PSI - Issue 16

Oleksiy Nemchuk et al. / Procedia Structural Integrity 16 (2019) 245–251 Oleksiy Nemchuk et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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cyclic loading by Polishchuk et al. (2015) has been taken into account. However, it is shown experimentally by Zvirko et al. (2018) that the metal from the cyclic compression zone undergoes almost the same worsening of crack growth resistance as the metal from the strain zone. Therefore, it doesn’t make sense to distinguish the strain zone in structural elements of the crane. Specimens from the chosen parts of the portal crane were cut for evaluation of mechanical properties, and for performing microstructural and electrochemical research. The results allowed us to match the properties of different crane units and their level of operational stresses. The tested material was low carbon ferritic-pearlite steel St-38b-2 (0.17C, 0.25Si, 0.50Mn, 0.035P, 0.035S). The method of experimental determination of the stress range Δσ e on the surface of steel sheets consisted in the following. For a certain part of the tested units (the most available) the strain gauges method were used. Strain gauges were fixed at the vertical surface of steel sheets under the angle of 0; 45 і 90  to the chosen axis, forming a set of strain gauges (Fig. 1). It is important if the direction of the main axes of deformation tensor is unknown. Data from the gauges were obtained for different loading conditions of the crane, including for the maximum allowable level. It should be pointed out that not absolute values of stress are important but their comparison for different crane units since just this differences maintain irrespective of the level of service loading. Then, using von Mises criterion, equivalent stresses σ e were calculated as a determinant for the estimation of the stress state at the steel surface. The stress range Δ  e were determined, as described by Nemchuk et al. (2008), for all the tested crane units.

Fig. 1. Illustration of strain gauges fixed on the right side of the column.

Standard mechanical characteristics of the steel, such as yield stress σ Y , ultimate stress σ UTS , elongation to fracture δ and reduction in area RA, were obtained by SSRT of cylindrical specimens with a working diameter of 5 mm cut along the rolling direction. Impact toughness was determined by Charpy testing; specimens were cut in two mutually perpendicular directions – longitudinal and transversal relative to the rolling direction. Corrosion activity of the tested steel was estimated using linear polarization method. Polarization curves in coordinates potential V – polarization current density I were obtained in the range of polarization potential ±30 mV from the corrosion potential. The value of polarization resistance R p was calculated from the curves due to Stern (1958) as a tangent slope to the curve in the point of the corrosion potential. Polarization resistance is inversely proportional to corrosion rate. Electrochemical measurements were performed in H 2 SO 4 water solution, pH 3.