JPH04121650A - Method for measuring high coefficient of thermal expansion - Google Patents

Abstract

PURPOSE:To determine heat conductivity and the coefficient of thermal expansion by heating a disc-shaped graphite test piece having a hollow hole by high frequency induction so as to impart a thermal shock thereto and measuring and analyzing the transient temp. distribution in the test piece and measuring the outer diameter of the test piece by a laser microgauge. CONSTITUTION:A graphite disc 11 having a hollow hole is heated by the eddy current generated in the outer peripheral part of said disc 11 using a high frequency induction heating method. The transient temp. change at a plurality of the places of the disc 11 in the radius direction thereof is recorded on a multi-pen transient recorder 3 and, at the same time, the displacement of the outer diameter of the graphite disc 11 is measured by a laser microgauge 2. The measurement of the transient temp. in the disc 11 at the time of a thermal shock test and the measurement of the displacement of the outer diameter of the disc 11 due to the laser microgauge at the same time are performed under various heating conditions and two measured data are analyzed according to a thermal elasticity relational expression to determine the coefficient of thermal expansion as the function of temp.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for measuring high coefficients of thermal expansion.

(Prior Art) Elucidating the problem of the strength of graphite materials against thermal shock and thermal fatigue is an important issue for improving the performance of industrial graphite products. The main stresses that occur during the operation of graphite fuel bodies and reflectors in high-temperature gas reactors are secondary stresses such as thermal stress and irradiation-induced stress.

Conventionally, the main method for measuring the coefficient of thermal expansion is to use a differential thermal dilatometer, but its normal temperature is 1,000 to 30
00°C, and the coefficient of thermal expansion is determined by comparing standard samples.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for measuring the coefficient of thermal expansion at higher temperatures.

(Means for Solving the Problems) As a result of intensive research, the inventors of the present application have determined that the temperature range of the disk test piece can be increased to 10% by selecting various outputs of the heating power source.
We achieved this goal by coming up with the idea that it is possible to raise the temperature from 00°C to 3000°C (near the melting point of the material) and to determine the coefficient of thermal expansion directly from the analysis of temperature and outer radius displacement data. Ta.

That is, the present invention etc. has 1. In the thermal shock test of disk samples for research on thermal shock fracture and thermal fatigue fracture, the first
As a step, a graphite disk test piece with a hollow hole is heated by thermal shock using high-frequency induction, and at that time, the transient temperature distribution inside the test piece is measured and analyzed, and the outer diameter of the test piece is measured using a laser microgauge. We have developed a measuring method and apparatus for determining thermal conductivity and thermal expansion coefficient as a function of temperature.

Therefore, the method of the present invention is particularly effective for measuring the coefficient of thermal expansion of high-temperature materials for use in nuclear fusion reactors, ultra-high temperature gas turbines, space rockets, and the like.

Below, an overview of the high thermal expansion coefficient measuring method and apparatus of the present invention will be explained, and the thermal expansion coefficient of isotropic graphite will be measured in the temperature range from room temperature to about 2000°C.
The results measured by the measuring method of the present invention will be explained in comparison with the measured values by the conventional method.

As shown in FIG. 1, the measurement method of the present invention basically consists of a thermal shock test method and a thermal expansion analysis method.

As a thermal shock test method, a graphite disk with hollow holes (outer diameter = 30 to 100 mm, thickness = 3
It is heated by eddy currents generated on the outer circumference (~8 mm). Transient temperature changes at multiple locations in the radial direction of the specimen are measured using R-type thermocouples in the low temperature range, and
In the high temperature range above 0℃, we use a Si element fiber radiation thermometer that can measure up to 1100℃ to 3000℃.
Record on a multi-vent transient recorder. Furthermore, by varying the output of the high-frequency induction power supply device up to a maximum of about 50° C., it is possible to obtain transient temperature measurement data from room temperature to about 3000° C. for a negative-shaped graphite test piece. At this time, the outer diameter displacement of the graphite disk is simultaneously measured using a laser micro gauge (manufactured by Tokyo Photonics Industry @/Hotaka Seiki ■).

The thermal expansion analysis method uses a general solution of the differential equation of displacement in an axisymmetric planar thermoelastic problem of a disk.

That is, when the average coefficient of thermal expansion is a function of temperature, the radial displacement U is given by the following equation.

Here, C: Poisson's ratio α: Temperature from room temperature T T: Temperature: Radial position R, inner radius C, Ct: Average coefficient of thermal expansion up to constant of integration Next, CI, Cff1 are expressed as the radial stress σr. Inner surface (
r=R+) and the outer surface (r=Ro) according to the following boundary conditions.

(r= = σ r (r= =0 Therefore, The radial displacement is given by the following equation.

In the formula, r= R.

The outer diameter displacement is given by the following formula. expressed.

Here, the average coefficient of thermal expansion of graphite is expressed as a linear function of temperature as follows, with reference to the measurement results from previous studies and this study.

α=a, +22 ”f Substituting equation (5) into equation (4), the outer diameter displacement of the graphite disk is determined by the temperature distribution T and the average coefficient of thermal expansion parameter a I
, az.

That is, the transient temperature measurement inside the disk during the thermal shock test and the simultaneous outer diameter displacement measurement using a laser microgauge are performed under various heating conditions.

This allows (4
) is numerically integrated, and the above parameters al,
az can be calculated. Furthermore, each a,
, az, the optimal al for the required temperature range
, az can be determined in any suitable manner.

(Example) The measurement method of the present invention will be specifically explained with reference to Examples.

The test material was IG-1, a non-purified processed material of petroleum coke-based, isostatically pressed fine-grained isotropic graphite IG410, which is a material for the fuel body graphite block of the High Temperature Engineering Test and Research Reactor (HTTR).
1 (manufactured by Toyo Gokuso ■) was used.

The disk test piece was manufactured so as to be perpendicular to the longitudinal direction of the material block (T direction). FIG. 2 shows the shape of the test piece and typical temperature measurement positions used in this example.

Note that all measurements were performed in a vacuum of 10-' Torr or less.

Measurement Results and Discussion FIG. 3 shows the transient changes in the measured temperature obtained with respect to the output level 450 of the high-frequency induction heating power source, and FIG. 5 shows the radial temperature distribution at three times. As expected from the eddy current density distribution of the graphite disk test piece, both figures show that the temperature difference in the radial direction of the test piece, especially the temperature difference near the outer periphery, is large. Furthermore, it can be seen that the closer to the inner periphery of the test piece, the later the temperature rise starts.

Furthermore, in the above-mentioned test at the high frequency output level 450, the outer diameter displacement of the graphite disk test piece measured simultaneously with a laser microgauge is shown in FIG. This figure shows that the outer diameter displacement increases as the temperature rises. Using this external diameter displacement data and transient temperature measurement data, the coefficients a, , a, of equation (5) were determined for the measurement temperature range from 1900°C to 1900°C. Furthermore, for measurements made with the high frequency output level changed to 200.275, coefficients a and a2 were similarly determined for the measurement temperature ranges of RT -1300°C and RT~1500''C, respectively.

The T-direction thermal expansion of IG-11 graphite determined at the above output levels is plotted in FIG. 6.

From this result, the optimal average coefficient of thermal expansion α for the measurement temperature range from RT to 1900'C is expressed by the following equation.

α=4.8 x 10-b+6.7 x 10-”T
(1/'C) (61 The average coefficient of thermal expansion α of this graphite was determined separately from 21 to 800 using a differential thermal dilatometer.
℃, RT to 1200℃, the results (average ± standard deviation) are 4.70 ± 0.10, respectively.
x 10-”/”C15,06±0.11 x 1
0-6/'c.

On the other hand, in the measurement method of the present invention, that is, α in equation (6) is 5.3 x 10-'/''C15,6X 10
-6/''C, which is about 10% higher.

From the above, it has been verified that the measuring method of the present invention is valid when compared with the conventional method, and that the average coefficient of thermal expansion from room temperature to about 2000° C. can be measured with appropriate accuracy.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram outlining the measurement method of the present invention. In the figure, (1) is a thermal shock device, 1 is a high-frequency induction power supply, 2 is a laser microgauge, 3 is a recorder (temperature), 4 is a recorder (output, outer diameter), (n) is a thermal expansion analysis system, and 5 is a thermal Strain analysis, 6 radial profile, and 7 outer diameter displacement. Furthermore, 11 sample piece, 12 vacuum container, 13 voltage,
I4 current, 15 pyrometer. FIG. 2 is a diagram showing the shape of the test piece used in Examples and typical temperature measurement positions. FIG. 3 shows the distribution (transient change) of measured temperatures obtained when the output level of the high-frequency induction heating power source was 450. In the figure, the horizontal axis shows time (seconds), and the vertical axis shows temperature ("
c). FIG. 4 shows the outer diameter displacement of the graphite disk test piece measured by a laser microgauge at the same time as the measurement in FIG. In the figure, the horizontal axis indicates time (seconds), and the vertical axis indicates outer diameter displacement (μm). FIG. 5 shows the temperature distribution in the radial direction at three times when the output level of the high-frequency induction heating power source is 450. In the figure, the horizontal axis shows the radius (mm), and the vertical axis shows the temperature (mm).
'C) is shown. FIG. 6 is a diagram plotting the relationship between the T-direction thermal expansion of IG-11 graphite and temperature, determined based on the output level. In the figure, the horizontal axis indicates temperature ("C), and the vertical axis indicates coefficient of thermal expansion (%).

Claims (1)

[Claims] A disk test piece is impulsively heated by high-frequency induction or arc discharge, transient temperatures are measured at multiple positions in the radial direction of the test piece, and at the same time, the outer radius of the disk at that time is measured using a laser displacement meter. A method of measuring a high coefficient of thermal expansion, which consists of measuring the coefficient of thermal expansion as a function of temperature by measuring with a laser micro gauge and analyzing the two measured data using a thermoelastic relational equation.