PSI - Issue 28

Anja Gosch et al. / Procedia Structural Integrity 28 (2020) 1184–1192 Anja Gosch/ Structural Integrity Procedia 00 (2019) 000–000

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zones in front of the crack tip, the determination of the exact crack tip position is more difficult and higher deviations were measured for this polymer. Concerning the other two investigated polymers, the influence of plastic deformations was smaller, which ended up in lower differences of the average values (Table 1). This leads to the assumption that the used automated crack length measurement methods work better for materials with more linear elastic material behavior and for polymers with huge plastic deformations the plastic zone size has to be considered. There is also an additional geometrical effect influencing the determined crack length differences, because the POM specimens displayed less than half the thickness of the PVC-U and PMMA specimens. Therefore, uneven crack growth is less pronounced for the tests with this polymer. 3.1. Crack growth kinetics curves Lifetime prediction of polymer components requires the evaluation of the crack growth kinetics curve, which is based on the crack length evolution during fatigue tests. On the crack growth kinetics curve, a power law equation is fitted in the area of stable crack growth, as proposed in literature (Anderson, 2005; Paris and Erdogan, 1963): � �����

Figure 5. Crack growth kinetics curves obtained via different testing set-ups: “Microscope” (Microscope vs. Microscope), “IRT” (Microscope vs. IRT) and “DIC” (Microscope vs. DIC) – for three different polymers (PVC-U, POM and PMMA) with the fitted material parameters A and m.