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Der für den Shell Eco-marathon entwickelte „Schluckspecht City“ soll als straßenzugelassene Variante weiterentwickelt werden. Dabei spielt das Verhalten des Fahrzeugs im Crashfall eine entscheidende Rolle. Um die Fahrzeugsicherheit zu überprüfen und zu optimieren, wurden Crashsimulationen des Aluminiumrahmens, angelehnt an Euro NCAP [3], durchgeführt. Beim simulierten seitlichen Pfahlaufprall trifft das Fahrzeug mit 29 km/h auf einen feststehenden Pfahl mit einem Durchmesser von 25,4 Zentimetern.
The dynamic material characterization shows different macroscopic strain rate effects. The causal mechanisms cannot be identified at this level in most cases. Micro-tests allow a local transient analysis, which is illustrated in this article using the example of a long-fibre reinforced thermoplastic (LFRT). After a general introduction, the development and validation of a micro-test for a large strain rate range is presented. The validation explained for steel shows the advantage of the small sample for the dynamic characterization, if a homogenous material behaviour of this magnitude still exists, especially in the case of low-vibration force measurement. For a heterogeneous LFRT material, the micro-test shows strongly scattering test results that are no longer representative of the homogenized mechanical material behaviour, but reflect the local characteristics. These local properties are directly caused by the injection moulding process. Further SEM analyses of the samples indicate different macromolecular deformation mechanisms of the matrix at the different strain rates.
Thermo-mechanical material considerations have been published since two centuries. A new method of correlating experimental field information of strain and heat generate data for a physical based thermo-mechanical modeling of strain rate dependent material properties. Strain rate dependent characterizations under tensile loading of glass-fiber reinforced thermoplastic (LFRT) and its matrix material polypropylene (PP) were conducted. Higher fracture strains of LFRT with raising strain rate could be ascertained in contrast to the decreasing fracture strain of PP. High-speed video based digital image correlation (DIC) in combination with high-speed infra-red (IR) measurements provide field data of the deformation and the temperature evolution. A precise IR calibration method, the correlation of the Lagrangian deformation field with the Eulerian temperature field, the contemplation of volume specific values and the incorporation of the thermo-elasticity allowed the determination of the heat transition values with respect to strain and strain rate. The results show clear difference of (βdiff) between PP and LFRT. While PP shows a higher βdiff with rising strain rate and therefore higher energy dissipation, βdiff of LFRT decreases with the strain rate. The predominant role of thermo-elasticity was identified as the key-factor of higher energy absorption of LFRT at higher strain rates.