PSI - Issue 54

Johannes Kaiser et al. / Procedia Structural Integrity 54 (2024) 26–33 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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value but rather a temperature range at which the chain mobility and the unwinding processes of the macromolecules begin. For PS, the glass transition temperature T g is about 100 °C, for both PC grades it is 140 °C. The different chain lengths of the PC grades used have only a slight influence on the transition temperature (see Fig. 2).

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Figure 2. Thermal properties; left: specific heat capacity; right: heat conductivity as function of temperature

4.2. Mechanical properties Fig. 3 demonstrates the dependence of the mechanical properties on the test speed and temperature and therefore the need to consider both factors in the description of the failure behavior. By looking only at one temperature, the testing speed has only a small influence both on the young’s modulus and on the poisson’s ration . When considering the influence of temperature, a clearer dependence is evident. Especially for PS, which was tested at 100 °C and therefore near the glass transition, a clear decrease of the Young's modulus can be seen. The poisson’s ratio is also clearly affected, but only for lower test speeds. Due to the higher chain mobility of the molecules, this results in a decrease in stiffness with a simultaneous increase in elongation.

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Young's modulus_23 °C Young's modulus_50 °C Young's modulus_75 °C Young's modulus_100 °C Poisson's ratio_23 °C Poisson's ratio_50 °C Poisson's ratio_75 °C Poisson's ratio_100 °C

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Figure 3. Mechanical properties as a function of test temperature and speed (top: PS; bottom: PC h )