PSI - Issue 56

Tamas Krausz et al. / Procedia Structural Integrity 56 (2024) 71–77 Krausz/ Structural Integrity Procedia 00 (2019) 000–000

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Aged MK8035 Non ‐ Aged MK8035 (c)

Stress [MPa]

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Strain [%]

Fig. 3. Force-deflection curves of aged and non-aged specimens for the three polycarbonate grades: (a) MK2405, (b) MK9415 and (c) MK8035.

Table 3 groups the values of the elastic modulus and yield strength of the aged and non-aged polycarbonate materials at room temperature conditions. From the values shown one can observe a slight increase (1.2%) in Young’s modulus and in yield strength (10%) in favor of the aged samples, but only for the unreinforced grade. In the case of the fiber reinforced materials the tendency will change, making the non-aged materials more stable for loads with magnitudes close to the yield limit.

Table 3. The variation of the elastic modulus and of the yield strength due to the aging of the specimens. Makrolon 2405 Makrolon 9415 Makrolon 8035 Elastic modulus [MPa] Yield strength [MPa] Elastic modulus [MPa] Yield strength [MPa] Elastic modulus [MPa] Yield strength [MPa] Aged 2487.45 65.21 4215.37 58.53 5846.45 54.69 Non-aged 2457.84 59.33 4042.02 60.26 5960.54 58.83

Although the behavior shown by the aged specimens is different from the one observed by Sonja et al. (Redjala et al., 2019), the sudden drop is expected to be due to the physical and chemical aging of the materials at microscale level, resulting in bond breakages which make room for degradations. 4. Conclusions Uniaxial monotonic tension behavior of unreinforced and reinforced polycarbonate grades was investigated at three temperatures - 22°C, 40°C and 80°C. The experimental findings demonstrated once again the temperature dependency of the material. The elastic modulus and yield stress values are decreasing with the increasing temperature, whereas the Poisson’s ratio remains stable, with almost insignificant variations, throughout the entire tested temperature range. In addition, thermal aging of the specimens from the selected polycarbonate grades has been conducted. After aging, the specimens have been tested for uniaxial tensile loading and compared to non-aged material behavior. The aging had an impact upon the base polycarbonate, by increasing its mechanical properties by up to 10%, however, with the increasing fiber ratio, the stiffening effect of the aging has been canceled. The specimens for the two reinforced grades showed a drop of up to 7% compared to the non-aged materials. Both the temperature dependency and the possibility of negative impact of aging should be considered before the selection of a specific polycarbonate grade for a certain engineering application.