PSI - Issue 40

A.M. Povolotskaya et al. / Procedia Structural Integrity 40 (2022) 359–364 A.M. Povolotskaya, A.N. Mushnikov / Structural Integrity Procedia 00 (2019) 000 – 000

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Kuleev et al. (2006), Nichipuruk et al. (2015). Those studies presented the results of studying the behavior of magnetization curves, magnetic hysteresis loops, and specific magnetic characteristics of materials under plastic tensile deformations. The influence of such factors of plastic deformation as increasing dislocation density, the occurrence of residual stresses and their growth with subsequent saturation, and the loading rate on this behavior was also considered. However, insufficient attention has been paid to the influence of plastic deformation on magnetostriction. Since the changes in the magnetic characteristics of ferromagnetic materials after deformation are associated with magnetostrictive and magnetoelastic effects, which are expressed in the behavior of magnetostriction under the action of deformations, such experiments are necessary, and they contribute to a more complete understanding of the evolution of the domain structure of ferromagnetic materials under deformation. This paper studies the effect of tensile deformation of the 20GN hull steel to various levels of plastic strain on the behavior of some magnetic characteristics, including linear magnetostriction, in order to reveal the nature of magnetic anisotropy induced by this force action. 2. Materials and research methods Dog-bone-shaped flat specimens were cut out from the 20GN hull steel. The gauge length of the specimens with a cross- section of 5×8 m m was 60 mm. Additional heat treatment of the specimens was not performed. Preliminary mechanical testing performed in a Tinius Olsen Super L60 universal testing machine has shown that, for the material under study, offset yield strength σ 0.2 is 440 МPа (yield drop is 450 МPа), tensile strength σ U is 550 МPа, percentage permanent elongation after rupture δ is 25 %. Figure 1 shows the stress-strain diagram of the steel under study.

Fig. 1. The stress-strain diagram of the 20GN steel.

Uniaxial tension of the specimens was carried out in a Tinius Olsen Super L60 testing machine to the following values of plastic strain ε measured after the specimens were unloaded: 0.75, 1.28, 1.96, 5.01, 7.53, and 10 %. One specimen was left in its original state (ε = 0 %). The magnetic characteristics were measured in a closed magnetic circuit along the loading axis by means of a Remagraph C-500 hysteresisgraph. The strength of the internal magnetic field H measured by a C-shaped magnetic potential meter reached 500 A/cm. The coercive force Н c and residual magnetic induction B r were determined from the magnetic hysteresis loops. Maximum magnetic permeability  max was found from the basic magnetization curve. The measurement error for the field and induction did not exceed 3 %. Longitudinal magnetostriction was measured by means of BF350-3AA foil strain gauges with a nominal resistance of 350 Ω and a base of 3 mm, connected according to the Wheatstone bridge circuit. The measuring strain gauges were glued in the middle of the gauge part of the specimen, and the temperature compensation ones were glued onto a copper plate placed near the specimen. The bridge was fed by stabilized direct current. Magnetization reversal and the measurement of the internal field for recording the field dependencies of magnetostriction were