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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
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 NTRS1990

Thermoplastic polyimide NEW-TPI (trademark)

Thermal and rheological properties of a commercial thermoplastic polyimide, NEW-TPI (trademark), were characterized. The as-received material possesses initially a transient crystallite form with a bimodal distribution in peak melting temperatures. After the melting of the initial crystallite structure, the sample can be recrystallized by various thermal treatments. A bimodal or single modal melting peak distribution is formed for annealing temperatures below or above 360 C, respectively. The recrystallized crystallinities are all transient in nature. The polymers are unable to be recrystallized after being subjected to elevated temperature annealing above 450 C. The recrystallization mechanism was postulated, and a simple kinetics model was found to describe the behavior rather satisfactory under the conditions of prolonged thermal annealing. Rheological measurements made in the linear viscoelastic range support the evidence observed in the thermal analysis. Furthermore, the measurements sustain the manufacturer's recommended processing window of 400 to 420 C for this material.

Hou, Tan-Hung↗
NASA NTRS1990

LaRC-I-TPI - A status report on a new high performance, thermoplastic polyimide

A new thermoplastic polyimide designated LaRC-I-TPI has been prepared from 4,4'-isophthaloyldiphthalic anhydride (IDPA) and 1,3-phenylenediamine (m-PDA), phthalic anhydride endcapped or unendcapped. It is closely related to the well-known commercial LaRC-TPI. A survey of the synthesis and some thermal, film, adhesive, fracture toughness, and composite properties of this new polyimide is presented. While both materials have similar properties at comparable stages of development, LaRC-I-TPI should be less expensive to manufacture as a result of the use of lower cost readily available monomers.

Pratt, J. Richard↗
NASA NTRS1991

Characterization of thermoplastic polyimide NEW-TPI

Thermal and rheological properties of a commercial thermoplastic polyimide, NEW-TPI, were characterized. The as-received material possesses initially a transient crystallite form with a bimodal distribution in peak melting temperatures. After the meltings of the initial crystallite structures, the sample can be recrystallized by various thermal treatments. A bimodal or single-modal melting peak distribution is formed for annealing temperatures below or above 360 C, respectively. The recrystallized crystallinities are all transient in nature. The polymers are unable to be recrystallized after being subjected to elevated temperature annealing above 450 C. The recrystallization mechanism was postulated, and a simple kinetics model was found to describe the behavior satisfactorily under conditions of prolonged thermal annealing.

Hou, T. H.↗
NASA NTRS1991

Elastic/viscoplastic constitutive model for fiber reinforced thermoplastic composites

A constitutive model to describe the elastic/viscoplastic behavior of fiber-reinforced thermoplastic composites under plane stress conditions is presented. Formulations are given for quasi-static plasticity and time-dependent viscoplasticity. Experimental procedures required to generate the necessary material constants are explained, and the experimental data is compared to the predicted behavior.

Gates, T. S.↗
NASA NTRS1989

Nonlinear mechanical behavior of thermoplastic matrix materials for advanced composites

Two recent theories of nonlinear mechanical response are quantitatively compared and related to experimental data. Computer techniques are formulated to handle the numerical integration and iterative procedures needed to solve the associated sets of coupled nonlinear differential equations. Problems encountered during these formulations are discussed and some open questions described. Bearing in mind these cautions, the consequences of changing parameters that appear in the formulations on the resulting engineering properties are discussed. Hence, engineering approaches to the analysis of thermoplastic matrix material can be suggested.

Arenz, R. J.↗
NASA NTRS1989

Orthotropic elastic-plastic behavior of AS4/APC-2 thermoplastic composite at elevated temperatures

Inelastic and strength properties of AS4/APC-2 composites were characterized with respect to temperature variation by using a one parameter orthotropic plasticity model and a one parameter failure criterion. Simple uniaxial off-axis tension tests were performed on coupon specimens of unidirectional AS4/APC-2 thermoplastic composite at various temperatures. To avoid the complication caused by the extension-shear coupling effect in off-axis testing, new tabs were designed and used on the test specimens. The experimental results showed that the nonlinear behavior of constitutive relations and the strength can be characterized quite well using the one parameter plasticity model and the failure criterion, respectively.

Sun, C. T.↗
NASA NTRS1992

Properties Of High-Performance Thermoplastics

Report presents review of principal thermoplastics (TP's) used to fabricate high-performance composites. Sixteen principal TP's considered as candidates for fabrication of high-performance composites presented along with names of suppliers, Tg, Tm (for semicrystalline polymers), and approximate maximum processing temperatures.

Johnston, Norman J.↗
NASA NTRS1992

Tough, high performance, addition-type thermoplastic polymers

A tough, high performance polyimide is provided by reacting a triple bond conjugated with an aromatic ring in a bisethynyl compound with the active double bond in a compound containing a double bond activated toward the formation of a Diels-Adler type adduct, especially a bismaleimide, a biscitraconimide, or a benzoquinone, or mixtures thereof. Addition curing of this product produces a high linear polymeric structure and heat treating the highly linear polymeric structure produces a thermally stable aromatic addition-type thermoplastic polyimide, which finds utility in the preparation of molding compounds, adhesive compositions, and polymer matrix composites.

Pater, Ruth H.↗
NASA NTRS1990

Development of thermoplastic components for structural validation

Recent activity directed toward advancing the development and validation of graphite reinforced thermoplastic primary and secondary structures is described. The efforts discussed include the design, manufacture and test of a highly-loaded multi-spar wing-box component, and the development of a flight-worthy article that is form, fit and functionally replaceable with the nose landing gear door of the V-22 Osprey.

Avery, John G.↗
NASA NTRS1992

Continuation of tailored composite structures of ordered staple thermoplastic material

The search for the cost effective composite structure has motivated the investigation of several approaches to develop composite structure from innovative material forms. Among the promising approaches is the conversion of a planar sheet to components of complex curvature through sheet forming or stretch forming. In both cases, the potential for material stretch in the fiber direction appears to offer a clear advantage in formability over continuous fiber systems. A framework was established which allows the simulation of the anisotropic mechanisms of deformation of long discontinuous fiber laminates wherein the matrix phase is a viscous fluid. Predictions for the effective viscosities of a hyper-anisotropic medium consisting of collimated, discontinuous fibers suspended in viscous matrix were extended to capture the characteristics of typical polymers including non-Newtonian behavior and temperature dependence. In addition, the influence of fiber misorientation was also modeled by compliance averaging to determine ensemble properties for a given orientation distribution. A design tool is presented for predicting the effect of material heterogeneity on the performance of curved composite beams such as those used in aircraft fuselage structures. Material heterogeneity can be induced during manufacturing processes such as sheet forming and stretch forming of thermoplastic composites. This heterogeneity can be introduced in the form of fiber realignment and spreading during the manufacturing process causing radial and tangential gradients in material properties. Two analysis procedures are used to solve the beam problems. The first method uses separate two-dimensional elasticity solutions for the stresses in the flange and web sections of the beam. The separate solutions are coupled by requiring that forces and displacements match section boundaries. The second method uses an approximate Rayleigh-Ritz technique to find the solutions for more complex beams. Analyses are performed for curved beams of various cross-sections loaded in pure bending and with a uniform distributed load. Preliminary results show that the geometry of the beam dictates the effect of heterogeneity on performance. The role of heterogeneity is larger in beams with a small average radius-to-depth ration, R/t, where R is the average radius of the beam and t is the difference between the inside and outside radii. Results of the anlysis are in the form of stresses and displacements and are compared to both mechanics of materials and numerical solutions obtained using finite element analysis.

Santare, Michael H.↗
NASA NTRS1991

Emerging polyheterocyclic films, coatings and resins - Thermoplastic polyquinolines

The processing and performance characteristics of a soluble, thermoplastic polyquinoline suggest its utility in a variety of high performance applications. The polymer is characterized by excellent thermal and oxidative stability, very low moisture absorption, good mechanical properties, very low dielectric constant, and an unusually low thermal expansion coefficient. This polymer, designated PQ-100 (TM), can be cast into strong, transparent, free standing films from common solvents. Coatings of variable thickness can be spin-coated on to silicon and other surfaces. After processing into films, PQ-100 (TM) can be rendered insoluble in a wide range of solvents using a proprietary process. The low CTE contributes to very low residual stress when the polymer is spin-coated onto silicon wafers. PQ-100 (TM) is currently under evaluation for use as an interlayer dielectric substrate in high-density interconnect applications, including multichip modules. Many of the characteristics of the polymer also suggest its utility as a high-performance film and as a matrix resin for specialty composite applications.

Hendricks, Neil H.↗
NASA NTRS1991

High performance addition-type thermoplastics (ATTs) - Evidence for the formation of a Diels-Alder adduct in the reaction of an acetylene-terminated material and a bismaleimide

Recently, the concept and demonstration of a new versatile synthetic reaction for making a large number of high-performance addition-type thermoplastics (ATTs) were reported. The synthesis shows promise for providing polymers having an attractive combination of easy processability, good toughness, respectable high temperature mechanical performance, and excellent thermo-oxidative stability. The new chemistry involves the reaction of an acetylene-terminated material with a bismaleimide or benzoquinone. In order to clarify the reaction mechanism, model compound studies were undertaken in solutions as well as in the solid state. The reaction products were purified by flash chromatography and characterized by conventional analytical techniques including NMR, FT-IR, UV-visible, mass spectroscopy, and high pressure liquid chromatography. The results are presented of the model compound studies which strongly support the formation of a Diels-Alder adduct in the reaction of an acetylene-terminated compound and a bismaleimide or benzoquinone.

Pater, R. H.↗
NASA NTRS1991

Characterization of elastic-plastic behavior of AS4/PEEK thermoplastic composite for temperature variation

Inelastic and strength properties of AS4/PEEK composites were characterized with respect to temperature variation by using a one-parameter orthotropic plasticity model and a one-parameter failure criterion. Simple uniaxial off-axis tension tests were performed on coupon specimens of unidirectional AS4/PEEK thermoplastic composite at various temperatures. To avoid the complication caused by the extension-shear coupling effect in off-axis testing, new tabs were designed and used on the test specimens. Experimental results showed that the nonlinear behavior of constitutive relations and the strength can be characterized quite well using the one-parameter plasticity model and the failure criterion, respectively.

Sun, C. T.↗
NASA NTRS1990

Nonlinear analysis of AS4/PEEK thermoplastic composite laminate using a one parameter plasticity model

A one-parameter plasticity model was shown to adequately describe the orthotropic plastic deformation of AS4/PEEK (APC-2) unidirectional thermoplastic composite. This model was verified further for unidirectional and laminated composite panels with and without a hole. The nonlinear stress-strain relations were measured and compared with those predicted by the finite element analysis using the one-parameter elastic-plastic constitutive model. The results show that the one-parameter orthotropic plasticity model is suitable for the analysis of elastic-plastic deformation of AS4/PEEK composite laminates.

Sun, C. T.↗
NASA NTRS1992

The development of an alternative thermoplastic powder prepregging technique

An alternative powder prepregging technique is discussed that is based on the deposition of powder onto carbon fibers that have been moistened using an ultrasonic humidifier. The dry fiber tow is initially spread to allow a greater amount of the fiber surface to be exposed to the powder, thus ensuring a significant amount of intimate contact between the fiber and the matrix. Moisture in the form of ultrafine water droplets is then deposited onto the spread fiber tow. The moisture promotes adhesion to the fiber until the powder can be tacked to the fibers by melting. Powdered resin is then sieved onto the fibers and then tacked onto the fibers by quick heating in a convective oven. This study focuses on the production of prepregs and laminates made with LaRC-TPI (thermoplastic polyimide) using this process. Although the process appears to be successful, early evaluation was hampered by poor interfacial adhesion. The adhesion problem, however, seems to be the result of a material system incompatibility, rather than being influenced by the process.

Ogden, A. L.↗
NASA NTRS1993

Portable Device Slices Thermoplastic Prepregs

Prepreg slitter designed to slit various widths rapidly by use of slicing bar holding several blades, each capable of slicing strip of preset width in single pass. Produces material evenly sliced and does not contain jagged edges. Used for various applications in such batch processes involving composite materials as press molding and autoclaving, and in such continuous processes as pultrusion. Useful to all manufacturers of thermoplastic composites, and in slicing B-staged thermoset composites.

Taylor, Beverly A.↗