PSI - Issue 43

Jaroslav Polák et al. / Procedia Structural Integrity 43 (2023) 197–202 Jaroslav Polák, Alice Chlupová / Structural Integrity Procedia 00 (2022) 000 – 000

201

5

high stress concentration has also been considered by many other researches (see e.g. Liu et al. (2020)). Intergranular fatigue cracks were believed to arise by brittle fracture when local stress exceeds the theoretical strength. Only recentl y Mazánová et al. (2022) and Chlupová et al. (2022) presented experimental evidence showing the grain boundary damage in fatigued austenitic steel and polycrystalline copper stems from extrusions and intrusions, emerging on the grain boundary. They proposed a novel interpretation of PSB-grain boundary cracking due to surface relief developed not only on the surface of the grain but also on the grain boundary. It was shown that PSBs in which cyclic plastic strain is localized produce not only the specific relief on the surface in the form of extrusions and intrusions but also a similar relief at the grain boundaries. The analysis of the specimens cycled at two strain amplitudes led to two types of the relation between the surface extrusions and intrusions on one side and the grain boundary extrusions and intrusions on the other, as schematically depicted in Fig. 6. Schemes in Figs 6a and Fig. 6b show a grain with the surface at the top, grain boundary on the left and normal cut in the front. Two PSBs run parallel to the primary slip plane, one producing a surface extrusion, the other a surface intrusion, identical in both images.

Fig. 5. Surface of the specimen from Sanicro 25 stainless steel cycled with  a = 6×10 -3 to fracture. (a) GB crack (b) The inset showing the detail marked by rectangle in (a). (c) EBSDPs of the grains 1, 2 and 3.

(a) Fig. 6. Schematic representation of the two types of PSMs; (a) active Burgers vector in the slip plane has component normal to the grain boundary b G in the direction towards the grain boundary, (b) active Burgers vector in the slip plane has component normal to the grain boundary b G in the direction away from the grain boundary. (b)