PSI - Issue 40

S.M. Zadvorkin et al. / Procedia Structural Integrity 40 (2022) 455–460 S.M. Zadvorkin, A.M. Povolotskaya / Structural Integrity Procedia 00 (2019) 000 – 000

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components of the magnetic leakage fields. The studies were carried out in the state of residual magnetization after removing the specimens from the testing machine. The specimens were magnetized by means of a magnetizing device based on high energy consuming permanent magnets, see Gorkunov et al. (2003). 3. Results and discussion Experiments have shown that, for specimens of both steel grades at the stage of uniform plastic deformation, the distribution of magnetic characteristics and the parameters of magnetic leakage fields are uniform. As an example, Fig. 1 shows the dependences of I c measured along and across the loading axis on the position of the transducer on the gauge length of one specimen of steel 45 plastically deformed to different values of plastic strain ε . Figure 2 shows the distribution of the tangential component of the magnetic leakage field on the surface of the St3 steel specimen without distinct PSLZs.

Fig. 1. The dependence of demagnetizing current I c measured along (curves 1 – 4) and across (curves 5 – 8) the loading axis on the transducer position on the plastically deformed specimens of steel 45: ε = 0.035 (curves 1, 5); ε = 0.063 (curves 2, 6); ε = 0.091 (curves 3, 7); ε = 0.12 (curves 4, 8). The specimens have no distinct PSLZs. A different picture was observed on specimens with clearly pronounced PSLZs. Figure 3 shows images of the left and right parts of the specimen of steel 45 with PSLZs. Studies performed by the VeecoWYKO NT 1100 OPTICAL profiling system have shown depression on the specimen surface along the PSLZs, the surface relief height difference reaches 20 μm. Moreover, an increase in the surface roughness parameters is observed in the PSLZs; namely, R a increases by more than a factor of 5 as compared to the roughness parameters for the undeformed portion of the specimen and its test portion free from distinct PSLZs. The dependences of the demagnetizing current I c on the transducer position along the specimen (Fig. 3) are presented in Fig. 4 a . The measurements were performed both along the entire gauge length and for the grip sections, which were not deformed during the loading (extreme left and right points in the dependences). It follows from Fig. 4 a that the dependences of the demagnetizing current, which was measured by the attached electromagnet arranged along and perpendicular to the tension direction, exhibit the opposite behavior. The magnitudes measured by the attached electromagnet arranged along the tension direction are maximal at the specimen center and they decrease when approaching the PSLZ. This can confirm the fact that the formation of microdiscontinuities (PSLZs) leads to the relaxation of internal stresses near them. The demagnetizing current measured by the attached electromagnet arranged perpendicular to the tension direction is minimal at the center of the test portion of the specimen; the maximum current is observed near the PSLZ.