JPH0776683B2 - Latent distortion detection method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a nondestructive method for non-destructively detecting latent strain accumulated in an object to be measured on which an unknown external force is applied, such as a steel support of a tunnel or a reinforcing bar in concrete. Regarding

[0002]

2. Description of the Related Art Conventionally, as a detection method of this kind, a method using magnetism, a method using ultrasonic waves, a method using X-rays, etc. are known.

[0003]

However, in the case of utilizing magnetism, the object to be measured must be a magnetic material, and the object to be detected is not limited. Since the value to be detected differs depending on the difference, it is necessary to know the composition in advance, and it takes time to prepare for detection. Further, in the case of using ultrasonic waves, in order to bring the ultrasonic wave source into close contact with the surface of the object to be measured, the work of polishing the mounting surface thereof is required, and the preparation thereof is troublesome. or,
In the case of using X-rays, there is a problem that they need to be handled with care and cannot be used easily. An object of the present invention is to provide a method for detecting a latent strain of an object to be measured which eliminates such inconvenience.

[0004]

A method for detecting latent strain of the present invention for achieving such an object is to provide a pair of electrodes on the surface of an object to be measured and a dummy piece, and apply an unknown external force to them. In a latent state, a direct current is instantaneously passed between the electrodes, and the latent strain is detected from the combined strain of the electromagnetic force generated when the current flows and the external force.

[0005]

According to the latent strain detecting method of the present invention, when a current is instantaneously applied between both electrodes, an electromagnetic force is generated in the object to be measured by the left-hand rule of framing.
The surface strain (composite strain due to external force and impact stress) is measured. If the correlation between the strain due to the external force and the synthetic strain is obtained, the strain due to the electromagnetic force becomes a constant by specifying the magnitude of the electric current, so that the latent strain can be easily known from the synthetic strain. The measurement of the surface strain, the strain gauge is attached to the surface between the pair of electrodes and the object to be measured other than between the electrodes with a space therebetween, and the Wheatstone bridge configured using both strain gauges is used. The surface strain is measured and the latent strain is obtained from this.

[0006]

EXAMPLES An example of the implementation of the measuring method of the present invention will be described with reference to FIGS. In FIGS. 1 (a) and 1 (b), M is a measured object such as a reinforcing bar, M'is a dummy piece made of the same material as the measured object M provided along with it, and the dummy piece M'is The electrically conductive coupling piece c and the electrically conductive coupling piece d are provided so as to be coupled to the device under test M. And
Electrodes a and b are provided on the object to be measured M and the dummy piece M ′ so that a current flows through the coupling piece d to the portions of the object M to be measured and the dummy piece M ′ which are parallel to each other. G is the electrodes a, b
A strain gauge, G ', which is provided on the surface of the object to be measured M so as to enter between the electrodes a and b when a current is passed between them, is provided at a position apart from the electrodes a and b of the object to be measured M. A strain gauge is shown, and the strain gauges G and G'assemble a Wheatstone bridge via a matching portion A as shown in FIG.
Connect to the recorder REC. In FIG. 2, B is a timer for controlling the energization time of the current flowing between the electrodes a and b to be 50 mS or less, DCS is a DC stabilized power supply, and the power supply DC
Set S to 50 amps. HS is a manual switch, T
Indicates a synchronization unit for matching the activation of the timer B and the recorder REC. Next, the measurement of latent strain by the method of the present invention will be described. Now, when the potential distortion E _X is present by an external force to the object to be measured M (such as tensile force P), the electrodes a, b
Apply current between them. Then, electromagnetic forces F ₁ and F _{2 in} opposite directions are applied between the measured object M and the dummy piece M ′, as shown in FIG. 1B. Then, in the recorder REC, a synthetic strain E _a commensurate with the latent strain E _X is detected. This will be described below. FIG. 3 shows the strain E _M synthesized by the latent strain E _X due to the external force P and the strain E _F caused by the electromagnetic force F ₁ . Since there is always a relation of E _M > E _X between the synthetic strain E _M and the latent strain E _X , there is a relation of E _M −E _X = E _a . Incidentally, E _F can be always a constant value by a constant amount of current. FIG. 4 is a diagram in which the difference E _a is decomposed into a component force E _{b in} the direction of the latent strain E _X and a component force E _c in the strain E _F direction due to the electromagnetic force F _1, and the sensing direction of the strain gauge G is shown. If the distortion is matched with the E _X direction, the component force E _b is applied to the recorder REC.
Can be detected. FIG. 5 shows a characteristic curve S showing the correlation between the latent strain E _X and the strain component E _a , which is previously detected by the verification strain gauge g shown in FIG. 1 and specified by the magnitude of the external force P. In this figure, the point P at which the value E _ai on the E _a line detected by the recorder M from the actual measured object M by the above-mentioned means intersects the curve is obtained, and a perpendicular line is drawn from the point P on the E _X line. The intersection Q is the latent distortion E _x required. In the above embodiment, the case where the tensile force acts on the measured object M as the external force P has been described.
Is a compressive force, the strain E _X has a negative value.

[0007]

As described above, according to the present invention, it is possible to easily and non-destructively detect the latent strain of the object to be measured by simply applying a current between both electrodes.

[Brief description of drawings]

FIG. 1 (a) is a schematic plan view illustrating a method of the present invention.

FIG. 1 (b) is a cross-sectional view of FIG.

FIG. 2 is a detection circuit diagram.

FIG. 3 is a diagram showing the relationship between latent strain and electromagnetic force.

FIG. 4 is a diagram showing a relationship in which a difference between combined strains is decomposed into a latent strain and an electromagnetic force direction.

FIG. 5 is a diagram showing a characteristic between a known latent strain and a difference between component strains.

[Explanation of symbols]

M DUT M'dummy piece a
Electrode b Electrode G Strain gauge
G'strain gauge

Claims (2)

[Claims] 1. A pair of electrodes are provided on the surfaces of the object to be measured and the dummy piece, and an unknown external force is latent in the object to be measured,
A method for detecting latent strain, which comprises detecting a latent strain from a combined strain of an electromagnetic force and an external force generated when a direct current is instantaneously passed between the electrodes and the current flows. 2. A strain gauge is provided on the surfaces of the electrodes and the surface of the other object to be measured with a space therebetween, and the Wheatstone bridge configured by using both of the strain gauges detects the composite strain. The latent distortion detecting method according to claim 1, wherein the latent distortion is detected.