PSI - Issue 41

Hryhoriy Nykyforchyn et al. / Procedia Structural Integrity 41 (2022) 326–332 Hryhoriy Nykyforchyn, Vitaliy Pustovyi, Olha Zvirko et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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Besides, in the tested excessively operated port equipment, cracks were detected visually, in some cases they have become the cause of abrupt fracture of an installation. Such a case is shown in Fig. 1 illustrating the portal crane with the broken bracket at the point of attachment of the boom to the column. The crack initiated and propagated due to fatigue, however, this does not imply the dominance of the fatigue crack growth stage in the durability of a structural element, since practice shows that it is the stage of macrocrack initiation that is crucial. During this stage, the main degradation processes occur in the metal, which can be detected mainly by a decrease in the resistance to brittle fracture, while fatigue characteristics can change ambiguously. Namely, fatigue performance increases at the stage of deformation ageing due to overall strengthening. However, when the main mechanism of the operational degradation becomes the development of microdamage (stage 2 of the degradation process, following deformation ageing as shown by Nykyforchyn et al. (2020), a decrease in the fatigue strength could be expected as a result of facilitated fatigue crack initiation.

Fig. 1. Abrupt fracture of the portal crane KPP5-30-10.5.

Analysing data from Table 1, it should be noted that the KCV values vary in a wide range of 14 – 210 J/cm 2 for the tested carbon steels having around 0.2% C. Such a drastic difference in the resistance to brittle fracture of the metal units from various seaport structures is supposed to be the result of a different intensity of their cyclic loading under operation. 3. Role of cyclic loading in operational loss of serviceability of hoisting and transporting equipment The stress ranges of certain units of the portal crane Sokol operated for 33 years have been analysed. The measurements were done on the surface of the crane under conditions that correspond to its normal operation using the strain gauge method described by Nemchuk (2019). The strain gauges were placed on 5 crane units, as depicted in Nemchuk et al. (2019); two points per unit were tested with the highest and lowest expected stress. This made it possible to evaluate cyclic stresses and, most importantly, the difference in their levels for the tested crane units. Similar results have been reported by Wen and Li (2021) for static and dynamic loading. As expected, the value of cyclic stresses, to which the crane components were subjected, contributed significantly to the intensity of degradation processes in them. A comparative assessment of in-service stresses and the corresponding resistance to brittle fracture for each unit is presented in Table 2.