without sacrificing polymer and composite processability is a major technical challenge.

Chuang, Kathy C.↗
DOE OSTI2025

Molecular Dynamics Simulation and Theoretical Analysis of Structural Relaxation, Bond Exchange Dynamics, and Glass Transition in Vitrimers

Vitrimers are a class of polymer networks featuring dynamic covalent cross-links that can undergo associative bond exchange. There has been recent interest in these materials due to their promise as recyclable thermosets or self-healing polymers because of the ability of vitrimer networks to rearrange at the molecular level and undergo macroscopic flow. However, the practical use of these materials often occurs in the supercooled regime or glassy state, where the implications of dynamic bonds are complicated by the interplay between slow activated segmental dynamics, cross-link (i.e., bond-exchange) kinetics, and ultimately material properties. Here, in this paper, we combine coarse-grained molecular dynamics simulation and microscopic statistical mechanical theory to understand how cross-linking kinetics affect material dynamics and how this couples to segmental relaxation of the polymeric network strands across a spectrum of length and time scales, especially in the supercooled regime. We characterize the Kuhn segmental alpha relaxation time and bond exchange time for vitrimer systems across various cross-link densities, temperatures, and bond exchange rates. Simulation and theory both exhibit a bending-up behavior for bond exchange time upon cooling, suggesting a coupling between bond exchange dynamics and segmental relaxation that intensifies with faster bond exchange kinetics. We also found bond exchange dynamics have an impact on Kuhn segment alpha relaxation time, which is most significant at higher cross-link densities. Both these effects are most prominent when the bond exchange time is similar to the Kuhn segment alpha relaxation time, and the resulting coupling of these two relaxation processes is tied to both the probability of a free end to find a bonded pair and the time scale of the constraints imposed by the dynamic cross-links. This relationship is reflected by a cross-link dependence of a theoretical parameter which represents the quantitative degree of coupling between bond exchange and segmental dynamics. Overall, the combination of simulation and theory clarifies the intricate interaction between bond kinetics and segmental relaxation and demonstrates the ability to provide molecular-level insights into vitrimer dynamics over a wide temperature range.

dynamic relaxation↗
NASA NTRS1973

Glass transition temperatures of liquid prepolymers obtained by thermal penetrometry

Thermal penetrometry is experimental technique for detecting temperature at which frozen prepolymer becomes soft enough to be pierced by weighted penetrometer needle; temperature at which this occurs is called penetration temperature. Apparatus used to obtain penetration temperatures can be set up largely from standard parts.

Potts, J. E., Jr.↗
NASA NTRS1983

Characterization of the matrix glass transition in carbon-epoxy laminates using the CSD test geometry

A new test geometry, referred to as centro-symmetric deformation (CSD), is proposed for characterizing the viscoelastic behavior of the matrix of carbon-epoxy laminates. The sample consists of a thin disk, typically 6-14 plies thick, having a nominal diameter of 30 mm. The disk is freely supported on a circular anvil; the load is applied to the center of the disk using an 8-mm-diameter ball bearing nosepiece. The CSD test geometry provides viscoelastic dispersion data which are independent of the angular orientation of the sample. The test geometry is sufficiently sensitive to matrix changes to allow its use for postcuring, humidity, crosslink density, and other matrix change studies. Test results are presented for a carbon-epoxy laminate.

Sternstein, S. S.↗
NASA NTRS2002

High-Glass-Transition-Temperature Polyimides Developed for Reusable Launch Vehicle Applications

Polyimide composites have been traditionally used for high-temperature applications in aircraft engines at temperatures up to 550 F (288 C) for thousands of hours. However, as NASA shifts its focus toward the development of advanced reusable launch vehicles, there is an urgent need for lightweight polymer composites that can sustain 600 to 800 F (315 to 427 C) for short excursions (hundreds of hours). To meet critical vehicle weight targets, it is essential that one use lightweight, high-temperature polymer matrix composites in propulsion components such as turbopump housings, ducts, engine supports, and struts. Composite materials in reusable launch vehicle components will heat quickly during launch and reentry. Conventional composites, consisting of layers of fabric or fiber-reinforced lamina, would either blister or encounter catastrophic delamination under high heating rates above 300 C. This blistering and delamination are the result of a sudden volume expansion within the composite due to the release of absorbed moisture and gases generated by the degradation of the polymer matrix. Researchers at the NASA Glenn Research Center and the Boeing Company (Long Beach, CA) recently demonstrated a successful approach for preventing this delamination--the use of three-dimensional stitched composites fabricated by resin infusion.

Chuang, Kathy↗
NASA NTRS2013

Superconducting Metallic Glass Transition-Edge-Sensors

A superconducting metallic glass transition-edge sensor (MGTES) and a method for fabricating the MGTES are provided. A single-layer superconducting amorphous metal alloy is deposited on a substrate. The single-layer superconducting amorphous metal alloy is an absorber for the MGTES and is electrically connected to a circuit configured for readout and biasing to sense electromagnetic radiation.

Hays, Charles C.↗
NASA NTRS1996

Crystallization of amorphous water ice in the solar system

Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated.

NASA Center ARC↗
NASA NTRS2012

Shape Memory Composite Hybrid Hinge

There are two conventional types of hinges for in-space deployment applications. The first type is mechanically deploying hinges. A typical mechanically deploying hinge is usually composed of several tens of components. It is complicated, heavy, and bulky. More components imply higher deployment failure probability. Due to the existence of relatively moving components among a mechanically deploying hinge, it unavoidably has microdynamic problems. The second type of conventional hinge relies on strain energy for deployment. A tape-spring hinge is a typical strain energy hinge. A fundamental problem of a strain energy hinge is that its deployment dynamic is uncontrollable. Usually, its deployment is associated with a large impact, which is unacceptable for many space applications. Some damping technologies have been experimented with to reduce the impact, but they increased the risks of an unsuccessful deployment. Coalescing strain energy components with shape memory composite (SMC) components to form a hybrid hinge is the solution. SMCs are well suited for deployable structures. A SMC is created from a high-performance fiber and a shape memory polymer resin. When the resin is heated to above its glass transition temperature, the composite becomes flexible and can be folded or packed. Once cooled to below the glass transition temperature, the composite remains in the packed state. When the structure is ready to be deployed, the SMC component is reheated to above the glass transition temperature, and it returns to its as-fabricated shape. A hybrid hinge is composed of two strain energy flanges (also called tape-springs) and one SMC tube. Two folding lines are placed on the SMC tube to avoid excessive strain on the SMC during folding. Two adapters are used to connect the hybrid hinge to its adjacent structural components. While the SMC tube is heated to above its glass transition temperature, a hybrid hinge can be folded and stays at folded status after the temperature is reduced to below its glass transition temperature. After the deployable structure is launched in space, the SMC tube is reheated and the hinge is unfolded to deploy the structure. Based on test results, the hybrid hinge can achieve higher than 99.999% shape recovery. The hybrid hinge inherits all of the good characteristics of a tape-spring hinge such as simplicity, light weight, high deployment reliability, and high deployment precision. Conversely, it eliminates the deployment impact that has significantly limited the applications of a tape-spring hinge. The deployment dynamics of a hybrid hinge are in a slow and controllable fashion. The SMC tube of a hybrid hinge is a multifunctional component. It serves as a deployment mechanism during the deployment process, and also serves as a structural component after the hinge is fully deployed, which makes a hybrid hinge much stronger and stiffer than a tape-spring hinge. Unlike a mechanically deploying hinge that uses relatively moving components, a hybrid hinge depends on material deformation for its packing and deployment. It naturally eliminates the microdynamic phenomenon.

Fang, Houfei↗
NASA NTRS1973

Thermomechanical behavior of a polynorbornadiene

A high-temperature linear amorphous hydrocarbon polymer synthesized cationically from 2,5-norbornadiene was studied thermomechanically with respect to physical transitions and stability in nitrogen. The glass transition temperature was determined to be 320 C (at less than 1 cps), which is probably the highest known for a linear hydrocarbon addition polymer. The thermomechanical technique of torsional braid analysis, together with thermogravimetric analysis, differential thermal analysis, infrared analysis, and solubility studies, was used to investigate the sequential events of the glass transition and degradation. The polymer is of particular interest since it is a high-temperature plastic which in the bulk form would probably need to be processed at high speeds in the vicinity of the glass transition temperature in an inert atmosphere. The presence of tertiary hydrogen atoms should render it amenable to degradation by the earth's environment.

Roller, M. B.↗
NASA NTRS1978

Transition from glass to graphite in manufacture of composite aircraft structure

The transition from fiberglass reinforced plastic composites to graphite reinforced plastic composites is described. Structural fiberglass design and manufacturing background are summarized. How this experience provides a technology base for moving into graphite composite secondary structure and then to composite primary structure is considered. The technical requirements that must be fulfilled in the transition from glass to graphite composite structure are also included.

Buffum, H. E.↗