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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Effects of thermal cycling on residual mechanical properties of C6000/PMR-15 graphite polyimide

An experimental study to determine the effects of thermal cycling on residual mechanical properties of a graphite/polyimide composite has been conducted. Interlaminar shear, flexure and compression strengths were measured at room temperature and 316 C on unidirectional and quasi-isotropic laminates subjected to 150 and 500 thermal cycles between -156 C and 316 C. Thermal cycling produced transverse microcracks and delaminations in the laminates. The linear density of the microcracks (35/cm) was about the same after 150 and 500 cycles. Although the crack density did not change from 150 to 500 cycles, crack growth did occur with intralamina cracks growing into adjacent lamina. The matrix controlled properties of the quasi-isotropic laminate at both room temperature and 316 C were significantly reduced by thermal cycling. However, the properties of the unidirectional laminate were significantly reduced only at 316 C.

Tompkins, S. S.↗
NASA NTRS1982

Kevlar/PMR-15 polyimide matrix composite for a complex shaped DC-9 drag reduction fairing

The Aircraft Energy Efficiency (ACEE) Program was established by NASA to improve the fuel efficiency of commercial transport aircraft and thereby to reduce the amount of fuel consumed by the air transportation industry. One of the final items developed by the program is an improved fairing which is the aft closure for the thrust reverser actuators on the JT8D nacelles on DC-9 aircraft. The reduced-drag fairing uses, in the interest of weight savings, an advanced composite construction. The composite material contains Kevlar 49 fibers in a PMR-15 matrix. Attention is given to the aerodynamic configuration, the material system, and aspects of fabrication development.

Kawai, R. T.↗
NASA NTRS1984

Elastomer-Modified Polyimides

New resins yield laminates with improved mechanical properties. Ingredients of Modified Polymer include bisimide of formula 1 and amine-terminated elastomer. Cure effected by heating to temperature suited to particular ingredients used, generally in range of 200 degrees to 300 degrees C. Solution of solvent and reactants used for fabricating fiber-reinforced structures or as adhesive.

Fohlen, G. M.↗
NASA NTRS1982

Lower-curing-temperature PMR polyimides

Partial substitution of a p-aminostyrene end-cap for the monomethyl ester of 5-norbornene-2, 3-dicarboxylic acid lowered the final cure temperature of typical PMR resins from 600 F to 500 F. The weight loss characteristics of neat resins and graphite fiber composites prepared by using the mixed end-cap approach were determined at 600 F. The room temperature and short-time elevated temperature mechanical properties of the composites at 550 F and 600 F were determined. The mechanical property retention characteristics of the composites at 550 F and 600 F are discussed.

Delvigs, P.↗
NASA NTRS1982

Surface characterization and failure analysis of thermally aged, polyimide bonded titanium

This study of high temperature stable adhesive systems using 6Al-4V titanium adherends found that certain adhesive/adherends exhibit a change from cohesive to adhesive failure mode during long term 450 F thermal aging. Lap-shear specimens which exhibited adhesive failures were subjected to failure analysis using scanning transmission electron microscopy (STEM) and surface analysis techniques. Data is presented which supports the conclusion of interfacial failures for these samples.

Peters, P. D.↗
NASA NTRS1983

Dynamic mechanical characterization of cure of a polyimide-graphite fiber composite (PMR 15/Celion 6000)

Dynamic mechanical studies of thermosetting PMR 15 polyimide/Celion 6000 composites were used to characterize cure behavior. Variation in composite shear modulus with cure time for laminates partially cured under 3.45 MPa pressure was compared with that of laminates fully cured under pressure to select a partially cured system whose behavior corresponded with that of the pressure-cured composites. An empirical kinetic model was developed that relates relative composite shear moduli to cure time and temperature. This model, coupled with standard statistical techniques, was used in the determination of an overall activation energy, E = 145 kj/mole (35 kcal/mole) and order of reaction, n, for the cure reaction(s). The empirical relationship defining dynamic modulus as a function of time and temperature remained linear well into the glassy region. Changes in dynamic glass-transition temperature and in the breadth of the transition peaks with cure time are discussed. Shear modulus and damping were found to be more sensitive measures of relative extent of cure than Fourier transform infrared spectroscopy.

Hurwitz, F. I.↗
NASA NTRS1982

Environmental effects on graphite fiber reinforced PMR-15 polyimide

Studies were conducted to establish the effects of thermo-oxidative and hydrothermal exposure on the mechanical properties of T300 graphite fabric reinforced PMR-15 composites. The effects of hydrothermal exposure on the mechanical properties of HTS-2 continuous graphite fiber composites were also investigated. The thermo-oxidative stability characteristics of T300 fabric and T300 fabric/PMR-15 composites were determined. Flexural strengths of specimens were determined. The useful lifetime of T300 fabric/PMR-15 composites in air at 316 C was found to be about 100 hours. The useful lifetimes in air at 228 and 260 C were determined to be 500 and 1000 hours, respectively. Absorbed moisture was found to reduce the elevated temperature properties of both the T300 fabricate and HTS-2 continuous fiber composites. The moisture effect was found to be reversible. Previously announced in STAR as N81-32194

Serafini, T. T.↗
NASA NTRS1983

Lower-curing-temperature PMR polyimides

Partial substitution of a p-aminostyrene end-cap for the monomethyl ester of 5-norbornene-2, 3-dicarboxylic acid lowered the final cure temperature of typical PMR resins from 600 F to 500 F. The weight loss characteristics of neat resins and graphite fiber composites prepared by using the mixed end-cap approach were determined at 600 F. The room temperature and short-time elevated temperature mechanical properties of the composites at 550 F and 600 F were determined. The mechanical property retention characteristics of the composites at 550 F and 600 F are discussed. Previously announced in STAR as N83-10118

Delvigs, P.↗
NASA NTRS1984

Characterization of PMR polyimide resin and prepreg

Procedures for the chemical characterization of PMR-15 resin solutions and graphite-reinforced prepregs were developed, and a chemical data base was established. In addition, a basic understanding of PMR-15 resin chemistry was gained; this was translated into effective processing procedures for the production of high quality graphite composites. During the program the PMR monomers and selected model compounds representative of postulated PMR-15 solution chemistry were acquired and characterized. Based on these data, a baseline PMR-15 resin was formulated and evaluated for processing characteristics and composite properties. Commercially available PMR-15 resins were then obtained and chemically characterized. Composite panels were fabricated and evaluated.

Lindenmeyer, P. H.↗
NASA NTRS1984

An investigation into the injection molding of PMR-15 polyimide

The chemorheological behavior of the PRM-15 molding compounds were characterized, the range of suitable processing parameters for injection molding in a reciprocating screw injection molding machine was determined, and the effects of the injection molding processing parameters on the mechanical properties of molded PMR-15 parts were studied. The apparatus and procedures for measuring viscosity and for determining the physical response of the material during heating are described. Results show that capillary rheometry can be effectively used with thermosets if the equipment is designed to overcome some of the inherent problems of these materials. A uniform temperature was provided in the barrel by using a circulating hot oil system. Standard capillary rheometry methods can provide the dependence of thermoset apparent viscosity on shear rate, temperature, and time. Process conditions resulting in complete imidization should be carefully defined. Specification of controlled oven temperature is inadequate and can result in incomplete imidization. For completely imidized PMR-15 heat at 15 C/min melt flow without gas evolution occurs in the temperature range of 325 C to 400 C.

Colaluca, M. A.↗
NASA NTRS1984

Preparation and characterization of siloxane-containing thermoplastic polyimides

Copolyimides and homopolyimides of bis(gamma-aminopropyl)tetramethyldisiloxane and 3,3'-diaminobenzophenone have been prepared with benzophenonetetracarboxylic dianhydride. The properties of the copolyimides were compared with those of the homopolyimides to assess the effect of incorporation of siloxane groups in the backbone. Applications of the polymers as adhesives and mouldings are discussed.

Maudgal, S.↗
NASA NTRS1985

Effect of substituted phenylnadimides on processing and properties of PMR polyimide composites

Three nitrophenylnadimide cure initiators and two phenylnadimides (without nitros) were evaluated as additives to PMR-15 resins and Celion 6000 graphite fiber composites. The results of a resin screening study eliminated all of the additives except 3-nitrophenylnadimide (NO2PN) for use as a low temperature curing additive for PMR-15. Thus, NO2PN and the two control additives were investigated in PMR-15 formulations from which Celion 6000 graphite fiber/PMR-15 composites were processed both with low temperature (274 C) and normal (316 C) cure cycles. Comparisons of the two processing cycles, the resultant glass transition temperatures (Tg), the ambient, 274 and 316 C composite mechanical properties determined before and after 316 C postcure, the 316 C thermo-oxidative weight losses and the retention of 316 C composite mechanical properties are presented. Empirical correlations of the type and amount of nadimide additives with processing parameters, Tg, composite mechanical properties, composite thermo-oxidative stability and long term retention of 316 C composite mechanical properties are also presented.

Alston, W. B.↗
NASA NTRS1984

Polyimides containing oxyethylene units. II - Polymerization of 3.3', 4.4'-benzophenonetetra carboxylic dianhydride and pyromellitic dianhydride

The study is concerned with the polymerization of diamines 2a-d with readily available dianhydrides, i.e., 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA). The synthesis and polymerization of asymmetric diamines containing substituted alkylene ether linkages are also investigated. It is assumed that the flexibility introduced into the polymer chain through the use of such diamines would result in moderate glass transition temperatures that would allow the systems to be melt processed. Mixtures of diamines are also copolymerized so as to further disrupt the polymer's symmetry and recurrence regularity. The properties of the resulting polymers are briefly discussed.

Harris, F. W.↗
NASA NTRS1986

Polyimide of Modified Melt Flow and Toughness

Linear aromatic polyphenylene ether sulfideimide (BDSDA/APB) polymer molded, used as resin, and cast into thin films. In effort to improve further both use properties and amenability to process BDSDA/APB, molecular weight of polymer varied by variations in percentage of end capping. Effect of end capping BDSDA/APB determined by measurement of polymer melt viscosity and fracture-energy values for different number average synthesized molecular weights.

St. Clair, T. L.↗
NASA NTRS1985

Evaluation of a high temperature adhesive for fabricating graphite/PMR-15 polyimide structures

Tests are conducted to measure shear strength, shear modulus and flatwise tensile strength of the A7F (amide-imide modified LARC-13) adhesive system. An investigation is also conducted to determine the effect of geometric material parameters, and elevated temperature on the static strength of standard joints. Single-lap and double-lap composite joints, and single, double and step lap composite to metal joints are characterized. A series of advanced joints consisting of preformed adherends, adherends with scalloped edges and joints with hybrid interface plies are tested and compared to baseline single and double-lap designs.

Hill, S. G.↗