Browsing by Author "Demleitner, Martin"

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    Development of a low-expansion and low-shrinkage thermoset injection moulding compound tailored to laminated electrical sheets
    (2024) Braunbeck, Florian; Schönl, Florian; Preußler, Timo; Reuss, Hans-Christian; Demleitner, Martin; Ruckdäschel, Holger; Berendes, Philipp
    This study presents a thermoset moulding compound designed for electrical machines with high power densities. The compound reduces residual stresses induced by the difference in thermal expansion during use and by shrinkage in the compound during the manufacturing process. To reduce the internal stresses in the compound, in the electrical sheet lamination and at their interface, first the moulding’s coefficient of thermal expansion (CTE) must match that of the lamination because the CTE of the electrical sheets cannot be altered. Second, the shrinkage of the compound needs to be minimized because the moulding compound is injected around a prefabricated electrical sheet lamination. This provides greater freedom in the design of an electric motor or generator, especially if the thermoset needs to be directly bonded to the electrical sheet. The basic suitability of the material for the injection moulding process was iteratively optimised and confirmed by spiral flow tests. Due to the reduction of the residual stresses, the compound enables efficient cooling solutions for electrical machines with high power densities. This innovative compound can have a significant impact on electric propulsion systems across industries that use laminated electrical sheets.
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    Influence of Skydrol immersion at elevated temperatures on the thermo‐mechanical properties of a high‐Tg anhydride epoxy resin toughened with a hydroxy‐terminated polyester
    (2022) Hübsch, Jan David; Demleitner, Martin; Bard, Simon; Berendes, Philipp; Altstädt, Volker; Mittelstedt, Christian
    Currently, the application of composites in aerospace parts exposed to higher temperatures and in aggressive media is still severely limited. To replace metal alloys, alternative resins systems with suitable long‐term heat resistance are needed. In this study, the effect of the aviation hydraulic fluid Skydrol on the thermal and mechanical properties of a high‐Tg, anhydride‐cured epoxy resin in the unmodified and toughened state at elevated temperature is investigated. An aliphatic polyester diol was selected as an intrinsic toughener and its impact on the thermal, mechanical, and aging properties was determined. Experimental characterization of the aging effects is carried out with dynamic‐mechanical characterization, infrared spectroscopy, and electron dispersion x‐ray spectroscopy. In addition, the fracture toughness and the fatigue crack propagation behavior are determined. Initially, the toughened system shows an improved fracture toughness. Since oxidation is blocked by the Skydrol fluid only thermal degradation takes place as determined by the decrease in glass transition temperature Tg and network density. The thermal degradation leads to a tougher behavior, which is observed in both systems in static and dynamic mode with toughness decreasing with aging time again.