RU2733582C1 - Method of non-destructive inspection of structures from composite materials - Google Patents

Abstract

FIELD: measurement.

SUBSTANCE: invention relates to measurement equipment and can be used for evaluation of reliability of complex spatial structures from polymer composite materials. Method includes using reference defect placed on surface or inside controlled article, measuring a threshold signal value using a reference defect, measuring an information signal from a real defect on the inspected article, comparing the measured information signal with a threshold signal value and generating a conclusion on the presence or absence of defects in the monitored article based on the comparison results. Prior to placing the reference defect on the surface or inside the inspected article, an article of composite material with a real defect is selected to obtain a reference defect for the article of composite material. That is ensured by preparation of selected article in layer-by-layer parallel layers in area of real defect. On each layer of preparation thickness of real defect is measured with pitch Δa from the beginning of the detected defect fragment to its end at points j = 1, 2, 3…, j_max, where j_max is the number of measurement points of thickness of the defect on the i^th layer of the preparation. Maximum and minimum values are selected from measured thickness values. Whole interval is divided into "P" intervals. Determining the defect length value corresponding to the thickness interval of the defect. Solving the equation for the function F(Sδ,) = δ_min , the value of the minimum length of the defect corresponding to the minimum thickness of the defect in the inspected article is determined. Performing the standard defect with certain parameters δ_min, S_min.

EFFECT: technical result is increase in reliability of detection of local defect areas in controlled composite material.

3 cl, 6 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), based on the results of thermal control when loading products 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. 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 destructive control methods, i.e. for destruction. In this case, it is required to reliably and with a minimum error determine potentially dangerous places (defects such as discontinuity, 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 are necessary strengthen.

State of the art

A promising direction in modern technology is the use of polymer composite materials that have a number of advantages over traditional materials - metals, especially in the aerospace industry, mechanical engineering, power engineering, 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 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 defects such as discontinuities, which, as a rule, are formed in places of reduced strength, or in a material that has discontinuities.

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.

The deterioration of fixed assets and technical equipment, a decrease in the quality of the 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, non-destructive methods of control 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.

Methods of non-destructive testing based on various physical principles and methods of detecting internal discontinuities that are reliable for the problem being solved by analyzing changes in the results of the interaction of physical fields with the controlled material are gaining great importance.

Methods for detecting defects and identifying defects such as discontinuity in the process of automated non-destructive testing are disclosed in detail in the following sources: EP 0486689 A1, SU 1396046 A1, SU 1158919 A, SU 319895, SU 1649414 A1, SU 824032, DE 4031895 A1, SU 2171469, SU 2676857, SU 145435, SU 2650711, SU 2654298, SU 2666158, SU 172618, as well as in a number of scientific and technical works, for example, 1. I.N. Ermolov, N. P. A. I. Aleshin POTAPOV. Unbrakable control. Acoustic control methods. Book. 2. - M .: Higher school 1991

A common disadvantage of almost all existing methods and means of automated non-destructive testing is a large error in determining the boundaries of defective areas when determining the signal threshold value for a reference defect and detecting defective areas, which is carried out by comparing the signal on the surface of the material under test with the signal threshold value.

This problem is related to the creation of the reference defect itself.

As a rule, the parameters of the reference defect are set based on the capabilities of the testing equipment and the possibility of manufacturing the reference defect itself.

In this case, the reference defect is a material that, when superimposed on the material to be inspected, provides the same response to the effect of a probing signal (for example, ultrasonic) as a real defect. As a rule, a certain minimum defect is used as a reference defect - a defect with minimum dimensions that can be detected by the testing equipment.

However, this approach leads to the appearance of a large error in the probability of detecting a real defect and determining its characteristics.

The main difficulty in solving this problem lies in determining the real values of the minimum real defect in a real controlled material.

As a rule, a defect in the material is represented in the form of a rectangular area, which has specific specific dimensions: length and height (see, for example, Fig. 1).

However, a real defect in the material has a completely arbitrary configuration, both in area and in thickness (see, for example, Fig. 2), and in this case, determining the minimum size of the defect is not a very simple task.

Thus, it is important to determine the size of the minimum defect based on the data of a real defect in a real controlled material.

The closest in technical essence to the presented method is the method described in the work of I.N. Ermolov, N. P. A. I. Aleshin POTAPOV. Unbrakable control. Acoustic control methods. Book. 2. - M .: Higher school, 1991, pp. 92-95.

The known method includes placing a reference defect on (or inside) a controlled product, measuring a signal threshold value using a reference defect in a controlled product, measuring an information signal on a controlled product, comparing the measured information signal on a product with a signal threshold value and, based on the comparison results, making a conclusion about the presence or absence of defects in the controlled product,

However, the known method has significant drawbacks inherent in the above technical solutions: it has a low reliability of detecting internal real defects, starting from a real minimal defect (having minimal dimensions), due to the fact that the real dimensions of the minimal defect in the controlled material are not previously determined.

This deteriorates the metrological characteristics of the control technology, increases the likelihood of determining the product's rejection characteristic.

The essence of the invention

The invention is aimed at solving the problem of increasing the reliability of monitoring the technical state of complex structures and their elements made of PCM during production and in real operating conditions (including under load conditions), identifying defective areas with the necessary reliability (areas that do not comply with regulatory documents) , development of recommendations for elimination of defects or restoration of the structure.

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

The technical result achieved with the use of the invention consists in increasing the reliability of detecting local defective areas in the controlled composite material, increasing the reliability of the results of assessing the technical and operational state of complex structures and their elements made of PCM.

The technical result is achieved due to the fact that in the method of non-destructive testing of products made of composite materials, including the use of a reference defect placed on the surface or inside the controlled product, measuring the signal threshold value using a reference defect, measuring the information signal from a real defect on the tested product, comparison the measured information signal with a threshold value of the signal and the development of a conclusion on the presence or absence of defects in the tested product based on the comparison results, before placing the reference defect on the surface or inside the tested product, select a product made of composite material with a real defect, obtain a reference defect for a product made of composite material, To do this: carry out a layer-by-layer parallel layer preparation of the selected product in the area of a real defect with a step between layers - Δs from the beginning of the defect i = 1, to the end of the defect i = N, where i is the number of the layer of the preparation ation, N is the number of preparation layers, on each i-th layer of the preparation, the thickness δ _{ji of a} real defect is measured with a step Δa from the beginning of the detected defect fragment to its end at points j = 1, 2, 3 ..., j _max , where j _max is the number of points for measuring the thickness of the defect on the i-th layer of the preparation, from the measured values of δ _ji select the maximum δ _{ji (max)} and minimum δ _{ji (min)} values, divide the interval {δ _{ji (min} ; δ _{ji (max)} } on "P" intervals, k = 1, 2, 3 ... P, where k is the number of the interval, determine the value of the length of the defect S _{k (.ij)} corresponding to the k-th interval of the defect thickness

- form the dependence F (S δ,) = 0 or

где F - функция зависимости величины протяженности (площади) дефекта от его толщины, занимаемой данной площадью,

where F is a function of the dependence of the length (area) of a defect on its thickness, occupied by a given area,

Solving the equation F (S δ,) = δ _min , the value of the minimum length of the defect S _min is determined, corresponding to the minimum thickness δ _{min of the} defect in the test item, a reference defect is made with the parameters δ _min , S _min .

The reference defect is made in the form of a parallelepiped, the walls of which are made of a composite material, and the inner cavity is filled with air.

The parameters of the minimum size of the reference defect are determined by solving the equation F (δ.S) = S _min .

Brief description of the figures of the drawings.

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

fig. 1 shows the configuration of a defect in a material of "ideal" shape,

fig. 2 shows photographs of elements and microsections of a complex spatial structure with real defects: macrodefects such as discontinuity and defects in structure disruption,

fig. 3 shows, as an example, graphs of the size distribution of real defects in the material, determined in accordance with the proposed method,

fig. 4 shows the method for determining the parameters of real defects in the material,

fig. 5 shows, as an example, a photograph of a section of a defective area on one of the preparation layers,

fig. 6 shows a defectogram and a table of defects in the control results in accordance with the proposed method.

i is the number of the preparation layer,

j is the number of the point for measuring the thickness of the defect on the i-th layer of the preparation,

N is the number of preparation layers,

S is the length of the defect,

ΔS - step between preparation layers,

Δа - step for measuring the thickness of the defect,

δ is the thickness of the defect in the measured section,

1 - the point of intersection of the graphs,

F is the function of the dependence of the length (area) S of the defect on its thickness (δ) occupied by a given area,

Preferred embodiment of the invention

FIG. 1 shows a drawing of an ideal defect. This form of defect is not found in real products. In order for such a form of defect to be used, it is necessary to determine the minimum dimensions of a real defect that occurs in a controlled item: δ, S.

The shapes of the various real defects are shown in the photographs of FIG. 2. It is obvious that the shape of an ideal defect (Fig. 5) is fundamentally different from the shape of real defects. And before making a reference defect with minimum dimensions, it is necessary to determine the actual minimum dimensions of defects in real products.

To determine the minimum size of a real defect in a controlled product, perform the following steps.

A layer-by-layer parallel layer preparation of a real product is carried out in the area of a real defect in it with a step between layers - Δs from the beginning of the defect i = 1 to the end of the defect i = N, here i is the number of the preparation layer, N is the number of preparation layers.

FIG. 5 shows a photograph of a defect in a product on one of the preparation layers.

Preparation is carried out, as a rule, by means of a thin diamond cutter (the method of cutting into layers), or by removing a layer of material between the layers at a given step. Next, the investigated layer is washed, for example, with acetone to flush out the waste of the preparation machining operation and to identify the contours of defects.

On each i-th layer of the preparation, the thickness δ _{ji of the} revealed real defect is measured with a step Δa from the beginning of the detected fragment of the defect to its end at points j = 1, 2, 3 ..., j _max , where j _max is the number of points for measuring the thickness of the defect on i -th layer of the preparation.

FIG. 4 shows a measurement scheme for determining the minimum size of a real defect.

From the measured values δ _ji select the maximum δ _{ji (max)} and minimum δ _{ji (min)} values.

Divide the interval {δ _{ji (min} ; δ _{ji (min)} } into "P" intervals, k = 1, 2, 3 ... P, where k is the number of the interval.

Determine the value of the area (length) of the defect S _{k (.ij)} corresponding to the k-th interval of the defect thickness

- form the dependence F (S δ,) = 0 or

- solving the equation, for example, F (S, δ) = δ _min , the value of the minimum length (area) of the defect S _min is determined, corresponding to the minimum thickness δ _{min of the} defect in the material under test,

FIG. 3 shows two graphs of this dependence:

dependence of the distribution of the length (area) of the defect on its thickness:

and the integral dependence of the length (area) of the defect on its thickness:

From dependence (2), it can be concluded, for example, that the highest density of defect areas falls on the defect thickness in the region of 0.4 mm, which implies certain technological actions to eliminate such defects.

From dependence (3), the minimum statistical dimensions of real defects are determined by solving equation (4) or equation (5):

The solution of equations (4), (5) can be done in different ways. The simplest one, which has an error sufficient for practice, is the graphical method. An example of solving the equation by this method is shown in Fig. 3.

In the coordinate system where the equation of the function

the equation is plotted

where const is a constant.

The intersection point (point 1, Fig. 3) of graphs (6) and (7) is the solution to the sought equation, which determines the minimum defect thickness and its minimum length corresponding to the minimum thickness.

For example, the range of defect thicknesses from 0 mm to 0.4 mm accounts for, approximately, defects with a length of 0 to 9 mm, or 81% of defects have dimensions: thickness more than 0.4 mm, length more than 9 mm.

Thus, in order to reveal 81% of all defects, it is necessary to adjust the flaw detector on a reference defect with a thickness of 0.4 mm and a length of 9 mm.

Experimental studies have shown that the dimensions of the reference defect, determined by the proposed method, are optimal for testing the product under study: an increase in the size of the reference defect decreases the percentage of detected defects, and a decrease in the size of the reference defect insignificantly increases the percentage of detected defects, but at the same time, the laboriousness of manufacturing the reference defect increases.

Next, a reference defect is made with parameters δ _min , S _min and control is carried out.

Experimental studies of the proposed method were carried out on the installation described in the work of the authors Rykov A.N., Budadin O.N., Borisenko V.V., Bogachev A.S. and other Automated system of non-contact ultrasonic industrial non-destructive testing of pipes made of polymer composite materials for pipelines. - The control. Diagnostics, 2019, No. 11, p. 20-29.

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

When setting up the control system for a reference defect, with the parameters according to the proposed method, the control carried out made it possible to identify all inherent artificial defects.

fig. 6 shows a defectogram and a table of defects in the control results in accordance with the proposed method.

The presented invention has the following advantages:

- increases the information content of the results of testing complex spatial structures,

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

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

- allows to reduce the likelihood of accidents by determining the actual technical characteristics of structures.

Claims (23)

1. Method for non-destructive testing of products made of composite materials, including: use of a reference defect placed on the surface or inside the controlled item, - measurement of the signal threshold value using a reference defect, - measurement of an information signal from a real defect on a controlled item, - comparison of the measured information signal with the signal threshold value and development of a conclusion on the presence or absence of defects in the controlled product based on the comparison results, characterized in that before placing the reference defect on the surface or inside the tested product, select a product made of composite material with a real defect, get a reference defect for a product made of composite material, for this: - carry out a layer-by-layer parallel layer preparation of the selected product in the area of the real defect with a step between layers - Δs from the beginning of the defect i = 1, to the end of the defect i = N, where i is the number of the preparation layer, N is the number of preparation layers, - on each i-th layer of the preparation, the thickness δ _{ji of the} real defect is measured with a step Δa from the beginning of the detected defect fragment to its end at points j = 1, 2, 3 ..., j _max , where j _max is the number of points for measuring the thickness of the defect at i -th layer of preparation, - from the measured values δ _ji select the maximum δ _{ji (max)} and minimum δ _{ji (min)} values, - divide the interval {δ _{ji (min} ; δ _{ji (max)} } into "P" intervals, k = 1, 2, 3 ... P, where k is the number of the interval, - determine the value of the length of the defect S _{k (.ij)} corresponding to the k-th interval of the defect thickness

, - form the dependence F (S δ,) = 0 or

where F is the function of the dependence of the size of the defect area on its thickness, occupied by a given area, - solving the equation F (S δ,) = δ _min , determine the value of the minimum length of the defect S _min , corresponding to the minimum thickness δ _{min of the} defect in the tested product, and - make a reference defect with parameters δ _min , S _min . 2. The method according to claim 1, characterized in that the reference defect is made in the form of a parallelepiped, the walls of which are made of a composite material, and the inner cavity is filled with air. 3. The method according to claim 1, characterized in that the parameters of the minimum size of the reference defect are determined by solving the equation F (δ.S) = S _min .

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