RU2736320C1 - Method for electric power thermal-optical control of spatial objects and device for its implementation - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment. Disclosed is a method for thermography of articles made from polymer composite materials, which involves loading the article, recording the temperature field formed on the surface as a result of internal thermomechanical processes, and detection of internal defects based on analysis of temperature field. Critical units with increased probability of destruction at application of load are determined in the article. In the process of product manufacture, a fiber-optic line with deformation sensors, which are fiber Bragg gratings, is laid in it so that deformation sensors are located in critical assemblies. Before the force action, the limit permissible deformation in the critical units of the article is determined. Prior to force action, electric current is passed through the article until it is heated. Electric current value is adjusted so that the article temperature does not exceed the allowable value. Temperature field of the surface is recorded and the magnitude and coordinates of its abnormal areas are measured. Deformation value is measured in critical nodes. By comparing values of maximum permissible load and value of deformation in critical units, possibility of further increasing mechanical load on article is determined. After termination of increase in mechanical load, product surface temperature field is registered. Difference of two thermograms of the surface of the article before and after application of the mechanical load is used to determine the presence of internal excess stresses and defects. Device for the method’s implementation has been described.

EFFECT: high reliability of detecting local areas.

2 cl, 16 dwg

Description

Technology area

The invention relates to the field of measuring technology and can be used to assess the reliability of complex spatial structures, in particular, structures made of polymer composite materials (PCM), which have limitations in the amount of material deformation, based on the results of thermal control when the products are loaded with a static or dynamic load.

The invention can be used to control the reliability of complex spatial structures made of PCM, both during production and during operation: spatial mesh structures: spacecraft compartments, rocket engines, pipelines, sealed vessels, i.e. products of this type that "work" under various loads and which are critical to the amount of deformation that occurs in the material when loads are applied.

It should be said that the peculiarities of the technological process of PCM products are that the formation of the material and the structure itself occurs simultaneously, in one technological cycle (in contrast to metal products, the technological process of which is divided into two stages: the production of metal - blanks and mechanical processing of metal blank, in the process of which the structure is formed). As a rule, complex structures made of PCM are not machined in order not to disrupt the internal structural structure of the material. This increases the likelihood of internal defects such as discontinuity of the material and the formation of areas of internal stresses. The most "dangerous" are "closed" defects that do not appear in the calm state of the product, but begin to appear when the product is operating under load.

The application of the invention is especially effective when testing potentially hazardous and expensive structures to manufacture, to which, on the one hand, high requirements for operational reliability are imposed, and on the other hand, they are expensive and time-consuming to manufacture for testing by methods of destructive control, i.e. for destruction. In this case, it is required to identify potentially dangerous places (structural units), which, first of all, can collapse (due to the presence of defects, reduced strength or other reasons) under loads, which can lead to accidents and which must be strengthened.

State of the art

A promising direction in modern technology is the use of polymer composite materials, which have a number of advantages over traditional materials - metals, especially in the aerospace industry, mechanical engineering, power engineering, etc. These advantages are the absence of corrosion, the ability to work in aggressive environments, optimal mass-dimensional characteristics and etc.

Such materials require a special approach, new solutions in the development and creation of methods and tools for assessing the reliability of their operation. This is due to a wide variety of types of such materials, specific features of their structures and manufacturing technology, as well as random changes in physical, mechanical and strength characteristics, a wide variety of types of defects that arise during the manufacturing process.

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 is the presence of stress concentrators and defects such as discontinuities, which, as a rule, are formed in places of reduced strength, or in a material that has discontinuities. At the same time, many types of defects are "closed" defects that do not appear in the usual "calm" state of the structure, but are potentially dangerous and manifest themselves sharply when the structure is loaded with various types of loads, which often leads to the destruction of products and various emergency situations.

Considering that such structures are usually expensive in terms of value and laborious to manufacture, it is necessary, on the one hand, each structure to be tested for compliance with its strength characteristics required, and on the other hand, these tests should minimize the "trauma" of the structure with maximum information content of the results tests.

Depreciation of fixed assets and technical equipment, a decrease in the quality of material and other similar reasons lead to a decrease in the reliability of operation of structures made of PCM.

For example, fatigue of PCMs, the peculiarities of their manufacturing technology lead to the appearance of residual internal stresses, which cause discontinuity and, ultimately, lead to the destruction of the material and structure. This phenomenon is widely described in the literature. Recently, a number of programs have been adopted aimed at correcting the situation: modernizing production facilities, improving the quality of materials. However, the complete solution of these problems is currently difficult for financial reasons.

In this regard, modern technologies for non-destructive testing and diagnostics of such structures are of great importance. They make it possible to objectively determine the actual state of the structure, assess the reliability of their operation and give recommendations for repair or restoration. Particularly promising are non-contact remote methods, in which information on the quality of a product in the form of some physical radiation is recorded remotely. This allows you to control potentially hazardous products that could accidentally break down when loads are applied during their control.

There is a known method for determining residual stresses in plates (ed. USSR certificate No. 1543259), according to which the control object is illuminated with coherent light, a surface hologram is recorded, a part of the material is removed, a local deformation zone is created by a point load in the displacement zone caused by material removal, a surface hologram is recorded secondary. The magnitude and sign of the residual stresses are determined by the number of interference fringes and their distortion. This method is applicable exclusively to flat parts, is associated with material destruction and is used for scientific research in laboratories.

There is a method for determining residual stresses according to RF patent No. 2032162, according to which a pyramidal indenter is statically pressed into the test material until an indentation with developing brittle cracks is formed, the force and parameters of the crack are measured, the topology of the cracks is estimated, the equilibrium and effective values of fracture toughness are determined, and the value of residual stresses calculated according to known ratios, taking into account the linear dimensions of the actual grain in the coating.

The method is complex and applicable only for laboratory purposes.

There is also known a method of non-destructive testing of the physical and mechanical properties of a polymer material or a structure made of a polymer material: patent BY 10472. It is based on force action on the material and analysis of the reaction of the material.

There is a known method of thermal control of residual stresses and structural defects and a system that implements it (RF patent No. 2383009). The known technical solution allows for thermal control of the reliability of structures. The known method includes a forceful impact on the controlled product and registration of the temperature field, the analysis of which is used to judge the state of the product. The system includes a thermogram recording device, a visualization unit and a processing device.

The disadvantage of the known technical solution is as follows.

When registering a temperature field, temperature fields belonging to both the controlled product and foreign objects fall into the field of view of the recording thermographic (thermal imaging) system. If the controlled item "occupies" the entire field of view of the recording system, this circumstance is not critical. When the controlled product is a complex spatial structure (for example, mesh), the recorded temperature field will belong to both the product (mesh) and the area located between mesh elements. This significantly complicates, and in some cases makes it impossible to reliably interpret the results, incl. detection and recognition of defects.

Therefore, this technical solution is applicable only to control a limited range of products.

In addition, the considered method provides the ability to control only internal excess stresses in the material; there is no possibility of monitoring defects such as discontinuity, for example, caused by shock loads, "closed" defects, i.e. defects with zero thickness (the edges of the defect are compressed, but there is no adhesion between them), defects in the form of pores. The known invention has low sensitivity due to the influence of external interfering factors.

Known technical solution, described in the patent of the Russian Federation No. 2506575, 02/10/2014, entitled "Method of thermal control of the reliability of structures from polymer composite materials for the analysis of internal stresses and a device for its implementation."

In the known method (patent 2506575), a controlled product made of polymer composite materials is subjected to force loading, as a result of which, due to internal thermomechanical processes, a temperature field is created inside the product, the analysis of which is used to judge internal defects.

The disadvantages of this technical solution are similar to those described above.

Known technical solution for the patent of the Russian Federation 2537520, published 10.01.2015, Bul. No. 1 "Method of thermal control of complex spatial objects and a device for its implementation." The disadvantages of this technical solution are similar to those described above.

Known technical solution for patent 2690033 "Method of electric power thermography of spatial objects and a device for its implementation", which is the closest analogue to the presented method and device.

The known method includes: force loading of the product, registration of the temperature field formed on the surface as a result of internal thermomechanical processes, identification of internal defects by analyzing the temperature field, before the force impact, an electric current is passed through the product until it warms up, the amount of electric current is adjusted so that the temperature of the product did not exceed the permissible, register the surface temperature field and measure the magnitude and coordinates of its anomalous areas, apply a mechanical load to the product, re-register the temperature field of the product surface, and determine the presence of internal excess stresses from the difference between two thermograms of the product surface before and after the application of a mechanical load and defects.

Heating of the product by electric current is carried out to a temperature 3-10 ° C higher than the ambient temperature. A static, cyclic and / or ultrasonic mechanical load is applied to the article.

The known device for thermography of products made of polymer composite materials includes thermographic equipment installed with the possibility of optical interaction with the product, a mechanical system of power loading of the product, a control unit for the mechanical system of power loading of the product, a threshold device and a recorder connected to its output, while the output of the control unit mechanical system of power loading of the product is connected to the input of the mechanical system of power loading of the product, and additionally includes an electric generator, an electronic control unit, a signal processing unit, a memory unit, an adder, while the output of the thermographic equipment is connected to the input of the signal processing unit, the first output of the electronic control unit connected to the input of thermographic equipment, the second output of the electronic control unit is connected to the input of an electric generator installed with the possibility of heating the product, the third output of the electronic unit is controlled iia is connected to the input of the control unit of the mechanical system of power loading of the product, the fourth output of the electronic control unit is connected to the input of the memory unit, the mechanical system of power loading of the product is connected to the product with the possibility of exciting mechanical vibrations of the product, the first output of the signal processing unit is connected to the third input of the memory unit, the second output of the signal processing unit is connected to the input of the electronic control unit, the third output of the signal processing unit) is connected to the second input of the memory unit, the output of the memory unit is connected to the input of the adder, and the output of the adder is connected to the threshold device.

The disadvantages of the known method and device are obvious.

The method is realized when a power load is applied to the controlled product and, obviously, the control results will be the more reliable, the greater the value of the applied load (the more the parameters of the defect will differ from the initial ones). However, another fact is also obvious - with an increase in the load, a transition through the threshold value of the load is possible and the product can be "broken". Determination of the threshold permissible load is not always possible, the result of such a determination depends on many factors (quality of the source material, adherence to technological regimes, the presence of randomly located unknown defects in the product, etc.). Therefore, this method, for all its attractiveness, has significant limitations in practical use.

Fundamentally, the approach to solving the problems of determining and localizing the areas of internal stress concentration and the defects caused by them, such as discontinuities (for example, "closed" cracks) became possible with the development of diagnostic tools based on the registration and analysis of rapidly changing (dynamic) temperature fields of the surface of the controlled structure. The most significant results have emerged in the last decade.

Today, there is an urgent need to create a method and device for diagnosing the technical state of real complex spatial structures with a complex design, which can be applied in practice for a wide range of objects using simple and accurate equipment and identify a wide class of defects from "closed" to pores and bundles.

This is due to the emergence of modern portable thermal imaging equipment, for example, see O.N. Budadin et al., Thermal non-destructive testing of products, M., Nauka, 2002, pp. 338-393, secondly, with the creation of a modern mathematical apparatus (ibid., Pp. 39-89), see also Klyuev V.V. .. Budadin O. N., Abramova E. V., Pichugin A. N., Kozelskaya S. O. Thermal control of composite structures under conditions of force and shock loading. - M .: Publishing house "Spectr", 2017, - 200 p .: with ill., ISBN 978-5-4442-0138-1 / allowing to solve direct and inverse problems of non-stationary heat transfer, which made it possible to switch from flaw detection (detection of defects ) to defectometry (recognition of internal defects, determination of their characteristics and assessment of the residual life of products).

There have been repeated attempts to solve this problem using flaw detection by various methods - ultrasonic, radio wave, etc. However, this did not lead to the desired results:

As a rule, flaw detection methods allow detecting macrodefects, while violations of a decrease in strength can be caused by microdefects (microcracks, micropores, "closed" defects, etc.) and a number of other factors that cannot be detected by existing flaw detection methods: violation of the composition material in the process of applying power loads, violation of manufacturing technology, etc .:

1. Microdefects and "closed defects, which cause a decrease in reliability, are mainly formed in the process of loading a controlled structure with any loads (static or dynamic force, internal pressure for cylinders, etc.), and flaw detection methods, in general, do not allow non-destructive testing during loading of structures. In addition, it is dangerous from the point of view of safety, because to carry out flaw detection of structures, there must be an operator - flaw detector near it.

2. When monitoring complex spatial structures, or objects that did not occupy the entire field of view of the recording system, along with the informative temperature fields, temperature noise was recorded, which significantly reduced the reliability of the control results, etc.

The essence of the invention

The invention is aimed at solving the problem of increasing the reliability of monitoring the technical condition of complex structures and their elements, incl. from PCM, during production and in real operating conditions, incl. under load conditions, determination of areas of reduced strength, defective areas (areas that do not comply with regulatory documents), identification of "closed" defects, ie defects that do not have an opening (thickness) in the initial state, provided that the integrity of the controlled product is preserved, the development of recommendations for eliminating defects or restoring the structure.

Those. Ultimately, the invention is aimed at improving the operational safety of complex potentially hazardous structures under continuous or cyclic loads (mechanical, internal pressure, etc.).

The technical result achieved when using the presented group of inventions is to increase the reliability of the detection of local areas with "closed" defects, areas of reduced strength, increase the reliability of the results of assessing the technical and operational state of complex structures and their elements made of PCM, provided that the integrity of the controlled product is guaranteed in the process of applying power loads to the product.

где j - номер критического узла в изделии, перед силовым воздействием через изделие пропускают электрический ток до его разогрева, регулируют величину электрического тока (J) таким образом, чтобы температура изделия не превышала допустимую - T_0max, осуществляют регистрацию температурного поля поверхности и измеряют величину и координаты его аномальных участков Т_0(х,у), здесь х,у - координаты поверхности контролируемого изделия, прикладывают к изделию механическую нагрузку P_i, здесь i=1…N - номер ступени прикладываемой ступенчато механической нагрузки, N - предельная ступень величины механической нагрузки, измеряют величину деформации в критических узлах

путем сравнения значений предельной допустимой нагрузки и величины деформации в критических узлах определяют возможность дальнейшего увеличения механической нагрузки на изделие следующим образом:The technical result is achieved due to the fact that in the method of thermography of products made of polymer composite materials, including force loading of the product, registration of the temperature field formed on the surface as a result of internal thermomechanical processes, and identification of internal defects by analyzing the temperature field, according to the invention, critical nodes are determined in the product with an increased probability of destruction when a load is applied, during the manufacturing process of the product, a fiber-optic line with strain sensors, which are fiber Bragg gratings, is laid in it so that the strain sensors are located in critical nodes, before the force effect, they determine the maximum permissible deformation in the critical nodes of the product

where j is the number of the critical node in the product, before the force is applied, an electric current is passed through the product until it warms up, the value of the electric current (J) is adjusted so that the temperature of the product does not exceed the allowable temperature - T _0max , the surface temperature field is recorded and the value of and is measured coordinates of its abnormal areas T _{0 (x, y)} , here x, y are the coordinates of the surface of the controlled item, a mechanical load P _{i is} applied to the item, here i = 1 ... N is the step number of the applied stepwise mechanical load, N is the limiting step of the mechanical load loads, measure the amount of deformation at critical nodes

by comparing the values of the maximum permissible load and the magnitude of deformation in the critical nodes, the possibility of further increasing the mechanical load on the product is determined as follows:

after stopping the increase in the mechanical load, the temperature field of the product surface T _i (x, y) is recorded, the difference in thermograms is measured:

ΔT (x, y) = T ₀ (x, y) -T _i (x, y)

and the presence of internal excess stresses and defects is determined by the difference between two thermograms ΔТ (x, y) of the product surface before and after the application of a mechanical load.

The technical result in terms of a device for thermography of products made of polymer composite materials, including thermographic equipment installed with the possibility of placing the product in its field of view, a mechanical system of power loading of the product, installed with the possibility of exciting mechanical vibrations in the product, a control unit for the mechanical system of power loading of the product, a threshold device, a recorder connected to its output, an electric generator, an electronic control unit, a signal processing unit, a first memory unit, and an adder, in which the output of the control unit of the mechanical power loading system of the product is connected to the input of the mechanical system of the power loading of the product, the output of the thermographic equipment is connected to the input of the signal processing unit, the first output of the electronic control unit is connected to the input of the thermographic equipment, the second output of the electronic control unit is connected to the input of the electric generator installed with the possibility of heating the product, the third output of the electronic control unit is connected to the input of the control unit of the mechanical system of the power loading of the product, and its fourth output is connected to the input of the first memory unit, according to the invention, an optical fiber embedded in the surface of the controlled product, a deformation recording device, a comparison unit are additionally introduced , a strain sensor, which is a fiber Bragg grating (FBG) included in an optical fiber, and a second memory unit, while the first output of the signal processing unit is connected to the second input of the adder, the second output of the signal processing unit is connected to the first input of the second memory unit, the first the output of the second memory unit is connected to the first input of the adder, the output of the adder is connected to the threshold device, the output of the optical fiber with strain sensors is connected to the input of the deformation recording device, the output of the deformation recording device is connected to the first input of the comparison unit, the second to the stroke of the comparison unit is connected to the fifth output of the electronic control unit, the third input of the comparison unit is connected to the output of the first memory unit, the first output of the comparison unit is connected simultaneously to the first input of the electronic control unit, to the second input of the signal processing unit and to the second input of the memory unit, and the second the output of the comparison unit is connected to the second input of the electronic control unit.

Brief Description of the Drawing Figures

The essence of the inventions 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 photographs of a fragment of a complex spatial structure made of PCM.

FIG. 2 shows photographs of elements and microsections of a complex spatial structure with real defects: macrodefects such as discontinuity and structural defects, "closed" defects,

fig. 3 shows, as an example, a thermogram of a complex spatial structure of pre-force loading with noise temperature fields,

fig. 4 shows a functional diagram of the thermal control system,

fig. 5 shows thermograms of fragments of a real product during testing:

5a - before passing the electric current,

5b - after passing an electric current (after warming up),

5v-d - in the process of applying a mechanical power load at various moments of increasing load,

5e - after the termination of the application of the power load,

fig. 6 - photograph of the experimental setup,

fig. 7 - photographs of two experimental samples with "closed" internal defects,

fig. 8 - photo of the information recording device,

fig. 9 - photograph of the process of introducing optical fiber with fiber Bragg gratings into the product,

fig. 10 - diagram of a model product with a defect,

fig. 11 - graph of the change in deformation in one of the critical nodes of the product,

fig. 12 - graph of temperature change on the sample surface in the crack area,

fig. 13 - graph of product destruction,

fig. 14 - photograph of the process of manufacturing a product by winding,

fig. 15 - photograph of the power load of the product,

fig. 16 is a graph of temperature changes versus product load.

The following positions are used in the figures shown:

1 - controlled item,

2 - a defect in the product (discontinuity, overvoltage),

3 - thermographic equipment,

4 - mechanical system of power loading of the product,

5 - electric generator,

6 - electronic control unit,

7 - signal processing unit,

8 - control unit for the mechanical system of power loading of the product,

9 - the first block of memory,

10 - adder,

11 - threshold device,

12 - registrar,

13 - field of view of thermographic equipment,

14 - optical fiber,

15 - deformation recording device,

16 - comparison block,

17 - strain gauge - fiber Bragg gratings (FBG),

18 - the second block of memory.

The following symbols are used in the figures:

P _i - the value of the mechanical load for the i-th thermogram,

P _omax is the ultimate power load on the product,

i = 1 ... N is the number of the step (value) of the mechanical load,

N is the limiting step of the magnitude of the mechanical load, P _N = P _0max ,

T - temperature (° С),

I - the magnitude of the electric current,

τ - time (s),

j _∞ is the current density at a distance from the defect,

a, b - semi-axes of the ellipse,

- предельная допустимая деформация контроля в критическом узле j изделия.

is the maximum permissible deformation of the control in the critical node j of the product.

ΔT (x, y) = T ₀ (x, y) -T _i (x, y) the difference in temperature values in the 10th critical node of the product j = 10.

Preferred embodiment of the invention

All used electronic units are built on the basis of standard microprocessor circuits and microprocessor assemblies with reprogrammable memory devices, and the control system for turning off / on the loading system is built on standard relay systems (see, for example, E.P. Ugryumov, Digital circuitry: textbook for universities - 3rd ed. Revised and additional - SPb .: - BHV-Petersburg, 2010.). As a thermal imaging device (thermography system), thermal imagers from FLIR, Testo, thermographs from IRTIS, for example, IRTIS-2000 or similar in technical characteristics, are used.

The method is implemented as follows.

In the process of identifying the product, changes in the configurations of internal defects (discontinuities) occur. For example, "closed" defects can "open" by different amounts depending on the applied load. In this case, their electrical resistance changes. When an electric current is passed through the product in the area of such defects in accordance with the known physical laws, energy will be released:

ΔQ = IxΔR (2R + ΔR)

ΔQ is the energy released at the defect,

I - the magnitude of the electric current,

R is the electrical resistance of the defect,

ΔR - change in electrical resistance of the defect.

The excess energy of the local internal area of the material in accordance with the laws of heat transfer forms a local temperature change on the surface of the product, which is recorded by the thermographic temperature and serves as a sign of the presence of an internal defect.

Therefore, this control method is relevant, since allows you to assess the quality (reliability) of the product in the process of quasi-real power loads by analyzing the temperature fields of the product surface.

The magnitude and application of the load are determined by the actual operating conditions of the product and are limited by the permissible level of deformation in the product. During loading, the product is rigidly fixed, because loads can reach significant values. In the process of control, the shape and geometric dimensions of the product may slightly change due to its deformation.

The device for recording thermograms (thermographic equipment) is placed in front of the controlled object from the condition of combining the field of view of the thermographic equipment and the controlled area of the controlled object.

Let's carry out a theoretical justification of the proposed method.

Formulation of the problem. Let a constant electric current of density j flow through a certain volume of material, for which it is true:

where j is the current density,

ρ - electrical resistivity,

E is the electrical potential.

An electric current in a conductive medium generates heat. The intensity of the heat source (the power released per unit volume) is determined by the Joule-Lenz law:

therefore, the heat conduction equation for the region with the passing electric current takes the form:

where α is the thermal diffusivity,

τ - time,

T is the temperature.

In a thin-walled structural element, the opening of cracks oriented at an angle to the current density vector can be considered equivalent to a decrease in the cross-sectional area. Then, in the first approximation, you can use the known results of work, in which the heating of a section of a smaller section is described by the formula:

where J and J _m are the current density in the sections of the main section and the smaller section;

S and S _m - sections of the main and reduced in size sections;

F and F _m - conductor cooling surfaces of the main and reduced in size sections;

ρ is the specific resistance of the conductor;

λ - coefficient of thermal conductivity of the conductor material;

k _T is the heat transfer coefficient.

Estimation by formula (4) shows that a decrease in the cross-sectional area leads to a slight increase in temperature. Let us carry out a more detailed analysis of heat release near the tip of an open crack.

Let us consider a model problem of the flow of a plane current in a plate containing an elliptical discontinuity (Fig. 10).

The dimensions of the plate are considered large in comparison with the dimensions of the discontinuity. Then the boundary conditions j _x = j _∞ , j _у = 0 can be set at infinity.

The solution to the system of equations (1) can be obtained by mapping the exterior of the ellipse to the exterior of the circle; the complex potential in this case is obtained as follows:

where z = x + iy, and the current density is found as the gradient of the real part (5).

In the limit, as the lesser semi-axis of the ellipse tends to zero (a), we obtain the distribution of the current density in the vicinity of the crack. So, for x = 0 we have:

Formula (6) can be transformed by replacing: y = b + Δr to the form that determines the asymptotic behavior of the current density at the crack tip:

whence it is seen that the current density is concentrated at the crack tip.

Here Δr is the change in distance from the crack tip.

The intensity of heat release according to the Joule-Lenz law (2) is proportional to the square of the current density, i.e.

and equation (3) takes the form:

The fundamental solution to equation (9) has the form:

where erfc is the error function,

q is the power of the heat source in the vicinity of the crack tip.

FIG. 12 shows a graph of the temperature change on the sample surface in the crack area as a function of time for different crack sizes and an initial temperature of 20 ° C. The plate width B was taken to be fixed and equal to the doubled crack length, the current value I = j _∞ B.

As a result, we obtain a significant increase in temperature in the region of a crack of very small dimensions, and the increase in temperature change is proportional to the length of the open crack.

Thus, the theoretical results show the possibility of detecting cracks when opening them by passing an electric current through a structural element containing a "closed" defect.

Electric power thermo-optical control of spatial objects is carried out as follows (Fig. 4).

Before starting the control, an electric current is passed through the controlled item 1 by means of an electric generator 5 under the control of an electronic control unit 6 to warm up the item.

The amount of electric current (J) is regulated so that the temperature of the product does not exceed the permissible _value - T _0max . For the experimental studies, the following parameters were determined: the approximate value of the current strength is 1-8A, the voltage is 0.2-0.4V.

Next, perform the actions:

Critical nodes (j) are determined in the controlled item 1 - nodes with an increased probability of destruction when a load is applied (P _i ),

here i = 1 ... N is the number of the step (value) of the mechanical load,

N is the limiting step of the magnitude of the mechanical load,

j = 1 ... J, where J is the largest number of critical nodes in the product.

In the process of manufacturing the product, a fiber-optic line 14 with strain sensors - fiber Bragg gratings (FBG) 17 - is laid in it in such a way that the strain sensors are located in critical nodes (j).

FIG. 9 shows a photograph of the introduction (insertion) of an optical fiber with FBG into a controlled product.

Before the force action, the maximum permissible deformation in the critical nodes (j) of the product is determined

Determination of the maximum permissible deformation can be carried out by a number of known methods of physical and mechanical tests, for example: Simple deformations: lab. workshop / comp .: B.C. Vakulyuk, O.V. Karanaeva, V.F. Pavlov [and others]. - Samara: SSAU Publishing House, 2015 .-- 76 p. ISBN 978-5-7883-1026-8

Under the control of the electronic control unit 6 by the thermographic equipment 3, the temperature field of the surface of the controlled item 1 is recorded and the value and coordinates of its anomalous areas T ₀ (x, y) are measured, which is stored in the memory unit 18, where x, y are the coordinates of the surface of the controlled item.

By means of the mechanical power loading system 4 of the product 1 and the control unit of the mechanical power loading system 8 of the product under the control of the electronic unit 6, a mechanical load P _{i is} applied to the product,

By means of optical fiber 14, strain sensors FBG 17 and a strain recorder 16, strain is measured in j = 1 ... J critical nodes at the i-th load

поступают на блок сравнения 16. Одновременно по команде электронного блока управления 6 на другой вход блока сравнения 16 поступает величина предельной допустимой нагрузки в критических узлах

Measured strain results

are fed to the comparison unit 16. At the same time, at the command of the electronic control unit 6, the value of the maximum permissible load in critical nodes arrives at the other input of the comparison unit 16

Comparison unit 16 compares the deformation values received at its inputs as follows:

то с выхода блока сравнения 16 на электронный блок управления 6 поступает сигнал на увеличение нагрузки на изделие и по команде блока 6 происходит увеличение прикладываемой нагрузки - P_i+1. Далее все измерения блоками 14, 17, 15 и сравнение результатов блоком 16 повторяется.- if a

then from the output of the comparison unit 16 a signal is sent to the electronic control unit 6 to increase the load on the product, and at the command of the unit 6 an increase in the applied load - P _{i + 1} occurs. Further, all measurements by blocks 14, 17, 15 and comparison of the results by block 16 is repeated.

с выхода блока сравнения 16 на электронный блок управления 6 поступает сигнал на прекращение увеличения нагрузки на изделие 1 и по команде блока 6 происходит завершение увеличения прикладываемой нагрузки. Одновременное по команде блока 6 на термографическую аппаратуру 3 осуществляется прекращение регистрации температурного поля поверхности изделия 1. Одновременно сигнал с блока сравнения 16 поступает на блок обработки сигналов 7, по команде которого на сумматор 10 из блока 7 на сумматор поступает текущий сигнал о значении температурного поля поверхности изделия 1 - T_i(х,у). Одновременно сигнал от блока 16 поступает на второй блок памяти 18, по команде которого блок 18 передает в сумматор 10 сигнал Т₀(х,у).- if a

from the output of the comparison unit 16 a signal is sent to the electronic control unit 6 to stop increasing the load on the product 1, and at the command of unit 6, the increase in the applied load is completed. Simultaneously, by the command of block 6, the thermographic equipment 3 terminates the registration of the temperature field of the surface of the product 1. At the same time, the signal from the comparison unit 16 goes to the signal processing unit 7, at the command of which the current signal about the value of the temperature field of the surface is sent to the adder 10 from unit 7 products 1 - T _i (x, y). At the same time, the signal from the unit 16 is fed to the second memory unit 18, at the command of which the unit 18 transmits the signal T ₀ (x, y) to the adder 10.

The adder 10 measures the difference in thermograms:

ΔT (x, y) = T ₀ (x, y) -T _i (x, y)

and the difference between two thermograms ΔT (x, y) of the product surface before and after the application of a mechanical load in the threshold device 11 determines the presence of internal excess stresses and defects. Further, the information received is recorded in block 12.

The threshold value in block 11 can be selected from various criteria. It depends on the type of product, inspection conditions.

The most general method for determining the threshold value is described in the book by the authors V.A. Barynin, O. N. Budadin, A.A. Kulkov. Modern technologies for non-destructive testing of structures made of polymer composite materials. - M .: Publishing House "Spectrum", 2013. - 243 p: silt and color. incl. 16 s. P. 20-26. It is a method of no-reference determination of the signal threshold value.

Experimental studies of the proposed method were carried out on an installation assembled in accordance with the functional diagram (Fig. 4) using a thermal imaging device IRTIS-2000. A photograph of the experimental setup is shown in Fig. 6.

Experimental studies were carried out according to the methodology and in accordance with the sequence of operations claimed in the claims.

FIG. 3, as an example, a thermogram of the entire surface of the controlled sample of the structure is shown before the experiments. Noise temperature fields are clearly visible on this thermogram.

For experimental research, special samples were made, similar to the design of a real product, in which "closed" defects were made during the manufacturing process.

A photograph of samples with "closed" defects is shown in Fig. 7.

FIG. 5a-c show thermograms of fragments of a real product during testing:

5a - before passing the electric current,

5b - after passing an electric current (after warming up),

5c - in the process of applying a mechanical force load at various moments of increasing load.

From those shown in FIG. 5a-c of the results, it is clearly seen how a local section of the temperature field corresponding to an internal "closed" defect appears on a fragment of the product during the application of a force load.

In the process of manufacturing a product by the winding method (Fig. 14), an optical fiber (14) with an FBG (17) is integrated into the controlled product (1).

FIG. 9 shows a photograph of the process of introducing an optical fiber with fiber Bragg gratings (FBG) into a product.

Further, the product (1) was subjected to mechanical stress.

FIG. 15, as an example, is a photograph of the power load of the product. Registration of deformation in critical units of the product was carried out by an information recording device, a photograph of which is shown in Fig. eight.

FIG. 11 is a graph of the change in deformation in the critical node No. 10 (j = 70) of the product.

нагружение изделия прекратилось и нагрузка была «снята» во избежание «травмирования» контролируемого изделия и без ущерба для достоверности результатов контроля. Это состояние соответствует термограмме 5г фиг. 5. Для наглядности процесс регистрации термограмм был продолжен после «снятия» нагрузки. Из термограмм наглядно видно уменьшение разности значения температуры на дефектном и бездефектном участках.In accordance with the proposed method, upon reaching the greatest permissible deformation in a given critical node

loading of the product was stopped and the load was “removed” in order to avoid “injury” of the controlled product and without prejudice to the reliability of the control results. This state corresponds to the thermogram 5d of Fig. 5. For clarity, the process of registration of thermograms was continued after the "removal" of the load. The thermograms clearly show a decrease in the temperature difference in the defective and defect-free areas.

FIG. 16 is an example of an experimental graph based on the thermograms of FIG. 5 dependences of the temperature change between the temperature value in the defective area before loading and the temperature value in the defective area during loading: ΔТ (x, y) = T ₀ (x, y) -T _i (x, y) on the value of the load (numbers of thermograms ).

Thus, the goal set for the technical solution being created has been achieved: reliable detection of "closed" defects is ensured with a gentle load on the controlled product.

Based on the results of the control, a conclusion is made:

- about the reliability of the product and its ability to withstand loads,

- about the presence of "weak" points of the product, i.e. recommendations are given to the developer on strengthening the structure or its specific elements,

- on the value of the residual resource of the product (according to the dynamics of changes in temperature fields in the places of stress concentrators),

- on the presence of internal defects such as discontinuity, incl. "Closed" defects.

The inventions have the following advantages:

- increase the information content of the results of monitoring complex spatial structures,

- increase the reliability of the process of monitoring products during their power loading in real operating and testing conditions.

- allow to increase the reliability of operation of controlled structures (especially those operating at the residual resource limit),

- allow to reduce the probability of accidents by determining the real technical characteristics of structures,

- provide reliable detection of dangerous "closed" defects with a "sparing" power load on the controlled product.

Claims (56)

1. A method of thermography of products made of polymer composite materials, including - force loading of the product, - registration of the temperature field formed on the surface as a result of internal thermomechanical processes, and - identification of internal defects by analyzing the temperature field, characterized in that - critical nodes with an increased probability of destruction when a load is applied are determined in the product, - in the process of manufacturing the product, a fiber-optic line with strain sensors is laid in it, which are fiber Bragg gratings so that the strain sensors are located at critical nodes, - before the force action, the maximum permissible deformation in the critical nodes of the product is determined

where j is the number of the critical node in the product, - before forceful action, an electric current is passed through the product until it warms up, - regulate the amount of electric current (J) in such a way that the temperature of the product does not exceed the permissible _value - T _0max , - register the surface temperature field and measure the magnitude and coordinates of its anomalous areas T ₀ (x, y), here x, y are the coordinates of the surface of the tested product, - apply a mechanical load P _i to the product, here i = 1 ... N is the step number of the applied stepwise mechanical load, N is the limiting step of the magnitude of the mechanical load, - measure the amount of deformation at critical nodes

- by comparing the values of the maximum permissible load and the magnitude of deformation in critical nodes, determine the possibility of further increasing the mechanical load on the product as follows:

- after the termination of the increase in the mechanical load, the temperature field of the product surface T _i (x, y) is recorded, - measure the difference in thermograms: ΔT (x, y) = T ₀ (x, y) -T _i (x, y) and the presence of internal excess stresses and defects is determined by the difference between two thermograms ΔТ (x, y) of the product surface before and after the application of a mechanical load. 2. A device for thermography of products made of polymer composite materials, including - thermographic equipment (3), installed with the possibility of placing the product in its field of view, - mechanical system of power loading of the product (4), installed with the possibility of excitation of mechanical vibrations in the product, - control unit for the mechanical system of power loading of the product (8), - threshold device (11), - a recorder connected to its output (12), - electric generator (5), - electronic control unit (6), - signal processing unit (7), - the first block of memory (9), and - adder (10), while - the output of the control unit for the mechanical system of power loading of the product (8) is connected to the input of the mechanical system of power loading of the product (4), - the output of the thermographic equipment (3) is connected to the input of the signal processing unit (7), - the first output of the electronic control unit (6) is connected to the input of the thermographic equipment (3), - the second output of the electronic control unit (6) is connected to the input of an electric generator (5) installed with the possibility of heating the product (1), - the third output of the electronic control unit (6) is connected to the input of the control unit for the mechanical power loading system of the product (8), and - its fourth output (6) is connected to the input of the first memory block (9), characterized in that it contains - optical fiber (14) embedded in the surface of the controlled product, - deformation recording device (15), - comparison block (16), - strain gauge, which is a fiber Bragg gratings (FBG) (17) included in an optical fiber, and - the second memory block (18), while - the first output of the signal processing unit (7) is connected to the second input of the adder (10), - the second output of the signal processing unit (7) is connected to the first input of the second memory unit (18), - the first output of the second memory block (18) is connected to the first input of the adder (10), - the output of the adder (10) is connected to the threshold device (11), - the output of the optical fiber (14) with strain sensors (17) is connected to the input of the strain recording device (15), - the output of the deformation recording device (15) is connected to the first input of the comparison unit (16), - the second input of the comparison unit (16) is connected to the fifth output of the electronic control unit (6), - the third input of the comparison block (16) is connected to the output of the first memory block (9), - the first output of the comparison unit (16) is connected simultaneously to the first input of the electronic control unit (6), to the second input of the signal processing unit (7) and to the second input of the memory unit (18), and - the second output of the comparison unit (16) is connected to the second input of the electronic control unit (6).

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