RU2746765C9 - Mechanical stress measurement sensor based on micro-wires with positive magnetostriction - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measuring equipment and performs the function of a mechanical stress sensor. The sensor consists of an amorphous ferromagnetic micro-wire with positive magnetostriction, located along the axis of the differential measuring coil, and an external coil that sets an alternating magnetic field along the axis of the micro-wire. The measuring differential coil is connected to an amplifier, the output of which is connected to an analog-to-digital converter (hereinafter – ADC), made as an individual device or as part of a microcontroller. The output of the signal from the ADC is implemented on a personal computer. The sensor design makes it possible to measure mechanical stresses by changing the coercive force, the switching field, and the time dependence of the electromotive force caused by the magnetic reversal of the micro-wire. At the same time, it is possible to remove the sensor case without completely separating it from the object under study to replace the amorphous ferromagnetic micro-wire during the operation of the sensor.

EFFECT: increase in the sensitivity of the stress recording system based on amorphous micro-wires, reducing interference, and ensuring the interchangeability of the sensitive element (amorphous ferromagnetic micro-wire).

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Description

The invention relates to the field of non-destructive testing and technical diagnostics of materials and can serve as a mechanical stress sensor.

A known sensor for measuring mechanical stresses (RU 2552124, publ. 06/10/2015), which includes a rectangular plate made of polymer material, on the upper surface of which a recess is made, in which the detector is placed, while inside the rectangular plate along the longitudinal axis there is a pre-stressed amorphous a ferromagnetic microwire made of cobalt-enriched alloys, placed inside a measuring coil in the form of counter-connected copper wire solenoids. This device makes it possible to obtain microwire hysteresis loops, analyze them on a personal computer and draw conclusions about the type of applied stresses (tensile, twisting) and their magnitude by changing the shape of the curves.

The disadvantage of this device is the location of the microwire in the polymer matrix, which can potentially deteriorate the magnetomechanical properties of microwires in the glass shell due to the effect of adhesion between the glass shell and the polymer. In addition, this device uses microwires with negative magnetostriction, which do not differ in the bistable nature of magnetization reversal, such as microwires with positive magnetostriction, but have an oblique hysteresis loop. Analysis of the magnetization reversal curves of microwires with positive magnetostriction can provide greater sensitivity to deformation and potentially more convenient for recording the magnetization reversal signal.

A composite sensor is known (WO 2010055282, publ. 20.05.2010). The composite sensor is also based on the location of the microwire in a polymer matrix. An alternating electric current is passed through the microwire and the voltage on the microwire is recorded. This composite sensor is based on the use of the giant magnetic impedance effect and the giant stress impedance effect.

The disadvantage of this device is the difficulty in measuring local mechanical loads due to the need to use long length microwires. At the same time, this device is highly sensitive to external magnetic fields, which can distort the results of measuring mechanical stresses.

A known sensor for measuring mechanical deformations (RU 2654827, publ. 05/22/2018). The sensor contains a rectangular plate with cross-sections that provide the possibility of stretching not only in the longitudinal but also in the transverse direction. A miniature solenoid is located in the plate seat, inside which a magnetically sensitive element is located. The miniature solenoid is connected to a DC power supply. An amorphous ferromagnetic microwire (magnetically sensitive element) is connected to an alternating current source. The voltage measurement sensor uses the effect of low-angle rotation of the magnetization relative to the microwire axis; in this case, a signal with a double frequency relative to the frequency of the current flowing through the microwire is recorded in the measuring coil. The change in the EMF signal of the doubled frequency makes it possible to register the change in the stress state of the microwire.

The disadvantage of this device is the complexity of recording a signal of the proposed type, which potentially lowers the sensitivity of the device, despite the originality of the proposed approach.

A known method for measuring physical quantities (WO 2007116218, publ. 18.10.2007). This method, which is closest to the proposed invention, uses a sensor based on amorphous ferromagnetic microwires with non-zero magnetostriction. The method is based on the registration of the electromotive force (EMF) arising in the measuring solenoid during magnetization reversal of the microwire in an alternating magnetic field. To register the change in the stress state, the switching field is measured, obtained by comparing the curves of the electromotive force and the external alternating magnetic field.

The disadvantages of this approach are only a general description of the signal registration system without specifying the execution mechanisms and achieving a technical result. In addition, the proposed method is sensitive to external magnetic fields and is based only on the registration of the switching field.

The invention achieves the technical result, which consists in measuring the level of mechanical stresses, increasing the sensitivity of the stress recording system based on amorphous microwires in comparison with existing analogues due to the use of a combined approach in recording various types of mechanical loads (tension, torsion), reducing noise and ensuring the replaceability of the sensitive element (amorphous ferromagnetic microwire).

The specified technical result is achieved as follows.

The proposed sensor for measuring mechanical stresses consists of an amorphous microwire with positive magnetostriction, which is a sensitive element of the measuring device. The amorphous microwire is held together with intermediate strands or plates using aluminum clamping holders. Intermediate filaments or plates are required to position the microwire in the center of the measurement circuit to eliminate external magnetic interference. Such a connected structure (microwire and filaments or plates) is located along one of the axes of the differential measuring coil, which is two oppositely connected and symmetrically located solenoids or a coil wound with a figure eight. A differential measuring coil with an amorphous microwire inside is placed on the axis of an external solenoid that sets an alternating magnetic field. An alternating electric current is supplied to the external solenoid. The alternating electric current in the external solenoid creates an alternating magnetic field in the area of the amorphous microwire and causes its magnetization reversal. As a result, an EMF signal appears in the differential measuring coil, caused by the magnetization reversal of the amorphous microwire. In this case, the EMF associated with the presence of the measuring coil in an external alternating field is compensated by the opposite connection of the solenoids of the differential measuring coil or winding the differential measuring coil with a figure eight. The outer ends of the intermediate threads or plates are fixed on the edge clamping movable holders located outside the outer solenoid. During measurement, the edge clamping movable holders are fixed to the test object by means of adhesive bonding or welding. In this case, the amorphous microwire and the intermediate filaments or plates associated with it are pulled between the edge clamping holders. Between the edge clamping movable holders and the external solenoid located in the removable housing of the device, there are intermediate plates with a circular cutout in the center, which prevent the movable holders from sliding inside the external solenoid in the event of negative deformation on the object under study. The body of the device has a cylindrical shape and contains an external and differential measuring solenoids and an amorphous microwire with intermediate threads or plates. The body diameter is smaller than the maximum transverse dimensions of the edge clamping holders. The design of the case provides for the possibility of its removal by separating the two halves of the case from each other by removing the screws fastening both halves of the case or in another way that allows the case to be removed without separating the edge clamping holders from the object under study.

The differential measuring coil is connected to an analog-to-digital converter (ADC) of a microcontroller or an isolated ADC with the possibility of further connection to a computer. If necessary, it is possible to install a signal amplifier from a differential coil to connect to the ADC. An external solenoid is connected to a sinusoidal pulse generator with the ability to generate oscillations with a frequency of up to 10 kHz. Such a maximum frequency value is necessary to exclude the influence of the dynamic effects of magnetization reversal of the microwire on the measurement results. If necessary, the measured signal of the microwire reversal EMF can be integrated to obtain a magnetic hysteresis loop and the values of the microwire coercive force. With an increase in the level of stresses in a microwire, for example, during stretching, its coercive force and the switching field increase. This dependence of the coercive force and the switching field on stresses is reversible up to stresses close to half the tensile strength of the material (value about 1.5 GPa) for amorphous microwires based on Fe.

An amorphous ferromagnetic microwire with positive magnetostriction can be made on the basis of alloys with a predominant iron content, for example: Fe _77.5 Si _7.5 B ₁₅ , Fe _73.8 Cu ₁ Nb _2.1 B _9.1 Si ₁₃ and others.

Amorphous ferromagnetic microwire can have a length of 20 to 150 mm.

An amorphous ferromagnetic microwire with and without a glass sheath can be used.

The external solenoid is made in the form of a multilayer coil wound coil to coil. The density and number of turns depends on the range of magnetic fields in which the sensor is required to operate, as well as the size of the sensor. The main shift of the dependences of the EMF signal measured by the sensor occurs in the range of maximum field values from -100 to 100 oersted. Accordingly, the main requirement is the operation of the solenoid in this range of fields.

The differential measuring coil is made of copper wire with a diameter of no more than 120 microns. The diameter of the winding wire can be selected based on the required sensor dimensions and the possibility of connecting the amplifier to a differential coil.

Intermediate threads or plates can be made of aluminum or other material that introduces small distortions into the EMF signal recorded from the differential measuring coil.

Increasing the sensitivity of the voltage registration system is associated with the possibility of simultaneous registration:

- coercive force, measured by the magnetic hysteresis loop, obtained by integrating the dependence of the electromotive force for;

- the switching field obtained by comparing the values of the intensity of the reversing field and the values of the EMF curve versus time;

- changes in the level of mechanical stresses by recording the time shift of the peaks of magnetization reversal on the curve of the electromotive force from time to time.

In addition, an increase in the sensitivity of the system is provided by:

- using amorphous microwires with positive magnetostriction, which are characterized by a bistable nature of magnetization reversal and, as a consequence, a large steepness and amplitude of the peaks corresponding to magnetization reversal on the EMF curve versus time;

- using a differential measuring coil in the form of two oppositely connected solenoids or a coil wound with a figure eight, which excludes the influence of the EMF on the measured signal, which is not associated with magnetization reversal of the amorphous microwire.

A significant range of microwire length (from 20 to 150 mm) allows the manufacture of a sensor for measuring loads with a greater or lesser degree of locality.

The features that distinguish the proposed voltage sensor from the closest to it, known from the patent WO 2007116218 (prototype), characterize the mechanism for placing the microwire along the axis of the external and differential solenoids, which makes it possible to eliminate the influence of interference from external magnetic fields, fixing the microwire through intermediate threads or plates with movable edge holders , the presence of a split body of the device, which makes it possible to replace the internal elements of the device body (external solenoid, differential measuring coil, amorphous microwire, aluminum clamping holders, intermediate threads or plates), the possibility of simultaneous recording of the coercive force, switching field and temporary shift of the peaks of magnetization reversal on the EMF curve from time to time, the use of microwires of various lengths (from 20 to 150 mm) to achieve more or less locality of the measured voltage level.

The invention is illustrated by drawings. FIG. 1 shows a top view of the sensor, FIG. 2 shows the electrical circuit of the sensor, FIG. 3 shows the change in the EMF signal arising from the magnetization reversal of the microwire, when the microwire is stretched.

FIG. 1, 2 show intermediate threads or plates 1, differential measuring coil 2, external solenoid 3, sensor housing 4, amorphous ferromagnetic microwire 5, edge clamping movable holders 6, intermediate plates with a circular cut in the center 7, aluminum clamping holders 8, sinusoidal generator pulses 9, ADC 10.

FIG. 3a on the presented graph on the Y axis shows the values of the EMF in mV arising in the differential coil during magnetization reversal of the microwire, along the X axis the values of time are plotted in μs. FIG. 3b on the presented graph along the Y axis the values of the magnetic sinusoidal field strength in oersteds are shown. The X-axis is the time in μs. As seen in FIG. 3a, when an external tensile load is applied, the position of the intense peak of the EMF of the magnetization reversal curve shifts to the right along the time axis. This fact is used to assess the change in the voltage level without comparing the values of the EMF signal and the external magnetic field.

The sensor works as follows. The sensor can be installed on the surface of the measurement object using adhesive bonding or welding the object with the edge clamping movable holders 6. When mechanical loads (tensile or twisting) are applied to the measurement object, the microwire 5 also experiences these loads, which leads to a change in the magnitude of the coercive force and the switching fields. This can be useful for analyzing the type of mechanical stress. In this case, the standard operating mode of the sensor is to analyze the shift of the EMF signal peak along the time scale when the stress state of the microwire changes. The nominal frequency of the sensor is 2.5 kHz. To increase the amplitude of the measured signal and the sensitivity, it is possible to increase this frequency up to 10 kHz.

The EMF signal arising from the magnetization reversal of the microwire in the absence of an external load is considered a reference and corresponds to a zero voltage value.

Fastening the microwire 5 with aluminum clamping holders 8 allows replacing the sensitive element (microwire 5) in case of damage or the need to change the sensitivity of the sensor to external mechanical influences. In this case, it is possible to remove the sensor body 4 to replace the microwire 5 without directly removing the sensor from the object under study. For this, the sensor body 4 must have smaller maximum transverse dimensions than the edge clamping movable holders 6.

Changing the range of mechanical stresses in which the sensor can operate is possible by using microwires: 1) of different diameters, which corresponds to a different initial level of hardening stresses; 2) with different thickness of the glass shell in relation to the diameter of the wire (the higher this parameter, the higher the internal voltage level of the microwire). Initially, the most stressed microwires have a sharper change in the coercive force, switching field, shift of the peak of the EMF curve when an external mechanical load is applied.

The proposed sensor achieves improved magnetomechanical characteristics in comparison with analogs due to: 1) the possibility of using microwires with different stress state and length; 2) the use of microwires with positive magnetostriction, characterized by the sharpest and most intense dependences of the EMF signal on time, arising in the measuring coil when the microwire is magnetized; 3) the possibility of using three methods of registering a change in the stress state (by changing the coercive force, switching field, by directly recording the time of the shift of the peak of the EMF curve during stretching). At the same time, the sensor implements the ability to replace the sensitive element in case of damage or the need to change the sensor parameters.

Claims (1)

A sensor for measuring mechanical stresses based on microwires with positive magnetostriction, consisting of an amorphous ferromagnetic microwire located along the axis of a differential measuring coil, which is two oppositely connected symmetrically located solenoids or a coil wound with a figure eight, and an external coil that sets an alternating magnetic field along the axis of the microwire, in which the ends of the microwire are fixed by clamping holders connecting the microwire with intermediate threads or plates, the other ends of which are fixed by edge clamping movable holders, limited from the coil side by stops that prevent the wire from bending relative to the coil axis, while the outer coil is connected to the generator of sinusoidal pulses for generation along the axis of the coil of a uniform sinusoidal magnetic field, and the differential coil is connected to the analog-to-digital converter directly or through a power amplifier, while the analog-to-digital the converter is connected to a personal computer, characterized in that the amorphous microwire is placed along the axis of the external and differential solenoids, eliminates the influence of interference from external magnetic fields, while the amorphous microwire is fixed between the edge movable holders through intermediate threads or plates, while the external solenoid, differential coil and amorphous microwire are placed in a detachable body of the device, which allows replacement of internal elements of the case, namely, an external solenoid, a differential measuring coil, an amorphous microwire, aluminum clamping holders, intermediate threads or plates, while there is a possibility of simultaneous recording of the coercive force, switching field and time shift of the peaks of magnetization reversal on the EMF curve versus time and the use of microwires of various lengths from 20 to 150 mm to achieve more or less locality of the measured voltage level.

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