RU2625261C1 - Method for determining thickness of two-layer materials and their constituent layers by means of elastic wave pulses introduced into control object and ultrasonic converter for its implementation - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: determination of the thickness of two-layer materials and their constituent layers by means of elastic wave pulses introduced into the control object is carried out by recording and analysing the arrival time of the acoustic pulses reflected from the surfaces of the control object and the boundaries of its layers. The thickness of the control object and its layers is determined by means of a combination of elastic body waves of different types, for which purpose both longitudinal and transverse waves are introduced into the same section of the control object. The thickness of the control object and its constituent layers is determined by recording and analyzing the arrival time of pulses reflected from the input surface and/or a set of pulses, resulting from both longitudinal and transverse waves propagating in the control object and interacting with the boundaries of its layers. The analysis is performed by solving simultaneous equations linking the determined parameters to known and measured quantities. The type of the solved simultaneous equations is determined by the specific configuration of the measuring system and the required measurement accuracy.

EFFECT: expansion of the range of material combinations of controlled bimetallic sheets, expansion of the possibilities for automation of the control process, and removal of restrictions on the nonparallelism of the interface of the base metal cladding layer of the ultrasonic input surface.

5 cl, 6 dwg

Description

Description of the invention

The invention relates to the field of non-destructive testing and thickness measurement of multilayer materials, for example, bilayer metal sheets and plates, and can be used to determine the thickness of bilayer materials and their constituent layers using pulses of elastic waves introduced into the object of control, as well as to detect defects: cracks, bundles etc. and areas of poor adhesion between the layers.

A known ultrasonic method for determining the thickness of the layers of the material using longitudinal waves, excited and received mainly normal to the surface of the control object. The method involves measuring the arrival times of signals reflected from the boundaries of the control object and layers, and calculating the thicknesses using very simple and well-known formulas. The method is implemented using a direct combined or separately combined ultrasonic transducer. The main disadvantage of this method is the limitation of its use if the numerical values of the acoustic impedances of the base material and the cladding layer are for longitudinal waves close to each other. In this case, a reflection acceptable from the measurement point of view cannot be detected from the layer boundary. Another disadvantage of the method and the device that implements it is its low sensitivity if the layer interface is not parallel to the ultrasound input surface. This situation often arises due to the technological features of the production of bimetallic plates and sheets. In automatic mode, control of weakly reflecting and non-parallel boundaries becomes very difficult or even impossible [1].

A device for measuring the thickness of surface layers and coatings is known, comprising a drill having at least one cutting edge, with each leading edge forming an angle of 45 ° with the axis of the drill; means for holding said drill and its rotation, a guide means comprising a guide plate having an opening passing through it with the possibility of rotation and reception of the specified drill during its operation; targeting means for measuring the width of the circular bands formed in the layer [2].

A known thickness gauge for measuring the thickness of the color coating layer on the steel substrate and the thickness of the non-conductive coating layer on the conductive substrate of non-ferrous metals, including a permanent magnet having poles creating a magnetic flux, a magnetic flux density sensor located near the poles of the specified permanent magnet so as to pick up magnetic field in the vicinity of these poles, electromagnetic coils located around these poles, as well as control means for receiving input signals from of said magnetic flux sensor, selecting one of said inputs for calculating the coating thickness based on the selected input [3].

A device for measuring the thickness of a film (adopted as a prototype) applied to a substrate not in contact with the film is known, in which the first ultrasonic sensor comprises means for measuring a first distance value between the upper surface of the film and a device in which the ultrasonic sensor contains an ultrasonic pulse generator, which generates an ultrasonic pulse directed to the surface of the film, and an ultrasonic transducer that receives the pulse after it is reflected from the surface of the film nki; a second electrical sensor is located in close proximity to said first means for measuring a second distance value between the upper surface of the substrate and the device; said first and second elements are located on the same side of the substrate; the means is operatively connected with the first and second means for calculating the film thickness by comparing the said values of the first and second distance values, the auxiliary sensor has a means containing sensors that are separated from the said means, a second electric sensor for measuring a third distance value between the upper surface of the substrate and the device ; all three sensors are located on one side of the substrate; the calculation of the film thickness is carried out by comparing the aforementioned first, second and third distance values [4].

A common disadvantage of the known method and device is the narrow range of material combinations of controlled bimetallic sheets, as well as the inability to simultaneously control the thickness of the coating layers and detect defects in the layers of materials: cracks, delaminations, etc., as well as areas of poor adhesion between the layers.

The aim of the present invention is to expand the range of material combinations of controlled bimetallic sheets, expand the capabilities for automating the control process, and also remove restrictions on the non-parallelism of the interface between the base metal / cladding layer of the ultrasound input surface.

This goal is achieved by the fact that in the known method for determining the thickness of bilayer materials and its constituent layers using pulses of elastic waves introduced into the object of control, it is carried out by recording and analyzing the time of arrival of acoustic pulses reflected from the surfaces of the object of control and the boundaries of its layers, while determining the thickness of the control object and its layers is carried out using a combination of elastic body waves of different types, for which both longitudinal and transverse waves, moreover, the thickness of the control object and its constituent layers is determined by recording the arrival time of pulses reflected from the input surface and / or a set of pulses due to both longitudinal and transverse waves propagating in the control object and interacting with the boundaries of its layers, and the analysis is carried out by solving a system of equations that connects the determined parameters with known values, and the form of the system of equations being solved is determined by a specific configuration walkie measuring system and the required measurement accuracy.

This goal is also achieved by the fact that longitudinal waves radiate into the material and receive from the material, as a rule, in a range of linear and / or solid angles α ₁ = 0 ± Δ ₁ , where α ₁ is the nominal input angle of the longitudinal wave, and the transverse waves as a rule, they radiate and accept at least in a range of linear angles α _t = α ₀ ± Δ _t with respect to the normal to the input surface, simultaneously satisfying two conditions, 8 ° ≤α _t ≤80 ° and α _t ≠ α _cr3 ± Δ _t, where α _t - nominal angle of input / reception of transverse waves to / from the material (s) adjacent / adjoining guide to the entry area, α _RP3 - a third critical angle of the material adjacent to the input area, and Δ _1, Δ _t - parameters defining the spectral range of input / reception angles depending on the nominal and extreme parameters control object.

If the input angle α _{t is} approximately equal to the third critical angle α _cr3 , then there is the possibility of the manifestation of the effect of the so-called “Non-mirror reflection” of the ultrasonic beam. This phenomenon can lead to errors in calculating the thickness of the layers. Therefore, the working range of angles α _t should not capture the third critical angle α _cr3 .

The achievement of the goal is also facilitated by the fact that the ultrasonic transducer, comprising a housing, as well as at least one group of one or more receiving, radiating or receiving-radiating elements. The converter housing is a box in which at least three blocks physically independent from each other are inserted and fixed in an adjustable spatial position, consisting of at least two active elements each, and the first of the blocks, as a rule, serves only to excite object control transverse elastic waves in a desired from the standpoint of the nominal geometry object and extreme control angle range satisfying conditions 8 ° ≤α _t ≤80 ° and α _t ≠ α _RP3 ± Δ _t, Torah block is usually only for reception of a control object transverse elastic waves arriving from the desired (in terms of nominal geometry and extreme control facility) directions range satisfying the conditions of 8 ° ≤α _t ≤80 ° and α _t ≠ α _RP3 ± Δ _t , and the third block, as a rule, serves both for radiation in the OK and reception of longitudinal elastic waves from the OK, carried out in a certain range of angles, corresponding to the condition α ₁ = 0 ± Δ ₁ . The working surfaces of at least two of these blocks are oriented and / or separated from each other so that the acoustic axes of the active elements of one of the blocks intersect in the object of control in a given depth range with the acoustic axes of the elements of the other block, and the acoustic axes of the elements of at least one more block nominally perpendicular to the surface of the object of control.

Achieving the goal is also facilitated by the fact that the transducer housing additionally contains components that make it possible to adjust at least the distance R between the blocks responsible for the excitation / reception of shear waves, and this distance is chosen from the condition that their acoustic axes (directly or after reflection from the boundaries of the control object ) intersect in the area of the nominal location of the common boundary of the materials, and the unit responsible for the excitation / reception of longitudinal waves is positioned so that the point / line of input of the longitudinal wave n was in the space between the two blocks responsible for the transverse waves.

This goal is also achieved by the fact that in the described converter the emitting and / or receiving and / or receiving elements of at least one of the blocks are made in the form of linear phased arrays, which allow controlling the direction of radiation and / or reception in the direction perpendicular to the axis of the block.

Implementation of the method and device

Consider two examples of the application of the proposed method and, accordingly, two possible configurations of the measuring system, which can be used for automatic control of multilayer materials.

Example 1

An example configuration with three converter blocks (emitting, receiving, and radiating / receiving) is shown in FIG. one.

Designations in figure 1:

P1 - radiating converter;

P2 - receiving converter;

P3 - emitting / receiving converter;

H ₀ - the thickness of the water layer;

H ₁ - the thickness of the base material;

H ₂ - the thickness of the cladding material;

H is the total thickness of the sheet;

C _0l is the longitudinal wave velocity in the water layer;

C _1l is the longitudinal wave velocity in the main material;

C _1t is the shear wave velocity in the main material;

C _2l is the longitudinal wave velocity in the cladding material;

C _2t is the shear wave velocity in the cladding material;

R is the distance between the emitting and receiving converters;

R / 2 - half the distance between the transmitting and receiving transducers;

BC - water layer;

OM is the main material;

PM - cladding material;

α, α * - angles of emission / reception of ultrasonic waves;

β, β * are the angles of refraction of ultrasonic waves at the interface between the water layer / base material;

γ is the angle of refraction of ultrasonic waves at the interface between the main material / cladding material.

Converters P1, P2, and P3 are placed in water. All transducers have fairly narrow or curved (de-focusing) active elements that create a fairly wide radiation pattern. Alternatively, part of the elements or all elements can be made in the form of phased arrays, providing the range of effective radiation-reception angles necessary for measurements.

The expected A-scan obtained with the help of the P2 converter, relevant to the circuit of FIG. 1 is shown in FIG. 2.

A typical A-scan view relating to P3 in FIG. 1 is shown in FIG. 3.

In FIG. 2 and FIG. 3 the following notation is introduced:

ZI - probe pulse;

C0 is the signal reflected from the surface;

C1 - signal reflected from the boundary of the main material (OM) / cladding material (PM);

C1.3 - the first bottom impulse;

C2 is the signal reflected from the lower border of the sheet;

C2.3 - second bottom impulse;

T0 is the time between ZI and CO;

T1 is the time between ZI and C1;

T2 is the time between ZI and C2;

T3 - time between C1.3 and C2.3;

A is the amplitude;

T is time.

The corresponding thicknesses of the layers H ₁ , H ₂ , and H (see FIG. 1) can be determined by at least two variants of the proposed method:

The first version of the definition of H1, H2, and H

This option is based on the initial calculation of the thickness of the base material H ₁ , after which the corresponding thicknesses of the cladding material H ₂ and the total thickness of the sheet are first N.

This is done as follows.

Having analyzed the circuit of FIG. 1, we can find for reflection C1 (see Fig. 2) that:

and

Correlations between angles are determined by Snell's law

For converter P3, the following expression is true:

Formulas (1) - (4) form a system of four equations with four unknowns:

- α;

- β;

- H ₀ ;

- H ₁ .

The first three elements seem known at first glance, but this is not entirely true. In the process of monitoring, the ultrasonic transducer inevitably changes its position, bounces, wears out, etc. Layer thicknesses can also vary with respect to nominal values. Therefore, the angles and the distance from the active elements to the control object can vary significantly.

The remaining elements of the above equations are obtained as a result of measurements, so we consider them known.

With the system of equations (1) - (4) by finding the unknown and calculating H ₁ it is trivial.

The thickness of the cladding material H ₂ and the total thickness of the sheet H are calculated from the following considerations.

Converter P3 transmits and receives longitudinal waves normal to the surface of the sheet.

Therefore:

Thus, the solution of the system of equations (1) - (4) allows you to get H ₁ , and formulas (5) and (6) - the missing unknowns - H ₂ and N.

The second option for finding H1, H2, and H

This option is based on measuring and using the value of the time interval T between C1 and C2 (see Fig. 2):

First we define H ₂ , and then H1 and N.

Taking into account all the assumptions made earlier, we compose the following system of equations:

From the expression (9) we can determine:

From the expression (8), we can determine γ = F2 (H ₀ , H ₁ , R).

From formulas (1) and (7), it is possible to determine the time T between pulses C1 and C2 (see Fig. 2):

Let's pretend that:

;

;

.

.

Since the values of A and B are small enough (we assume that H ₁ >> H ₂ ), we have the right to make the following assumption:

Given (11) for calculating H _2, we can take just the nominal (theoretical) value of H ₁ .

For H ₀ , the result of constant measurements of P3 can be used.

From (7) - (10) we can find H ₂ :

H ₂ = ((T ₂ -T ₁ ) -A + B) × (C _1t × cos γ / 2).

The thickness of the base material H ₁ and the total thickness of the sheet H are calculated as follows:

Converter P3 transmits and receives longitudinal waves normal to the surface of the sheet.

therefore

Example 2

An example of an alternative configuration of a measuring system with four transducer blocks is shown in FIG. four.

The notation in FIG. four:

P1 - radiating converter;

P2 - receiving converter;

P3-receiving converter;

P4 - emitting / receiving converter;

H ₀ - the thickness of the water layer;

H _1, is the thickness of the base material;

H ₂ - the thickness of the cladding material;

H is the total thickness of the sheet;

C ₀₁ is the velocity of the longitudinal wave in the water layer;

C _1l is the longitudinal wave velocity in the main material;

C _1t is the shear wave velocity in the main material;

C _2l is the longitudinal wave velocity in the cladding material;

C _2t is the shear wave velocity in the cladding material;

R ₁ is the distance between the emitting P1 and the receiving transducer P2;

R ₂ is the distance between the emitting P1 and the receiving transducer P3;

BC - water layer;

OM is the main material;

PM - cladding material;

α is the angle of emission / reception of ultrasonic waves (in water);

β is the angle of ultrasonic waves in OM;

γ is the angle of ultrasonic waves in the PM.

This configuration looks somewhat more complicated, because instead of three (as for Example 1) converter blocks four are used here. However, this configuration has an important advantage, namely, that the emitting unit of the converters can have a fixed angle and a narrow radiation pattern, which allows, under certain conditions, to increase the noise immunity of the measuring system and simplify the calculations.

The system of basic equations for this configuration is shown below:

H ₀ defined as in Example 1.

The final formula for calculating H ₂ :

Other parameters can be found by analogy with Configuration 1.

An example of a device (ultrasonic transducer) for automatic thickness gauging of multilayer sheets.

An example of an ultrasonic transducer for automatic thickness gauging of a multilayer sheet is shown in FIG. 5.

The converter comprises a housing 1, filled with water 2 through fittings 3, and a replaceable tread 4, which is in direct contact with the surface of the sheet during inspection. Three transducer blocks 5-7 are physically independent relative to each other and are inserted into the housing parallel to each other.

The housing of the transducer 1 contains components 8 that allow you to adjust and measure at least the distance R between the blocks 5 and 6, responsible for the excitation / reception of shear waves. Block 7, responsible for the excitation / reception of longitudinal waves, is positioned so that the point / line of input of the longitudinal wave is in the space between the two blocks responsible for the transverse waves.

The working surfaces of at least two of these blocks are separated from each other in such a way that the acoustic axes of the active elements of one of the blocks intersect in the control object in a given depth range with the acoustic axes of the elements of the other block, and the acoustic axes of the elements of the third block are nominally perpendicular to the surface of the control object ( see Fig. 6).

In the converter, all emitting, receiving, and receiving-emitting elements of the blocks are made in the form of linear phased arrays, which make it possible to control the direction of radiation and / or reception in the direction perpendicular to the axis of the block. Thus, mechanical adjustment of the position of the acoustic blocks may not be necessary, or it will be required, but relatively rarely, only with a significant change in the nominal value of the thickness of the object of control N.

Simultaneously with thickness measurement, all converter blocks can perform the tasks of detecting defects: cracks, delaminations, etc., as well as areas of poor adhesion between the layers.

Information sources

1. Non-destructive testing: Reference: B 7 T. Under the general. ed. V.V. Klyueva T. 3: ultrasound monitoring / I.I. Ermolov, Yu.V. Lange, - M.: Mechanical Engineering, 2004, - 864 p.

2. US patent 4235018.

3. US patent 5343146.

4. US patent 5062298.

Claims (5)

1. The method of determining the thickness of bilayer materials and its constituent layers using pulses of elastic waves introduced into the object of control, carried out by recording and analyzing the time of arrival reflected from the surfaces of the object of control and the boundaries of its layers of acoustic pulses, characterized in that determining the thickness of the object of control and its layers is carried out using a combination of elastic body waves of different types, for which both longitudinal and transverse waves are introduced into the same section of the object of control, and the thickness of the control object and its layers is carried out by recording and analyzing the arrival time of pulses reflected from the input surface and / or a set of pulses due to both longitudinal and transverse waves propagating in the control object and interacting with the boundaries of its layers, and the analysis is performed by solving a system of equations connecting the determined parameters with known and measured quantities, and the form of the solved system of equations is determined by the specific configuration of the measurement tion system and the required measurement accuracy. 2. The method according to p. 1, characterized in that the longitudinal waves radiate into the material and receive from the material, as a rule, in a certain range of linear or solid angles α ₁ = 0 ± Δ ₁ , where α ₁ is the nominal input angle of the longitudinal wave, and transverse waves, as a rule, emit and receive at least in some spectrum of linear angles α _t = α ₀ ± α _t with respect to the normal to the input surface, simultaneously satisfying two conditions: 8 ° ≤α _t ≤80 ° and α _t ≠ α _cr3 ± Δ _t , where α _t is the nominal angle of input / reception of the transverse wave to / from the material (a) adjacent / adjacent to the input region, α _cr3 is the third critical angle in the material adjacent to the input region, and Δ ₁ , Δ _t are the parameters defining the range of the spectrum of the input / reception angles, depending on the nominal and extreme parameters of the control object. 3. An ultrasonic transducer, comprising a housing, as well as at least one group of one or more receiving, emitting or receiving-radiating elements, characterized in that the housing is a box in which at least three physically embedded and fixed in an adjustable spatial position blocks independent of each other, consisting of at least one active element each, and the first of the blocks serves, as a rule, only for excitation of transverse elastic waves in the range of angles required from the point of view of the nominal and extreme geometry of the control object, satisfying the conditions 8 ° ≤α _t ≤80 ° and α _t ≠ α _cr3 ± Δ _t , the second of which, as a rule, serves only for receiving from the control object transverse elastic waves coming from the required (from the point of view of the nominal and extreme geometry of the test object) range of directions satisfying the conditions 8 ° ≤α _t ≤80 ° and α _t ≠ α _cr3 ± Δ _t , and the third block, as a rule, serves simultaneously and for radiation in OK and receiving from OK longitudinal elastic in ln carried out in a certain angle range corresponding to the condition α ₁ = 0, ± Δ _1, wherein the working surfaces of at least two of these blocks are oriented and / or withdrawn from each other so that the acoustic axis of the active elements, one of these units intersect in the object control in a given depth range with the acoustic axes of the elements of another block, and the acoustic axes of the elements of at least one block are nominally perpendicular to the surface of the control object. 4. The transducer according to claim 3, characterized in that the transducer housing additionally contains components that allow you to change the distance R between at least the blocks responsible for the excitation / reception of shear waves, and this distance is chosen from the condition that their acoustic axis (directly or after reflections from the boundaries of the object of control) intersect in the area of the nominal location of the common border of the materials, and the unit responsible for the excitation / reception of longitudinal waves is positioned so that the point / line of input of the longitudinal wave It was located in the space between two blocks responsible for transverse waves. 5. The Converter according to claim 3, where the radiating and / or receiving and / or receiving-radiating elements of at least one of the blocks are made in the form of linear phased arrays that allow you to control the direction of radiation and / or reception in the direction perpendicular to the axis of the block.

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