SU1712852A1 - Method of infra-red investigating of the presence of inner flaws - Google Patents

Abstract

The invention relates to thermal non-destructive testing and can be used to detect defects in multilayer and composite structures. The purpose of the invention is to increase the reliability of the Internal Defect Control by suppressing interference caused by the non-uniformity of the radiation-absorbing properties of the products. This goal is achieved through the fact that it includes heating the product and registering the thermal radiation of the surface of the product in three moments of additional heating of the product before the second and third registration of the heat source to equal the mean values of the thermal radiation fields. frame by frame at the moments of their registration. Mathematical image processing consists in Fourier filtering of the relative contrasts of the recorded thermal fields. 1 il. ,

Description

 The invention relates to thermal non-destructive testing and can be used to detect defects in multi-layer and composite structures.

There is a method of active thermal control, which consists in heating the object of control, recording thermal radiation at two points in time and forming the ratio of these sietes, as a result of which the emissivity entering the output signal by the factor is reduced. The sensitivity of thermal control is increased due to partial suppression of interference, since the signal from the defect is maximum at the first time instant and is close to 13 UD at the second time instant.

The disadvantage of this method is the low sensitivity to internal defects due to incomplete suppression of signals from radiative absorption absorption due to inhomogeneities of the heating source. The preservation of the effect of the radiation-absorbing properties of the product and the quality of the heater on the thermal control result is due to 3 factors: in the method, temperature is measured at 2 points in time during the cooling phase of the product: the average temperatures of the product can differ significantly from each other (for example, for heating The temperature after heating may be 100-T50 C, and after 5-15 C 2540 C), since the emission coefficients are

absorption depends on temperature, then dividing multi-temporal signals results in an incomplete reduction of the emissivity; the operation of the method is based on the linear coupling of the photodetector signal and the recorded temperature, which is true according to Planck’s law only in small temperature ranges (up to) and can lead to additional error at the indicated large temperature ranges; anomalies of the temperature field distribution on the surface of the product, caused by heating inhomogeneities, due to the three-dimensional nature of the occurrence (ESH14x with this, thermal processes vary not only in magnitude but also in shape over time, therefore full suppression of the interferences caused by them does not occur .

The closest technical solution to the present invention is a method of thermal imaging control of internal defects, which consists in recording the thermal field three times from the section of the surface of the test product and judging the presence of internal defects after filtering the recorded two-dimensional thermal bedding in the Fourier plane.

The disadvantage of this method is the presence of an uncontrolled error due to the dependence of the emissivity of the surface and the temperature on the temperature.

The purpose of the invention is to increase the reliability of kbrol by suppressing interference caused by the non-uniformity of the radiating and absorbing properties of the products.

This goal is achieved tew, that after heating the control object during time T2 and recording thermal radiation U {r,) at time tm, the first preheating heating takes place during time T2 and recording thermal radiation and (g, T2) at time t, and then the second additional heating during the Guise time and the registration of thermal radiation U (i t s moment of time r3, and the heating times H 2 and Hs are chosen so that the average values of the fields of thermal radiation J (r, g) of the product per frame at times rt, r2 and gz were equal to each other. Mathematical processing of measurement results includes the formation of functions (r, Ti} / U (f, r2): Ui3 - U {fC riJ / UCrlra), (r, G2) / and (rz), averaging over coordinates Oi2, Oi3. U23 functions, formation of relative contrasts Al2 Ut2 / Ul2-1, Al3 Ul3 / Ul3-1, A23 U23 / CI23-1, formulated AII. Ai3, Agz functions At2, Ai3, A23, filtering received Fourier transforms in accordance with the expression (V, t, .t.) .- A ,, e- "-.

:., a.) - Ae, (e e-1) -A ,, (.)

where vy} is a spatial vector

frequencies;

 vy a is the thermal diffusivity of the material of the product, and the implementation of the inverse Fourier transform of the AND functions. About defects

judged by two-dimensional spatial images j, which are thermograms synthesized from the original thermal images U, ri), U (r; (f.T.

The essence of the method lies in the fact that when using the new information processing algorithm that required the introduction of new control operations, the interference associated with the heating and emissivity inhomogeneities is suppressed. as a result, the reliability of the control of internal defects is increased.

The drawing shows a device that implements the method

Product 1 with defect 2 is heated by a heating source 3 according to a control program touched by computer 4 during times Hn1, Hn2 ,. After heat

the radiation of the object is recorded by the thermal image of the OromV and recorded into the external storage device 6. The experiment results in the initial thermograms of the product at times rt, 72,

gz. According to the proposed algorithm of synthesis, two new thermograms corresponding to the functions I.

The experiments were performed on a sample of textolite 70x80 mm thick b

mm with model defects in the blind hole VID with a diameter of 3 and 5 mm, lying at a depth of 3 mm from the surface from which the inspection was carried out. Heating is carried out with a halogen lamp power

1 kW, the first heating time was

 c, thermograms were recorded in

moments of time with, with, with,

first and second additional heatings (

, 5 s, 5 s) were made immediately

after the termination of registration of the corresponding thermograms. Heterogeneities of heating and emissivity of the surface of the object, specially reinforced with soot spots of various shapes and areas randomly arranged on the sample surface, reached 30%, the expected temperature contrast from the defect with the minimum dimensions did not exceed 5-10%. Measurements and processing of the results were carried out using an information-measuring complex based on a CM-4 computer, coupled with a Raduga-MT thermal imager.

On the synthesized thermogram it was possible to reliably determine the presence of both defects, as well as to establish their position and approximate value.

The proposed method in a number of cases allows not only more than an order of magnitude to reduce the amplitude of radiating-absorbing and similar interference with active thermal control, and thereby increase its reliability and expand the scope of application, but also to reject the use of special blacking coatings, which can give a significant economic effect.

Formula and goiter e ni

The method of thermal imaging control of internal defects, including heating of the surface of the product during the time Gn1, registration of thermal radiation and (rTrtJi.UrTa) and the surface of the product at MOments of time Tt,, gz, where,} are the coordinates of the product surface, the operation of processing the measurement results by forming a two-dimensional spatial function and (TiVUt, ha) or (g, ri) / U (r gz), which is a synthesized product surface thermogram, differing in that. which, in order to increase

reliability of control due to suppression of interference caused by the non-uniformity of the radiation-absorbing properties of the products, after registration of the field of thermal radiation and (rt) at the moment of time ri, the product is heated for a time of 7–2. after registering the heat radar field, eHtM U (f; at the time TZ, the product is heated during the time of the pumping time (the heating time of the TI2 and the HNS is chosen so that the average values of the thermal radiation fields (Dg, G {Gizdeli frame) , z and tz were equal to each other, and the mathematical processing of measurement results includes the averaging of the functions (rij / U (Tjz), Ui3 and (l Ti) 73), U23H) {r, (city Gz) over the coordinates 1T. "Oi3 and U23, the formation of relative contrasts Aw "Ui2 / Ui2-1: Ai3 Ui3 / Ui3-1; Dzz Oaz / Oaz-1, the formation of spatial Fourier transforms of Aia, t3 and s fu Commands Ai2, Ai3 and A23, filtering the obtained Fourier transforms in accordance with the expression (v, S a} -A ,,,;

/.

.V (we..g,). A (.... -A {e- «v4 e-4-faV, j /

where, Vy} are the spatial frequency vectors,

and the thermal diffusivity of the product material:

performing the inverse Fourier transform of the functions; in this case, the presence of defects is judged on two-dimensional spatial images, which are the final thermograms synthesized from the original thermograms U (r ri), and (rG T2), and ().

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Algorithm

Claims (1)

Formula 30 invented A method of thermal imaging control of internal defects, which includes heating a portion of the surface of the product over time Гн1, registration of thermal radiation U (η p), Tsgdg) and Tsgtz) of the surface of the product at 35 p, tg, tz. where r = {x, y) are the coordinates of the surface of the product, the operation of processing the measurement results by forming a two-dimensional spatial function U (i \ τι) / υ (τ, η) or U (r, n) / and (n tz), which a synthesized thermogram of the surface of the product, characterized in that, in order to increase the reliability of the control by suppressing interference caused by the uneven radiation-absorption properties of the products, after registering the thermal radiation field U (7, l) at time L, the product is heated for a time Tn2 after registering the field lovogo radiation U (rt Tr) at time tg produce heating of the product during the time t _n of> 10 and heating times t _H2 and TNZ are chosen such that the average values of the thermal radiation fields 0 (r, Τι) the product over the frame at the instants times l, n, and tz were equal to each other, and the mathematical processing of the measurement results includes averaging of the functions U | 2 =? U ^ ri) / U (^), U13 = U (r; n) / U (^ тз). igzChDg, l) / and (r, tz) along the coordinates of U12. 013 and U23. formation of relative contrasts Ai2 ”Ui2 / Ui2 ~ 1; Ai3 = Ui3 / Ui3 ~ 1; Arg ^ igz / brz ^ 1, the formation of n spatial Fourier images of Au, Jtz and Dzz functions A12. A13 and Agz. filtering the obtained Fourier-images according to the expression ^s; where v = {v _x , v _y ) are the spatial frequency vectors, v ² = v _x ² + vy ² , · а is the thermal diffusivity of the product material, the inverse Fourier transform of the functions is performed, and the presence of defects is judged by the two-dimensional spatial images being 40 final thermograms synthesized from the initial thermograms U (r *? L), U (rt Т2), Utf ТЗ). . .