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  • 1
    facet.materialart.
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    Development of polyisocyanurate pour foam formulation for space shuttle external tank thermal protection system (1988)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Four commercially available polyisocyanurate polyurethane spray-foam insulation formulations are used to coat the external tank of the space shuttle. There are several problems associated with these formulations. For example, some do not perform well as pourable closeout/repair systems. Some do not perform well at cryogenic temperatures (poor adhesion to aluminum at liquid nitrogen temperatures). Their thermal stability at elevated temperatures is not adequate. A major defect in all the systems is the lack of detailed chemical information. The formulations are simply supplied to NASA and Martin Marietta, the primary contractor, as components; Part A (isocyanate) and Part B (poly(s) and additives). Because of the lack of chemical information the performance behavior data for the current system, NASA sought the development of a non-proprietary room temperature curable foam insulation. Requirements for the developed system were that it should exhibit equal or better thermal stability both at elevated and cryogenic temperatures with better adhesion to aluminum as compared to the current system. Several formulations were developed that met these requirements, i.e., thermal stability, good pourability, and good bonding to aluminum.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-CR-183511 , NAS 1.26:183511 , UDR-TR-88-96
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
    facet.materialart.
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    Pourable Foam Insulation (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Report describes search for polyisocyanurate/polyurethane foam insulation with superior characteristics. Discusses chemistry of current formulations. Tests of formulations, of individual ingredients and or alternative new formulations described. Search revealed commercially available formulations exhibiting increased thermal stability at temperatures up to 600 degree C, pours readily before curing, presents good appearance after curing, and remains securely bonded to aluminum at cryogenic temperatures. Total of 42 different formulations investigated, 10 found to meet requirements.
    Keywords: MATERIALS
    Type: MFS-27217 , NASA Tech Briefs (ISSN 0145-319X); 13; 10; P. 52
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
    Electronic Resource
    Electronic Resource
    Development of a curved layer LOM process for monolithic ceramics and ceramic matrix composites (1999)
    Bingley : Emerald
    Rapid prototyping journal 5 (1999), S. 61-71 
    Details
    ISSN: 1355-2546
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A novel rapid prototyping technology incorporating a curved layer building style was developed. The new process, based on laminated object manufacturing (LOM), was designed for efficient fabrication of curved layer structures made from ceramics and fiber reinforced composites. A new LOM machine was created, referred to as curved layer LOM. This new machine uses ceramic tapes and fiber prepregs as feedstocks and fabricates curved structures on a curved-layer by curved-layer basis. The output of the process is a three-dimensional "green" ceramic that is capable of being processed to a seamless, fully dense ceramic using traditional techniques. A detailed description is made of the necessary software and hardware for this new process. Also reviewed is the development of ceramic preforms and accompanying process technology for net shape ceramic fabrication. Monolithic ceramic (SiC) and ceramic matrix composite (SiC/SiC) articles were fabricated using both the flat layer and curved layer LOM processes. For making curved layer objects, the curved process afforded the advantages of eliminated stair step effect, increased build speed, reduced waste, reduced need for decubing, and maintenance of continuous fibers in the direction of curvature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/13552549910267362
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Viscoelastic properties of branched polyethylene melts (1970)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 455-465 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dynamic mechanical properties of branched polyethylenes in the molten state were determined in the frequency range 10-3-10 radians/sec. The materials tested have remarkably similar rheological properties even though they vary greatly in molecular weight and molecular weight distribution. The similarity in properties is attributed to the influence of long chain branching on the relaxation spectra. A mechanistic argument is proposed to relate the observed behavior to molecular entanglement coupling. The concept of entanglement coupling involving long-chain branching leads to the expectation that the quasi-Newtonian and non-Newtonian viscosities of branched polymers may be either greater or less than those of linear polymers of the same species, which have comparable molecular weights. This is borne out by experiment.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1970.160080311
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  • 5
    Electronic Resource
    Electronic Resource
    Toughening of unsaturated polyester and vinyl ester resins with liquid rubbers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1086-1097 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A comprehensive study of toughening unsaturated polyster and vinyl ester resins by addition of liquid rubbers was carried out by considering the effects of cure temperature and gel time on final resin/rubber morphology. The objective was to produce a dispersed rubber phase consisting of particles less than 15 μm in diameter with the addition of limited amounts of rubber, so as not to seriously reduce the modulus and strength of the base resin. A variety of liquid rubbers was used including those based on poly(butadiene acrylonitrile), poly(epichlorohydrin), and two poly(acrylates). Fracture toughness of unmodified and rubber modified materials was measured using the compact tension (CT) test geometry. Significant improvements in fracture toughness were achieved with little to no change in Young's modulus or glass transition temperature. With modest rubber additions, the fracture toughness increased up to 62% for the polyester resin and up to 116% for the vinyl ester resin. In general, fracture toughness increases with increases in volume fraction of rubbery second-phase particles. However, results suggest that two-phase particles may be more effective tougheners than single-phase particles. The toughening mechanism appears to depend on the type of rubbery particle morphology present.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760351304
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  • 6
    Electronic Resource
    Electronic Resource
    A process model for nonisothermal photopolymerization with a laser light source. I: Basic model development (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 483-492 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical model for a laser-induced photopolymerization process has been developed. This model simulates important aspects of stereolithography, a rapid prototyping process used for the production of three-dimensional plastic parts. The model consists of a set of coupled partial differential equations and considers irradiation, chemical reaction, and heat transfer in a small zone of material exposed to a stationary UV laser source. Numerical techniques are used for an approximate solution of the model equations, and the output includes spatial and temporal variations in the conversion of monomer to polymer, depletion of photoinitiator, and local variations of temperature in and around the region contacted by the laser light. Maximum conversions of approximately 60% and peak temperature rises of approximately 35° C were calculated for the cylindrical exposed region. Results have provided insights concerning laser dwell time, depth penetration, and the uniformity of polymer formed during the stereolithography process.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350605
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  • 7
    Electronic Resource
    Electronic Resource
    A process model for nonisothermal photopolymerization with a laser light source. II: Behavior in the vicinity of a moving exposed region (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 493-498 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical process model that stimulates important aspects of stereolithography, a rapid prototyping technique used for the production of three-dimensional plastic parts, has been developed. The model consists of a set of coupled partial differential equations and considers irradiation, chemical reaction, and heat transfer in a vat of photomonomer exposed to a moving UV laser source. Laser motion occurs in a straight line (vector path), and the model thus simulates the production of a single strand of plastic. Numerical techniques are used for approximate solution of the model equations, and output includes spatial and temporal variations in conversion of monomer to polymer, depletion of photoinitiator, and variations of temperature along the line of exposed material. The formation of a temperature wave that moves along the line of plastic is observed, together with the fact that the leading edge of the wave is steeper than the trailing edge, i.e., the material heats considerably faster than it cools. The maximum temperature of the wave reaches a pseudo-steady state after a short time. The results have provided useful information concerning the temperature at which the majority of the polymerization occurs; provided information on overall transient temperature behavior; allowed computer prediction of stereolithography working curves (cure depth and cure width vs. laser scan rate); and afforded a means for evaluating the amount of reaction that occurs in the dark period after light exposure.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350606
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamic mechanical properties of polymer melts: The effect of molecular weight distribution on the temperature dependence of viscoelastic properties (1968)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 8 (1968), S. 126-129 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An experimental investigation of the dynamic mechanical response of molten polymers was performed using the Maxwell Orthogonal Reheometer. One purpose of the study was to evaluate the effect of molecular weight distribution on the temperature dependence of viscoelastic properties. Data were obtained over a range of temperatures for both monodisperse and polydisperse materials which indicate that viscoelasticity is highly temperature dependent only for monodisperse polymers. On a molecular basis the reduction in temperature sensitivity for polydisperse materials logically can be attributed to the influence of the low molecular weight species present in a distribution on the relaxation spectrum. Since the relaxation spectrum largely determines all viscoelastic functions, the observations made from th dynamic data shown in this paper can be generalized to all viscoelastic experiments.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760080208
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  • 9
    Electronic Resource
    Electronic Resource
    A study of crosslinking in polyimides by viscoelastic and diffusion techniques (1980)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 244-251 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper is concerned with detecting crosslinking and changes in crosslink densities in cured polyimides. The methods used include diffusional weight gain and dynamic mechanical measurements on thin films of the cured polymers. In this study changes in diffusivities (D) for dimethylformamide (DMF) sorption into polyimide films as well as dynamic mechanical moduli and loss tangents are shown to be related to differences in polyimide cure schedule and composition. In all cases studied there is a β loss dispersion in the range 120 to 150°C and a γ loss dispersion in the range -50 to -80°C. The position and intensity of the β and γ relaxation processes vary primarily with cure cycle. There is a significant correlation between the magnitude of the diffusion coefficient and β and γ transition temperatures (Tβ and Tγ). Tβ increases and Tγ decreases with higher values of D so that T*, the difference Tβ - Tγ, is directly proportional to the diffusivity. By relating these results to data in the literature and the known curing behavior of polyimides, this trend is shown to be consistent with the presence of crosslinking and to be related to the crosslink density of the polymers. The data of this study indicate that measurements of diffusion coefficients for solvent sorption can be used to study changes in crosslink densities in glassy thermosetting polymers. Since the method is best suited for studying one dimensional diffusion, it also is suggested as a possibility for determining relative crosslink densities in adhesives bonded between substrates.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760200404
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  • 10
    Electronic Resource
    Electronic Resource
    Morphology and mechanical properties of rubber modified aromatic-ether bismaleimide matrix resins (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 563-566 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An aromatic ether bismaleimide (BMI) was modified by copolymerization with various CTBN and ATBN liquid elastomers. Dynamic mechanical (DMA), flexural, and SEM fractography studies indicate that cured specimens containing various amounts of the different elastomers have widely varying morphologies and properties. The experimental parameters of interest in this study included the type of elastomer reactive end group, elastomer acrylonitrile content, elastomer concentration, and cure reaction conditions. The ATBNs are clearly more compatible than CTBNs. CTBN modified compositions show a distinct, low temperature rubber phase mechanical loss dispersion, reduced modulus and ultimate strength values, and only slight improvements in elongation. Cured compositions with small amounts of ATBN elastomers (5 phr), however, show no reduction in modulus but improved elongation and ultimate strength values. The “rubber” domains in these systems are small, typically 〈 5 μm, and consist of copolymerized BMI and elastomer. DMA data for these systems show no distinct low temperature elastomer peak but a broad “interphase” loss dispersion covering a wide range of temperatures. Failure in the ATBN modified BMIs involves initiation of numerous microcracks with obvious crack deflection at the rubber particles. No cavitation of rubber particles occurs, as is frequently the case with the CTBNs.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760310805
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