JPH0226722B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a strain measuring method, and particularly to a strain measuring method and a measuring device that measure displacement between two points and measure strain in a range surrounded by these two points. be.

Conventionally, strain measurement at high temperatures (here, high temperature is defined as a temperature range in which organic materials cannot exhibit stable performance) involves (1) bringing the strain detection part of a strain detector into direct contact with a high-temperature object to be measured; Method,
There are two methods: (2) a method of externally measuring the deformation that occurs in the object to be measured using a detection rod, and (3) an optical method. Of these, (1)
In this method, welded resistance wire strain gauges or welded capacitive high temperature gauges are used, but since the gauge length is 10 mm or more, they are not suitable for measuring local strain at the bottom of a notch or fillet corner. cannot be used. Furthermore, resistance wire strain gauges have the disadvantage of breaking due to fatigue when subjected to repeated large strains. Furthermore, methods (2) and (3) have spatial constraints, so the measurement positions are strictly limited.

In addition, two electrodes fixed to each of these elastic plates and facing each other are provided between two elastic plates having different radii of curvature and convex in the same direction, which are joined at both ends. A plate-like elastic body having a means for measuring the capacitance between the two electrodes is spot-welded to the object to be measured at both ends, and the change in the distance between the two ends of the plate-shaped elastic body spot-welded to the object to be measured is measured. A method is also used in which the strain between two points is measured by measuring the change in capacitance between two electrodes caused by the deformation of two elastic plates. Compared to electric resistance strain gauges, this method results in smaller changes in measured values when repeated measurements are taken, but the length between the two ends to be spot welded is approximately 25 mm.
Therefore, like the above-mentioned method, it cannot be used to measure local strain at the bottom of a notch or a fillet corner.

The purpose of the present invention is to eliminate these drawbacks and make it possible to measure strain in a narrow part of the measurement space, such as a stress concentration area, in a high-temperature environment. In the method of measuring strain in a range surrounded by points, one end of two thin plate-shaped electrodes facing each other is held at a predetermined distance, the other movable end is brought into contact with the object to be measured, and two points are measured. The first feature is that the strain between two points is measured by measuring the capacitance change between the electric electrodes based on the displacement between them, and the second feature is that the strain between two points is measured.
In a device that measures the displacement between points and the strain in the range surrounded by the two points, one end is held and fixed at a predetermined distance, and the other end is movably brought into contact with the object to be measured. The relative displacement of the position of the other end in contact with the object to be measured between two thin plate electrodes facing each other and the two electrodes in contact with the object to be measured is calculated as follows: A second feature of the device is that the device measures displacement between two points and measures strain in a range surrounded by the two points. two thin plate-shaped electrodes facing each other with a dielectric adhered thereto; an insulating member provided at one end of the electrode and brought into contact with the object to be measured; and an insulating member provided on the electrode via the dielectric, A third feature is that the device includes a compensation electrode that compensates for changes in capacitance of the electrodes due to temperature changes.

In other words, it is possible to measure a minute relative displacement between two points as a change in capacitance between two conductors that are in contact with it.

The capacitance C of two metal plates is as follows: C=A・ε・S/D, where D is the distance between the metal plates, S is the facing area of the metal plates, and ε is the relative dielectric constant between the metal plates. (1) becomes. Therefore, when the environmental temperature and the distance between the metal plates change, ΔC/C=Δε/ε−ΔD/D...(2) If Δε/ε is compensated, ΔC can be changed electrically. By measuring, ΔD can be determined. Compensation for Δε/ε can be achieved by placing a third metal plate exposed to the same temperature on one of the two opposing metal plates and using it as a dummy in the electrical balancing circuit for measuring ΔC. .

Examples will be described below.

FIG. 1 is a sectional view of a main part of an embodiment of the strain measuring device of the present invention, and 1 and 2 are, for example,
SUS304, Inconel (product name), Hastelloy X
Metal plates (hereinafter referred to as electrodes), 3a and 3b, are attached to the tips of the electrodes 1 and 2 and are provided in point contact with the object 4 to be measured. ), 5a is the electrode 1
and 2 is coated with a heat-resistant dielectric such as alumina (Al ₂ O ₃ ); 6 is a temperature compensation electrode fixed to the electrode 2 via the dielectric 5b; 7a; , 7b and 7c are lead wires constituting a capacitance measurement balancing circuit, and A and B indicate points where the insulating members 3a and 3b are in contact with the object to be measured 4.

This strain measuring device is installed on the surface of the object to be measured 4 with insulating members 3a and 3b, with electrodes 1 and 2 parallel to each other, and one end of the electrodes 1 and 2. is fixed to the support part 8. D indicates the distance between electrode 1 and electrode 2 in this state, and L indicates the distance between insulating members 3a and 3b.

Now, a force acts on the object to be measured 4, and a relative displacement occurs between points A and B as shown by the dotted line in Figure 2, and the distance between points A and B increases from L to L+.
Assuming that ΔL is reached, the distance between electrode 1 and electrode 2 at this time is D+ΔL on the side to be measured, and D on the opposite side. In other words, the relative displacement of the distance between the two electrodes changes linearly from O to ΔL, as shown in Figure 3, where the horizontal and vertical axes show the distances X and ΔD from the ends of the electrodes, respectively. do.

Next, calculation of the amount of change in capacitance in this strain measurement method will be explained using FIG. 4. When the length of the electrode is a, the width is b, and the spread of the distance between the insulating members of the electrode is ΔL, the overall capacitance change is C=εa・b/D...(3) The surface of dx・b The electrostatic capacitance dC due to the element is dC=ε・b・dx/D...(4) When the distance between the surface elements of dx・b changes from D to D+Δl・x/a, the capacitance d(C+ΔC) is, d(C+ΔC)=ε・b・dx/D+Δl・x/a...(5
) d(ΔC)=ε・b(−Δl/ax・dx)/D……(6) Therefore, ΔC=∫ ^a _p d(ΔC)=∫ ^a _p ε・b・(−Δl/a) /D
x・dx =−ε・b・a/2・Δl/D=−Δl×C/2D……(7
) ΔC/C=−Δl/2D (8) Therefore, the change Δl in the distance between electrode 1 and electrode 2 is proportional to the capacitance change ΔC between the two electrodes 1 and 2.
ΔC can be determined by measuring the imbalance amount ΔE using an electrical equalization circuit as shown in FIG. In Figure 5, C _A is the capacitance between electrodes 1 and 2, C _D is the capacitance between electrodes 2 and 6, R _O is a fixed resistance, and R _bal is a balanced resistance. _L1 ,
L ₂ and L ₃ have lead wires 7a and 7b shown in FIG.
7c is connected.

FIG. 6 is a cross-sectional view illustrating a mounting method when measuring a notch as an embodiment of the strain measuring method of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. , 9 is a holding jig for bringing the electrodes 1 and 2 into contact with the object to be measured 4, and this holding jig 9 has an engaging portion 10 at the bottom that serves as a support for the electrodes 1 and 2, and A flange 11 is provided on the side, and a bellows 12 is provided in the middle of the body.

To measure strain using this strain measuring device, electrodes 1 and 2 are connected to their insulating members 3a and 3.
After the tips A and B of b are installed so that they are in contact with the inner wall of the notch of the object to be measured 4, the holding jig 9 is placed over the holding jig 9, and the flange 11 is fixed to the object to be measured 4 by spot welding. Since this holding jig 9 is provided with a bellows 12, the supporting parts of the electrodes 1 and 2 are fixed by the engaging part 10, and the electrodes 1 and 2 are brought into elastic contact with the object to be measured 4. be able to. And lead wire 7
a, 7b and 7c as L ₁ and L ₂ in Fig. 5, respectively.
and L ₃ for measurements. In addition,
This holding jig 9 also serves as a protective cover that prevents the heat insulating coating 13 used when the object to be measured 4 reaches a high temperature from touching the electrodes 1 and 2. Note that this holding jig may be constructed of a band-like member having a U-shaped cross section, or may be constructed of a cylindrical cap-like member.

FIG. 7 is a sectional view illustrating an installation method when measuring a fillet portion as another embodiment of the strain measuring method of the present invention, and the same parts as in FIG. 6 are given the same reference numerals. There is. This embodiment differs from the embodiment shown in FIG. 6 in that the shape of the presser jig 9 is different, and the flange 11 of the presser jig 9 is attached to the object to be measured.
The function and effect are the same as those of the embodiment shown in FIG. 6 in that the shape is such that it can be attached to two sides forming a right angle to each other.

The strain measuring device of these embodiments uses a thin plate-like electrode, uses a heat-resistant dielectric material on the electrode surface, and can make the electrode thin and have a thickness of about 1 to 0.5 mm. At high temperatures, it is possible to measure the change in distance between two points over a very small area. Not only is it possible to measure local strains such as notches or fillet corners, but there is almost no change in measured values due to repeated measurements, making it possible to perform highly accurate measurements.

That is, the strain measuring method and measuring device of the present invention can measure strain in a narrow part of the measurement space such as a stress concentration area in a high temperature environment, and has a great industrial effect. .

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of an embodiment of the strain measuring device of the present invention, FIG. 2 is an explanatory diagram of the positional relationship between the electrodes, and FIG. 3 is a diagram showing the position within the electrodes and the electrode spacing. A diagram showing the relationship, FIG. 4 is an explanatory diagram for calculating the amount of change in capacitance, and FIG. 5 is an electrical balance diagram for capacitance measurement of an embodiment of the strain measuring device of the present invention. The circuit diagrams of the circuit, Figures 6 and 7, are
FIG. 3 is a cross-sectional view illustrating different embodiments of the strain measurement method of the present invention. 1, 2... Electrode, 3a, 3b... Insulating member, 4
...Object to be measured, 5a, 5b...Dielectric material, 6...Electrode for temperature compensation, 7a, 7b, 7c...Lead wire, 9...Press jig, 10...Engaging portion, 11...
Tsubabe, 12... bellows.

Claims (1)

[Claims] 1. In a method of measuring displacement between two points and measuring strain in a range surrounded by the two points, one end of two thin plate electrodes facing each other is held at a predetermined distance. and the strain between the two points is measured by bringing the other displaceable end into contact with the object to be measured and measuring the change in capacitance between the electrodes based on the displacement between the two points. Measuring method. 2. The method for measuring strain according to claim 1, wherein the other ends of the two thin plate-like electrodes facing each other are brought into contact with the object to be measured substantially perpendicularly and elastically. 3. The elastic contact of the electrode to the object to be measured is achieved by fixing a U-shaped or cylindrical pressing jig with a bellows in the middle to the object to be measured at its open end. A strain measuring method according to claim 2, which is carried out. 4 In a device that measures displacement between two points and measures strain in the range surrounded by the two points, one end is held at a predetermined distance and runs fixedly, and the other end is movable and touches the object to be measured. The relative displacement of the position of two thin plate electrodes that are in contact with each other and the other end that is in contact with the object to be measured between the two electrodes that are in contact with the object to be measured is calculated as follows. A strain measuring device characterized by comprising: means for measuring changes in capacitance between two electrodes. 5. A device that measures the displacement between two points and the strain in the range surrounded by the two points, which consists of two thin plate-shaped electrodes facing each other with dielectrics coated on their surfaces, and It is characterized by comprising an insulating member provided on one end side and brought into contact with the object to be measured, and a compensation electrode provided on the electrode via a dielectric material to compensate for changes in capacitance of the electrode due to temperature changes. Strain measuring device.