TWI416086B - Strain measurement devic and measurement method - Google Patents

Abstract

The invention provides a strain measurement device, which includes a strain sheet, a clamp device for clamping and stretching said strain sheet. The strain sheet will generate longitudinal strain in stretched direction and a transversal strain in the direction perpendicular to the stretched directions, and a transversal strain recorder used for measuring said transversal strain of the strain sheet. The strain sheet contains a carbon nanotube film structure where the carbon nanotube film structure has a plurality of carbon nanotubes, the carbon nanotubes are respectively arranged in preferable orientations along a first and a second directions. The carbon nanotubes arranged in a preferable and predetermined orientation along a first direction are overlapped and crossed with those arranged in a preferable and predetermined orientation along a second direction, and an inclined angle between the first direction and the second direction is greater than zero degree and less than one hundred and eighty degrees.

Description

Strain measuring device and measuring method

The present invention relates to a strain measuring device and a measuring method, and more particularly to a carbon nanotube-based strain measuring device and a measuring method using the same.

"Strain" is the change caused by the action of external forces. Strain gauges use electrical resistance to indicate the amount of strain caused by an external force. There are many different types of strain gauges, the most common being resistance strain gauges. A strain gage is a sensitive device that converts the strain change on the device under test into an electrical signal. The most widely used resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges. The metal resistance strain gauge has two kinds of filament strain gauges and metal foil strain gauges. Usually, the strain gauge is tightly bonded to the mechanical strain matrix by a special adhesive. When the stress changes due to the force of the substrate, the strain gauges are also deformed together, so that the resistance of the strain gauge changes, thereby adding The voltage across the resistor changes. The strain gauges typically have a small change in resistance when stressed. Typically, such strain gauges form a strain bridge and are amplified by a subsequent instrumentation amplifier and transmitted to the processing circuitry (usually A/D conversion and CPU) display or actuator.

This type of strain measuring device has many disadvantages. For example, the value range of the resistor should be noted that the resistance value is too small, the required driving current is too large, and the heat of the strain gauge causes the temperature itself to be too high, and is used in different environments. The resistance value of the strain gauge is changed too much, the output zero drift is obvious, and the zero adjustment circuit is too complicated. The resistance is too large, the impedance is too high, and the ability to resist external electromagnetic interference is poor. Generally, it is about tens of euros to several tens of kiloohms. In addition, in order to realize the function of strain amplification, it is necessary to lap a set of subsequent circuit systems, which is cumbersome and complicated, and is not conducive to measuring deformation of minute objects.

In view of this, it is necessary to provide a novel strain measuring device and a method for measuring strain using the strain measuring device, which is simple in structure and is advantageous for measuring minute deformation of an object.

A strain measuring device comprising: a strain gauge; a clamping device for clamping and stretching the strain gauge, the strain gauge generates longitudinal strain in a tensile direction, and is generated perpendicular to the tensile direction Transverse strain; and a transverse strain logger for measuring the transverse strain of the strain gauge. The strain gauge comprises a carbon nanotube membrane structure, the carbon nanotube membrane structure comprises a plurality of carbon nanotubes, and the plurality of carbon nanotubes are respectively arranged along a first direction and a second direction. And the carbon nanotubes aligned in the first direction and the aligned orientations of the carbon nanotubes are arranged in an overlapping manner, wherein the first direction has an angle with the second direction, and the angle is greater than 0. The degree is less than 180 degrees, and in use, the direction of the bisector of the angle between the first direction and the second direction in the strain gauge coincides with the stretching direction.

A method for measuring strain, comprising the steps of: firstly providing a strain measuring device; secondly, calibrating the strain of the strain gauge to obtain a transverse strain as a function of longitudinal strain of the strain gauge; Measuring the sample, bonding the strain gauge to the sample to be tested; finally, fixing the sample to be tested to which the strain gauge is attached is fixed to the clamping device, applying a longitudinal tensile force to the sample to be tested, and passing the transverse direction The strain logger measures the transverse strain of the sample to be tested, and calculates the longitudinal strain of the sample to be tested by the data processing device.

Compared with the prior art, the strain measuring device measures the strain of the sample to be tested by using a strain gauge including a carbon nanotube film structure, and does not require a subsequent circuit system, making the measuring method simple, easy to operate, and easier to implement.

The invention will be described in detail below with reference to the drawings and specific embodiments.

Referring to FIG. 1 , an embodiment of the present invention provides a strain measuring device 100 . The strain measuring device 100 includes a transverse strain recorder 102 , a clamping device 108 , a strain gauge 12 , and a data processing device 101 . The clamping device 108 includes a first holder 104 and a second holder 106. The first holder 104 and the second holder 106 are relatively movable. The data processing device 101 is electrically connected to the lateral strain recorder 102 through a data line, so that data transmission can be realized. In use, the strain gauge 12 can be laid on the surface of a sample 16 to be tested, and the opposite ends of the sample 16 to be tested are bonded to the portion in contact with the strain gauge 12, and then the sample 16 to be tested is relatively The two ends are respectively fixed to the first holder 104 and the second holder 106, and the strain is applied by relatively moving the first holder 104 and the second holder 106. The sheet 12 and the sample to be tested 16 are subjected to stress.

The clamping device 108 is used to fix and stretch the sample 16 to be tested and the strain gauge 12 . The first holder 104 and the second holder 106 each have a clamping end, and the clamping end can fix the sample 16 to be tested with the strain gauge 12 on the surface. The first holder 104 and the second holder 106 may be made of metal, ceramic or plastic.

The transverse strain recorder 102 is used to measure the transverse strain of the strain gauge 12, and the transverse strain recorder 102 can record the lateral length of the strain gauge 12 in the initial state and the lateral length when subjected to stress. The lateral strain recorder 102 can be a digital camera, a video camera, a camera, etc., for recording an image recording device in the form of an object. In this embodiment, the lateral strain recorder 102 is a digital camera.

The data processing device 101 is used to calculate the longitudinal strain of the strain gauge 12. The data processing device 101 is a computing device having a data calculation function, and specifically may be a small computer, a notebook, a server, or a supercomputer. In this embodiment, the data processing device 101 is a small computer.

The strain gauge 12 is a sheet having a certain thickness and can be arbitrarily cut according to the shape of the surface of the sample 16 to be tested. Referring to FIG. 2, in the embodiment, the strain gauge 12 is a carbon nanotube film structure. The carbon nanotube film structure is formed by extending a plurality of carbon nanotubes 145 along the surface of the film, wherein a portion of the carbon nanotubes 145 are arranged in a preferred orientation along a first direction X, and another portion of the carbon nanotubes 145 is substantially along the surface. The second direction Y is optimally oriented. The first direction X and the second direction Y form a certain angle α, and α is greater than 0 degrees and less than 180 degrees. The carbon nanotubes 145 aligned substantially in the first direction X and the carbon nanotubes 145 aligned substantially in the second direction Y intersect each other to form a plurality of meshes. When the strain gauge 12 is stretched in a direction perpendicular to the bisector of the strain gauge 12 in the first direction X or the second direction Y, the strain gauge 12 will contract in a direction perpendicular to the stretch direction; When the strain gauge 12 is compressed in a direction perpendicular to the bisector of the strain gauge 12 in the first direction X or the second direction Y, the strain gauge 12 expands perpendicular to the compression direction. Therefore, the strain gauge 12 has a property of a positive Poisson's ratio. In this embodiment, the angle α is 90 degrees.

Please refer to FIG. 3, which is a diagram showing the relationship between the Poisson's ratio and the tensile strain of the strain gauge 12 of the present invention. As can be seen from the figure, the strain gauge 12 provided by the embodiment of the present invention has a Poisson's ratio of 2.25 when the tensile strain in the direction of the bisector of the angle between the first direction X or the second direction Y is 5%; When the tensile strain in the direction at an angle of 45 degrees to the first direction X or the second direction Y is 20%, the Poisson's ratio is 3.25.

Referring to FIG. 4, the carbon nanotube film structure is formed by cross-stacking at least two layers of carbon nanotube films. The carbon nanotube film is composed of a plurality of carbon nanotubes, and the plurality of carbon nanotubes are arranged end to end in a preferred orientation in one direction. In each of the two adjacent carbon nanotube films, the carbon nanotubes in one of the carbon nanotube membranes are arranged in a preferred orientation along a first direction X, and the nanoparticles in the other carbon nanotube membrane are The carbon tubes are arranged substantially along a second direction Y, wherein the first direction X and the second direction Y are perpendicular to each other, and the carbon nanotubes in the adjacent two carbon nanotube films cross each other to form Multiple grids. The carbon nanotube membrane structure may comprise 10 to 5000 layers of carbon nanotube membranes stacked in a stack, the carbon nanotube membrane having a thickness of 0.5 nm to 1 μm. In this embodiment, the carbon nanotube membrane structure comprises a 100-layer carbon nanotube membrane.

Figure 5 is a scanning electron micrograph of a carbon nanotube film in the carbon nanotube film structure of Figure 4, the carbon nanotube film being a self-supporting structure composed of a plurality of carbon nanotubes. The plurality of carbon nanotubes are arranged in a preferred orientation along the same direction. The preferred orientation means that the majority of the carbon nanotubes in the carbon nanotube film extend substantially in the same direction. Moreover, the overall direction of extension of the majority of the carbon nanotubes is substantially parallel to the surface of the carbon nanotube film. Further, most of the carbon nanotubes in the carbon nanotube membrane are connected end to end by Van der Waals force. Specifically, each of the carbon nanotubes in the majority of the carbon nanotube membranes extending in the same direction and the carbon nanotubes adjacent in the extending direction are connected end to end by van der Waals force. Of course, there are a few randomly arranged carbon nanotubes in the carbon nanotube film, and these carbon nanotubes do not significantly affect the overall orientation of most of the carbon nanotubes in the carbon nanotube film. The self-supporting carbon nanotube film does not require a large-area carrier support, but can maintain a self-membrane state as long as the supporting force is provided on both sides, that is, the carbon nanotube film is placed (or fixed on) When the two supports are disposed at a certain distance, the carbon nanotube film located between the two supports can be suspended to maintain the self-membrane state. The self-supporting is mainly achieved by the presence of a continuous carbon nanotube in the carbon nanotube film which is continuously arranged by van der Waals force.

Specifically, most of the carbon nanotube membranes extending substantially in the same direction in the same direction are not absolutely linear, and may be appropriately bent; or may not be completely aligned in the extending direction, and may be appropriately deviated from the extending direction. Therefore, partial contact between the carbon nanotubes juxtaposed in the majority of the carbon nanotubes extending substantially in the same direction of the carbon nanotube film cannot be excluded.

The embodiment of the invention further provides a method for measuring strain by using the strain measuring device 100, which is implemented by the following steps:

In step S1, a strain measuring device 100 is provided.

In step S2, the strain gauge 12 is stretched and calibrated to obtain the transverse strain of the strain gauge 12. Longitudinal strain The function relationship.

Referring to FIG. 6, the direction a is defined as the longitudinal strain direction of the strain gauge 12, and the direction a is at an angle of 45 degrees to the first direction X in the strain gauge 12. The direction b is defined as the transverse strain direction of the strain gauge 12, and the direction b is perpendicular to the direction a. Defining the transverse strain of the strain gauge 12 to Longitudinal strain is . The lateral transverse strain of the strain gauge 12 can be obtained by numerical fitting. With longitudinal strain The function relationship. Specifically, the strain gauge 12 may be cut into a square shape such that the long side of the rectangular strain gauge 12 is parallel to the direction a. The two ends of the short side of the rectangular strain gauge 12 are respectively fixed, and then the strain gauge 12 is stretched a plurality of times in the direction a, and the transverse strain is recorded for each time. And its corresponding longitudinal strain is . Finally, the transverse strain of the strain gauge 12 can be obtained by quadratic polynomial fitting. Longitudinal strain Functional relationship . Lateral strain of the strain gauge 12 Longitudinal strain The relationship curve is shown in Fig. 7. As can be seen from the figure, the transverse strain of the strain gauge 12 is arbitrary at any point on the curve. Both are much larger than the corresponding longitudinal strain . Therefore, when the strain gauge 12 is longitudinally strained When it is difficult to measure, it can measure the transverse strain of the strain gauge. By function relationship Calculate the longitudinal strain of the strain gauge 12 . In this embodiment, the strain gauge 12 includes a 100-layer carbon nanotube film, and the transverse strain of the strain gauge 12 after numerical fitting is used. Longitudinal strain The functional relationship is: .

Referring to FIG. 8, in order to increase the Poisson's ratio of the strain gauge 12, the rectangular strain gauge 12 may be cut along a middle portion of the two long sides into a symmetrical arc so that the strain is made. The sheet 12 is cut into a dumbbell shape so that a larger Poisson's ratio can be obtained to facilitate measurement.

In step S3, a sample 16 to be tested is provided, and the strain gauge 12 is attached to the sample 16 to be tested.

The sample to be tested 16 is a sheet having a certain thickness and has the same shape as the strain gauge 12. In use, a layer of adhesive may be applied to both ends of one surface of the sample 16 to be tested, and then the strain gauge 12 is adhered to the surface of the sample 16 to be tested by an adhesive. Thereby, the sample to be tested 16 and the strain gauge 12 have the same longitudinal strain direction a and the same transverse strain direction b. It can be understood that the strain gauge 12 can also be directly attached to the surface of the sample 16 to be tested without adding a binder.

In step S4, the sample 16 to be tested to which the strain gauge 12 is attached is fixed to the clamping device 108, and a longitudinal tensile force is applied to the sample 16 to be tested, so that the sample 16 to be tested and the strain gauge 12 have the same longitudinal direction. strain .

Specifically, along the longitudinal strain direction a of the sample 16 to be tested, one end of the sample 16 to be tested to which the strain gauge 12 is attached is fixed to the first holder 104, and the test piece to which the strain gauge 12 is attached is fixed. The other end of the sample 16 is to the second holder 106. The first holder 104 and the second holder 106 are relatively moved along the longitudinal strain direction a of the sample 16 to be tested, and the strain gauge 12 generates the same longitudinal strain as the sample 16 to be tested. .

Step S5, measuring the transverse strain of the sample 16 to be tested by the transverse strain recorder 102 Calculating the longitudinal strain of the sample 16 to be tested by the data processing device 101 .

When a longitudinal tensile force is applied to the sample 16 to be tested to which the strain gauge 12 is attached, the transverse strain of the strain gauge 12 It can be measured by the transverse strain recorder 102, and the data processing device 101 can pass the transverse strain of the strain gauge 12. Longitudinal strain Functional relationship Calculated to obtain the longitudinal strain of the sample 16 to be tested .

Compared with the prior art, the strain measuring device 100 measures the strain of the sample 16 to be tested by using the strain gauge 12 including the carbon nanotube film structure, and does not require a subsequent circuit system, so that the measuring method is simple, easy to operate, and easier to implement. .

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

12‧‧‧ strain gauges

16‧‧‧Test samples

100‧‧‧ strain measuring device

101‧‧‧ data processing device

102‧‧‧Horizontal strain recorder

104‧‧‧First holder

106‧‧‧Second gripper

108‧‧‧Clamping device

145‧‧・Nano carbon tube

FIG. 1 is a schematic perspective structural view of a strain measuring device according to an embodiment of the present invention.

2 is a schematic view showing the structure of a carbon nanotube film in a strain gauge in a strain measuring device according to an embodiment of the present invention.

3 is a graph showing the relationship between Poisson's ratio and tensile strain of a nano-carbon tube Poisson's ratio material according to an embodiment of the present invention.

4 is a scanning electron micrograph of a structure of a carbon nanotube film in a strain gauge in a strain measuring device according to an embodiment of the present invention.

Fig. 5 is a scanning electron micrograph of a carbon nanotube film in a strain gauge in a strain measuring device according to an embodiment of the present invention.

FIG. 6 is a schematic view showing the orientation of a strain gauge of a strain measuring device according to an embodiment of the present invention.

Fig. 7 is a schematic view showing the relationship between the longitudinal strain and the transverse strain of the strain gauge according to the embodiment of the present invention.

FIG. 8 is a schematic structural view of a strain gauge according to an embodiment of the present invention.

12‧‧‧ strain gauges

16‧‧‧Test samples

100‧‧‧ strain measuring device

101‧‧‧ data processing device

102‧‧‧Horizontal strain recorder

104‧‧‧First holder

106‧‧‧Second gripper

108‧‧‧Clamping device

Claims (20)

A strain measuring device comprising:
a strain gauge;
a holding device for holding and stretching the strain gauge, the strain gauge generating longitudinal strain in a tensile direction, generating a transverse strain perpendicular to the tensile direction; and a measuring strain gauge Lateral strain logger for transverse strain;
The strain gauge comprises a carbon nanotube membrane structure, the carbon nanotube membrane structure comprises a plurality of carbon nanotubes, and the plurality of carbon nanotubes are respectively arranged along a first direction and a second direction. And the carbon nanotubes aligned in the first direction and the aligned orientations of the carbon nanotubes are arranged in an overlapping manner, wherein the first direction has an angle with the second direction, and the angle is greater than 0. The degree is less than 180 degrees, and in use, the direction of the bisector of the angle between the first direction and the second direction in the strain gauge coincides with the stretching direction. The strain measuring device of claim 1, wherein the carbon nanotube membrane structure comprises at least two laminated carbon nanotube membranes, each of which is connected end to end and substantially Forming a carbon nanotube arranged in a preferred orientation, wherein the carbon nanotubes in the carbon nanotube membrane extend along the surface of the carbon nanotube membrane, one in each of two adjacent carbon nanotube membranes The carbon nanotubes in the carbon nanotube film are arranged in a preferred orientation along the first direction, and the carbon nanotubes in the other carbon nanotube film are arranged in a preferred orientation along the second direction. The strain measuring device according to claim 2, wherein in the carbon nanotube film structure, adjacent carbon nanotube films are tightly bonded by van der Waals force. The strain measuring device according to claim 2, wherein the carbon nanotube film structure comprises 10 to 5000 layers of carbon nanotube film, and the thickness of the carbon nanotube film is 0.5 nm. 1 micron. The strain measuring device according to claim 4, wherein the carbon nanotube membrane structure has a Poisson ratio of 0.5 to 3.5. The strain measuring device of claim 1, wherein the clamping device comprises a first holder and a second holder, and the first holder and the second holder are Relative movement in the direction of longitudinal strain. The strain measuring device of claim 6, wherein the transverse strain recorder is a digital camera, a camera or a camera. A method of measuring strain using a strain measuring device according to any one of claims 1 to 7, comprising the steps of:
Stretching the strain gauge and calibrating to obtain a transverse strain as a function of longitudinal strain of the strain gauge;
Providing a sample to be tested, and attaching the strain gauge to a surface of the sample to be tested;
Fixing a sample to be tested with a strain gauge to the clamping device, applying a longitudinal tensile force to the sample to be tested, causing the sample to be tested to generate the same longitudinal strain as the strain gauge; and measuring by the transverse strain recorder The transverse strain of the strain gauge is calculated by the data processing device to calculate the longitudinal strain of the strain gauge. The method of measuring strain as described in claim 8, wherein the transverse strain of the strain gauge is obtained as a function of longitudinal strain by a quadratic polynomial fit. The method of measuring strain according to claim 9, wherein the strain gauge is a rectangular sheet, and a long side of the rectangular strain gauge is parallel to a longitudinal strain direction of the strain gauge. The method of measuring strain according to claim 10, wherein the strain gauge is cut into a symmetrical arc along a middle portion of the two long sides of the rectangular strain gauge. The method of measuring strain according to claim 8, wherein the sample to be tested has the same longitudinal strain direction as the strain gauge, and the same transverse strain direction. A strain measuring device comprising:
a strain gauge;
a clamping device for clamping and stretching the strain gauge, the strain gauge generates longitudinal strain in a tensile direction, and generates transverse strain perpendicular to the tensile direction, the clamping device including a first a holder and a second holder, the first holder and the second holder for relatively moving in a longitudinal strain direction and stretching the strain gauge; and a transverse direction for measuring the strain gauge Strained transverse strain recorder;
The strain gauge comprises a carbon nanotube membrane structure, the carbon nanotube membrane structure comprises a plurality of carbon nanotubes, and the plurality of carbon nanotubes are respectively arranged along a first direction and a second direction. And the carbon nanotubes aligned in the first direction and the aligned orientations of the carbon nanotubes are arranged in an overlapping manner, wherein the first direction has an angle with the second direction, and the angle is greater than 0. The degree is less than 180 degrees. In use, the direction of the bisector of the angle between the first direction and the second direction in the strain gauge coincides with the direction of the first holder to a second holder. The strain measuring device of claim 13, wherein the carbon nanotube membrane structure comprises at least two laminated carbon nanotube membranes, each of which is connected end to end and substantially Forming a carbon nanotube arranged in a preferred orientation, wherein the carbon nanotubes in the carbon nanotube membrane extend along the surface of the carbon nanotube membrane, one in each of two adjacent carbon nanotube membranes The carbon nanotubes in the carbon nanotube film are arranged in a preferred orientation along the first direction, and the carbon nanotubes in the other carbon nanotube film are arranged in a preferred orientation along the second direction. The strain measuring device according to claim 14, wherein the strain gauge is a rectangular sheet, and a long side of the rectangular strain gauge is parallel to a longitudinal strain direction of the strain gauge. The strain measuring device according to claim 15, wherein the strain gauge is cut into a symmetrical arc along a middle portion of the two long sides of the rectangular strain gauge. The strain measuring device of claim 14, wherein the transverse strain recorder is a digital camera, a camera or a camera. A method of measuring strain using a strain measuring device according to any one of claims 13 to 17, comprising the steps of:
Stretching the strain gauge and calibrating to obtain a transverse strain as a function of longitudinal strain of the strain gauge;
Providing a sample to be tested, and attaching the strain gauge to a surface of the sample to be tested;
Fixing a sample to be tested with a strain gauge to the clamping device, applying a longitudinal tensile force to the sample to be tested, causing the sample to be tested to generate the same longitudinal strain as the strain gauge; and measuring by the transverse strain recorder The transverse strain of the strain gauge is calculated by the data processing device to calculate the longitudinal strain of the strain gauge. A method of measuring strain as described in claim 18, wherein the transverse strain of the strain gauge is obtained as a function of longitudinal strain by a quadratic polynomial fit. The method of measuring strain according to claim 18, wherein the sample to be tested has the same longitudinal strain direction as the strain gauge, and the same transverse strain direction.