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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Electrostatic prepregging of thermoplastic matrices

Thermoplastic towpregs of PEEK/AS-4, PEEK/S-2 glass and LaRC-TPI/AS-4, produced by electrostatic deposition of charged and fluidized polymer powders on spread continuous fiber tows, are described. Processing parameters for combining PEEK 150 powder with unsized 3k AS-4 carbon fiber are presented. The experimental results for PEEK 150/AS-4 reveal that electrostatic fluidized bed coating may be an economically attractive process for producing towpreg.

Muzzy, John D.↗
NASA NTRS1990

LARC-I-TPI: A New Thermoplastic Polyimide

"LARC-I-TPI" denotes improved version of LARC-TPI class of thermoplastic polyimides: high-performance polymers developed for manufacture of strong, lightweight aircraft structures. Melt-flow and adhesive properties of new polymers make them attractive for use as matrix resins for composites, molding powders, adhesives, and coating films. Less toxic, improved LARC-I-TPI polymers formulated without 3, 3'-diaminobenzophenone, which is mutagenic and commercially unavailable.

St. Clair, Terry L.↗
NASA NTRS1989

Orthotropic elasto-plastic behavior of AS4/APC-2 thermoplastic composite in compression

Uniaxial compression tests were performed on off-axis coupon specimens of unidirectional AS4/APC-2 thermoplastic composite at various temperatures. The elasto-plastic and strength properties of AS4/APC-2 composite were characterized with respect to temperature variation by using a one-parameter orthotropic plasticity model and a one-parameter failure criterion. Experimental results show that the orthotropic plastic behavior can be characterized quite well using the plasticity model, and the matrix-dominant compressive strengths can be predicted very accurately by the one-parameter failure criterion.

Sun, C. T.↗
NASA NTRS1990

Dissipation of mechanical work and temperature rise in AS4/PEEK thermoplastic composite

The dissipated mechanical work per cycle of sinusoidal stress in the thermoplastic composite material AS4/PEEK was measured as a function of stress amplitude for fixed frequency and fiber orientation. The experimental result shows that the dissipated work per cycle is proportional to the square of the stress amplitude. Using the concept of the equivalent isotropic material, it is shown that the relaxation modulus satisfies a proportionality condition. Also, the rate of temperature rise due to sinusoidal stresses has been measured as a function of stress amplitude. The result shows that the rate of temperature rise is not proportional to the square of the stress amplitude.

Georgiou, I.↗
NASA NTRS1990

A constitutive model for AS4/PEEK thermoplastic composites under cyclic loading

Based on the basic and essential features of the elastic-plastic response of the AS4/PEEK thermoplastic composite subjected to off-axis cyclic loadings, a simple rate-independent constitutive model is proposed to describe the orthotropic material behavior for cyclic loadings. A one-parameter memory surface is introduced to distinguish the virgin deformation and the subsequent deformation process and to characterize the loading range effect. Cyclic softening is characterized by the change of generalized plastic modulus. By the vanishing yield surface assumption, a yield criterion is not needed and it is not necessary to consider loading and unloading separately. The model is compared with experimental results and good agreement is obtained.

Rui, Yuting↗
NASA NTRS1989

Low dielectric thermoplastic polyimide resin

NASA-Langley studies of polymer structure-property relationships have led to the development of a method for the reduction of dielectric constants in polyimides through chemical alterations of polymer backbone composition to reduce chain-chain electronic interactions, as well as through the incorporation of fluorine atoms into the polymer molecular structure. Still-greater dielectric constant reductions are obtainable by means of a physical incorporation of diamic acid additives into these low-dielectric polyimide systems; the resulting thermoplastic resins are applicable to polymer matrices for composite structural materials.

Stoakley, D. M.↗
NASA NTRS1989

Thermoplastic matrix composites - Finite-element analysis of mode I and mode II failure specimens

A finite-element analysis was conducted to evaluate the stress distributions within mode I and mode II failure specimens, assuming both isotropic and orthotropic elastic material properties. The effects of anisotropy on both the magnitude and the location of the highest stress concentration at the vicinity of the crack tip are significant. The results from modeling realistic blunt crack tip geometry and resin-rich zones imply that local variations in the microstructure strongly influence the stress state near the crack tip and therefore the measured fracture properties. In addition, the features of a viscoelastic model for thermoplastic matrices are described. This model will be used in future investigations of matrix-dominated failure phenomena.

Bankert, Ray J.↗
NASA NTRS1990

Elastic/viscoplastic behavior of fiber-reinforced thermoplastic composites

An elastic/viscoplastic constitutive model was used to characterize the nonlinear and rate dependent behavior of a continuous fiber-reinforced thermoplastic composite. This model was incorporated into a finite element program for the analysis of laminated plates and shells. Details on the finite element formulation with the proposed constitutive model were presented. The numerical results were compared with experimental data for uniaxial tension and three-point bending tests of (+ or - 45 deg)3s APC-2 laminates.

Wang, C.↗
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.↗