RU2776464C1 - Method for automated ultrasonic thermo-optical non-destructive testing of composite materials in hard-to-reach zones and device for its implementation - Google Patents

Abstract

FIELD: measuring technology.

SUBSTANCE: inventions relate to the field of measuring technology and can be used to assess the reliability of complex spatial structures made of polymer composite materials. The method for automated ultrasonic thermo-optical non-destructive testing of products made of composite materials includes ultrasonic excitation of a temperature field in the region of a defect, registration of the temperature field, and detection of defective regions by comparing the magnitude of the temperature field with a threshold level. Before testing, fiber-optic temperature sensors are integrated into the composite material at a distance from each other not exceeding the distance of the heat front spreading in the material from the defect. Further, the source of ultrasonic excitation of the temperature field is continuously moved along the location of the fiber-optic sensors. The temperature value is sequentially recorded from fiber-optic sensors. The temperature values ​​are compared with the threshold value and the defective area is detected when the temperature from the fiber-optic sensors of the set threshold level is exceeded. A device for implementing the method is presented.

EFFECT: providing control in hard-to-reach areas.

2 cl, 11 dwg

Description

Technical field

The invention relates to the field of measuring technology and can be used to assess the reliability of complex spatial structures made of polymer composite materials (PCM), based on the results of thermal control when loading products with mechanical vibrations.

The invention can be used to control the reliability of complex spatial structures made of PCM both during the production process and during operation of spatial mesh structures: spacecraft compartments, rocket engines, pipelines, sealed vessels, etc. The application of the invention is especially effective when testing potentially dangerous and expensive structures, which, on the one hand, are subject to high requirements for operational reliability, and, on the other hand, they are expensive and time-consuming to manufacture, so that a sufficiently large number of structures can be tested by destructive methods. control, i.e. destroy, as well as structures with hard-to-reach places to control by traditional methods (for example, mesh structures).

At the same time, it is required to identify potentially dangerous places (structural units) that in the first place can collapse (due to the presence of defects, reduced strength or other reasons) under loads, which can lead to accidents and which may need to be strengthened.

The invention can be effectively used for structures that are difficult to load with heat flow over the area (heat with area heaters) for thermal control, but in which it is necessary to evaluate the location of defects in the material of the structure, i.e. perform tomography.

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 engineering, mechanical engineering, energy, etc. Such materials require a special approach, new solutions in the development and creation of methods and means for assessing the reliability of their operation.

This is due to a wide variety of types of such materials, specific features of their structures, manufacturing technology, random changes in physical, mechanical and strength characteristics, and a wide variety of types of defects that occur during the manufacturing process. Spatial mesh structures are widely used, in which the control of defects in narrow ribs is relevant, where traditional methods of control are not applicable.

In addition, these materials in most industries operate under static and dynamic loads, and structures made of such materials have a complex spatial structure that makes it difficult to use traditional control technologies.

It is impossible to improve the quality of structures without a reliable assessment of the criteria for their quality and, 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 defects such as discontinuity (laminations, cracks, porosity, etc.), which, as a rule, are formed in places of reduced strength, or in a material that tends to discontinuity.

Considering that such structures are, as a rule, quite expensive, both in terms of cost and labor intensity of manufacture, it is necessary, on the one hand, to test each structure for compliance with its strength characteristics to the required ones, and on the other hand, these tests should be minimal. "injure" the design with the maximum information content of the test results.

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

As the statistics show and recorded by the Decree of the President of the Russian Federation dated May 6, 2018 No. 198 “Comparative analysis of accident rates for the period from 2005 to 2019 indicates general trends in improving the level of safety ... Thus, over the specified period, the total number of accidents decreased ... by 32 percent , the number of accidents ... by 61 percent.

At the same time, 60-70 percent of the equipment used at hazardous production facilities has worked out its standard service life. Under such conditions, the socio-economic damage from accidents can be estimated at 600-700 billion rubles a year, which will negatively affect the economic stability of the Russian Federation.”

The same decree emphasizes “The objectives of the state policy in the field of industrial safety are the prevention of accidents and incidents ... incl. minimization of the human factor ..., introduction of scientific and technological achievements and best practices in order to ensure industrial safety, development and implementation of uniform criteria for assessing the risks of accidents at industrial facilities, etc.”

For example, PCM fatigue, features of their manufacturing technology, etc. lead to the formation of internal defects such as discontinuity, the occurrence 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: modernization of production facilities, improvement of the quality of materials, etc. However, a complete solution of these problems is currently difficult for financial reasons.

In this regard, non-destructive methods for monitoring and diagnosing such structures are of great importance, providing not only the detection of internal defects, but also the determination of their characteristics, the depth of occurrence in the material, etc., i.e. perform tomography of such structures. They allow you to objectively determine the actual state of the structure, evaluate the reliability of their operation and give recommendations for its repair or restoration.

A known method for determining defects, residual stresses and defects in plates (ed. mon. USSR No. 1543259), according to which the object of control is illuminated with coherent light, a hologram of the surface is recorded, part of the material is removed, a local deformation zone is created by a point load in the zone of displacements caused by removal material, the hologram of the surface is recorded a second time. The magnitude of defects and the sign of residual stresses are determined by the number of interference fringes and their distortion. This method is quite laborious, requires high qualification, is financially intensive, is applicable only for flat parts, is associated with the destruction of the material, and is used for scientific research in laboratories.

A known method for determining defects and residual stresses according to the patent of the Russian Federation No. 2032162, according to which, a pyramidal indenter is statically pressed into the test material until an imprint with developing brittle cracks is formed. The strength and parameters of the crack are measured, the topology of the cracks is evaluated, the equilibrium and effective values of the fracture toughness are determined, and the magnitude of potential defects and residual stresses is calculated from known ratios, taking into account the linear dimensions of the actual grain in the coating.

The method is difficult to implement and applicable only for laboratory purposes.

There is also known a method for non-destructive control 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 the force effect on the material and the analysis of the reaction of the material. The disadvantage of this method is similar to the disadvantages of the method according to the previous patent.

There is also known a method and system for thermal control of residual stresses and structural defects and a system that implements it (RF patent No. 2383009). Known technical solution allows to carry out thermal control of the reliability of structures. The known method includes a force 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:

- the method does not allow to determine the characteristics of defects in the material;

- when registering a temperature field, the field of view of the recording thermographic (thermal imaging) system includes temperature fields belonging to both the controlled product and foreign objects. If the controlled product "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, a mesh), the recorded temperature field will belong to both the product (grid) and the area located between the grid elements. In addition, spatial areal heating of such products is difficult, because both elements of the controlled structure and foreign objects, especially for mesh structures, get into the heating area. This greatly complicates, and in some cases makes it impossible to interpret the results reliably, incl. detection and recognition of defects.

In addition, this method requires free access, 2-3 m. to the surface of the product to accommodate thermographic equipment (thermal imager), which is not always feasible, so this technical solution is applicable only to control a limited range of products.

To date, there is an urgent need to create a method and device for diagnosing the technical condition of real complex spatial structures, which can be applied in practice for a wide range of objects using simple and accurate equipment.

In principle, an approach to solving the problems of determining and localizing defects, determining their characteristics and areas of concentration of internal stresses and defects caused by them such as discontinuities (for example, cracks) became possible with the development of diagnostic tools based on the registration and analysis of temperature fields of the surface of a controlled structure. The most significant results have appeared in the last decade.

This is due, firstly, to the advent of modern portable thermal imaging equipment (see O.N. Budadin et al., Thermal non-destructive testing of products, M., Nauka, 2002, pp. 338-393), and secondly, with the creation of a modern mathematical apparatus (ibid., pp. 39-89), which makes it possible to solve direct and inverse problems of non-stationary heat transfer, which made it possible to switch from flaw detection (detection of defects) to tomography (recognition of internal defects, determination of their characteristics and assessment of the residual life of products) .

There are repeated attempts to solve the problem of detecting defects in hard-to-reach places of a PCM structure (for example, in narrow ribs with limited access to the testing equipment to the testing area, using various methods of flaw detection - ultrasonic, radio wave, etc. However, this did not lead to the desired results. This associated with a number of reasons.

1. As a rule, flaw detection methods require free access to inspection areas for their application and allow detecting macrodefects, while violations of strength reduction can be caused, as a rule, mainly by microdefects (microcracks, micropores, “sticky defects” - defects that do not have adhesion between surfaces, etc.).

2. Microdefects, which cause a decrease in reliability, are mainly formed in the process of loading a controlled structure with some kind of loads (power static or dynamic - shock, 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 a safety point of view, because. to carry out flaw detection of structures, an operator - a flaw detector operator must be near it.

3. During the control of complex spatial structures, or objects that did not occupy the entire field of view of the recording system, along with informative temperature fields, temperature noises were recorded, which, falling into the area of thermal loading, significantly reduced the reliability of the control results.

Closest to the claimed invention is the method and device described in the work: Nesteruk D.A., Khorev B.C., Korobov K.N. Infrared - ultrasonic control of water in the honeycomb panels of aircraft. Control and Diagnostics, 2011. No. 11. pp. 11-14.

The known method includes ultrasonic excitation of a temperature field in the area of a material defect, registration of a temperature field, detection of defective areas by comparing the magnitude of the temperature field with a threshold level,

The known device contains thermographic equipment (5), a mechanical vibration generator (4), a mechanical vibration input device (3), a threshold device (6), a results recorder (7), a mechanical vibration input device (3) mechanically connected to the controlled product (1 ) and connected to the generator of mechanical oscillations (4), the output of the thermographic equipment (5) is connected to the threshold device (6), the output of the threshold device (6) is connected to the recorder input (7). The generator of mechanical vibrations (4) excites the controlled object with mechanical vibrations and internal defects are detected based on the registration of the temperature fields of the product surface by thermographic equipment (5), which arise due to the transition of the energy of mechanical vibrations into the internal energy of the product in areas of discontinuity.

The disadvantage of this technical solution lies in the fact that using the known method and device is impossible to control in a limited amount, because. it requires the presence of thermographic equipment, which is located at a distance of up to 2-3 meters from the controlled surface, which is not always possible in practice. In addition, special environmental conditions are required for the operation of thermographic equipment (darkened room, clean air, etc.), which is not always possible in production conditions; this can lead to the destruction of the product and injury to the operator carrying out the control, it is impossible to control thin ribs due to heat spreading to the walls, and not to the surface on which the temperature field is recorded.

The essence of the invention

The invention is aimed at solving the problem of improving the accuracy, information content, reliability and expanding the scope of use of monitoring the technical condition of complex structures and their elements, incl. from PCM both in the production process and in real operating conditions, as well as under load conditions, determining areas of reduced strength, defective areas (areas that do not comply with regulatory documents), developing recommendations for eliminating defects or restoring the structure.

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

The technical result achieved when using the claimed group is to ensure quality control of the structure in conditions of limited access, in production conditions and the ability to control thin structural elements made of PCM, where the "spreading" of heat to the walls of the structure plays a significant role, which significantly reduces the temperature change by defect, which is the main information sign of the presence of a defect in the material.

The technical result is achieved due to the fact that in the method of automated ultrasonic thermo-optical non-destructive testing of products made of composite materials, including

- ultrasonic excitation of the temperature field in the area of the defect,

- registration of the temperature field, and

- identification of defective areas by comparing the magnitude of the temperature field with the threshold level,

- before testing, fiber-optic temperature sensors are integrated into the composite material at a distance from each other not exceeding the distance of the thermal front spreading in the material from the defect,

- carry out a continuous movement of the source of ultrasonic excitation of the temperature field along the location of the fiber-optic sensors,

- sequentially register the temperature value from the fiber-optic sensors,

- and reveal the defective area when the temperature from the fiber-optic sensors of the set threshold level is exceeded.

The technical result is also achieved due to the fact that in the device for automated ultrasonic thermo-optical non-destructive testing of products made of composite materials, including: thermographic equipment (5), mechanical vibration generator (4), mechanical vibration input device (3), mechanically connected to the controlled product ( 1) and connected to the generator of mechanical oscillations (4), a threshold device (6), to the input of which the output of thermographic equipment (5) is connected, a result recorder (7), to the input of which the output of the threshold device (6) is connected, additionally introduced: system (10), fiber optic line (8) with fiber optic temperature sensors (9), device for recording the results of measurements of fiber optic sensors (11), while the scanning system (10) is mechanically connected to the controlled product (1) and to the device input of mechanical vibrations (3), the output of the device for recording the results of measurements of fiber o-optical sensors (11) is connected to the second input of the threshold device (6), the input of the device for recording the results of measurements of fiber-optic sensors (11) is connected to the output of the fiber-optic line (8) with fiber-optic sensors (9), the output of the scanning system ( 10) is connected to the second input of the recorder (7), the second output of the mechanical oscillation generator (4) is connected to the input of the scanning system (10), and the third output of the mechanical oscillation generator (4) is connected to the input of the device for recording the results of measurements of fiber-optic sensors (11 ).

The thermographic equipment may be a thermal imager, a thermograph or other similar equipment.

Brief description of the figures of the drawings

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

fig. 1 - a block diagram of the device is shown,

fig. 2 - diagram of the distribution of heat flow from a defect in a PCM rib,

fig. 3 - photograph of a mesh structure element,

fig. 4 - the process of integrating the fiber optic line into the rib of the mesh structure,

fig. 5 - generator of mechanical oscillations,

fig. 6 - device for inputting mechanical vibrations,

fig. 7 - thermographic equipment,

fig. 8 - an example of detecting a defect in a structure rib,

fig. 9 - photograph of the device in the process of control,

fig. 10 - graph of "spreading" of temperature inside the material from a point defect.

The following designations are used in the given figures:

1 - controlled product,

2 - internal defect,

3 - mechanical vibration input device,

4 - generator of mechanical oscillations,

5 - thermographic equipment,

6 - threshold device,

7 - registrar of results,

8 - fiber optic line,

9 - temperature sensors (fiber-optic sensors - FOD),

10 - scanning system,

11 - device for recording the results of measurements of the FOS,

12 - mesh structure rib,

13 - defective area on the temperature distribution,

14 - threshold signal level,

15 - temperature profile,

T (deg. C) - temperature in degrees Celsius.

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 Ugryumov E.P. Digital circuitry: textbook for universities. - 3 -e edition revised and additional - St. Petersburg: - BHV-Petersburg, 2010). Thermal imagers from FLIR, FESTO, thermographs of the IRTIS-2000 type or similar in technical characteristics are used as thermographic equipment (5).

The method for automated ultrasonic thermo-optical non-destructive testing of products made of composite materials (in hard-to-reach areas) is carried out using a device (Fig. 1, 9) for automated ultrasonic thermo-optical non-destructive testing of products made of composite materials as follows

The scanning system (10) carries out mutual movement of the controlled product (1) with an internal defect (2) relative to the mechanical vibration input device (3), mechanical vibration generator (4) and thermographic equipment (5) (Fig. 1).

Before the start of the non-destructive testing process in the manufacturing process of the product (1) (Fig. 3), a fiber-optic line (8) with fiber-optic sensors (9), for example, of the Bragg grating type (Fig. 4), is laid into it. In some cases, when the controlled product is large enough, the fiber optic line (8) is glued to the surface of the product (8). In some cases, it is possible to use a fiber-optic line with distributed temperature sensors, the principle of operation of which is based on back Raman scattering or Rayleigh scattering.

The output of the fiber optic line is connected to the input of the device for recording the results of measurements FOS (11).

In the process of scanning the product (1) at the command of the scanning system (10), the mechanical vibration input device (3) (Fig. 6) introduces into the product (1) mechanical vibrations with frequencies from 20 kHz to 50 kHz (depending on the type of material) and amplitude from 5 µm to 40 µm. Propagating in the material, mechanical vibrations from the device for introducing mechanical vibrations (3) in accordance with the known laws of physics form a local temperature field in the region of the defect (2) (Fig. 2, 11).

This thermal field, according to the laws of heat transfer, propagates (Fig. 11) in the controlled product (1) in different directions and, in accordance with the laws of heat transfer, passes into air at the material-air boundary (Fig. 2).

In thin-walled products (for example, in ribs, Fig. 3), this process proceeds quite quickly, because the thermal field quickly reaches the boundary of the material. Therefore, the gradient of the temperature field due to the presence of a defect in the material (the temperature difference on the surface of the product, between the temperature of the local area due to the presence of the defect and the temperature of the rest of the surface of the product) has a small value and remains for a rather short time.

Thermographic equipment (5) (Fig. 7) may not register this temperature change for a number of reasons:

- a small change in the temperature field, comparable to the temperature resolution of the equipment,

- a small surface area of the product, from which the temperature field is recorded by thermographic equipment (5) due to the small size of the tested product itself (rib surface),

- access to the controlled item is limited, there is no possibility to mark the thermographic equipment (5) at a certain distance from the surface of the controlled item (1),

- the product "works" under conditions of power loads, which can lead to its destruction and, accordingly, to the failure of thermographic equipment. Given that the cost of thermographic equipment is quite high, this option is undesirable.

The use of a fiber optic line with the appropriate sensors built into it avoids these problems.

The fiber optic line itself is located inside the controlled product (Fig. 2), i.e. in close proximity to the heat source (defect), the body will not have time to "spread" over the product and the FOS will be registered.

In this case, the distance between the fiber-optic sensors should not exceed the heat spreading distance (Fig. 11) in order to register a defect.

Further, the signal - a change in the temperature field (Fig. 8) - about the presence of a defect in the product from the device for recording the measurement of the results of the FOS (11) (Fig. 10) enters the threshold device (6). Here it is compared with the threshold value of the signal that separates the signals of defective and high-quality areas of the controlled product and enters the recorder (7). Simultaneously, the recorder (7) receives signals from the scanning system (10), carrying information about the coordinates of the detected defective area (2) in the product (1).

As a built-in fiber optic line temperature sensor (8), it is promising to use distributed temperature sensors along the length of standard multimode optical fibers based on the Raman backscattering effect. FOS based on the Rayleigh scattering effect can also be used.

Thus, the operation of the proposed device is carried out.

Experimental studies of the proposed device.

Experimental studies of the possibility of the proposed device were carried out on the installation, the functional diagram of which is shown in Fig. 1, and a photograph of the setup is shown in Fig. 9.

The research was carried out in the following way.

A product with an artificial defect was made (Fig. 4).

The product was a flat sample of a mesh structure made of PCM in size (Fig. 3).

An artificial defect with a diameter of 1 mm is embedded in the edge of the product during its manufacture.

Further, the product moved relative to the thermographic equipment (5) and the mechanical vibration input device (3) in such a way that the mechanical vibration input device moved along the rib (12). At the same time, the device for introducing mechanical vibrations (3) introduced mechanical (low-frequency ultrasonic) vibrations into the product.

The temperature field was recorded by a fiber optic line in accordance with Fig. 1 and measured by device (11).

In FIG. 8, the measured temperature distribution along the rib is shown as an example. The region (13) is clearly visible, the change in temperature due to the defect (2). The threshold signal level (14) separates the defective and quality regions of the rib.

The presented method has the following advantages:

- allows to carry out control in conditions of limited access to the product,

- increases the reliability of the process of testing products of complex spatial design, incl. in the process of their force loading in real operating conditions and tests with limited access to the product,

- allows you to increase the reliability of operation of controlled structures (especially those operating at the limit of residual life),

- allows you to reduce the likelihood of accidents by determining the real technical characteristics of structures,

- allows you to detect "sticky" defects and microdefects, which are difficult to detect by other methods, and determine their depth.

Claims (26)

1. Method for automated ultrasonic thermo-optical non-destructive testing of composite materials in hard-to-reach areas, including: - ultrasonic excitation of the temperature field in the area of the defect, - registration of the temperature field, and - identification of defective areas by comparing the magnitude of the temperature field with the threshold level, characterized in that - before testing, fiber-optic temperature sensors are integrated into the composite material at a distance from each other not exceeding the distance of the heat front spreading in the material from the defect, - carry out a continuous movement of the source of ultrasonic excitation of the temperature field along the location of the fiber-optic sensors, - sequentially register the temperature value from the fiber-optic sensors, - and reveal the defective area when the temperature from the fiber-optic sensors of the set threshold level is exceeded. 2. A device for automated ultrasonic thermo-optical non-destructive testing of composite materials in hard-to-reach areas, including: - thermographic equipment (5), - generator of mechanical oscillations (4), - mechanical vibration input device (3), mechanically connected to the controlled product (1) and connected to the mechanical vibration generator (4), - threshold device (6), to the input of which the output of thermographic equipment (5) is connected, - results recorder (7), to the input of which the output of the threshold device (6) is connected, differing in that it contains - scanning system (10), - fiber optic line (8) with fiber optic temperature sensors (9), - a device for recording the results of measurements of fiber-optic sensors (11), at the same time, the scanning system (10) is mechanically connected to the product (1) and to the device for introducing mechanical vibrations (3), - the output of the device for recording the results of measurements of fiber-optic sensors (11) is connected to the second input of the threshold device (6), - the input of the device for recording the results of measurements of fiber-optic sensors (11) is connected to the output of the fiber-optic line (8) with fiber-optic temperature sensors (9), and - the output of the scanning system (10) is connected to the second input of the results recorder (7), - the second output of the generator of mechanical oscillations (4) is connected to the input of the scanning system (10), - the third output of the generator of mechanical oscillations (4) is connected to the input of the device for recording the results of measurements of fiber-optic sensors (11).

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