JPH0610283Y2 - Crack length measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a measuring device for measuring the length of a crack generated in a test piece such as a CT test piece, and in particular, by applying an electric current to the test piece, The present invention relates to a crack length measuring device that generates a voltage in the vicinity of both sides and measures the crack length based on the voltage.

2. Description of the Related Art When a test piece having a certain shape, such as a CT test piece, is repeatedly subjected to a load, a crack is generated from a substantially fixed point and its length gradually increases. When a current is passed from both ends of the CT test piece that sandwich the crack by a constant current power source or the like, the current flows through a portion where no crack is generated. As the length of the crack increases, the cross-sectional area through which the current can flow decreases, so that the resistance value between the both sides of the crack increases. This increase in the resistance value appears as an increase in the voltage generated between both sides of the crack.

Focusing on this effect, conventionally, the length of the crack has been measured based on the voltage generated between both sides of the crack.

Problems to be solved by the invention Since the conductivity differs depending on the material of the test piece, the voltage generated between both sides of the crack differs depending on the material even if the crack length is the same, and the test piece is placed Since the conductivity also changes depending on the ambient temperature, when the crack length is measured by the above method, it is necessary to perform a calculation on the measured value based on the material of the test specimen and the ambient temperature.

The present invention was created to solve the above problems,
It is an object of the present invention to provide a crack length measuring device that is not affected by the material of the test body or the ambient temperature.

Means for Solving the Problems In order to achieve the above object, the crack length measuring device of the present invention is
A pair of electrodes that feed a pair of ends sandwiching the crack of the test body, a first pickup that detects a voltage between the ends, and a second pickup that detects a voltage between a pair of neighborhoods that sandwich the crack. And a contrast calculation circuit for calculating the ratio between the voltage detected by the first pickup and the voltage detected by the second pickup, and a crack length for calculating the crack length according to the calculation result of the comparison calculation circuit. And an arithmetic circuit.

Action The voltage generated at both ends of the test specimen is expressed as the product of the current value and the function of the two variables of the conductivity and the ambient temperature due to the material, and the voltage generated between both sides of the crack does not show a crack. Therefore, since the portion through which the current flows is made of the same material as the other portions of the test body, it is expressed as the product of three values of the function of conductivity and atmosphere temperature, the function of crack length, and the current value. By performing a contrast calculation to find the ratio of these two voltages, the conductivity and ambient temperature functions and the current value are erased, and a measured value represented only by the crack length function is obtained.
Based on this measured value, the crack length calculation circuit calculates the crack length.

Embodiment FIG. 1 is an external perspective view showing an embodiment of the present invention. An example using a CT test piece 14 as a test body is shown. A notched portion 32 having an acute tip is formed, a jig mounting portion 33 of the CT test piece 14 made of a conductive material is formed with a round hole, and a round bar 22 is inserted therein. Both ends of the round bar 22 are fixed to a pulling jig 21 (smaller than the actual size in order to make the drawing easy to see), and in the direction of tearing the notch 32 through the pulling jig 21, that is, the pulling jig. A load test is performed by repeatedly applying a load to the CT test piece 14 by generating a load 21a upward and a tension jig 21b downward.

A crack 15 is generated at the top 31 of the notch 32 by the load test. Electrodes 13 for power feeding are attached to a pair of end portions 34 of the CT test piece 14 sandwiching the crack 15 with a conductive adhesive or the like (the other lower electrode is not shown). A pair of first pickups 11 for detecting the voltage between the pair of ends 34 are attached to the center of the side edges of the CT test piece 14, and a pair of second pickups 12 are provided near both sides of the crack 15. Is also attached.

FIG. 2 is a block diagram showing the electrical construction of the present invention.

A constant current power supply is used for the electrode 13 attached to the CT test piece 14.
41 is connected. The first pickup 11 is guided to the differential amplifier 42 and the second pickup 12 is guided to the differential amplifier 43, and the outputs of the differential amplifiers 42 and 43 are sent to the comparison calculation circuit 44. The output is guided to the crack length calculation circuit 45 and is sent to the display unit 46 from there.

FIG. 3 is an equivalent circuit diagram showing the CT test piece 14 by a resistor.
The operation of the crack length measuring device of the present invention will be described below.

The resistors R1 and R3 represent resistors generated between the first pickup 11 and the second pickup 12, and the resistor R2 is a pair of second pickups.
The resistance generated between the pickups 12 is shown. A constant current power supply 41 causes a current I to flow in this circuit.

The resistances R1 and R3 have constant values irrespective of the length of the crack 15, and when the conductivity of the CT test piece 14 is represented by d and the temperature is represented by t, R1 = R3 = k1 × f (d, t) (K1 is a constant determined by the shape of the CT test piece 14 and the mounting position of the first pickup 11).

The resistance R2 changes according to the value of l when the length of the crack 15 is 1, and the material in the vicinity of the crack 15 is the same as the other parts, so R2 = k2 × f (d, t) × g (l) (K2 is the shape of the CT test piece 14 and the second
Constant determined by the mounting position of the pickup 12).

The voltage V1 detected by the first pickup 11 is: V1 = I × (R1 + R2 + R3) The voltage V2 detected by the second pickup 12 is V2 = I × R2.

The comparison calculation circuit 44 calculates V2 / V1. V2
When / V1 = S, S becomes as shown by the following equation.

That is, the shape of the CT test piece 14 and two sets of pickups
The measured values S determined by the constants k1 and k2 determined by the mounting positions of 11 and 12 and the length 1 of the crack 15 are obtained.

The calculation for obtaining the length 1 of the crack 15 from the above-mentioned measured value S is performed by the crack length calculation circuit 45, and the calculation method is a plurality of different crack lengths and known crack lengths. An arithmetic expression experimentally derived from the test body or an arithmetic expression obtained by the finite element method is used. The calculation result is guided to the display unit 46 and displayed.

The present invention is not limited to the above-mentioned embodiment, and the test body 14 can be applied to a test body in which the position where a crack is generated is almost determined by a three-point bending test or the like. Further, the constant current power supply 41 is not limited to the constant current power supply as long as it is a current source that can stably supply a current required for the test body 14.

Effect of the Invention The crack length measuring device of the present invention calculates the crack length based on the ratio of the voltage generated at both ends of the test body and the voltage generated near both sides of the crack by applying a current from both ends. Since this is done, it becomes possible to measure the crack length without being affected by the material of the test body or the ambient temperature.

Further, the display unit 46 can be shared with a display unit provided for another purpose, for example, a display unit displaying the test result of the load test or the like.

[Brief description of drawings]

FIG. 1 is an external perspective view showing an embodiment of the present invention, FIG. 2 is a block diagram showing an electrical configuration of the present invention, and FIG. 3 is an equivalent circuit diagram showing a test body by a resistance. 11 ... First pickup, 12 ... Second pickup, 13 ... Electrode, 14 ... Test body, 15 ... Crack,
44 ... Comparison arithmetic circuit, 45 ... Crack length arithmetic circuit.

Claims (1)

[Scope of utility model registration request] 1. A crack length measuring device for measuring the length of a crack generated in a test body, wherein a pair of electrodes for feeding power to a pair of end portions of the test body sandwiching the crack, and the pair of end portions. A first pickup that detects a voltage between the two; a second pickup that detects a voltage between a pair of neighborhoods that sandwich the crack; a voltage that is detected by the first pickup;
A comparison calculation circuit for calculating the ratio with the voltage detected by the pickup, and a crack length calculation circuit for calculating the length of the crack according to the calculation result of the comparison calculation circuit. Crack length measuring device.