JP3148898B2 - Strain / stress detector and method for detecting strain / stress in structures using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strain / stress detector and a method for detecting strain / stress in a structure using the same.
A strain / stress detector using a conductive fiber bundle and detecting a strain or stress state according to the electric resistance value of the conductive fiber bundle or a change state thereof, and a strain / stress of a structure using the same. Regarding the detection method.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of using a resistance wire strain gauge as a means for determining the stress generated in a member. As is well known, a resistance wire strain meter is usually a flat plate having resistance wires made of platinum or the like arranged in a meandering manner. This strain gauge is attached to the outer surface of the object whose stress is to be measured, and the distortion of the object is grasped by the change in the resistance value due to the shape change (length change and cross-sectional area change) of the resistance wire accompanying the distortion of the object. The stress is calculated from the strain.

However, in the case of the above-mentioned conventional means, there are disadvantages in that the strain gauge is expensive and the dimensions are restricted to some extent. Further, in the strain gauge, since the load and the strain display have a linear relationship, even when a large live load is temporarily added, the strain display is 0 when the live load is unloaded. (Zero), and if the timing of measurement is missed, there is a serious disadvantage that the fact that a live load that reaches a dangerous area is actually applied and excessive stress is generated cannot be recognized. Moreover, since the strain gauge can be provided only on the outer surface of the object, there is also a disadvantage that when the object is large, it is impossible to know the internal stress in an accurate sense.

[0003] The present invention has been made in view of the above circumstances, has an extremely simple structure, can be manufactured relatively inexpensively,
It can be installed in any place, and furthermore, it is possible to grasp the history of the stress degree even from fragmentary data
An object of the present invention is to provide a stress detection method.

[0004]

A strain and stress according to claim 1.
The detector is a collection of conductive fibers that are conductive.
Measure the electrical resistance of the conductive fiber bundle at both ends of the conductive fiber bundle
And a conductive fiber bundle.
It is arranged for the structure, as the conductive fiber bundle,
Those whose breaking strength is not more than the proof stress of the structure are used.
The conductive fiber bundle generated with the distortion of the structure
The rate of increase in the electrical resistance of the sample showed a rate of increase equal to or higher than a predetermined value.
It is characterized by issuing an alarm when it occurs.

[0005] A strain / stress detector according to claim 2 is provided.
2. The strain / stress detector according to claim 1, wherein the conductive fiber bundle is used.
Are used as reinforcing members in the structure.
It is characterized by:

According to a third aspect of the present invention, there is provided a strain / stress detector.
3. The strain / stress detector according to claim 1 or 2, wherein
The fiber bundle is a carbon fiber bundle. Claim
The strain / stress detector according to claim 4 is any one of claims 1 to 3.
The strain / stress detector according to any of claims 1 to 3, wherein the conductive fiber bundle
Is coated with a resin material.

A method for detecting strain / stress in a structure according to claim 5
Is a conductive fiber that is an aggregate of continuous fibers having conductivity.
The electric resistance value of the conductive fiber bundle was measured at both ends of the bundle.
Strain / stress detector with terminals for
Or buried, the strain and stress detector of the conductive fiber bundle
Measure the electrical resistance value beforehand.
Detecting the strain / stress in the structure by the change state
Or stress state or stress of the part where the vessel is installed
It is configured to know the history, as the conductive fiber bundle
Use less than the proof stress of the structure and increase the measured value
The fact that the rate has risen to a predetermined value or more is regarded as a condition for the stress state.
It is characterized in that it is an alarming means for performing. Claim 6
The method for detecting strain / stress of a structure according to claim 5, wherein
A method for detecting strain / stress of an object, wherein the rate of increase of the measured value is
After rising to a predetermined value or more, the electric resistance value in that case
Based on the shift amount of the maximum stress degree and stress
It is characterized by estimating the degree history.

[0008]

In the strain / stress detector according to claim 1, the conductive fiber is provided.
The advantage is that the electrical resistance of the bundle increases sharply just before breaking.
Use a conductive material with a breaking strength corresponding to the proof stress of the structure
By arranging the conductive fiber bundle on the structure,
Determine whether the stress generated in the structure is near the proof stress
be able to. In the strain / stress detector according to claim 2,
Use of conductive fiber bundles as reinforcing members in structures
Allows the structure to be reinforced, while the structure
Internal strain and internal stress can be directly searched for.

In the strain / stress detector according to the third aspect , a relatively common carbon fiber is used as the conductive fiber.
The versatility of the strain / stress detector can be improved.

In the strain / stress detector according to the fourth aspect, the strain / stress detector can be easily handled, and can be directly attached to or embedded in the electric conductor.

A method for detecting strain / stress in a structure according to claim 5
, The electrical resistance value of the conductive fiber bundle increases sharply immediately before breaking.
Utilizing the ascending, the breaking strength corresponding to the strength of the structure
A conductive fiber bundle with a degree is arranged for the structure
Is the stress generated in the structure near the proof stress?
Whether the stress is near the proof stress or not.
An alarm can be issued for the condition. Claims
In the method for detecting strain / stress of a structure according to Item 6, the conductive fiber bundle is used.
Is subjected to high strain near the breaking point, its electrical resistance value
The structure shifts to a high value by utilizing
Or more likely
can do.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a strain / stress detector according to an embodiment of the present invention. This strain / stress detector 1A includes a large number of continuous carbon fibers (continuous fibers having conductivity) 2,
Terminals 4 and 4 for measuring the electrical resistance of the carbon fiber bundle 3 are provided at both ends of a carbon fiber bundle (conductive fiber bundle) 3 composed of 2,.

The terminals 4 and 4 shown in FIG. 1 are obtained by winding a strip-shaped metal plate having excellent conductivity around the carbon fiber bundle 3. It also has the function of binding 2, 2,.

FIG. 2 shows another embodiment of the strain / stress detector according to the present invention. This strain / stress detector 1B
The carbon fiber bundle 3 of the strain / stress detector 1A shown in the previous embodiment is covered with a resin material 5. Terminals 4 and 4 are provided at both ends of the carbon fiber bundle 3, and these terminals 4 and 4 are configured to be exposed to the outside.

Next, an embodiment of the method for detecting strain / stress of a structure according to the present invention will be described together with the operation of the strain / stress detector configured as described above. FIG. 3 shows a situation where the strain / stress detector 1B is attached to a required portion of the structure 7. Here, the structure 7 may be, for example, a bridge 8a of a bridge 8 as shown in FIG. 4 or a slab of a building, and the type is not limited. The distortion
In this case, the stress detector 1B is provided with an adhesive 9 as shown in FIG.
The whole length is adhered and fixed to the structure 7 by the above.

After the strain / stress detector 1B is attached to a predetermined portion of the structure 7 as described above, a resistance measuring device 10 (see FIG. 4) is connected to the terminals 4 and 4, and the terminals 4 and 4 are connected. The electric resistance value of the carbon fiber bundle 3 in the above is measured. 3 and 4, reference numeral 10a denotes a wiring from the resistance measuring instrument 10.

Here, experimental examples carried out by the present inventors to clarify the working principle of the present invention will be described below. FIG. 5 and FIG. 6 show a test piece T used in the experiment, which has a structure close to the strain / stress detector 1B. The test piece T was pulled under the following experimental conditions, and the resulting load P (t), the amount of strain ε (μm) of the test piece T,
The relationship with the electrical resistance value R (Ω) of the carbon fiber bundle 3 was determined.
The “strain amount” mentioned here is not a distortion generally expressed in a dimensionless manner, but indicates a so-called change amount with respect to the original size of the test piece.

<Experimental example> ΔTest piece T Conductive fiber bundle 3: Carbon fiber (PAN-based high-strength type) Other fiber bundle: Glass fiber Resin material 5: Vinyl ester resin Dimensions: 8 mm □, length 700 mm △ Experiment Condition R ₀ (initial resistance value): 5.6Ω Room temperature: 23 ° C. Current I: 0.9 mA Voltage V: 0.05 mV / cm Peeling speed: 1 mm / min. △ Power generator YEW DC Voltage Current Standard Type
2553

FIG. 7 shows the results of the above experiment. In the figure, ΔR
Indicates an increase resistance (Ω) with respect to the initial resistance value R ₀ . Further, in the diagram showing this ΔR, after the ΔR value exceeds the maximum value (point d in the diagram) and then reaches the point e in the diagram, the strain ε of the test piece T is 1.6 mm (16000 μm). , And shows a curve when the load P is unloaded. The test piece T was broken when the load P was further applied and the strain ε reached 1.7 mm.

FIG. 7 shows that the electrical resistance value R of the carbon fiber bundle 3 gradually increases with an increase in the strain amount ε due to an increase in the tensile load P. The electric resistance value R with the increase in the load P shows a tendency of a three-stage transition in which the electric resistance value R between the points a and b is relatively steep, the point between the points bc is gradual, and the point from the point c rapidly increases. ing. Also smell after point c
Therefore, the rate of increase of the electric resistance value R is sharper than before the point c.
It is understood that it has risen sharply. Further, it is understood that the resistance value R does not return to the point a, that is, the initial resistance value R ₀ , and shifts to a higher value even after the load P is removed.

Regarding the above-mentioned matter, the inventor of the present invention has found that, even when various conditions are changed, the above-mentioned tendency, that is, the three-step shift of the resistance value R and the resistance value when a load is applied to a high strain region up to near fracture. Experiments have confirmed that a tendency such as a shift of R toward a higher value side occurs. The “conditions” mentioned above include the magnitude of the load P, the pulling speed, the type of the conductive fiber, and the like.

Further, from those experiments, the amount of shift of the resistance value R to the higher value side after unloading, that is, the value between points ae, is the amount that changed abruptly in the high strain range, that is, the value between points cd. We understood that it was almost equal to the value. Further, after completely removing the load P, when the load is applied again to the first maximum strain value, the resistance value R (ΔR) rises by tracing the curve between the points ed and d almost as it is. It was found that when the load was unloaded, the same curve was drawn again from point d to point e. Hereafter, the same holds true even if this is repeated. Further, the position where the point c appears and the resistance value change (shift amount) between the points cd differ depending on the strength and elongation of the conductive fiber bundle. By shifting the strength to the high strain range side,
The amount of change in the resistance value between the -d points becomes larger when the conductive fiber bundle is made to have high strength and high elongation.

Regarding the above phenomena, it can be considered that the phenomenon between the points d and e is due to the reversible structural change of the carbon fiber bundle 3 and the phenomenon between the points cd is due to the irreversible structural change.

When a single wire of the carbon fiber 2 is used instead of the carbon fiber bundle 3, an increase in the electric resistance value with an increase in strain is observed. And a clear hysteresis as described above does not appear.

As shown in the experimental example, the strain / stress detector 1B attached to the structure 7 shows a change in the resistance value R with the strain of the structure 7. Therefore, by measuring the electric resistance value R of the strain / stress detector 1B, the strain of the structure 7 can be grasped, and the stress degree can be known thereby.

Not only this, but also as described above, the strain / stress detector 1 B
Shows a peculiar change.
It can be used as a kind of sensor that informs the stress state of.

For example, when the breaking strength of the carbon fiber bundle 3 in the strain / stress detector 1B is set in accordance with the proof stress of the counterpart structure 7, when the electric resistance value R shows a sharp rise, the time is short.
KazuSatoshi, can be configured to emit an alarm at the indicated time points the value of the point c (Mark points) in FIG. 7. (In this case, to detect the point c, the carbon fiber bundle 3
Whether the rate of increase of the electrical resistance R of the battery has risen above a predetermined value
Should be determined. Further , in this case, if the strain / stress detector 1B is further replaced, the strain / stress detector 1
It is not impossible that the breaking strength of B is intentionally set to be smaller than the proof strength of the structure 7 so that the breaking of the carbon fiber bundle 3 is detected and an alarm is issued.

Further, when the strain / stress detector 1B receives a high strain near the breaking point, the electric resistance value R of the carbon fiber bundle 3 shifts to a high value. It is possible to know whether or not 3 has caused a high strain, or to the extent by the shift amount, and to grasp the stress history of the structure. Therefore, for example, it is possible to know the current stress level generated in the structure, or the maximum stress level generated by an external force such as an earthquake and the like, and the stress level history, which can be used for monitoring the strength of the structure.

As described above, the strain / stress detector 1 shown in FIG.
Although the function of B has been described, the strain / stress detector 1A having no resin material 5 as shown in FIG. However, when the strain / stress detector 1A is attached to the structure 7, unless the structure 7 is an electrical insulator, the carbon fiber bundle 3 (and the terminal 4) is attached to the structure 7.
Must be installed so that it is not directly connected to

The mounting method in this case is, for example, as shown in FIG.
In the same manner as shown in FIG. 8, it may be fixed by bonding with an insulating adhesive material 9 or by a fixing method as shown in FIG. In FIG. 8, reference numerals 11,
Reference numeral 11 denotes a fixing jig for the carbon fiber bundle 3, which is configured such that both ends of the carbon fiber bundle 3 are sandwiched between the upper piece 11a and the lower piece 11b. Bolt insertion holes are provided in the upper piece 11a and the lower piece 11b, and the bolts 12, 12,
Are fixed to the structure 7 so that the carbon fiber bundle 3 is stretched. The upper piece 11a is a conductor, and the lower piece 11b is an insulator. In this case, the upper pieces 11a, 11a
Form a terminal 4 for resistance measurement. According to such fixing means, even when the structure 7 is a conductor, it is possible to attach the strain / stress detector 1A without bringing the carbon fiber bundle 3 into contact with the structure 7.

However, as shown in FIG. 2, a carbon fiber bundle 3 is covered with a resin material 5 to form a strain / stress detector 1B.
According to this, since the strain / stress detector 1B has a so-called independent structure, the strain / stress detector can be handled independently and conveniently. Moreover, the carbon fiber bundle 3 is made of the resin material 5
Since the strain / stress detector 1 </ b> B is protected by the above, it is possible to bury the strain / stress detector 1 </ b> B directly in a structure such as concrete or the ground.

FIG. 9 shows a strain / stress detector 1C obtained by further developing the strain / stress detector 1B. This distortion
The stress detector 1C is configured by assembling the strain / stress detectors 1B in a lattice shape. That is, the lattice-shaped strain / stress detector 1C is provided with the string-shaped vertical stripes 13 and 1.
Yokojo 1 which is also formed in a string shape and intersects them
4, 14, ..., these vertical stripes 13,
, And the horizontal stripes 14, 14,... Have substantially the same configuration as the strain / stress detector 1B. However,
The vertical stripes 13 and the horizontal stripes 14 are configured to have a glass fiber bundle (not shown) for reinforcing the resin material 5 in addition to the carbon fiber bundle 3. The vertical stripes 13 and the horizontal stripes 14 are integrated at intersections 15, 15,..., But the carbon fiber bundle 3 forming the vertical stripes 13 and the carbon fiber bundle 3 forming the horizontal stripes 14 are formed. Are not in contact with each other at the intersection point 15, and have a configuration as if they were so-called three-dimensionally crossed through the resin material 5. Terminals 4 for measuring the electric resistance value of the carbon fiber bundle 3 are provided at both ends of at least some of the selected vertical and horizontal stripes 13 and 14.

The strain / stress detector 1C can be used as a reinforcing member, for example, by burying it inside the structure to be reinforced. For example, FIG. 10 shows a state in which the strain / stress detector 1 </ b> C is buried inside shotcrete 18 as a reinforcing member for ground surface 17. The strain / stress detector 1C reinforces the shotcrete 18 while measuring the electric resistance R of each carbon fiber bundle 3 by applying a current between the terminals 4 to thereby determine the strain on the ground surface 17 The stress state and the stress history can be grasped.
Moreover, in the strain / stress detector 1C, by measuring the electric resistance value R of a large number of the vertical lines 13 and the horizontal lines 14, the vertical lines 13 and the horizontal lines
It is possible to grasp even the stress distribution state as the Y coordinate. Further, since the strain / stress detector 1C can be buried inside the structure as described above, the internal strain and internal stress can be directly searched, and more reliable data can be obtained.

In the strain / stress detector 1C also serving as a reinforcing member, the one formed in a two-dimensional shape by the vertical stripes 13 and the horizontal stripes 14 has been described. It is also possible to construct a three-dimensional shape such as a so-called reinforced cage composed of a shaft reinforcing bar and a shear reinforcing bar, and to embed the reinforcing bar in, for example, the interior of concrete as a reinforcing member. In this case, similarly to the strain / stress detector 1C, the carbon fiber bundle in the shaft muscle and the carbon fiber bundle in the shear reinforcing muscle are configured not to contact with each other. What is necessary is just to form the terminal for electricity supply.

In the strain / stress detector 1C, the carbon fiber bundle 3 of the vertical stripe 13 and the carbon fiber bundle 3 of the horizontal stripe 14 are arranged.
Does not intersect. However, if a configuration in which both of the carbon fiber bundles 3 do not directly contact each other, that is, a configuration in which the two are not electrically conducted, a configuration in which both of the carbon fiber bundles 3 intersect may be adopted. Means for that purpose include, for example, both carbon fiber bundles 3
Means such as providing an electrical insulator at the intersection (contact point) of. The same applies to the reinforcing member configured in the three-dimensional shape described above.

In the strain / stress detector according to the present invention, an example in which the strain / stress detector is used for detecting strain / stress of a structure is shown in the above embodiment, but the strain / stress detector to which the present strain / stress detector is applied is used. The object is not limited to a structure, but may be, for example, a simple member. Further, even when the present strain / stress detector is used for detecting strain / stress of a structure as in the above example, the target structure is not limited to the above-described bridge 8a or the ground surface 17; It is applicable and effective to any structure that bears loads, such as beams, columns, slabs, embankments, artificial ground, underground continuous walls, retaining walls, and tunnel structures of general structures.

[0037]

As described above, according to the first aspect of the present invention, the electric resistance value of the conductive fiber bundle sharply changes immediately before breaking.
Utilizing the fact that it rises sharply, it responds to the strength of the structure
A conductive fiber bundle having breaking strength is disposed on a structure.
The stress generated in the structure near the proof stress
It can be determined whether or not there is. This makes it extremely
Simple and inexpensive to know the strain and stress state of the structure
And the distortion and stress conditions are dangerous.
Or not. Claim 2
According to the invention, the conductive fiber bundle is used for reinforcing members in a structure.
Can be used to reinforce structures
On the other hand, it is necessary to directly search for the internal strain and internal stress of the structure.
And accurately measure the stress state of the structure to its interior
can do.

According to the third aspect of the present invention, a relatively general carbon fiber is used as the conductive fiber,
The versatility of the strain / stress detector can be improved. Claim
According to the invention of claim 4, the strain / stress detector is used by itself.
It can be self-standing and easy to handle.
In addition, the strain / stress detector is
It can be buried in the detection target as it is,
Direct detection of internal strain and internal stress of elephant
Becomes possible.

According to the fifth aspect of the present invention, the conductive fiber
Utilizes the fact that the electrical resistance of a bundle rises sharply just before breaking
With a breaking strength corresponding to the proof stress of the structure
By arranging the fiber bundle to the structure,
Determine whether the stress generated in the object is near the proof stress, and
When the force is near the proof stress, an alarm for the stress state
Can be very easily generated,
And the stress state,
It is possible to grasp whether the stress state is in the danger area
You.

According to the sixth aspect of the present invention, the conductive material
When the conductive fiber bundle receives high strain near the breaking point,
Taking advantage of the fact that the air resistance shifts to a higher value,
Is highly distorted or even more
Degree can be estimated, making it easy to monitor the structural strength of structures.
And can be.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration example of a strain / stress detector according to the present invention.

FIG. 2 is a perspective view showing another configuration example of the strain / stress detector according to the present invention, with a part thereof being omitted;

FIG. 3 is a partial perspective view showing an example of an installed state of a strain / stress detector according to the present invention.

FIG. 4 is a front view showing a use mode when the strain / stress detector according to the present invention is used for strain / stress detection of a bridge.

FIG. 5 is a front view showing a test piece partially omitted in an experiment according to the present invention.

FIG. 6 is a side view of FIG. 5;

FIG. 7 is a graph showing the relationship between the load of the strain / stress detector according to the present invention, the amount of strain, and the increased resistance.

FIG. 8 is a partial perspective view showing another example of the installed state of the strain / stress detector according to the present invention.

FIG. 9 is a partial perspective view showing another configuration example of the strain / stress detector according to the present invention.

FIG. 10 is a partial perspective view showing a use mode of the strain / stress detector shown in FIG. 9 in a partial cross section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1A, 1B, 1C Strain / stress detector 2 Carbon fiber (continuous fiber having conductivity) 3 Carbon fiber bundle (conductive fiber bundle) 4 Terminal 5 Resin material 7, 18 Structure

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Norio Muto 1-5-5 Miyashitahonmachi, Sagamihara-shi, Kanagawa 18 (72) Inventor Minoru Sugita 1-3-2 Shibaura, Minato-ku, Tokyo Shimizu Corporation ( 72) Inventor Teruyuki Nakatsuji 1-3-2 Shibaura, Minato-ku, Tokyo, Shimizu Corporation (72) Inventor Yasushi Otsuka 1-3-2 Shibaura, Minato-ku, Tokyo, Shimizu Corporation (56) References JP-A-56-30610 (JP, A) JP-A-52-91478 (JP, A) JP-A-3-114403 (JP, U) JP-A-62-182430 (JP, U) International publication 89 / 11633 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01L 1/18 G01B 7/16 G01L 1/00 G01D 21/00

Claims (6)

(57) [Claims] 1. An aggregate of continuous fibers having conductivity.
The electrical resistance value of the conductive fiber bundle is applied to both ends of the conductive fiber bundle.
A terminal for measurement is provided, and the conductive fiber bundle is provided.
To the structure, As the conductive fiber bundle, the breaking strength
Of less than the proof stress of The voltage of the conductive fiber bundle generated due to the distortion of the structure
An alarm is issued when the rate of increase in air resistance rises above a predetermined value.
A strain / stress detector that emits light. 2. The strain / stress detector according to claim 1, wherein
The conductive fiber bundle is a reinforcing member of the structure.
And stress detection characterized by being used as
vessel. 3. The method according to claim 1, wherein the conductive fiber bundle is a carbon fiber bundle.
3. Strain / stress detection according to claim 1 or 2,
vessel. 4. The conductive fiber bundle is covered with a resin material.
A strain / stress probe according to any one of claims 1 to 3,
Detector. 5. An aggregate of continuous fibers having conductivity.
The electrical resistance value of the conductive fiber bundle is applied to both ends of the conductive fiber bundle.
A strain / stress detector equipped with terminals for measurement
Attached to or buried in the structure, and the conductive type of the strain / stress detector
Measure the electrical resistance of the conductive fiber bundle,
Is the strain in the structure depending on the state of change of the measured values.
.Strain or stress state of the part where the stress detector is installed
Or it is configured to know the stress history, As the conductive fiber bundle, those having a proof stress of the structure or less are used.
Use That the rate of increase of the measured value has risen to a predetermined value or more,
Characterized as alarm means for the stress state
A method for detecting strain and stress in structures. 6. A method for detecting strain and stress in a structure according to claim 5.
Law, After the rate of increase of the measured value rises above a predetermined value, the
Based on the shift amount of the electric resistance at the time of
Estimate large stress level and stress level history
A method for detecting strain and stress in structures.