JPH05180741A - Extensometer - Google Patents

Abstract

PURPOSE:To obtain an extensometer which can detect the amount of thermal deformation of a test piece. CONSTITUTION:When the environmental temperature of a test piece 1 and an extensometer is set at a prescribed high or low temperature, offset signals in the same amounts as changes in the resistivity of strain gages are outputted due to the changes from bridge circuits 15 and 16 respectively. To the output from the bridge circuit 15, an offset amount due to the thermal deformation of the test piece 1 is added with the thermal deformation of the test piece and with the consequent flexural deformation of a first sensing plate. The output of the bridge circuit 16 is subtracted from that of the circuit 15, and therefore only the offset amount due to the thermal deformation of the test piece is inputted to a data processing part 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extensometer for measuring the elongation of a test piece using a strain gauge when a tensile load is applied to the test piece by a material testing machine.

[0002]

2. Description of the Related Art Conventionally, such a strain gauge type extensometer has a pair of arms whose tip is fixed to a gauge point of a test piece,
It is composed of a sensing plate that connects the base ends of both arms and a strain gauge attached to the sensing plate. And
When a tensile load is applied to the test piece and elongation occurs between the gauge points, the tip ends of both arms open following the elongation between the gauge points,
The sensing plate flexes. Along with this, the strain gauge attached to the sensing plate experiences bending of the sensing plate, that is, strain proportional to the opening amount of both arms, and the change in the resistance value is detected by the bridge circuit to extend the test piece. Is measured.

When a conventional strain gauge type extensometer is used in a high temperature or low temperature environment, the extensometer is attached to a test piece,
The test environment is set to a predetermined temperature, and the output from the bridge circuit is adjusted to zero just before starting the test.

[0004]

When the strain gauge type extensometer is used in a high temperature or low temperature environment, an offset occurs in the output from the bridge circuit due to the thermal deformation of the test piece itself and the change in the resistivity of the strain gauge. , The conventional strain gauge type extensometer cancels both the offset due to the thermal deformation of the test piece itself and the offset due to the change of the resistance of the strain gauge, so the thermal deformation amount of the test piece cannot be detected. It was The present invention was devised to solve the above problems, and an object thereof is to provide an extensometer capable of detecting the amount of thermal deformation of a test piece.

[0005]

The extensometer of the present invention is connected between a pair of arms, the tip of which is fixed to each marked line of the test piece and which moves in conjunction with the extension of the test piece, and between the both arms. A first sensing plate that is flexibly deformed by the arm; a first strain gauge that is attached to the first sensing plate to detect the amount of bending of the first sensing plate; A second sensing plate fixed in the same environment as the sensing plate, a second strain gauge attached to the second sensing plate, and an output of the first strain gauge to the second strain gauge. The strain gauge has a subtraction circuit for subtracting the output of the strain gauge. The output from the subtraction circuit before the start of the test is the amount of thermal deformation of the test piece.

[0006]

When the extensometer of the present invention is attached to the test piece and the test environment is set to a predetermined temperature, the offset amount due to the change in the resistivity of the strain gauge is the same in the first and second strain gauges. .. On the other hand, when the gauge length changes due to thermal deformation of the test piece, the pair of arms move and the first sensing plate bends and deforms, and the first strain gauge has an offset amount due to thermal deformation of the test piece. Is added. Then, from the sum of the offset amount due to the thermal deformation of the test piece detected by the first strain gauge and the offset amount due to the change in the resistivity of the strain gauge, the resistivity of the strain gauge detected by the second strain gauge is calculated. By subtracting the offset amount due to change with the subtraction circuit,
The offset amount due to the thermal deformation of the test piece is detected, and the thermal deformation of the test piece is detected.

[0007]

EXAMPLE An extensometer of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a view showing the structure of the extensometer of the present invention. Reference numeral 1 is a test piece to be subjected to a tensile test, and its upper and lower ends are held by an upper grip and a lower grip of a tensile tester (not shown). 2 and 3 are arms with an edge 4 at the tip
And 5 are attached, and the edge tip is attached to the test piece in conformity with the test piece gauge point position by a coupling tool (not shown). The base ends of the arms 2 and 3 are attached to blocks 6 and 7, respectively, and the blocks 6 and 7 are connected by a first sensing plate 8 made of a leaf spring. The block 7 is fixed to a frame 9 having a substantially U-shaped cross section. On the other hand, blocks 10 and 11 are fixed to the frame 9, and the blocks 10 and 11 are connected by a second sensing plate 12 made of a leaf spring. First sensitive plate 8 and second sensitive plate 12
A set of four first strain gauges 13 and second strain gauges 14 are attached to both surfaces of each.

FIG. 2 is a circuit diagram of the extensometer of the present invention.
A set of four first strain gauges 13 and 14 is connected to a bridge, respectively, and input ends 15a and 16a of the bridge circuits 15 and 16 are connected to a DC power source (not shown).
The output terminals 15b and 16b are input to the subtraction circuit 17. The output from the subtraction circuit 17 is processed by the data processing unit 18.

Next, the operation of the extensometer of this embodiment will be described. First, an extensometer is attached to the test piece 1 at room temperature. At that time, the edges 4 and 5 are attached by a coupling tool (not shown) so that the edges 4 and 5 are aligned with the reference mark position of the test piece 1. At this time, both arms 2 and 3 are in a parallel state, and the deflection of the first sensing plate 8 becomes zero. Therefore, the offset amount due to the thermal deformation of the test piece of the bridge circuit 15 including the first strain gauge 13 becomes zero. Further, since the extensometer body is in a room temperature environment, a bridge circuit 15 including the first strain gauge 13 and a bridge circuit 16 including the second strain gauge 14 are provided.
Also, the offset amount due to the change in the resistivity of the strain gauge becomes zero. In this state, the bridge circuits 15 and 16 are adjusted so that the output from the subtraction circuit becomes zero.

Next, the environmental temperature of the test piece 1 and the extensometer is set to a predetermined high temperature or low temperature. Then strain gauge 13
The resistivities of 14 and 14 change, and the bridge circuits 15 and 16 output the same amount of offset signal due to the change of the resistance of the strain gauge. Here, the output from the bridge circuit 15 causes the test piece 1 to be thermally deformed, the pair of arms move accordingly, and the first sensing plate is flexibly deformed, whereby the offset amount due to the thermal deformation of the test piece is added. It Since the subtraction circuit 17 subtracts the outputs of the bridge circuits 15 to 16, only the offset amount due to the thermal deformation of the test piece is input to the data processing unit 18. In this way, the thermal deformation of the test piece can be detected.

In the above embodiment, the first and second sensitive plates are attached to a common frame having a substantially U-shaped cross section, but the second sensitive plate is the first sensitive plate. Any fixing method may be used as long as it is fixed in the same environment as the sensitive plate and the offset outputs from the two bridge circuits due to the change in the resistivity of the strain gauge become the same. Further, the shape of the edge and the structure of the coupling tool may be arbitrary. Further, in the present embodiment, the subtraction circuit subtracts the outputs from the two bridge circuits and outputs the subtracted output to the data processing unit. However, the output from the subtraction circuit is amplified by the amplification circuit and connected to the recorder to displace the test piece. May be recorded directly.

[0012]

[Effect] Since the extensometer of the present invention is constructed as described above, it has the following effects. That is, the first sensitive plate flexibly deformed by the arm, the first strain gauge attached to the first sensitive plate, and the first sensitive plate are fixed in the same environment. A second sensing plate, a second strain gauge attached to the second sensing plate, and a subtraction circuit for subtracting the output of the second strain gauge from the output of the first strain gauge. Since it is provided, the amount of thermal deformation of the test piece can be detected.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of an extensometer of the present invention.

FIG. 2 is a circuit diagram of an extensometer of the present invention.

[Explanation of symbols]

 1: Test piece 2, 3: Arm 8, 12: Sensing plate 9: Frame 13, 14: Strain gauge 17: Subtraction circuit

Claims (1)

[Claims] 1. A pair of arms having a tip fixed to each marked line of a test piece and moving in association with the extension of the test piece; A sensitive plate, a first strain gauge that is attached to the first sensitive plate and detects the amount of bending of the first sensitive plate, and is fixed in the same environment as the first sensitive plate. A second sensitive plate,
An extension comprising: a second strain gauge attached to the second sensing plate; and a subtraction circuit for subtracting the output of the second strain gauge from the output of the first strain gauge. Total.