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  • 1
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 13 (1992), S. 197-206 
    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: As part of an engineering analysis and experimental methodology to characterize prepreg tack, a compression-to-tension test was optimized to enhance reproducibility and generate intrinsic property data. With the resulting stress-strain compression and tension data, a theoretical model was developed to describe tack as a bulk viscoelastic property of a prepreg laminate stack. Using the viscoelastic analysis, four intrinsic material parameters to characterize prepreg tack could be defined. These were 1) relaxed modulus, 2) unrelaxed modulus, 3) relaxation time, and 4) initial void content of the prepreg stack. Relaxed and unrelaxed moduli of the prepreg stack were independent of temperature, while the relaxation time was highly dependent on temperature and matrix viscosity. In addition, the relaxation time was found to be influenced by resin/fiber content and prepreg surface characteristics, which also influenced the void content of the prepreg stack. Using these measured parameters, good agreement was observed between theory and experimental data for both the stress-strain curve of the tack test and the simplified compression tack index (CTI*), defined as the ratio of output energy of the prepreg stack during tensile unloading to input energy during compressive loading.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 12 (1991), S. 146-152 
    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 simple apparatus was designed and constructed capable of measuring the unsteady-state permeability and the capillary pressure simultaneously in a simulated composite impregnation experiment. It was found that the Kozeny-Carman equation used to describe the permeability of composites during impregnation adequately described experimental results for woven fabric preform up to porosity values of 0.5. Above this value, observed deviations were attributed to interfacial effects between adjacent woven fabric layers. For woven fabric preforms made of T-300 carbon fibers, a maximum capillary pressure of 3.7 × 104 Pa (=5.4 psi) was observed at low porosity values. Thus, the capillary pressure may compete with other pressure sources in low pressure processes, such as the prepregging process. The woven fabric preform used in this study is observed to have a permeability similar to a unidirectional fibrous preform along the transverse direction. Furthermore, an existing modeling methodology capable of predicting permeability and capillary pressure through different preforms was found to be valid for fibrous preforms of complex orientation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 14 (1993), S. 349-360 
    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 description of the hot-melt prepreg process was developed by coupling resin matrix flow at the coating and impregnation zones with heat transfer considerations. Both bismaleimide (BMI) and epoxy resin systems were used as matrices. With continuous carbon fiber reinforcement. For the laboratory scale prepregger utilized in this study, the thickness of the resin film produced in a doctor blade was approximately 63% of the blade distance, showing good agreement with experimental data. In addition, the measured heat transfer coefficient between prepreg and atmosphere indicated that surface convective resistance is large compared to the internal conductive resistance and thus the chill plate in the prepregging operation plays on important role in determining prepreg quality. By formulating an analytical methodology in terms of the “Prepreg Flow Number” (PFN) that combined important operating parameter (e.g., temperature, pressure, and production rate), a temperature-pressure-velocity superposition was confirmed for the prepregging process. In addition, the model could easily be extended to different scales and types of prepregging processes with the aid of dimension-less parameters that are quite descriptive of the operating conditions employed in prepreg manufacturing.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 399-406 
    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: Thermoanalytical measurements and tack tests were both performed using a commercially available carbon fiber/epoxy prepreg system (Hercules 3501-6) to examine changes caused by aging as they affect handling and processability of thermosetting matrix-based composites. Combining these techniques, a relationship between prepreg bulk and surface characteristics in relation to aging was investigated. Isothermal kinetic studies at low temperatures showed maximum conversions (αm) that increased with increasing cure temperatures. In addition, a linear relationship between glass transition temperatures (Tg) and conversions (α) was observed regardless of aging (or cure) temperatures. Energy of separation of prepreg stacks, which may be viewed as a measure of prepreg tack, showed a maximum value at a specific temperature. The maximum energy of separation was observed in the temperature range of 20-25°C above the glass transition temperature for a given sample. However, the maximum energy of separation values decreased with increasing aging times (or conversions), implying that prepreg tack was a viscoelastic property rather than a viscous property of the resin matrix in the prepreg.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 1177-1188 
    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: Resin flow and fiber spreading during the prepregging process were investigated experimentally using a scale-down version of a commercial hot-melt prepregger with bismaleimides and carbon fibers as model systems. Specifically, several dimensionless parameters such as the Prepreg Flow Number, fractional resin uptake, resin distribution function, fractional width change, and prepregging efficiency were defined to characterize the prepregging process as well as the quality of the prepreg. Fiber spreading during the prepregging process was observed to be a viscoelastic phenomenon depending on the impregnation temperature. For resin impregnation into collimated fiber tows, all the experimental data points obtained at different operating conditions were superimposed onto a single line showing a temperature-pressure-velocity superposition for the prepregging process as predicted by the definition of the Prepreg Flow Number (PFN). Finally, three fundamental steps of the prepregging process were identified and confirmed with cross-sectional micrographs of unaged prepregs produced at different temperatures.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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