JPH0476446A - Thermal physical characteristic measuring method - Google Patents

Abstract

PURPOSE:To obtain a distribution of thermal characteristics of a macroscopically nonuniform material, which varies in a direction perpendicular to that of the laminated surface, by uniformly blackening the front and rear surfaces of a sample on which nonuniformity is present in an interface direction, and by measuring an internal distribution of transient temperature rises on the rear surface of the sample after the front surface is heated by pulse radiation with a uniform energy density. CONSTITUTION:A planar sample 2 in which a nonuniformity is present in an interface direction is cut out from a microscopically nonuniform material whose composition and physical characteristics vary in a direction perpendicularly to the laminated surface, the front and rear surfaces thereof is blackened uniformly. Further, the front surface of the sample 2 is irradiated with a pulse laser beam having uniform energy density distribution, and after it is instantly and uniformly heated by pulse radiation 1, transient variation in the temperature distribution of the rear surface of the sample 2 is measured so as to measure the absolute value of a thermal diffusion rate at each position, and the distribution of relative value of heat capacity per unit volume. Further, the distribution of the absolute values of the heat capacity per unit area is obtained from the heat capacity, and the distribution of the absolute values of specific heat is obtained from the heat capacity. Further, it is possible to obtain the distribution of the thermal conductivity in the sample 2 from the thermal diffusion rates and the heat capacities.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to the thermal diffusivity and specific heat of macroscopically heterogeneous materials such as functionally graded materials and layered materials whose composition and physical properties change along the vertical direction of the laminated surfaces. , which relates to the measurement of the distribution of thermophysical property values such as thermal conductivity.

[Prior art and problems] Conventional methods for measuring thermophysical properties of uniform and dense solid materials include the laser Fra-Souch method based on thermal diffusivity;
The adiabatic method, differential scanning calorimetry, and drop method are generally used for specific heat, and the steady state method is used for thermal conductivity, and the measurement technology can be considered to be established. (For example, Magritchi, Césaryan, and Pellet Az-eds.
Introduction to Thermophysical Property Measurement Methods, Volume 1, Review of Measurement Techniques J
(1984) Breena 11 Breath, New York;
Maglic, Ceza+r-yan, Pele
tskey edition r Compendium of The
rmo-physical Property Mea
Surement Methods.

Volume l, 5urvey of Measu
rement Techniques J, (1984), Plenum Press, New York)
However, in recent years, progress has been made in the development of macroscopically heterogeneous materials such as functionally graded materials and multilayer materials that macroscopically introduce controlled compositional heterogeneity. The above measurement methods used for materials cannot be applied as is. For example, Nobuyuki Araki, “Advances in thermal conductivity measurement methods and how to choose a measurement method,” Journal of the Japan Society of Mechanical Engineers, vol. 90, no. 822, pp. 79-84.
．． (1987) Furthermore, such macroscopically heterogeneous materials are often assumed to be used at high temperatures, and thermophysical properties up to high temperatures are required. When measuring normal uniform and dense solid materials at high temperatures of 1000°C or higher, first measure the thermal diffusivity using the laser flash method, and then calculate the thermal conductivity from the specific heat value determined by the drop method etc. and the density of the sample. It is common to calculate However, in macroscopically heterogeneous materials such as functionally graded materials, thermal diffusivity and specific heat are determined as average values, so it is not possible to calculate thermal conductivity using a simple formula, as in the case of homogeneous materials. In other words, for macroscopically heterogeneous materials, it is not possible to measure the average value of thermal diffusivity of the entire sample or the heat capacity of the entire sample, but to measure the distribution of thermal diffusivity and specific heat that change depending on the position inside the sample. This is necessary.

In the normal laser flash method, the distribution of the spatial energy density of the pulsed laser beam is non-uniform, so a one-dimensional heat flow state is not necessarily achieved inside the sample, and there is also a transient heat flow at only one force point at the center of the back surface of the sample. Since it measures the temperature rise, it cannot be applied to the measurement of thermal diffusivity and specific heat distribution. Therefore, at present, there is no method to measure the distribution of thermal properties such as thermal diffusivity, specific heat, and thermal conductivity of macroscopically heterogeneous materials at high temperatures of 1000°C or higher; This is an urgent issue in evaluating the thermophysical properties of thermally heterogeneous materials.

[Object of the Invention] The present invention aims to improve thermal diffusivity, specific heat, thermal conductivity, etc. for macroscopically heterogeneous materials such as functionally graded materials and multilayer materials whose composition and physical properties change in the direction perpendicular to the laminated surface. It is an object of the present invention to provide a thermophysical property measurement method that can measure the distribution of thermal properties inside a material as a function of position.

[Means for solving problems] In order to eliminate the above drawbacks, the present invention takes the following measures.

That is, a flat sample exhibiting in-plane inhomogeneity is cut out from a macroscopically inhomogeneous material whose composition and physical properties change in the direction perpendicular to the laminated surface, and its front and back surfaces are uniformly blackened to make the sample surface uniform. After pulsed radiation heating with energy density,
Measuring the in-plane distribution of transient temperature rise on the back side of the sampleζ
From this, the macroscopic heterogeneity kA that changes in the vertical direction of the laminated plane
The distribution of thermal properties of Kyo 4 was determined.

As a distribution of thermal properties, the thermal diffusivity of a macroscopically heterogeneous material that changes in the vertical direction of the laminated surface is determined from the in-plane distribution of the transient temperature rise rate determined from the in-plane distribution of the transient temperature on the back side of the sample. We calculated the distribution of

As the distribution of thermal properties, the in-plane distribution of the maximum value of the transient temperature rise obtained from the in-plane distribution of the transient temperature increase on the back side of the sample shows that per unit volume of the macroscopically heterogeneous material changing in the vertical direction of the laminated surface. The distribution of relative values of heat capacity was calculated.

As the distribution of thermal properties, the distribution of the absolute value of heat capacity per unit volume was determined by proportionally distributing the heat capacity of the entire flat sample, which was separately measured using a general method, according to the distribution of the relative value of heat capacity per unit volume. .

As the distribution of thermal properties, the quotient obtained by dividing the distribution of the absolute value of heat capacity per unit volume for each position inside the sample by the distribution of density, which is separately measured by a general method, is calculated in the vertical direction of the laminated surface. The distribution of the specific heat of a macroscopically heterogeneous material that changes as follows.

The heat of a macroscopically inhomogeneous material that changes in the vertical direction of the laminated surface is expressed as the product of the distribution of thermal diffusivity and the distribution of the absolute value of the heat capacity per Ω body at each position ζ, as a vI time characteristic distribution. The conductivity distribution was determined.

If the thickness of the macroscopically heterogeneous material is small and a sample cut perpendicular to the lamination plane is not large enough for measurement, a flat sample is cut along a plane ζ that is inclined to the lamination plane. .

[Operation] In the method described in 2, by uniformly blackening the front and back surfaces of a flat sample whose composition and physical properties change along the surface, the absorption rate of the sample surface to the laser beam is increased. Uniform Nors radiation heating becomes possible.

Furthermore, since the emissivity of the back surface of the sample at the radiation thermometry wavelength is uniform, accurate relative temperature distribution measurement is possible.

By irradiating the surface of the semi-decomposed sample in this manner with a pulsed laser beam with a uniform spatial energy density distribution, a one-dimensional heat flow distribution inside the sample is achieved.
Furthermore, by measuring transient changes in the temperature distribution on the back surface of the sample after pulse heating using a high-speed thermal imaging device, we can estimate the distribution of the absolute value of thermal diffusivity and the relative value of heat capacity per unit volume at each position along the sample surface. Measurement becomes possible.

The heat capacity of the entire sample can be measured by well-known methods such as the adiabatic method, differential scanning calorimetry, and drop method, and the results are proportional to the distribution of the relative value of heat capacity per unit volume obtained by the above method. By allocating, the distribution of absolute values of heat capacity per unit volume can be determined.

Furthermore, by measuring the density of each part of the sample using a standard method such as a vicinometer method or a density balance method, the distribution of absolute values of specific heat can be determined from the distribution of absolute values of heat capacity per unit volume.

The distribution of thermal conductivity within the sample is determined as the product of the value of thermal diffusivity at each position within the sample obtained as described above and the absolute value of heat capacity per unit volume.

In addition, if the thickness of the material is small and it is not possible to obtain a flat sample of sufficient width by cutting perpendicular to the laminated surface, cut along a surface inclined by about 5° to 20° with respect to the surface direction of the plate-like material. Thickness 0.
Measurement is possible by cutting out a flat plate with a thickness of about 2 mm to 2 mm.

[Embodiments of the Invention] Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the principle of measuring thermophysical properties according to the present invention.

Pulse radiation heating 1 with a spatially uniform energy density instantaneously and uniformly heats the surface of a macroscopically heterogeneous material sample 2 cut out into a flat plate so that the composition and physical properties change along the surface direction. At that time, in order to keep the absorption rate of the sample surface for radiant heating light and the emissivity of the sample back surface during radiation temperature measurement constant, the front and back surfaces of the sample are uniformly blackened.
If the sample is thin enough with respect to the characteristic length along the plane of change in physical properties, heat can be considered to flow perpendicularly and one-dimensionally from the surface to the back surface of the sample in each part of the sample. . In this state, a high-speed thermal imaging device or a -dimensional scanning radiation thermometer 3 is used to measure changes in the one-dimensional temperature distribution on the back surface of the macroscopically heterogeneous material sample along the direction in which the formation and physical properties change. The results are organized as a transient temperature rise 4 at each position on the back side of the sample shown on the right side of the figure.
One-dimensional rise time distribution 5 and maximum temperature rise distribution 6 along the direction of formation of macroscopically heterogeneous material and change in physical properties are determined.

This measurement corresponds to simultaneous measurement of thermal diffusivity and heat capacity by the usual laser flash method at each position on the sample surface. It is known that the temperature on the back surface of a sample after pulsed radiation heating increases according to the curve shown in FIG. After a certain period of time has elapsed, the temperature rise reaches the maximum value ΔT and thereafter remains at a constant value.If the time until reaching the half value ΔT/2 of the maximum temperature rise is expressed as t172, the thermal diffusivity is given by the following equation.

π　2　t　I・2 Here! is the thickness of the sample.

At the same time, the heat ffff1 per unit body is given by the following equation.

22q is the pulse radiation heating energy absorbed by a unit area of the sample.

However, in this case, it is not easy to evaluate the absolute values of q and ΔT, and the value of C is usually a relative value.

By performing the analysis in Figure 2 on the measurement curve of the transient temperature rise 4 at each position The distribution of absolute values of thermal diffusivity and the distribution of relative values of heat capacity per unit volume along the direction of

If the heat capacity of the entire sample is measured separately using an established method such as the adiabatic method, differential scanning calorimetry, or drop method, the unit volume can be calculated by proportionally distributing the total heat capacity using the relative value of the heat capacity distribution per unit volume. The absolute value of the heat capacity distribution per unit is determined. FIG. 3 shows an example of measurement for a multilayer material. position lx
Therefore, the rise time distribution 5 is t+z
2 (X), the maximum temperature increase distribution 6 is expressed as ΔT (x), the thermal diffusivity distribution 7 is expressed as α(X), and the heat capacity distribution 8 per unit volume is expressed as C(x).

The thermal conductivity distribution 9 is expressed by the following equation by definition.

Enter (X) = α (X) ・C
(x) (3)I Therefore, if distribution 7 α(X) of thermal diffusivity and distribution 8 C(x) of heat capacity per unit volume are known, λ(x) can be easily determined.

Furthermore, if the density distribution ρ(X) of each part of the sample is measured using a vicinometer, a density balance, etc., the specific heat distribution C(X) can be determined from C(X) using the following equation.

C(x) c(x)=(4)ρ(X) FIG. 4 shows an example of the configuration of a measuring device based on the wooden sword method. Since the laser beam 11 emitted by the high-output pulse laser 10 is normally spatially non-uniform due to multi-mode oscillation, the spatial energy distribution is made uniform by passing it through the laser beam homogenizing optical system 12. The thus homogenized laser beam 1 is reflected by a mirror 13, guided into a vacuum chamber 14 through an upper window, and irradiated onto a macroscopically heterogeneous material sample 2 placed in a sample holder 16. Note that sample 2 was heated from room temperature to 2000°C by heater 15.
It is heated to a temperature range of ℃ or higher, making it possible to perform measurements over a wide temperature range R. Changes in the one-dimensional temperature distribution on the back surface of sample 2 can be observed through the lower window v! Ii@measured by an imager or a -dimensional scanning radiation thermometer 3. Measurement results are recorded in high-speed multi-channel data in synchronization with the tri-force signal from the laser! Apparatus】7. The measurement results sent to the personal computer 1B are recorded on a floppy disk and analyzed, and a transient temperature rise curve at each position on the back surface of the sample is displayed on the CRT.

Furthermore, the total heat capacity of the sample, which was measured separately, and the density distribution of each part of the sample are manually prepared. From this, the distribution of thermal properties such as thermal diffusivity, specific heat, and thermal conductivity of each part of the sample is calculated.

Note that since the functionally graded material has a thickness of approximately 1 to 10 mm, if a flat sample is cut out perpendicular to the laminated surface, the width of the sample cannot be made wide enough to measure one-dimensional temperature distribution changes. In such cases, measurements can be made by cutting out a flat sample with a thickness of 0.2 to 2 mm and a radius of 10 to 20 mm at an angle of 5° to 206° from the laminated surface as shown in Figure 5. Become.

[Effects of the Invention] As described above, this method of measuring thermophysical properties can be used to measure the thermal diffusivity, specific heat, and thermal conductivity of a macroscopically heterogeneous material whose composition and physical properties change along the vertical direction of the laminated surface. It becomes possible to measure the distribution of thermophysical property values according to the position within the sample. The present invention makes it possible to measure the thermophysical properties of macroscopically heterogeneous materials such as functionally graded materials and multilayer materials, which has been more difficult with conventional methods. Since this thermophysical property measurement method can be easily applied to high temperatures of 2000°C or higher, there is a demand for the use of new materials in high-temperature environments, especially in the advanced energy use, peaceful use of nuclear energy, aerospace fields, etc. This is expected to promote the development and use of macroscopically heterogeneous materials in the fields of research and development.

[Brief explanation of drawings]

FIG. 1 is a principle diagram showing the principle of thermophysical property measurement according to the present invention. FIG. 2 is a graph showing the calculation of thermal diffusivity and heat capacity per unit volume from the measurement curve of transient temperature rise at each position on the back surface of the sample. FIG. 3 is a graph showing a measurement example for a multilayer material and the distribution of thermal diffusivity, heat capacity per unit volume, and thermal conductivity obtained by M analysis of the measurement. FIG. 4 is a configuration diagram of a measuring device showing an embodiment of the present invention. FIG. 5 is a perspective view showing that a sample to which the present thermophysical property measuring method can be applied can be prepared by cutting out a thin macroscopically heterogeneous material diagonally. 5゜6゜7゜8゜Skin 10゜1 1゜12゜13゜14゜15゜16゜17゜18゜19゜Uniform pulse radiation heating Macroscopic heterogeneous material sample thermal imaging device or -dimensional scanning radiation temperature Distribution of transient temperature rise rise time at each position on the back surface of the sample Distribution of maximum temperature rise Distribution of thermal diffusivity Distribution of heat capacity per unit volume Distribution of thermal conductivity High power pulsed laser Direct laser beam Laser beam homogenization optical system Mirror Vacuum chamber Heater Sample holder High-speed multi-channel data recording device Personal computer Macroscopically heterogeneous materials such as functionally graded materials and multilayer materials 20, direction along the laminated surface 21, direction in which composition and physical properties change 22, relative to the laminated surface Figure 4: A flat sample cut along a plane with an inclination.

Claims (7)

[Claims] (1) A flat sample with in-plane non-uniformity is cut out from a macroscopically heterogeneous material whose composition and physical properties change in the direction perpendicular to the laminated surface, and its front and back surfaces are uniformly blackened to darken the sample surface. After pulsed radiation heating with uniform energy density,
A thermophysical property measuring method characterized by determining the distribution of thermal properties of a macroscopically heterogeneous material that changes in the direction perpendicular to the laminated surface by measuring the in-plane distribution of the transient temperature rise on the back surface of the sample. (2) Thermal diffusion of a macroscopically heterogeneous material changes in the vertical direction of the laminated surface from the in-plane distribution of the transient temperature increase rate determined from the in-plane distribution of the transient temperature increase on the back side of the sample as the distribution of thermal properties. The method for measuring thermophysical properties according to claim 1, characterized in that a distribution of the ratio is determined. (3) As a distribution of thermal properties, the in-plane distribution of the maximum transient temperature rise obtained from the in-plane distribution of the transient temperature increase on the back side of the sample shows that the distribution of macroscopically heterogeneous materials that changes in the vertical direction of the laminated surface The method for measuring thermophysical properties according to claim 1, characterized in that a distribution of relative values of heat capacity per unit volume is determined. (4) As the distribution of thermal properties, the heat capacity of the entire flat sample measured separately by a general method is proportionally distributed according to the distribution of the relative value of heat capacity per unit volume obtained in claim (3). The method for measuring thermophysical properties according to claim 1, characterized in that the distribution of the absolute value of the heat capacity per unit is determined. (5) As the distribution of thermal properties, the distribution of the absolute value of heat capacity per unit volume obtained in claim (4) is divided for each position inside the sample by the distribution of density separately measured by a general method. 2. The method for measuring thermophysical properties according to claim 1, wherein the distribution of specific heat of the macroscopically heterogeneous material that changes in the direction perpendicular to the laminated surface is determined as the quotient obtained by the method. (6) As the distribution of thermal properties, the product at each position of the distribution of thermal diffusivity determined in claim (2) and the distribution of the absolute value of heat capacity per unit volume determined in claim (4), The method for measuring thermophysical properties according to claim 1, characterized in that the distribution of thermal conductivity of the macroscopically heterogeneous material that changes in the direction perpendicular to the laminated surface is determined. (7) If the thickness of the macroscopically heterogeneous material is small and a sample cut perpendicular to the laminated surface is not large enough for measurement, a flat sample is cut along a plane inclined to the laminated surface. The method for measuring thermophysical properties according to claim 1, characterized in that the method comprises cutting out the thermophysical properties.