RU2023237C1 - Method of determining layer thickness - Google Patents

Abstract

FIELD: measurement technology; flaw detection. SUBSTANCE: method involves the steps of: periodically thermally affecting a specimen surface on one side, recording variations in its temperature in a check point and determining a phase difference between oscillations of heat flow and layer temperature in check points. The device for effecting method has electric power source 1 coupled with heat flow source 2, heat flow modulator 3, infra-red radiation sensor 5, DC potentiometer, amplifier 7, and mirror- galvanometer oscillograph. EFFECT: enhanced accuracy and widened range of layers to be measured by determining their thickness of low heat condition materials and cylindrical layers. 3 cl, 3 dwg

Description

 The invention relates to measuring equipment and can be used for defectometric studies.

 A known method for determining the thickness of a flat layer, the disadvantage of which is the low accuracy of determining the desired value [1].

 Closest to the proposed technical solution is the method [2], which includes a one-sided pulsed action on the layer by a thermal pulse flow, constant during the action of the pulse and uniformly distributed over the layer surface, recording the temperature change on one of the layer surfaces and determining its thickness taking into account the density of the absorbed heat flow and volumetric heat capacity of the material of the layer, and the temperature changes are recorded continuously during the pulse and determine the speed at roar surface layer, and layer thickness is determined by the stability of the auxiliary function portion.

 The known method is characterized by low accuracy. Its scope is limited.

 The aim of the invention is to improve the accuracy and expansion of the range of measured layers by determining the thickness of the layer of material with low thermal conductivity and cylindrical layers.

 In the proposed method there is no error associated with the temperature dependence of thermophysical properties and the need to determine heat fluxes. The method provides the ability to determine latent defects that are revealed during the deformation of the material.

, где а - коэффициент температуропроводности материала;
ω- частота колебаний теплового потока;
κ - безразмерный критерий, величина которого для фиксированного числа Био зависит только от l, a, ω и который определяется по результатам измерения величины сдвига фаз между колебаниями теплового потока и температуры в контрольной точке.This goal is achieved by the fact that the material creates periodic temperature fluctuations by modulating the heat flux alternately at two frequencies, the layer thickness is determined by measuring the phase difference between the heat flux and temperature fluctuations at a control point for one of the frequencies and determining the heat transfer correction (Biot criterion ) by the measured values of the phase difference for two frequencies. For example, for a flat layer, the layer thickness can be determined by the formula
l =

where a is the coefficient of thermal diffusivity of the material;
ω is the oscillation frequency of the heat flux;
κ is a dimensionless criterion, the value of which for a fixed Bio number depends only on l, a, ω and which is determined by measuring the phase shift between the fluctuations in the heat flux and temperature at the control point.

 The thickness of the cylindrical layer of the material is determined by the dependencies, fundamentally similar to the given. Flat multilayer samples are subjected to alternating bending during the passage of a temperature wave through the sample. Bending is carried out in the region of elastic deformations of the material without loss of layer stability on the compressed side and without fracture. The phase difference between the fluctuations in the heat flux on the surface and the temperature at the control point is measured at several fixed positions of the curved plate or at a slow change in the magnitude of the bending moment and subsequent change in the direction of its action. If there is a latent defect in the laminate in one of the plate positions, the defect size, for example, the height of the gap of the air gap, will be maximum, which will lead to an increase in phase shift.

 The correction for heat transfer is determined directly in the experiment as an integral characteristic, which helps to reduce the measurement error, since the heat transfer coefficient and degree of blackness in the experiment are not determined and are not calculated.

 Figure 1 shows a diagram of an experimental setup that allows to implement the method; figure 2 and 3 are graphs illustrating the method.

 The installation includes an electric power source 1 connected to a heat flux source and a heat flux modulator 3, a material layer 4, an infrared radiation sensor 5 connected to a DC potentiometer 6, an amplifier 7, and a loop oscilloscope 8. An incandescent lamp is used as a heat flux source 2 with a parabolic reflector. The radiation flow is periodically interrupted by a shutter with an electromagnetic drive controlled by the signals of the multivibrator. These elements make up the heat flux modulator 3, an alternating signal proportional to the change in the heat flux power, is sent from the heat flux modulator 3 to the oscilloscope 8. A photodiode (not shown) is used as a power change sensor. A photodiode is also used as an infrared radiation sensor 5. Instead of a photodiode, a thermocouple with corresponding dynamic properties can be used. When studying materials with high thermal conductivity and a high frequency of oscillations of the heat flux, a double-beam electronic oscilloscope can be used instead of a loop 8.

 The invention is as follows.

= 1,005·10 $\genfrac{}{}{0ex}{}{\text{2}}{\text{м}}$ . = 1,005 ˙ 10² м. Величину κ определяют при условии B_i ≈ 0, так как материал обладает высокой теплопроводностью в условиях незначительного теплообмена с окружающей средой.A layer of the investigated material 4 is placed between the heat flux modulator 3 and the sensor 5. After turning on the energy sources 1 and heat flux 2, the modulator 3 is turned on and an alternating heat flux is supplied to the surface of the material layer 4, causing temperature fluctuations in it. The registration of temperature fluctuations on the opposite surface of the layer 4 is carried out using a photodiode 5. Using a constant current potentiometer, compensate for the constant component of the electrical signal. The variable component is amplified by an amplifier 7 and recorded on photographic paper of the H 117-8 oscilloscope. Using an oscilloscope 8, the oscillations of the heat flux after the modulator 3 are also recorded. The phase shift between the fluctuations in temperature and the heat flux is determined. For example, for a layer of height l consisting of plates, the effective thermal diffusivity is
and _eff = 0.46 ˙ 10 ^-5 m ² / s. Intermittent heat flux is supplied to the surface of the sample with a frequency ω of 0.736 rad / s. The phase shift between the temperature and heat flux, which is φ 208 ^about . The size of the dimensionless criterion κ is determined according to the graph of figure 2, with κ = 4.05,
l = l =

= 1.00510 $\genfrac{}{}{0ex}{}{\text{2}}{\text{m}}$ . = 1.005 ˙ 10 ² m. The value of κ is determined under the condition B _i ≈ 0, since the material has high thermal conductivity in conditions of low heat exchange with the environment.

If the value of the criterion B _i differs significantly from 0, the phase shift φ ₁ (ω) and φ ₂ (2ω) are measured at two frequencies ω and 2 ω. According to the graph of FIG. 3 determine the value of criterion B _i , then the value of φ ₁ (ω) and the graph of FIG. 2 determine the value of κ and, using the above formula, calculate the layer height l.

Claims (3)

 1. THE METHOD FOR DETERMINING THE THICKNESS OF THE MATERIAL LAYER, which consists in the fact that a one-sided action of the heat flux on the material layer is carried out, a change in the temperature of the material layer is recorded and its thickness is determined, characterized in that, in order to increase the accuracy and expand the range of the measured layers by determining the layer thickness material with low thermal conductivity and cylindrical layers, carry out periodic fluctuations in the temperature of the material layer by modulating the heat flux alternately at two frequencies, changing The phase difference between the fluctuations of the heat flux and the temperature of the layer at the control point for one of the frequencies and for two frequencies is determined, the correction for heat transfer is determined by the phase difference for the two frequencies, and the thickness of the material layer is determined by the phase difference for one of the frequencies taking into account the obtained correction.  2. The method according to claim 1, characterized in that, in order to increase information content by identifying latent defects of the material layer, when exposed to a heat flow on the material layer, it is deformed, and the phase difference is measured under various fixed deformed states of the material layer.  3. The method according to claims 1 and 2, characterized in that, in order to increase productivity, the phase difference is measured in the process of changing the deformed state of the material layer.

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