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Browsing by Author "Yan, Shuang"

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    Characterization of cure behavior in epoxy using molecular dynamics simulation compared with dielectric analysis and DSC
    (2021) Yan, Shuang; Verestek, Wolfgang; Zeizinger, Harald; Schmauder, Siegfried
    The curing behavior of a thermosetting material that influences the properties of the material is a key issue for predicting the changes in material properties during processing. An empirical equation can describe the reaction kinetics of the curing behavior of an investigated material, which is usually estimated using experimental methods. In this study, the curing process of an epoxy resin, the polymer matrix in an epoxy molding compound, is computed concerning thermal influence using molecular dynamics. Furthermore, the accelerated reaction kinetics, which are influenced by an increased reaction cutoff distance, are investigated. As a result, the simulated crosslink density with various cutoff distances increases to plateau at a crosslink density of approx. 90% for the investigated temperatures during curing time. The reaction kinetics are derived according to the numerical results and compared with the results using experimental methods (dielectric analysis and differential scanning calorimetry), whereby the comparison shows a good agreement between experiment and simulation.
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    In‐situ investigation of dielectric properties and reaction kinetics of a glass‐fiber‐reinforced epoxy composite material using dielectric analysis
    (2021) Yan, Shuang; Zeizinger, Harald; Merten, Clemens; Schmauder, Siegfried
    Monitoring the curing behavior of a thermosetting material is a key issue for ensuring a stable manufacturing process (e.g., injection molding). Dielectric analysis (DEA), which is applicable for online‐monitoring, is used to investigate the curing behavior of a glass‐fiber‐reinforced epoxy molding compound. At first, the influences of experimental settings (pressure, temperature, and frequency) on dielectric responses (dielectric loss and ion viscosity) are characterized in a fully crosslinked material. Results show a significant impact of temperature and frequency on dielectric responses. Furthermore, DEA is combined with differential scanning calorimetry (DSC) to investigate dielectric properties depending on crosslink density under non‐isothermal and isothermal conditions. The results show that DEA can detect cure changes only for a crosslink density <80%. Finally, reaction kinetics, which can predict the crosslink density, is derived using DSC and validated through DEA for determining the best suitable kinetic expression for the investigated material. The crosslink density, estimated by reaction kinetics, can be correlated with the dielectric properties.
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    Numerische Simulation des Materialzustandes einer Epoxidformmasse im Spritzgießprozess
    (2022) Yan, Shuang; Schmauder, Siegfried (Prof. Dr. rer. nat. Dr. h. c.)
    Ziel dieser Arbeit ist es, ein vertieftes Verständnis bzw. die quantitative Beschreibung der interagierenden Materialzustandsgrößen, beschrieben durch die Temperaturverteilung und den Vernetzungsgrad einer duroplastischen Formmasse, unter Berücksichtigung der thermochemischen Mechanismen bei der Spritzgießverarbeitung zu ermöglichen. Die Arbeit konzentriert sich einerseits auf die numerische Simulation von Materialzustandsgrößen wie Temperatur und Vernetzungsgrad, andererseits wird die Online-Überwachung des Vernetzungsgrads mittels dielektrischer Analyse und IR-Spektroskopie im Spritzgießprozess untersucht. Die in dieser Arbeit durchgeführten Simulationen und Experimente werden auf einer realen Spritzgießmaschine mit einem Plattenspritzgießwerkzeug für einen duroplastischen Werkstoff durchgeführt. Als Beispielmaterial wird eine Epoxidformmasse, die üblicherweise in der Industrie angewendet wird, ausgewählt und untersucht.
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