PSI - Issue 65

Yu.V. Khudorozhkova et al. / Procedia Structural Integrity 65 (2024) 121–126 Yu.V. Khudorozhkova, A.M. Povolotskaya / Structural Integrity Procedia 00 (2024) 000–000

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performed with the use of a pickup coil wound directly on the gauge length of the specimen. The pickup coil was connected to the EF-5 fluxmeter of a Remagraph C-500 magnetic measurement device, and the magnetizing coil was connected to the stabilized current source of this device. A Zetlab DAC/ADC module was used to record the signals of the values of the current in the magnetizing winding, correlating with the value of magnetic field strength, and the value of the magnetic flux in the pickup winding, correlating with the value of magnetic induction. The recording was performed through the Remagraph C-500 device. The magnetic hysteresis loops of the specimen were obtained this way, and the evolution of their parameters is qualitatively (though not quantitatively) related to the behavior of the magnetic properties of the material under study. Magnetic hysteresis loops were also measured in weak fields at maximum magnetic induction b = 0.05 T in the specimen. The reason for making measurements in weak fields is that the magnetic characteristics of a minor magnetization reversal cycle may have other correlations with the structural and stress-strain states, and in such cases it is necessary to determine the magnetizing fields at which a change occurs. The error in measuring the field and induction in the maximum applied field did not exceed 3%, and in weak fields (the Rayleigh region) it was at most 8%. The surface roughness parameters were determined in the studied regions by means of a Wyko NT 1100 optical profilometer. The profilometer allows the surface relief to be studied with a magnification of ×1.25 to ×100 in the field of view ranging from 50 μm to 4.95 mm, with a vertical measurement range of 160 nm to 2 mm and a resolution of less than 0.1 nm. The measurements were carried out with the application of the vertical scanning interferometry (VSI) technique in automatic mode. The VSI technique enables one to measure surfaces with high roughness values, as well as various relief elements with a height (depth) of up to several millimeters. Surface roughness measurements were made before and after loading both along the entire gauge length of the specimen and on the specimen heads, i. e. the regions experiencing no deformation during loading (the leftmost and rightmost points in Fig. 2b). The dependences of the roughness parameters R a and R q on the distance from the specimen center are shown in Fig. 2. The values of R a and R q before deformation are fairly similar through the entire specimen length (Fig. 2a). Due to the appearance of defects on the specimen surface and the rotational modes of plasticity, a relief of a deformational nature is formed, which is closely related to the alteration of the surface roughness (Fig. 2b). The amount of plastic strain correlates with the change in elevation. Thus, the maximum values of R a and R q are observed in the plastic strain localization zone. As can be seen from fig. 2b, the values of R a and R q are maximum in the specimen center, in zone of local plastic strain, and they decrease as the undeformed regions (specimen heads) are approached. A sharp decrease is observed outside the gauge length of the specimen. In the undeformed regions the values of the roughness parameters correspond to the initial ones. Proceeding from the obtained data, we can assume that the plastic strain localization zone was in 6th and 7th measurement sectors. a b 3. Results and discussion

Fig. 2. The roughness parameters as functions of the distance from the specimen center before loading (a) and after loading (b).