RU2577037C1 - Method for eddy current monitoring of thickness of composite materials on non-metal substrates and device therefor - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: group of inventions relates to measurement equipment and can be used for evaluation of reliability and quality of multilayer structures from polymer composite materials based on control of thickness of layers. Method is characterised by that calibration characteristic is measured first, area of measuring thickness of composite material is fitted with metal inserts of small surface area, eddy current converter is installed on surface of controlled composite material in centre of zone of measuring thickness, signal proportional to measured period oscillator and thickness of measured composite material, additionally generated signals support a self-excited oscillator, value proportional to period. Method includes determining a signal proportional to difference of period of oscillation measuring and reference oscillator. Method includes linearising received signal. Before each measurement of thickness, eddy current converter is installed outside zone of control and method then includes measuring a signal proportional to difference of signal periods of reference and measuring active oscillators, and specifying linearised signal, value of thickness on recording device. Method is carried out using a device including an eddy current converter with inductance coil, a measuring self-oscillator, a recording device, a reference generator with a second inductance coil, meter of period of oscillation oscillator, meter of period of oscillation of reference oscillator, a subtractor/adder meters oscillation period, time correction unit, control unit of time correction unit and transfer function lineariser.

EFFECT: technical result is improved measurement accuracy and reliability of results of evaluation of technical and operational state of structures and their elements.

2 cl, 4 dwg

Description

Technical field

The group of inventions relates to the field of measurement technology and can be used to assess the reliability and quality of multilayer structures made of polymer composite materials (PCM) based on control of the thickness of the layers.

The invention can be used to control the reliability and quality of complex spatial multilayer PCM structures both during production and during operation: spatial mesh structures, spacecraft compartments, rocket engines, pipelines, pressurized vessels, etc.

Particularly effective is the application of the claimed invention in testing potentially dangerous and expensive to manufacture structures, which, on the one hand, have high demands on reliability and quality of operation, and on the other hand, they are quite expensive and time-consuming to manufacture in order to be large enough the number of designs could be replaced by other products having the required parameters. An accurate measurement of thickness is very important for rocket and space technology products, where mutually exclusive requirements exist: when, on the one hand, it is necessary to provide heat-shielding characteristics of the structure (i.e., increase the thickness of the structure), and on the other hand, there are restrictions on weight and overall sizes that require a reduction in material thickness. In this case, it is necessary to identify potentially dangerous places (structural units), which in the first place can collapse (due to a change in thickness compared to a given one), which can lead to an accident and which may need to be strengthened.

State of the art

Measuring the thickness of the material is an urgent task in the process of creating effective and reliable structures from various materials.

There are a fairly large number of methods for measuring the thickness of a material: the X-ray method, the ultrasonic method, the visual optical method, and the eddy current method.

All methods have their own characteristics and applications for controlling the thickness of various materials. So, the X-ray method is mainly used to control the thickness of metal; the ultrasonic method has a large scope for various materials, but requires a media interface and an appropriate degree of homogeneity of the controlled material in terms of the passage of acoustic waves; the optical method requires visual access to a controlled surface; The eddy current method has a wide range of applications, but is applicable only to non-conductive materials with dielectric characteristics that are fairly uniform in volume of the material.

A promising direction in modern technology is the use of polymer composite materials, which have several advantages over traditional materials - metals, especially in the aerospace industries, engineering, energy, etc. Such materials require a special approach, new solutions in the development and creation of methods and means of assessing their reliability operation. This is due to the wide variety of types of such materials, the specific features of the structures made of them and the manufacturing technology and the random change in the physicomechanical and strength characteristics, a large variety of types of materials and their characteristics.

In addition, these materials in most industries operate under static and dynamic loads.

It is impossible to improve the quality of structures without a reliable assessment of quality criteria. Accordingly, it is impossible to develop measures and technologies to improve the quality of structures. One of the signs of the quality of structures, especially in the aerospace and aerospace industries, is the overall dimensions and energy characteristics, which are determined including and thicknesses of materials used in the construction.

Given that such structures are, as a rule, quite expensive both in cost terms and in the complexity of manufacturing, and it is obvious that failure of a structure leads to large financial and other losses, it is necessary, on the one hand, to test each structure for testing the subject of compliance of its strength characteristics with the required, and on the other hand, these tests should minimize “injure” the structure with maximum information content of the test results.

Here, non-destructive testing methods, including methods for controlling the thickness of construction materials. They allow you to objectively determine the actual state of the structure, evaluate the reliability of operation and give recommendations for repair or restoration.

There are repeated attempts to solve the problem of measuring PCM thickness by various methods - ultrasound, X-ray, etc. However, they did not lead to the desired results, due to a number of reasons.

1. A large random variation in the physical and mechanical characteristics of the PCM.

2. The absence of a pronounced interface between the layers.

3. The absence of a metal substrate under the measured PCM layer.

4. A change in the dielectric characteristics of the measured materials and a number of other reasons.

There are a large number of methods and means for controlling the thickness of RMBs without direct visual access. The analysis and experimental studies showed that the PCM thickness is most optimally controlled by the eddy current method. This is due to the following factors:

lack of direct access to the inner layers, which makes it impossible to use optical visual control,

the presence of a large spread of acoustic characteristics and the absence of a media interface, which makes acoustic control practically inapplicable,

large overall dimensions and complex configuration of structures, which significantly complicate the use of the x-ray method.

Methods for controlling the thickness of a PCM by the eddy current method are described, in sufficient detail, in the following materials.

1. V.V. Klyuev, Yu.K. Fedosenko, V.A. Korovyakov and V.O. Watermelons. USSR copyright certificate No. 1087768, cl. G01B 7/06 04/23/84, bull. No. 15 dated 04/23/84.

2. S.V. Krivonosov. Patent for invention No. 2198384, RF, bull. No 4 on 02/10/03.

3. Patent No. 2419763. Zhavoronko Alexander Ivanovich (RU), Krivonosov Sergey Vladimirovich (RU), Khlupnov Vladimir Alexandrovich (RU). Vortex Thickness Gauge. Publ. May 27, 2011, and others.

A common drawback of all currently known methods and means of eddy current control of the thickness of the PCM is the following:

- all methods and tools provide acceptable accuracy of controlling the thickness of materials only on a continuous metal substrate, which is associated with the physical processes of the propagation of eddy currents, and do not allow measuring the thickness of PCM on polymer substrates,

- there are no ways to exclude the influence of random changes in the dielectric properties of controlled materials on the results of thickness measurements.

Therefore, today there is a need to create a method and device for measuring the thickness of layers of multilayer real structures from PCM, which can be applied in practice for a wide range of objects using simple and accurate equipment suitable for operation in industrial conditions (i.e., in noise conditions interference, etc.).

The present invention is aimed at solving the problem of providing operational control of the thickness of the layers of multilayer complex structures and their elements from PCM in the production process and in real operating conditions, determining areas of thickness mismatch of regulatory documentation, developing recommendations for eliminating defects or restoring the structure.

That is, ultimately, the invention is aimed at improving the safety of the operation of complex potentially dangerous structures from PCM.

Closest to the claimed method and device is a method of eddy current control of the thickness of the PCM and a device for its implementation, described in the work: Potapov A.I., Syasko V.A. Non-destructive methods and means of controlling the thickness of coatings and products: Scientific, methodological and reference manual. - SPb., 2009 .-- 904 s., Ill. (p. 92-93).

A known method of eddy current control of the thickness of coatings of composite materials on non-metallic substrates includes installing a metal embedded element under the PCM, installing an eddy current transducer on the surface of the material under control at a thickness measuring point, measuring a signal proportional to the frequency of the measuring oscillator U _ISM with a period T _ISM , while the signal period measuring generator T _{ISM is} proportional to the thickness of the measured coating, the registration of the thickness value on the recording device swarm.

The known eddy current device for controlling the thickness of a PCM on a metal substrate includes an eddy current transducer with an inductor, a measuring oscillator, a recording device, while an eddy current transducer inductor is included in the oscillating circuit of the measuring oscillator, and the output of the measuring oscillator is connected to a recording device. The disadvantages of the known method and device is the low sensitivity, which does not allow measuring with small error large thicknesses (greater than the diameter of the eddy current transducer) on a discontinuous and small area embedded metal element.

SUMMARY OF THE INVENTION

Thus, there is a need to create a method and a device implementing it, providing a measurement of the thickness of the PCM in real products.

The technical result achieved by using the claimed group of inventions is to increase the accuracy of measuring the thickness of the PCM layers, increase the reliability of the results of assessing the technical and operational status of complex structures and their elements from PCM.

The technical result in terms of the method is achieved due to the fact that the calibration characteristic is preliminarily constructed, which reflects the relationship between the measured signals and the thickness value on the reference samples U _et = U _et (h), where h is the thickness of the reference sample, in the thickness measurement zone of the composite material Embedded metallic elements of small area, eddy current transducer mounted on the surface of controlled composite material in the center of the thickness measurement zone is measured U _MOD signal proportional to Heat-T _MOD measuring oscillator and the measured thickness of composite material, further comprising generating the reference signals autogenerator U _op, the magnitude proportional to the period T _op is determined signal proportional to the difference in the period of measuring and the reference oscillator oscillation _with U = U _a (T _op T _meas), linearize the received signal as follows: U _l = U _s × U _et (h), while the signal U _{l is} proportional to the thickness h, before each thickness measurement the eddy current transducer is installed outside the control zone and the signal is measured cash U _c0 = U _c0 (T _op -T _ISM ), proportional to the difference of the periods of the signals of the reference and measuring oscillators, and specify the linearized signal U _l = U _s × U _et (h) as follows: U _l ^y = (U _s + U _c0 (T _op -T _ISM )) × U _et (h), the thickness value is recorded on a recording device.

The technical result in terms of the device is achieved due to the fact that the eddy current device controls the thickness of composite materials on non-metallic substrates, including an eddy current transducer with an inductor, a measuring oscillator and a recording device, while the transducer inductor is included in the oscillating circuit of the measuring oscillator, and the output of the measuring the oscillator is connected to a recording device, according to the invention additionally introduced reference a generator with a second inductor, an oscillator of a measuring oscillator, an oscillator of a reference oscillator, a subtractor / adder of an oscillator, a time correction unit, a control unit for a temporary correction and a linearizer of a transfer function, while the eddy current transducer inductor is connected to the input of a measuring oscillator , the second inductor is connected to the input of the reference oscillator, the output of the measuring autogen the oscillator is connected to the input of the oscillation period meter of the measuring oscillator, the output of the reference oscillator is connected to the input of the oscillation period meter of the reference oscillator, the first outputs of the oscillation period meter of the oscillator and the oscillation period meter of the reference oscillator are connected respectively to the first and second inputs of the subtractor / adder of oscillation period meters, the second outputs of the oscillation period meter of the measuring oscillator and Nogo oscillator connected to first and second inputs of the correction unit of time, the control unit output is connected to the third input time correction block units outputs a subtractor / adder and temporary adjustments are connected to first and second inputs of the linearizer of the transfer function, whose output is connected to the recording device.

Brief Description of the Drawings

The invention and the possibility of achieving a technical result will be more clear from the following description with reference to the position of the drawings, where:

FIG. 1 shows a functional diagram of a device for controlling thickness,

FIG. 2 shows the calibration curve of the device for controlling the thickness,

FIG. 3 shows the layout of the eddy current transducer when measuring thickness

FIG. 4 - an example of the implementation of one of the blocks of the device is a circuit diagram,

In the drawings, the following notation:

1 - eddy current transducer,

2 - measuring oscillator,

3, 16 - inductors,

4 - reference oscillator with a second inductor,

5 - meter oscillation period of the measuring oscillator,

6 - meter oscillation period of the reference oscillator,

7 - a subtractor (adder) of measuring instruments of the period of oscillations

8 - block time corrections,

9 - linearizer transfer function,

10 - recording device,

11 - control unit block time corrections,

12 - electronic unit

13 - metal embedded element of a small surface area: for example, a metal ring,

14 - controlled polymer composite material,

15 - non-metallic substrate.

Preferred Embodiment

As an example in FIG. 4 shows a circuit diagram of a set of functionally connected blocks 6-11 with an indication of standard designations of electrical elements in the diagram.

The device contains an eddy current transducer 1 with an inductor 16, a measuring oscillator 2, a recording device 10, a reference oscillator 4 with a second inductor 3, a measuring period of oscillation of a measuring oscillator 5, a measuring period of oscillation of a reference oscillator 6, a subtractor / adder of measuring instruments of oscillating period 7, block time corrections 8, the control unit of the time corrections block 11, the linearizer of the transfer function 9. The output of the eddy current transducer 1 with an inductor 16 is connected to the input of the measuring oscillator 2. The inductor 3 is connected to the reference oscillator 4.

The output of the measuring oscillator 2 is connected to the input of the meter of the oscillation period of the measuring oscillator 5. The output of the reference oscillator 4 is connected to the input of the meter of the oscillation period of the reference oscillator 6. The first outputs of the meter of the oscillation period of the measuring oscillator 5 and the meter of the oscillation period of the reference oscillator 6 are connected respectively to the first and second inputs of the subtractor / adder of the oscillation period meters 7, the second outputs of the oscillation period meter of the measuring oscillator 5 and the oscillation period meter of the reference oscillator 6 are connected to the first and second inputs of the time correction block 8, the output of the control unit 11 is connected to the third input of the time correction block 8, the outputs of the subtractor / adder blocks of the oscillation period meters 7 and time corrections 8 are connected to the first and the second inputs of the linearizer transfer function 9, the output of which is connected to the recording device 10.

The method is as follows.

In the manufacturing process of the product or before conducting a thickness measurement between the composite material 14, the thickness of which is measured and a non-metallic substrate 15, a metal ring 13 or a metal mesh is installed. The difference between these embedded elements from a solid metal substrate is that they do not introduce additional defects such as discontinuities in the structure and practically do not increase the content of metal elements in the PCM structure. This is especially important for observing the conditions of radar detection of the structure. The small sizes of such embedded elements realize small values of the eddy currents induced in them, which required the creation of a special highly sensitive thickness gauge that provides accurate measurement of large thickness with high accuracy.

The eddy current transducer 1 is installed on a controlled surface 14 outside the control zone, i.e. outside the location of the embedded metal element 13.

A feature of the device is the ability to control the operation of the block of time corrections, which is carried out using block 11 by means of a button located on the eddy current transducer. When the button of the control unit 11 is pressed in the unit, the periods of the measuring and reference self-oscillators are fixed, and after about 2 seconds one more fixation. Then, the drift of the period difference is calculated and a time-extrapolation correction signal is generated for block 9. This operation is performed before each measurement on the embedded element 13, which eliminates the accumulated signal drift and significantly increases the sensitivity of the device and reduces the measurement error.

Then directly measure the thickness of the material above the embedded element. The eddy current transducer 1 is installed above the center of the embedded element 13. The location of the center of the embedded element is determined in two ways:

- at a previously marked location during the installation of the embedded element,

- to determine the maximum signal on the device or the minimum value of the thickness of the material 14 by moving the eddy current transducer 1 along the surface of the material 14 in the location area of the embedded element.

After installing the eddy current transducer 1, the frequency of the measuring oscillator 2 is set in accordance with the thickness of the dielectric coating. To increase the sensitivity using the subtractor / adder 7, the difference period is determined by subtracting the period of the reference oscillator 4 from the period of the measured signal. The resulting difference depends on the thickness of the coating according to a nonlinear law. For the purpose of linearization in the device for thickness control - eddy current thickness gauge - using a linearizer 9, a signal proportional to the thickness is generated, which is fed to the indicator 10. The block of time corrections 8 periodically compares the periods of the measuring and reference oscillators when the transducer is located outside the control range, then forms extrapolation correction signal to clarify the operation of the linearizer 9.

The calibration characteristic is preliminarily measured, which reflects the relationship between the measured signals and the thickness value on the reference samples U _et = U _et (h), where h is the thickness of the reference sample. In the zone of measuring the thickness of the composite material set metal embedded elements 13 of a small area. Install the eddy current transducer 1 on the surface of the controlled composite material 14 in the center of the thickness measurement zone. The signal U _ISM is proportional to the period T _{ISM of the} measuring oscillator 2 and the thickness of the measured composite material 14. Additionally, signals are generated by the reference oscillator 4 U _op , proportional to the period T _op. Determine the signal proportional to the difference in the oscillation period of the measuring and reference oscillator U _c = U _c (T _op -T _ISM ). The received signal is linearized as follows: U _l = U _c × U _et (h), while the signal U _{l is} proportional to the thickness h. Before each thickness measurement, the eddy current transducer is installed outside the control zone and the signal U _с0 = U _с0 (Т _op -T _ISM ) is measured, proportional to the difference between the periods of the signals of the reference 4 and the measuring oscillators 2, and the linearized signal U _l = U _c × U _{et is} specified ( h) as follows: U _l ^y = (U _c + U _c0 (T _op -T _ISM )) × U _et (h). The thickness value is recorded on the recording device 10.

In order to increase the productivity and reliability of the control, some additional functions are implemented in the device:

- preliminary separation of the measured thickness into arbitrary ranges;

- sound and LED indicator for combining the center of the eddy current transducer with the center of the embedded element (ring or grid).

The thickness control scheme is shown in FIG. 3.

Experimental studies were carried out on structures made of composite materials. The design was a spherical PCM substrate with a rubber-like coating applied to it. Between the substrate and the coating are metal rings 0.1 mm thick, with an outer diameter of 15 mm, and an inner diameter of 11 mm. The table shows the main results of experimental studies of the developed device-thickness gauge and thickness gauge, adopted as the closest analogue.

The claimed device was certified, which confirmed the technical characteristics of the device: the limiting measurement of the coating thickness is 32 mm (in fact, experiments showed that the device allows measuring thickness up to 40-45 mm without loss of accuracy and changing the eddy current transducer).

All used in a device that implements a method of eddy current control of the thickness of composite materials, electronic components are built on the basis of standard microprocessor circuits and microprocessor assemblies with reprogrammable memory devices (see Ugryumov EP Digital circuitry: Textbook for universities. - 3rd ed ., rev. and add. - SPb .: BHV - Petersburg, 2010), therefore, the invention is industrially applicable.

Claims (2)

1. The method of eddy current control of the thickness of composite materials on a non-metallic substrate, characterized in that
preliminarily, a calibration characteristic is constructed that reflects the relationship between the measured signals and the thickness value on the reference samples U _et = U _et (h), where h is the thickness of the reference sample,
in the zone of measuring the thickness of the composite material set metal embedded elements of a small area,
install the eddy current transducer on the surface of the controlled composite material in the center of the thickness measurement zone,
measuring the signal U _ISM proportional to the period T _{ISM of the} measuring oscillator and the thickness of the measured composite material,
additionally generate signals by the reference oscillator U _op , in magnitude proportional to the period T _op ,
determine a signal proportional to the difference in the oscillation period of the measuring and reference oscillator U _s = U _s (T _op -T _ISM ),
linearize the received signal as follows: U _l = U _s × U _et (h), while the signal U _{l is} proportional to the thickness h,
before each thickness measurement, the eddy current transducer is installed outside the control zone and the signal U _с0 = U _с0 (Т _op -T _ISM ) is measured, proportional to the difference between the periods of the signals of the reference and measuring oscillators, and the linearized signal U _l = U _c × U _et (h) is specified in the following way:

,
register the thickness value on the recording device. 2. An eddy current device for controlling the thickness of composite materials on non-metallic substrates, including an eddy current transducer with an inductor, a measuring oscillator and a recording device, while the transducer inductor is included in the oscillating circuit of the measuring oscillator, and the output of the measuring oscillator is connected to a recording device, characterized in that it additionally includes a reference oscillator with a second inductor, a perimeter meter yes oscillations of the measuring oscillator, oscillator of the oscillator reference oscillator, subtractor / adder of the oscillation period meters, time correction unit, control unit of the time correction unit and the linearizer of the transfer function, while the inductor of the eddy current converter is connected to the input of the measuring oscillator, the second inductor is connected to the input reference oscillator, the output of the measuring oscillator is connected to the input of the oscillation period meter a self-oscillator, the output of the reference oscillator is connected to the input of the oscillation period meter of the reference oscillator, the first outputs of the oscillation period meter of the measuring oscillator and the oscillator of the reference oscillator are connected respectively to the first and second inputs of the subtractor / adder of the oscillation period meters, the second outputs of the oscillation period meter of the measuring oscillator and measuring oscillation period of the reference oscillator connected to the first and second inputs of the block time corrections, the output of the control unit is connected to the third input of the time correction unit, the outputs of the subtractor / adder blocks and the time corrections are connected to the first and second inputs of the linearizer of the transfer function, the output of which is connected to the recording device.

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