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DDC: 530 × Subject: Composite ×

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Now showing 1 - 3 of 3
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    Predicting the dominating factors during heat transfer in magnetocaloric composite wires
    (Amsterdam : Elsevier B.V., 2020) Krautz, M.; Beyer, L.; Funk, A.; Waske, A.; Weise, B.; Freudenberger, J.; Gottschall, T.
    Magnetocaloric composite wires have been studied by pulsed-field measurements up to μ0ΔH = 10 T with a typical rise time of 13 ms in order to evaluate the evolution of the adiabatic temperature change of the core, ΔTad, and to determine the effective temperature change at the surrounding steel jacket, ΔTeff, during the field pulse. An inverse thermal hysteresis is observed for ΔTad due to the delayed thermal transfer. By numerical simulations of application-relevant sinusoidal magnetic field profiles, it can be stated that for field-frequencies of up to two field cycles per second heat can be efficiently transferred from the core to the outside of the jacket. In addition, intense numerical simulations of the temperature change of the core and jacket were performed by varying different parameters, such as frequency, heat capacity, thermal conductivity and interface resistance in order to shed light on their impact on ΔTeff at the outside of the jacket in comparison to ΔTad provided by the core.
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    Bioinspired polydimethylsiloxane-based composites with high shear resistance against wet tissue
    (Amsterdam : Elsevier, 2016) Fischer, Sarah C.L.; Levy, Oren; Kroner, Elmar; Hensel, René; Karp, Jeffrey M.; Arzt, Eduard
    Patterned microstructures represent a potential approach for improving current wound closure strategies. Microstructures can be fabricated by multiple techniques including replica molding of soft polymer-based materials. However, polymeric microstructures often lack the required shear resistance with tissue needed for wound closure. In this work, scalable microstructures made from composites based on polydimethylsiloxane (PDMS) were explored to enhance the shear resistance with wet tissue. To achieve suitable mechanical properties, PDMS was reinforced by incorporation of polyethylene (PE) particles into the pre-polymer and by coating PE particle reinforced substrates with parylene. The reinforced microstructures showed a 6-fold enhancement, the coated structures even a 13-fold enhancement in Young׳s modulus over pure PDMS. Shear tests of mushroom-shaped microstructures (diameter 450 µm, length 1 mm) against chicken muscle tissue demonstrate first correlations that will be useful for future design of wound closure or stabilization implants.
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    Statistical Analysis of Mechanical Stressing in Short Fiber Reinforced Composites by Means of Statistical and Representative Volume Elements
    (Basel : MDPI, 2021) Breuer, Kevin; Spickenheuer, Axel; Stommel, Markus
    Analyzing representative volume elements with the finite element method is one method to calculate the local stress at the microscale of short fiber reinforced plastics. It can be shown with Monte-Carlo simulations that the stress distribution depends on the local arrangement of the fibers and is therefore unique for each fiber constellation. In this contribution the stress distribution and the effective composite properties are examined as a function of the considered volume of the representative volume elements. Moreover, the influence of locally varying fiber volume fraction is examined, using statistical volume elements. The results show that the average stress probability distribution is independent of the number of fibers and independent of local fluctuation of the fiber volume fraction. Furthermore, it is derived from the stress distributions that the statistical deviation of the effective composite properties should not be neglected in the case of injection molded components. A finite element analysis indicates that the macroscopic stresses and strains on component level are significantly influenced by local, statistical fluctuation of the composite properties.