Vol 54, No 12 (2018)

Comparative analysis of the distribution of magnetic-induction vector components over the volume of a bulk homogeneous sample of 40Kh steel has been carried out under its local magnetization by an attached magnetic device in the absence of a gap in the composite “attached magnetic device–sample” circuit and in the presence of a nonferromagnetic gap under both poles of the attached magnetic device. It is shown that with the gap present in the composite circuit, the most significant drop in the magnetic flux density in the interpole zone of the object near its surface occurs in a section that coincides with the inner face of the electromagnet pole. The influence of the size of the gap in the composite “attached magnetic device–sample” circuit on the magnetic flux density has been investigated at different depths from the sample surface.

Experimental dependences of the electric voltage U (t) across an induction magnetic head as it scans a magnetic carrier containing the recordings of magnetic fields due to artificial continuity defects in aluminum plates with a thickness from 1.5 × 10^–5 to 3.0 × 10^–3 m are presented. The strength of the primary magnetic field in pulses created by a flat inductor varied in the range of (2–50) × 10³ A/m. The rise time of the pulses with field spikes was in the range (1.5–100) × 10^–6 s. A method for testing objects made of electroconductive materials has been developed that ensures the optimum geometrical dimensions of the inductor, the optimum amplitude, direction, rise time, and shape of the leading and trailing edges of the main field pulse, as well as the optimum amplitude, rise time, number, and polarity of field spikes. The method performs the operations of smoothing, computation, and extraction of desired signal with removal of background and recognizes information recorded on the magnetic carrier by comparing the obtained signal distributions with reference or design ones when establishing signals from minimum defects. The method improves the accuracy and increases the speed of testing by several times.

A method is proposed for solving the inverse problem of magnetostatics with allowance for a nonlinear dependence of the relative magnetic permeability of a ferromagnet on the applied external field. The method has been investigated for metal loss defects located on the ferromagnetic-plate side opposite to magnetic transducers, without imposing any conditions on defect shape. The ferromagnetic plate is magnetized in the direction of the abscissa axis; the dependence of the magnetic induction of metal on the applied external magnetic field corresponds to a nonlinear segment of the magnetization curve. The problem has been solved for the three-dimensional case. Defects were simulated and the direct problem was solved with software developed by the authors in FORTRAN language. The program for constructing lines of force and solving the inverse problem of reconstructing magnetic field components was written using the Scilab package of applied mathematical programs.

The paper considers how elastic displacements and mechanical stresses are distributed along a laminated transducer consisting of two piezoelectric plates with different amplitude-phase excitation that are separated by an intermediate layer and have their outer surfaces loaded on arbitrary input impedances. We analyze the extent to which the nature of the distribution of elastic displacements and mechanical stresses is affected by the geometry of the elements of the laminated transducer and its amplitude-phase excitation. This analysis is based on solving the problem of synthesis aimed at forming uniform amplitude-frequency and linear phase-frequency characteristics of radiation by this transducer in a wide frequency band. Calculation results are discussed for different laminated-transducer designs and compared with the maximum values of elastic displacements and mechanical stresses achieved by in-phase excitation of piezoelectric plates in these transducers.