PSI - Issue 42

Jessica Hinczica et al. / Procedia Structural Integrity 42 (2022) 139–146 Hinczica et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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material series 1, toughness decreases already by 10 % even with a small amount of PP-r1, whereas material series 2 shows a slight increase. Comparing both series, no significant influence is detectable by blending with PP-r2 up to a ratio of 25 %. Starting with the 50/50 blend, a decrease in notched impact toughness is measurable in both material series. Lower molecular weight (Fig. 1) as well as higher amount of inorganic impurities lead to a more brittle behavior and therefore, to a lower notched impact toughness. It should be also considered, that due to the introduced notch, the location of failure is predefined, the specimen does not fail at the weakest point. This reduces the influence of inorganic impurities. Nevertheless, the combination of both effects (molecular weight and inorganic impurities) result in a drop of the notched impact toughness even with 10 % PP-r1. Whereas a low amount of inorganic impurities and higher molecular weight of PP-r2, influences the notched impact toughness only from 25 % recyclate content.

Fig. 5. Notched impact toughness related to PP-v (100 %) as a function of the recyclate content for material series 1 and 2.

The results of the CRB tests are summarized in Fig. 6 which show the failure cycle numbers N f as a function of the stress intensity factor  K . By means of the loading frequency of 10 Hz, N f can directly be transferred into the testing time until failure. For a better visualization, the failure curves of the two material series are shown in two separate log-log diagrams, in Fig. 6 a) for material series 1 and in Fig. 6 b) material series 2. Adding 10 % PP-r has no significant influence on the SCG resistance compared to the pure PP-v. However, further increase of the PP-r content decreases the SCG resistance dramatically, especially considering the logarithmic scale for N f and testing time, respectively. Each material and blend itself depicts a linear failure curve in the double-logarithmic diagram.

a

b

Fig. 6. CRB measurements at the different stress intensity factors  K (left y-axis), stresses   (right y-axis) and cycles until failure N f for (a) material series 1 and (b) material series 2.