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  • 1
    Electronic Resource
    Electronic Resource
    Hydrolytic degradation mechanism of Kevlar 49 fibers when dissolved in sulfuric acid (1992)
    Springer
    Polymer bulletin 27 (1992), S. 689-696 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The hydrolytic degradation of Kevlar 49 fibers when dissolved in H2SO4 is characterized from (i) Fourier transform infrared (FTIR), CNH analyses and optical microscopy studies of insoluble crystals formed in the PPTA-H2SO4 dope and (ii) the rates of H2SO4-catalyzed hydrolysis of model compound aromatic amides. After hydrolysis of a PPTA amide linkage, the amide linkage adjacent to the freshly formed-COOH macromolecular end group rapidly hydrolyses resulting in the formation of terephthalic acid which then forms insoluble crystals in the PPTA-H2SO4 dope.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297440
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  • 2
    Electronic Resource
    Electronic Resource
    The microscopic failure processes and their relation to the structure of amine-cured bisphenol-A-diglycidyl ether epoxies (1977)
    Springer
    Journal of materials science 12 (1977), S. 1966-1980 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Electron and optical microscopy are used to study the relation between the structure and the microscopic flow and failure processes of diethylene triamine-cured bisphenol-A-diglycidyl ether epoxies. By straining films directly in the electron microscope, these epoxies are found to consist of 6 to 9 nm diameter particles which remain intact when flow occurs. It is suggested that these particles are intramolecularly crosslinked molecular domains which can interconnect to form larger network morphological entities. Epoxy films, either strained directly in the electron microscope or strained on a metal substrate, deform and fail by a crazing process. The flow processes that occur during deformation are dependent on the network morphology in which regions of either high or low crosslink density are the continuous phase. The fracture topographies of the epoxies are interpreted in terms of a crazing process. The coarse fracture topography initiation regions result from void growth and coalescence through the centre of a simultaneously growing poorly developed craze which consists of coarse fibrils. The surrounding smooth slow-crack growth mirror-like region results from crack propagation either through the centre or along the craze—matrix boundary interface of a thick, well developed craze consisting of fine fibrils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00561968
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  • 3
    Electronic Resource
    Electronic Resource
    The failure processes, morphology and mechanical properties of a co-polyimide glass based on benzophenone tetracarboxylic acid dianhydride (1977)
    Springer
    Journal of materials science 12 (1977), S. 1338-1348 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The phyiscal structure, failure processes and mechanical properties of solution-soluble copolyimide films based on benzophenone tetracarboxylic acid dianhydride are reported as a function of sample preparation. The failure processes and mechanical response are modified by the presence of residual solvent and microvoids, which are produced by the elimination of solvent clusters from the glass. The polyimide is amorphous, with the exception of a few isolated clusters of poorly formed spherulites and networks of 50 to 500 nm wide lamellae. The deformation modes observed when thin films were strained directly in the electron microscope were crazing, shear-band deformation and an edge-yielding phenomena. Edge-yielding, which has characteristics of both crazing and shear-banding, occurred in ∼1 μm wide bands which were 20 to 30° to the tensile stress direction. Shear-band deformation occurred in fine ∼-100 nm wide bands, which exhibited a sharp boundary between themselves and their surroundings. TEM indicated that the shear strain was uniform within these bands. Microvoids, 1.5 to 15 nm diameter, were found to initiate shear bands some of which were ∼ 1 nm wide. These bands increased in width by tearing at the microvoid initiation sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00540847
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  • 4
    Electronic Resource
    Electronic Resource
    The structure, modes of deformation and failure, and mechanical properties of diaminodiphenyl sulphone-cured tetraglycidyl 4,4′diaminodiphenyl methane epoxy (1979)
    Springer
    Journal of materials science 14 (1979), S. 109-124 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The tensile mechanical properties of diaminodiphenyl sulphone (DDS) — cured tetraglycidyl 4,4′diaminodiphenyl methane (TGDDM) epoxies [TGDDM-DDS (12 to 35 wt% DDS)] are reported as a function of temperature and strain rate. TGDDM-DDS (20 to 35 wt% DDS) epoxies, which exhibit broadT gs near 250° C, are not highly cross-linked glasses because diffusional and steric restrictions limit their cross-link density. TGDDM-DDS (10 to 20wt% DDS) epoxies are more brittle with lowerT gs as a result of lower molecular weights and/or lower cross-link densities. Electron diffraction and X-ray emission spectroscopy studies indicate that TGDDM-DDS (〉25wt% DDS) epoxies contain crystalline regions of unreacted DDS which can be eliminated from these epoxies during cure resulting in microvoids. TGDDM-DDS (12 to 35wt% DDS) epoxies predominantly deform and fail in tension by crazing, as indicated by fracture topography studies. These glasses also deform by shear banding as indicated by right-angle steps in the fracture topography initiation region and mixed modes of deformation that involve both crazing and shear banding. No evidence was found for heterogeneous cross-link density distributions in TGDDM-DDS (15 to 35wt% DDS) epoxies on straining films in the electron microscope.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01028334
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of moisture on the physical and mechanical integrity of epoxies (1980)
    Springer
    Journal of materials science 15 (1980), S. 751-764 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The effect of specific combinations of moisture, heat, and stress on the physical structure, failure modes, and tensile mechanical properties of diaminodiphenyl sulphone (DDS)-cured tetraglycidyl 4,4′diaminodiphenyl methane (TGDDM) epoxies [TGDDM-DDS (27 wt% DDS)] are reported. Sorbed moisture plasticizes TGDDM-DDS epoxies and deteriorates their mechanical properties in the range 23 to 150° C. Studies of the initiation cavity and mirror regions of the fracture topographies of these epoxies indicate that sorbed moisture enhances the craze initiation and propagation processes. The effect of tensile stress-level, applied for 1 h on dry epoxies, on the subsequent moisture sorption characteristics of the epoxies was also investigated. Such studies indicate that the initial stages of failure that involve both dilatational craze propagation and subsequent crack propagation enhance the accessibility of moisture to sorption sites within the epoxy to a greater extent than in the latter stages of failure which involve crack propagation alone. The amount of moisture sorbed by TGDDM-DDS epoxies is enhanced by ∼ 1.6 wt% after exposure to a 150° C thermal spike, as a result of moisture-induced free volume increases in the epoxies that involve rotational—isomeric population changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00551743
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of fillers on the interfacial polymer properties from cryogenic dynamic mechanical measurements (1974)
    Springer
    Journal of materials science 9 (1974), S. 1219-1226 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Dynamic mechanical measurements were used to study the effect of high surface area carbon black and fused silica fillers and a number of simple organic diluents on the SBR (31.6 mol% styrene) β peak, which is associated with small main chain motions of trans polybutadiene units. The amount of molecular motion eliminated from the glassy state by carbon black was greater than fused silica, indicating stronger polymer-filler interaction. The degree of interaction between polymer and filler at the interface affects polymer motion further removed from the filler surface. The reasons for this phenomenon are discussed. It is proposed that dilatational stresses resulting from the mismatch in the coefficients of expansion of filler and matrix are the cause of shifts in relaxation spectra to lower temperatures, which are more pronounced when polymer-filler interaction is weak. The toughness of the matrix near the interface is discussed in terms of polymer-filler interaction, the dilatational stresses and resulting shifts in the relaxation spectra. The effect of diluents on polymer motion in relation to diluent structure show no significant trends and is difficult to interpret without information on the percentage of diluent molecules existing in diluent clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00551834
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  • 7
    Electronic Resource
    Electronic Resource
    Tow impregnation during resin transfer molding of bi-directional nonwoven fabrics (1993)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 14 (1993), S. 335-340 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A model has been developed for analyzing resin impregnation of fiber tows during resin transfer molding of bi-directional nonwoven fiber performs. The model is based on the existence of two main regions of resin flow: the macropore space formed among fiber tows and the micropore space formed among individual fiber filaments within a tow. The large difference in permeability between these two regions of flow leads to the potential for void formation during resin transfer molding. The model was formulated for both constant flow rate and constant pressure mold filling. For ambient pressure mold filling, the model predicts a difference in the size of the voids and distribution between axial tows (oriented along the flow direction) and transverse tows (oriented in the transverse direction). When vacuum is imposed on the mold, the model predicts the same resin impregnation behavior for both axial and transverse tows. Furthermore, given sufficient time, voids generated under vacuum mold filling will eventually collapse because of the absence of an opposing internal void pressure. In addition to insights on void formation, the model also provides a basis for the study of the relationship between resin transfer molding parameters and the resin impregnation process.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750140409
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of thermal history and strain rate on the mechanical properties of diethylenetriamine-cured bisphenol-A-diglycidyl ether epoxies (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 23 (1979), S. 2711-2717 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: The tensile mechanical properties of diethylenetriamine (DETA)-cured bisphenol-A-diglycidyl ether (DGEBA) epoxies prepared from 9, 11 and 13 phr DETA are reported as a function of thermal history, strain-rate and test temperature. These epoxies exhibit macroscopic yield stresses and 〉10% ultimate elongations. The mechanical properties of these epoxies exhibit a free-volume dependence as a function of thermal history. Annealing below Tg causes an increase in the macroscopic yield stress and a decrease in the ultimate elongation, whereas quenching from above Tg lowers the yield stress and increases the elongation. These mechanical property modifications are shown to be reversible with reversible thermal-anneal cycles. The activation volumes associated with Eyring's theory for stress-activated viscous flow for the DGEBA-DETA epoxies are within the range of values (9-12 nm3) reported for noncrosslinked polymers. These observations suggest that the DGEBA-DETA epoxies are not as highly crosslinked as would be expected from normal addition reactions of epoxide groups with primary and secondary amines. The formation of lower crosslink density networks is discussed in terms of potential chemical reactions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1979.070230916
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  • 9
    Electronic Resource
    Electronic Resource
    Differential scanning calorimetry studies of the cure of carbon fiber-epoxy composite prepregsWork performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48. (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 30 (1985), S. 289-296 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: Diaminodiphenyl sulfone (DDS) cured tetraglycidyl-4,4'-diaminodiphenyl methane (TGDDM) epoxies, whose cure reactions are accelerated by BF3:amine catalysts, are the most common composite matrices utilized in aerospace high performance, fibrous composites. To process reproducible composites requires an understanding of the cure reactions and how these reactions are modified by the BF3:amine catalysts. In this article we report systematic differential scanning calorimetry (DSC) studies of (i) the constituents of BF3:NH2C2H5-catalyzed TGDDM-DDS epoxies and their mixtures, (ii) the effect of BF3:NH2C2H5 concentration on the cure reactions, (iii) the nature of the catalyzed cure reactions, and (iv) the environmental sensitivity of the catalyst. DSC studies are also reported on the cure reaction characteristics and environmental sensitivity of commercial C fiber-TGDDM-DDS epoxy prepregs.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1985.070300123
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  • 10
    Electronic Resource
    Electronic Resource
    Epoxy matrices for filament-wound carbon fiber compositesWork performed in part under Rockwell Science Center Independent Research and Development Program and in part under U.S. Department of Energy, Lawrence Livermore National Laboratory, Contract No. W-7405-ENG-48. (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 34 (1987), S. 37-46 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: Epoxies suitable for filament-winding fibrous composites must be processible at ambient temperatures, nontoxic, chemically simple, undergo full cure at ≤ 100°C and, also, be tough and exhibit a Tg 〉 120°C. In this paper, we report the cure characteristics, processibility, toxicity, and mechnical and physical properties of a number of amine-cured diglycidyl ether of bisphenol-A (DGEBA) epoxide candidate systems suitable for filament-wound carbon fiber composites. 2,5-Dimethyl-2,5-hexane diamine (DMHDA)-cured DGEBA epoxy was found to be the most promising candidate. The good processibility and thermal properties, together with the low cure characteristics of the DGEBA-DMHDA epoxy system, are discussed in terms of molecular structure of the amine molecule. The network structural parameters that control epoxy toughness and subsequent embrittlement upon plastic flow are discussed. Evidence is presented for plastic flow-induced thermal and mechanical property deterioration of epoxies as a result of network chain scission.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1987.070340103
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