PSI - Issue 43

Lukáš Trávníček et al. / Procedia Structural Integrity 43 (2023) 148 – 153 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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scattered. Therefore, testing of more pipe specimens would be needed to obtain more accurate results. It must be also noted here that the testing times of the extruded pipe specimens were approximately 2 times longer, which is caused by the generally lower stress intensity factor range at which these specimens must be tested to obtain representative results. That is another great drawback of the pipe specimens. The comparison of both tests is depicted in Fig. 6, where normalized number of cycles is plotted for five materials, for which both types of specimens were tested. The results of material 1 are taken as the reference values, i.e., the results of N f for materials 2, 6, 7 and 8 are divided by the N f of material 1. The comparison shows that the resistance against SCG of the materials 1 and 2 is the same according to both types of tests. However, the difference in SCG performance of materials 6, 7 and 8 is notable only in the case of CRB tests. This demonstrates the higher sensitivity of the CRB test as the new pipe test shows similar performance for these three materials.

Fig. 4. Photo of fracture surface of an extruded pipe specimen made of PE80 – material 1 taken by optical microscope. The area of ductile failure is shown in the detail. No SCG occurred.

Fig. 5. Experimental results of SCG resistance measured on (a) extruded pipe specimens and (b) CRB specimens.

4. Conclusions This paper presents research of SCG resistance on nine different PE materials from the pipe grades PE80, PE100 and PE100RC. The SCG resistance was measured using two types of specimens: the standardized CRB specimens manufactured from compression molded plates and new extruded pipe specimens proposed in this paper. It can be concluded from the presented results that the new pipe specimens sorted the materials into pipe grade groups (PE80, PE100 and PE100RC) correctly. However, the results of all the tested materials suffer by high scatter and therefore, more specimens would be needed for testing to obtain at least slightly more accurate results. The reason for the high scatter of the results is generally the thin wall of the pipe specimens. It causes that the slow crack growth

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