RU1768963C - Mechanical stress measurement technique - Google Patents

Abstract

The invention relates to a measurement technique. The purpose of the invention is to increase sensitivity. The test sample is placed in an alternating magnetic field selected depending on its material, and a light beam is directed. A change in the magnetization of the illuminated portion of the surface of the sample under the influence of an alternating external magnetic field changes the intensity of the light reflected from the test sample due to the magneto-optical effect and is detected by a photodetector, in the circuit of which two signals appear: constant - proportional to the intensity of the light reflected from the sample in the absence of a magnetic field , and the variable is proportional to the depth of light modulation due to the magneto-optical effect arising from remagnetization - Vania sample. Moreover, the mechanical effects on the test sample can be judged by the increase or decrease (depending on the sign of constant magnetostriction) of the magneto-optical effect, measured at a fixed value of an alternating magnetic field. The size of the floor depends on the material being studied. 1 ill. next to

Description

The invention relates to a control and measuring technique and can be used to create devices and devices for measuring mechanical stresses in assemblies made of magnetically ordered materials.

Known methods for measuring mechanical stresses using magnetoelastic sensors are based on the inverse magnetostrictive effect, which consists in the effect of elastic stresses on magnetization. Magnetoelastic sensors have a wide variety of designs. In any case, the sensor is a magnet core made of magnetostrictive material, which is fixed or in contact with the surface of the test

the details. The magnitude of the applied stresses to the tested part is judged by the change in the magnetic permeability or EMF of the used magnetic core

The disadvantage of these methods is the instability of the measured values due to the strong influence on the operation of magnetoelastic sensors of the phenomena of magnetic hysteresis and residual magnetization

The closest in technical essence is the method of measuring mechanical stresses based on the use of the piezoelectric effect (photoelasticity), which consists in the appearance of optical anisotropy in initially isotropic solids under the action of elastic stresses. Piezoelectric

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the effect is a consequence of the dependence of the dielectric constant of a substance on deformation and is manifested in the form of birefringence and dichroism. Polarization-optical sensors use optically sensitive materials made in the form of rectangular plates. The plates are attached to the surface of the test piece. During uniaxial tension or compression, an optically sensitive substance acquires the properties of an optically uniaxial crystal with an optical axis parallel to the axis of tension or compression. Linearly-polarized light, passing through a polarization-optical sensor, under the presence of elastic stresses experiences linear birefringence An (And p is the difference in refractive indices for ordinary and extraordinary waves). The mechanical stresses applied to the test piece are judged by the value of An. Polar-optical strain gauges relate to overhead type sensors.

The disadvantages of this method are the low sensitivity and limitation of the types of test samples, which is due to the fact that the gap between the sensor and the test material affects the output signal of the overhead type sensor, and the sensor itself has a certain shape of a given size.

The aim of the invention is to increase the sensitivity of the measurement of mechanical stresses and the expansion of the objects of study.

The aim of the invention is achieved by the fact that the object under study is placed in the gap of a toroidal magnet, polarized radiation is focused on the surface of the object five times smaller than the characteristic size of the voltage distribution inhomogeneities, the action is carried out by an alternating magnetic field at a frequency other than the network, as the recorded characteristics, the values of the constant and variable components of the intensity of the reflected radiation are selected, the mechanical stresses at the point are determined by the ratio of the composition constituents using graded paid-curve, scanning the surface of an object by a focused radiation, determining stress distribution in two alignments.

In the proposed method for the first time uses the effects of magnetoreflection (magneto-optical effects), consisting in

a change in linearly polarized light reflected from a magnetically ordered material subjected to mechanical stress. Thus, the proposed

the method meets the criterion of significant differences.

The drawing shows a diagram that implements the proposed method.

The method is carried out as follows. In the arcuate magnet 1 with a magnetizing winding 2 is placed the test piece 3 (plate, wire, etc.). The light from light source 4 passes through the polarizer 5 and falls on the sample.

5 The reflected light is collected at the photodetector 6. An alternating current is applied to the magnetized winding 2 from the sound generator 10 through a power amplifier 11 to ensure magnetization reversal of the sample (including from Ms to - Ms; Ms is the saturation magnetization of the tested mother, m).

A change in the magnetization of the illuminated part of the surface of the part by the action of an alternating external magnetic field leads to a change in the intensity of the light reflected from the test sample due to the magneto-optical effect. It is convenient to use the equatorial Kerr effect (EEC), as well as the meridional intense effect (MIE). In the first case, the magnetic field applied to the sample and the plane of incidence of light are perpendicular. EEC is measured at the P component of the incident light. Bo-second - the magnetic field and the plane of incidence of light are parallel. MIE is measured at some intermediate (between P - and S - waves, the vector E lies respectively

0 parallel and perpendicular to the plane of incidence of light) the position of the plane of polarization.

A change in the intensity of the light reflected from the test sample5 is recorded by a photodetector 6, in the circuit of which two signals appear: constant - proportional to the intensity of the light reflected or from the sample in the absence of a magnetic field, and variable - proportional to the depth of light modulation due to the magneto-optical effect that occurs when re-magnetization of the sample. The first signal is measured with a dc microvoltmeter 8, the second with selective

5 by an amplifier 7 with a synchronous detector 9. The ratio of the readings of the synchronous detector 9 and the microvoltmeter 8 determines the magnitude of the magneto-optical effect d.

It is known that with a constant magnetic field strength and exposure to

a sample of external mechanical stresses (tension or compression), changes in magnetization (magnetoelastic effect) should be detected in it. The magnetoelastic effect and the magnetoelastic energy associated with it are due to the presence of magnetostriction in the crystal. Magnetoelastic energy creates additional, advantageous and disadvantageous, energy directions M3 (magnetoelastic anisotropy). As a result, the course of the magnetization curves is determined by the competing contributions of magnetoelastic energy and crystallographic magnetic anisotropy.

In materials having a negative sign of magnetostriction, unilateral tension tends to establish the vectors Ms in a plane perpendicular to the direction of tension. In this case, the magnetization curves degenerate in straight lines, because in this case a much larger field H is required in order to orient the vectors Ms in the direction of the applied field.

In materials with positive magnetostriction, the magnetization curves acquire a rectangular shape as the elastic tension increases.

Magnetization curves can be measured using magneto-optical effects, while the mechanical effects on the test sample can be judged by the increase or decrease (depending on the sign of constant magnetostriction) of the magneto-optical effect, measured at a fixed value of the alternating magnetic field. The size of the floor depends on the material being studied.

The invention is illustrated by the following example.

A steel wire with a diameter of 0.2 mm is placed in an external alternating magnetic field of 200 Oe. A beam of light is directed at it and the magnetic reflection e is measured depending on the tensile stress applied to the wire. The observed increase in q with increasing applied voltage indicates that the test piece is characterized by positive magnetostriction.

The minimum value of the magneto-optical effect d (in relative units), measured using the technique used, is 5 -10. This means that the minimum recorded voltage applied to the test sample is 5–10 MPa, which is almost an order of magnitude lower than the strain gauges described above.

The proposed method provides for focusing a light beam in spots with a diameter of up to several microns and scanning it over the surface of the test material. This makes it possible to measure the stress distribution in the longitudinal and transverse directions relative to the axis of the applied mechanical loads, as well as to study various types of samples - up to microwires and film coatings.

Thus, with this method of measuring mechanical stresses, the sensitivity and signal-to-noise ratio are increased, the surface quality of the tested part is not affected, and measurements of the stress distribution in the longitudinal and transverse directions are acceptable

relative to the axis of the applied mechanical loads, the types of measured samples are expanding.

Claims (1)

SUMMARY OF THE INVENTION A method for measuring mechanical stresses is as follows. that they direct polarized radiation towards the object under study, affect the object, record the radiation characteristics and from them determine the mechanical stresses and the strength and so that, in order to increase sensitivity, the studied object is placed in the gap of the toroidal magnet, the polarized radiation is focused on the surface of the object is spot, much smaller than the characteristic size of the heterogeneity of the voltage distribution, the effect is carried out by an alternating magnetic field at a frequency different from network, as the recorded characteristics, choose the constant and variable components of the intensity of the reflected radiation, the mechanical stresses at the point are determined by the ratio of the components using the calibration curve, scanning the surface of the object with focused radiation, determining the voltage distribution in two directions.