PSI - Issue 50

V.N. Kostin et al. / Procedia Structural Integrity 50 (2023) 151–154

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V.N. Kostin et al./ Structural Integrity Procedia 00 (2022) 000 – 000

ferromagnets during magnetization reversal in a solenoid by an alternating field. There are a few works which present the results on the application of laser interferometry for thin films magnetostriction measurement (Bellesis et. al., 1993) and speckle photography to measure bulk ferromagnets magnetostriction (Salazar et. al., 2009). Since a laser vibrometer is an expensive system, it is advisable to develop a setup for measuring the magnetostrictive characteristics of bulk ferromagnets by the speckle-interferometry method, which provides the theoretical sensitivity to microdisplacements of at least 10-7 m. This work presents the model setup of an optical system for non-contact measurement of the magnetostriction of ferromagnetic materials, as well as experimental results of the ferromagnet magnetostriction measurements using laser vibrometer. The purpose of this work was to develop methods for measuring the magnetostrictive characteristics of ferromagnetic materials using laser interferometry and dynamic speckle interferometry. 2. Samples and equipment The sample group consists of ten samples, which were made from commercially pure nickel. The workpieces were subjected to cold plastic deformation by 60%, then processed by grinding to the required dimensions. Then the samples were annealed at different temperatures from 100 to 900 °C, with one hour hold and subsequent cooling in air. Final dimensions of samples amounted to 65,00 x 5,45 x 5,45 mm. All the ferromagnets magnetic characteristics were measured using Remagraph C-500 magnetic measuring complex. A PSV-500-HV POLYTEC laser scanning vibrometer was used for non-contact measurement of the magnetostriction of bulk ferromagnets by laser vibrometry. The vibrometer is designed for non-contact measurement of high-frequency surface vibrations in the frequency range up to 25 MHz. The vibrometer is made according to the scheme of a heterodyne Mach – Zehnder interferometer with the Doppler measurement method. In the developed optical setup for measuring the magnetostrictive characteristics of ferromagnets, speckle images can be obtained using a Videoscan-415/P/K-USB camera. The camera registers changes on its photodetector matrix only in the visible range. The camera has a SONY ICX415 CCD photodetector matrix 6.5x4.8 mm in size, containing 780x582 cells 8.3x8.3 μm in size, providing a frame rate of 25 Hz and a program -controlled exposure from 1 μs to 500 s. As a source of coherent light radiation, a semiconductor laser module KLM-650/20, manufactured by FTI Optronik, with a la ser radiation wavelength of λ = 660 nm and an adjustable laser radiation power of up to 20 mW, is used. The divergence of the light spot of laser radiation in a parallel plane is not more than 0.7 mrad, adjustment lens allows to change the spot width. The remote induction sensor method was used as a reference method for measuring magnetostriction. The sample was placed in a vertically standing solenoid and remagnetized by a quasi-static magnetic field, the frequency of which is less than 0.1 Hz, with a maximum current in the solenoid windings of 60 A, which provides a field of up to 240 000 A/m. A quartz rod, which has a low coefficient of thermal expansion, transmitted the magnetostrictive elongation of the sample on a permanent magnet, which is located in a remote coil induction sensor to eliminate the influence of the magnetic field of the solenoid. 3. Results and discussion The laser interferometry method is inherently non-contact. Measurement of the magnetostriction can be carried out in magnetic fields of the order of 15 kA/m in the initial sections of the field dependence of magnetostriction.