JP4230250B2 - Maximum strain memory type sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for detecting a deformation or damage state, and more particularly to a technique for detecting a deformation or damage state in an important structure such as a general social infrastructure structure and an aircraft fuselage. More specifically, the maximum value of stress and strain such as tension and compression acting on metal materials such as steel structures, inorganic materials such as concrete structures, or composite materials applied to aircraft structures, etc. is conducted. The present invention relates to a sensor technology that can be detected by a change in rate or resistivity.
[0002]
[Prior art]
In recent years, rapid deterioration of social infrastructure structures such as railways and roads has become apparent, and social problems such as concrete collapse accidents have emerged. Furthermore, in the event of a disaster such as an earthquake, accurate evaluation of damage given to these structures is an important issue that leads to early recovery after a disaster. Under such circumstances, there has been a strong demand for a health monitoring technique that can detect the maximum strain for diagnosing damage, destruction, and deterioration in these important structures that require high safety.
[0003]
On the other hand, as an existing general health diagnosis system, a system using a metal stay gauge, an optical fiber sensor, or the like is known. However, these systems are based on constant monitoring that enables detection of distortion at the time of measurement, and in order to diagnose the maximum distortion using these systems, measurement devices are always connected for each of these sensors. It is necessary to continue the measurement in the state and accumulate data, and to analyze the maximum strain based on the measurement result. The structure to be monitored is an extremely large structure, and it requires a huge amount of cost to install a measuring device for each sensor installed in each place, and the monitoring period must be assumed to be a decade. It is virtually impossible to perform continuous measurement and analysis.
[0004]
On the other hand, several methods have been proposed as a diagnostic system having a maximum distortion memory function. First, as a modularized system, a maximum value storage type displacement meter having an irreversible mechanical mechanism has been commercialized. In this system, the expansion and contraction of the rod is transmitted to the rotation mechanism of the resistor (potentiometer), and the maximum displacement is stored as the maximum number of rotations. From the specifications in this system, the measurement accuracy is ± 3%, and if the measurement section is 500 mm, the displacement measurement accuracy is ± 15 mm. However, considering the strain range (1000με or less) required for concrete structures, the required displacement measurement accuracy is extremely small at 0.05mm, and it is expected that this system will not exhibit sufficient performance in structural deformation diagnosis. The
[0005]
Patents relating to technologies that apply composite materials composed of carbon fibers and technologies that apply composite materials in which conductive particles are dispersed in a matrix resin are available as intelligent materials capable of diagnosing the maximum strain that has been applied. There are examples and reported examples.
[0006]
Regarding the technology to apply composite materials composed of carbon fibers, in the long fiber reinforced plastics composed of carbon fibers, the phenomenon that the conductivity change remains by breaking the carbon fibers corresponding to the maximum strain Application of (residual resistance phenomenon) has been attempted (Patent Document 1). However, the fracture of the carbon fiber requires a tensile strain of about 0.5% or more, so that the memory function of the maximum strain is limited to a strain region beyond that. The diagnostic strain region required for the structure to be monitored is, for example, that the elastic strain range of the steel material is 0.2% or less, and the cracking strain in concrete is 0.1% or less. Considering this, the diagnosable strain region in this prior art is out of the category. Therefore, it is considered to be an extremely important issue to enable diagnosis in the strain region to be monitored in an actual structure by setting the strain (expressed strain) that causes this residual resistance phenomenon to be at least 0.1% or less. It was.
[0007]
Also, in composite materials in which conductive carbon particles are dispersed in a matrix resin of glass fiber reinforced plastics and the conductivity is provided by the continuous contact structure of the particles, the structure of the conductive path corresponding to the maximum strain is changed. Attempts have been made to apply the phenomenon that the conductivity change remains (Patent Document 2). However, in the results reported so far, although the strain of the residual resistance phenomenon was as good as about 0.05%, the resistance change at the time of loading (R _max ) To the resistance change (ΔR) remaining after unloading _res ) Ratio (residual rate = ΔR _res / ΔR _max ) Is 60% at the maximum, and the diagnostic accuracy of the maximum distortion is 50% or more, and from the results so far, the storage function of the maximum distortion has been impossible (Non-Patent Document 1). . Therefore, it has been regarded as an extremely important technical issue to improve the diagnostic accuracy of the maximum strain by making the residual rate close to 100%.
[0008]
In addition, a composite material in which conductive carbon particles are dispersed in a matrix resin and made conductive by the continuous contact structure of the particles is pasted onto a metal substrate having a low yield point, and the plasticity of the substrate Attempts have been made to apply a phenomenon in which a change in conductivity remains corresponding to the maximum strain due to deformation (Patent Document 3). In this method, the residual resistance phenomenon of the sensor material itself is not applied, but the change in conductivity of the sensor due to plastic deformation of the base material is measured. Therefore, when not only tension but also compressive stress / strain acts on the structure to be monitored, the amount of plastic deformation of the base material may change following the compression deformation, and the maximum strain It is feared that the memory function does not appear. In addition, since the plastic deformation of the metal base material appears at a tensile strain of about 0.2% or more, the maximum strain memory function cannot be expected in the strain region below that, that is, the elastic deformation region of the metal material.
[0009]
[Patent Document 1]
Japanese Patent No. 3201837
[Patent Document 2]
Japanese Patent Laid-Open No. 9-100356
[Patent Document 3]
Japanese Patent Laid-Open No. 2001-153603
[Non-Patent Document 1]
Functional Materials, 2001 (Vol. 21), No. 6, p. 29-35, issued by CMC Co., Ltd.
[0010]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to obtain a sensor that can accurately measure the maximum value of strain applied to a structure according to an assumed or desired strain range.
[0011]
[Means for solving the problems and actions / effects]
In solving the above-mentioned problems, the inventors apply the breaking behavior of the conductive path formed continuously by the conductive body, that is, the breaking behavior of the conductive path corresponding to the maximum strain of the composite material imparted with conductivity. I focused on that. As a result, using a long fiber reinforced composite material composed of conductive fibers and applying tension to the structure after synthesis or after synthesis, a technique to reduce the strain at which the conductive fibers break I found. In addition, by using a composite material in which conductive particles are dispersed in a matrix resin of a long fiber reinforced composite material composed of insulating fibers, by optimizing the structure of the conductive path composed of the conductive particles, We found a method to achieve a very high resistance residual ratio. Furthermore, as a result of these, it was found that each composite material enables diagnosis of the maximum strain in a desired strain region, and the present invention was completed.
According to the present invention, the following means are provided.
[0012]
(1) a sensing material having a conductive path by a percolation structure of conductive particles, and a covering layer made of an insulating material and covering the sensing material,
The sensing material has a composition in which the volume ratio of conductive particles: polymer material is 80:20 to 100: 0,
The conductive particles are aggregates formed by aggregation of conductive fine particles,
The conductivity changes due to the tensile strain acting on the conductive path, and after the strain is removed, information on the maximum residual strain is obtained by permanently retaining 80% or more of the changed amount of conductivity before the strain is removed. A maximum strain memory type sensor that can be stored in itself and is configured to increase the amount of change in conductivity that is retained according to the maximum value of tensile strain.
(2) comprising a sensing material having a conductive path by a conductive fiber, and a coating layer made of an insulating material and covering the sensing material;
The sensing material is The volume ratio of the conductive fiber in the total amount of the polymer material and the conductive fiber is 7.5 to 30 vol%. And
The sensing material is maintained in a tensioned state,
The conductivity changes due to the tensile strain acting on the conductive path, and after the strain is removed, information on the maximum residual strain is obtained by permanently retaining 60% or more of the changed amount of conductivity before the strain is removed. A maximum strain memory type sensor that can be stored in itself and is configured to increase the amount of change in conductivity that is retained according to the maximum value of tensile strain.
(3) The maximum strain memory type sensor according to (1) or (2), wherein the sensing material and / or the coating layer contains an electrically insulating fiber along the conductive path.
(4) The maximum strain memory type sensor according to any one of (1) to (3), which is a sheet-like body.
(5) The maximum strain memory type sensor according to any one of (1) to (3), which is a rod-shaped body.
(6) Sensing material having a conductive path with conductive fibers And a strain memory type sensor comprising an insulating material and a coating layer covering the sensing material A manufacturing method of
Comprising a step of producing the conductive fiber in a state in which tension is applied; Maximum strain memory type sensor Manufacturing method.
(7) The sensing material is molded by a hot press method in a state where tension is applied only to the conductive fibers. Maximum strain memory type sensor Manufacturing method.
(8) A step of mounting the maximum strain memory type sensor according to any one of (2) to (5) in a state where tension is applied to the maximum strain memory type sensor;
Detecting a change in conductivity in the maximum strain memory type sensor.
[0013]
The sensor of the present invention has a conductive path that exhibits an irreversible breakdown behavior with respect to the maximum strain, improves the residual rate of the residual resistance phenomenon, and reduces its manifestation strain, thereby achieving high accuracy. The maximum distortion is monitored and memorized.
One form of such a conductive path is a conductive path formed by a continuous contact structure of conductive particles in a matrix resin reinforced with insulating fibers. By adjusting the particle shape and / or the volume ratio of the particles to the resin matrix in this conductive path, the residual ratio of the residual resistance phenomenon is improved and the strain region that is expressed is reduced, and the maximum strain accuracy stored. Is improved.
Another form is a conductive path formed of conductive fibers in a resin matrix reinforced with glass fibers. In this conductive path, by applying tension to the conductive fiber, the residual ratio of the residual resistance phenomenon is improved, the developed strain is reduced, and the stored maximum strain accuracy is improved.
As a result, according to the sensor having such a conductive path, it is possible to sense the maximum strain with high accuracy in a desired or assumed low strain region. As a result, highly accurate sensing and monitoring are possible even for structures that require high safety.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
The maximum strain sensor in the present invention has a conductive path that exhibits an irreversible structural change with respect to the maximum value of tensile strain. The first sensor of the present invention includes a sensing material having a conductive path formed of conductive particles, and the second sensor includes a sensing material having a conductive path formed of conductive fibers. Hereinafter, different conductive path forms in these two types of sensors will be described, and then a common form will be described. Further, sensing and monitoring of the maximum strain for each sensor will be described.
[0015]
(Conductive path in the first sensor)
The first maximum strain sensor in the present invention has a conductive path formed by a continuous contact structure (percolation structure) of conductive particles. This conductive path is held in a polymer material matrix and takes the form of a sensing material called a polymer material molded body. Further, it can be formed only by a percolation structure of particles without providing a polymer material matrix.
(Conductive particles)
The conductive particles can be used without particular limitation as long as the material has conductivity. For example, carbon black, ketjen black, acetylene black, graphite, activated carbon, carbon short fiber, fullerene, carbon whisker, carbon nanotube, metal powder, conductive ceramic particles such as nitriding, carbonizing, and titanium oxide are selected. The conductive particles can be used alone or in combination of two or more.
The form of the conductive particles is not particularly limited. For example, various shapes such as a structure (aggregate) shape, a spherical shape, a fiber shape, a rod shape, an indefinite shape, and a flake shape can be used alone or in combination of two or more. Preferably, a structure (aggregate) form can be used, and the particle size of each particle forming the structure is not particularly limited, but is preferably 10 nm to 100 nm, for example. More preferably, a structure (aggregate) -like form composed of particles of 20 nm or more and 60 nm or less is used. Furthermore, the DBP (Dibutyl Phthalate) absorption amount (JIS K6217), which is an index indicating the degree of this structure (aggregation), is preferably 10 to 1000 cm. ^Three / 100g. More preferably, 100-500cm ^Three / 100g. Further, as the spherical or flaky particles, preferably spherical or flaky particles having a size of 1 μm to 100 μm can be used. Such aggregates are generally often formed in carbon black particles. Specifically, it takes the form of dumplings or grapes stabbed on skewers.
[0016]
(Conductive path in the second sensor)
The conductive path of the second sensor is formed of a conductive fiber. The second conductive path is preferably held in a polymeric material matrix. Therefore, it is preferable to adopt a sensing material form called a polymer material molded body.
(Conductive fiber)
The conductive fiber is not particularly limited as long as it is a conductive fiber. For example, pitch-based, PAN-based, vapor-grown carbon fiber, ceramic fiber such as SiC, and fiber having a conductive film formed on the surface thereof. A metal fiber or the like is selected. As the conductive fibers, various conductive fibers can be used alone or in combination of two or more.
The conductive fiber may be a monofilament or a multifilament. The diameter is not particularly limited, but is preferably 1 μm to 100 μm, for example. More preferably, it is 2 μm or more and 10 μm or less.
[0017]
(Holding form of conductive path in this sensor (common form))
These conductive paths can be formed in the polymeric material matrix. Examples of the polymer material used include polyester, polypropylene, acrylic, nylon, polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polysulfone, polyacetal, polyurethane, polyformal, polybutyral, polyamide, polycarbonate, and polyacetic acid. Vinyl, a copolymer of two or more of the above polymers, a fluororesin, a silicone resin, an epoxy resin, and a vinyl ester resin can be used. These can be used alone or in combination of two or more.
[0018]
The polymeric material matrix can also include a fiber material. As the fiber material, for example, one kind or two or more kinds of glass fiber, vinylon fiber, aramid fiber, silicon carbide fiber, alumina fiber and the like can be used. Here, in order to develop a sensing function using the contact structure of conductive particles or conductive fibers as a conductive path, these fibers need to have electrical insulation.
Furthermore, the directionality of these fibers can be a parallel direction or a perpendicular direction with respect to the conductivity measuring direction by the present sensor or the strain direction acting on the applied structure as one direction. In the case of unidirectionality, a fiber bundle in which fibers oriented in the same direction are bundled can also be used. It is also possible to use a cloth material in which fibers that are parallel and perpendicular to the strain direction to be measured are combined. Specifically, it is preferably provided along the conductive path.
[0019]
The sensing materials of the first and second sensors can have a form of a molded body of a polymer material having a conductive path. In this case, a sensing material using a known polymer material molding method such as a pultrusion molding method, a mold molding method, a hot press method, an autoclave method, a resin transfer molding (RTM) method, or a sheet molding compound (SMC) method. Can be formed.
For example, when the sensing material of the first sensor is provided with a polymer matrix, a slurry in which conductive particles are dispersed in an uncured polymer material is prepared, and the slurry on the fiber material is dipped. It can be obtained by supplying by the method and curing. In order to increase the compounding ratio of the conductive particles in the conductive path, it is necessary to disperse the particles in a high concentration in the uncured polymer material. For this purpose, an organic solvent for suppressing an increase in viscosity of the uncured polymer material can be used. The organic solvent only needs to be compatible with the uncured polymer material, and for example, methyl ethyl ketone, acetone, styrene monomer, and the like can be selected. When the polymer material matrix is not provided, only conductive particles are dispersed in the solvent.
In the first sensing material, the blending ratio of the conductive particles is preferably 20 vol.% Or more with respect to the total amount (volume) of the polymer material and the conductive particles. If the content is less than 20 vol.%, A remarkable expression of the residual resistance phenomenon cannot be expected, so that the performance exceeding the conventional residual rate of 60 vol% cannot be achieved, and the expression distortion cannot be reduced to 0.05% or less. More preferably, it is 50 vol% or more, and further preferably 80 vol% or more. For example, if the blending ratio is 60 vol% or more, the residual ratio of the residual resistance phenomenon can be 80% or more, and the expression strain can be further reduced to 0.05%. Furthermore, if the blending ratio is around 100 vol%, the residual ratio of the residual resistance phenomenon can be made 95% or more, and the expression strain can be reduced to 0.02% or less. In addition, when a mixture ratio is 100 vol%, it becomes a sensing material form which does not have a polymer matrix.
[0020]
Further, for example, the sensing material of the second sensor can be obtained by supplying uncured polymer material slurry to a linear or cloth conductive fiber by dipping or the like and curing it. In addition, as described later, at this time, tension can be applied to the conductive fiber using various molding methods.
In the second sensing material, the volume ratio of the conductive fibers in the total amount of the polymer material and the conductive fibers is preferably, for example, 50 vol.% Or less. This is because if it exceeds 50 vol.%, The increasing tendency of the resistance change rate due to the breakage of the conductive fiber is reduced and the occurrence of the residual resistance phenomenon is suppressed. More preferably, it is 30 vol.% Or less. For example, if the volume ratio is 12.5% or less, the residual ratio can be increased to 90% or more, and the strain of the residual resistance phenomenon can be reduced to 0.05%.
[0021]
(Coating layer)
These sensing materials preferably include a coating layer formed of an insulating polymer material. According to this insulating coating material, a stable sensing function can be expressed by electrically insulating the conductive composite material responsible for the sensing function from the structure to be applied or its surrounding environment. For example, in application to steel-based structures, it is indispensable to insulate from highly conductive steel materials, and in embedding in concrete, conductivity is affected by the effects of moisture in the concrete. Necessary to prevent change.
[0022]
Examples of the polymer material used for the insulating coating material include polyester, polypropylene, acrylic, nylon, polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polysulfone, polyacetal, polyurethane, polyformal, polybutyral, Polyamide, polycarbonate, polyvinyl acetate, copolymers of two or more of the above polymers, fluorine resins, silicone resins, epoxy resins, and vinyl ester resins can be used. Moreover, as a fiber material used for this insulating resin molding, insulating fibers, such as glass fiber, a vinylon fiber, an aramid fiber, a silicon carbide fiber, an alumina fiber, can be used, for example.
[0023]
In applying the coating layer, a molding method such as a pultrusion method, a mold forming method, a hot press method, an autoclave method, a resin transfer molding (RTM) method, or a sheet molding compound (SMC) method can be employed. .
[0024]
(Tension load on the second sensor)
The second sensor can be preliminarily imparted (acted) with a conductive path tension at the time of sensor manufacture. The tension load can be applied, for example, during molding using a polymer material. Therefore, tension can be applied when holding the conductive path in the polymer material matrix and / or when forming the coating layer.
The tension load is preferably set to a stress or strain in the vicinity of a transition from a linear relationship to a nonlinear relationship in the relationship between the rate of change in resistance of the sensor and the tensile strain when the tensile stress is increased. In the stress or strain range showing a linear relationship, the conductive path exhibits elastic deformation behavior, and therefore, the effect of reducing the strain appearing in the residual resistance phenomenon is small even when the tension in the range is applied. In addition, it is not preferable that the tension is applied exceeding the stress or strain range in the vicinity of the nonlinear relationship because the strain range until the subsequent conduction path breaks becomes small.
[0025]
In applying the tension, for example, a hot press method can be employed. Moreover, in order not to recover the tensile deformation when the tension is released after the polymer material is cured, it is preferable to cure the polymer material by applying a tension only to the conductive fiber. In order to suppress the relaxation of tensile strain, it is preferable to integrally mold with a polymer material matrix containing insulating fibers, and it is preferable to reduce the volume ratio of the conductive fibers.
[0026]
The two types of sensing materials obtained as described above have various forms depending on the form of the fiber material used, the polymer material matrix, and the coating layer. The form of the sensing material is not particularly limited. For example, a linear shape, a planar shape, a tube shape, or a designed two-dimensional or three-dimensional shape can be taken.
[0027]
A method for measuring the conductivity or resistivity of these sensing materials is not particularly limited, and a two-terminal method or a four-terminal method is employed. Although the resistivity of the conductive composite material varies depending on the material, the first sensing material has a relatively high resistivity and can be measured by the two-terminal method. On the other hand, the second sensing material has a relatively low resistivity and may require measurement by the four-terminal method. In addition, as the direction of measuring the conductivity, it is preferable to pay attention to the directionality of the strain acting on the structure to be monitored and to match the direction in which the strain acts.
[0028]
The electrode installed for the conductivity measurement is not limited with respect to the material and fixing method. For example, a metal wire such as copper or silver can be selected as the electrode material, and soldering or conductive paste is used as the fixing method. Can be fixed or fixed with crimp terminals. Further, when the conductive composite material is in the form of a thin film, thin film formation by metal vapor deposition, sputtering, or the like can also be employed as a method for installing the electrode. However, since the conductive composite material includes a polymer material, a method that can be fixed at a temperature lower than the heat resistant temperature is preferable.
[0029]
In the first sensor, the maximum strain sensor manufactured as described above is based on the conductive particle form and / or the mixing ratio of the first sensor. In the second sensor, the conductive path is determined according to the mixing ratio of the conductive fibers. It is configured to have a residual ratio of the residual resistance phenomenon that is effective in maintaining the conductivity corresponding to the maximum value of the strain acting on. According to these sensors, it is easy to configure such that the residual ratio (the ratio of the amount of change in conductivity to be retained) exceeds 60%. More preferably, it is 80% or more, more preferably 90% or more, and most preferably 95% or more.
Similarly, the conductivity of the continuum changes with respect to the strain acting on the conductive path, and after the strain is removed, at least a part of the changed conductivity change before the strain removal is retained and the strain is reduced. It can also be said that the amount of change in conductivity retained and retained is increased in accordance with the maximum value.
And a sensor capable of storing information on the maximum strain in the sensor itself by changing the conductivity or resistivity with respect to the maximum value of the strain and at least part of which remains permanently after the strain is removed. You can also
[0030]
Such a sensor of the present invention is installed in a structure to be monitored. Thereby, a structure provided with the sensor is provided.
Although the material of the structure used as this object is not specifically limited, A concrete structure is mentioned as an example in a social infrastructure structure.
In this case, the form of installation differs depending on whether a new structure or an existing structure is assumed. In application to an existing structure, a sheet shape is assumed as the form of the maximum strain sensor, and the maximum strain sensor is installed in a form to be attached to the surface of the structure.
[0031]
When the sensor is in the form of a sheet, it can have a form that can be attached to the surface of the structure. In this case, when constructing a new structure, not only can it be applied to the surface of a steel structure or concrete structure, but also the existing structure can be monitored only by attaching it to the surface of the structure. And can. In addition, for surface sticking to the structure, an adhesive method or a mechanical jig method such as screwing can be selected, and when bonding to the structure, it is optimal for bonding to the structure. A polymer material matrix or a coating resin material can be selected.
[0032]
Moreover, when making a sensor into a rod shape, it can have a form which can be embedded inside a structure. In this case, when constructing a new structure, it can be embedded in, for example, a concrete structure, and has a reinforcing function by using high-elasticity and high-strength long fiber reinforced plastics for the above polymer material matrix and coating layer. The self-diagnosis function that the structural material itself performs the sensing function can be achieved.
[0033]
Furthermore, when embedding in concrete, applying the pre-tension to the second sensing material composed of conductive fibers such as carbon fibers to the structure provides the maximum strain memory function. It is valid.
At the same time, it contributes to improving the strength characteristics of concrete structures. This is because a concrete structure generally has a high strength against compressive deformation but a low strength against tensile deformation. In addition, the improvement of the tensile strength by the technique of introduce | transducing a reinforcing bar into a concrete structure is aimed at. By embedding in the state that pre-tension is applied to the reinforcing steel to be embedded, and releasing the tension after the concrete is hardened, the compressive stress acts on the concrete, and the strength against tensile deformation can be improved. Yes.
[0034]
Note that the direction in which the maximum strain sensor is installed can be measured with higher sensitivity by matching the conductivity measurement direction of the conductive composite material with the strain direction that is assumed to act on the structure. I can expect.
[0035]
This sensor can be applied to various structures, but it is also suitable for application to steel-based structures in addition to the concrete structures described above as social infrastructure structures. Materials and composite materials are also preferable applications because it is an important structure to grasp the maximum strain.
In these cases, a sheet shape is assumed as the form of the maximum strain sensor, and the maximum strain sensor is installed on the surface of the structure. According to this installation form, it is possible to install not only a newly constructed structure but also an existing structure. In attaching to the surface of the structure, fixing with a resin-based material with an adhesive, mechanical fixing with a jig such as a screw, nut, or bolt, and a combination of both are assumed. In any case, since it is required to accurately transmit the deformation of the structure to the sensor, the adhesive is required to have high elasticity and high adhesive strength, and high fixing strength is required even for mechanical fixing.
[0036]
As an embodiment of monitoring in a structure in which the maximum strain sensor is installed, periodic measurement or measurement according to necessity is assumed. When attempting to monitor the maximum strain using a strain gauge as a conventional technology, install this strain gauge in the structure, and always install a measurement system, data storage device, and power supply (wiring) to continuously collect data. It was necessary to continue. On the other hand, when this maximum strain sensor is installed, the sensor itself has a function to store the maximum strain information. Therefore, in addition to this sensor, anything such as a measurement system or a data storage device is always installed. There is no need to carry out monitoring, and monitoring is possible by carrying a measuring instrument periodically or only when necessary. This not only saves energy but also significantly reduces the running costs required for monitoring, and is extremely versatile without being limited by the space and installation environment where measurement equipment is permanently installed. Can be built.
[0037]
As described above, the sensor of the present invention is characterized in that the conductive path has a function of permanently storing a change in conductivity with respect to the maximum strain and storing information on the maximum strain by the sensor itself. . As a result, the maximum strain that has acted on the structure is stored and stored in the installed sensor itself, and there is a need to perform continuous measurement, data storage, and analysis with a measurement device connected to this sensor at all times. Disappear.
Therefore, information on the maximum value of the strain applied in the past can be obtained only by measuring the conductivity of the sensor periodically or as necessary. As a result, it is possible not only to be deployed as a highly versatile technique without being restricted by space and weight related to the installation of measuring equipment, but also to greatly reduce the operation cost. Furthermore, since the rate of conductivity change remaining for this maximum strain, that is, the rate of conductivity change remaining after strain removal is high compared to the conductivity change at the time of strain action, stress / strain acts on the structure. It is possible to accurately detect the information on the maximum strain even in a situation as it is or in a situation where the stress is removed and a strain due to plastic deformation remains.
[0038]
【Example】
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described with reference to FIGS. These examples are intended to specifically describe the present invention, and the present invention is in no way limited by these examples.
[0039]
In the following examples, two types of sensors, a second sensor having a conductive path made of carbon fiber as a conductive fiber and a first sensor having a conductive path made of conductive particles, are manufactured. A demonstration test was conducted by a tensile test.
[0040]
(Example 1: Conductive composite material composed of carbon fiber)
[Fabrication of maximum strain sensor]
A structural schematic diagram of the maximum strain sensor 1 produced in this example is shown in FIG.
The maximum strain sensor 1 has a rod shape as a whole, and is composed of a conductive composite material 2 composed of conductive carbon fibers 6 and a polymer material 5, and an insulating composite composed of glass fibers 4 and a polymer material 5. It has a structure in which the periphery is covered with the material 3.
[0041]
Hereinafter, a manufacturing process of the maximum strain sensor 1 will be described.
First, a PAN-based carbon fiber filament was selected as the conductive carbon fiber 6. As will be described later, it is preferable that the rate of increase in the resistance change rate with respect to the tensile strain is large in order to develop the residual resistance phenomenon for the maximum strain memory function. With this in mind, the type of carbon fiber and the sizing agent (surface treatment agent) were selected, and the ratio was set to 7.5 to 22.5 vol.% In order to optimize the volume ratio. This carbon fiber was impregnated in a liquid thermosetting resin and cured by applying a heat treatment at 130 ° C. for 90 minutes in a state where it was introduced into the mold. The outer diameter of the conductive composite material after curing was 2 mmφ. The resin molded body was cut into a predetermined length (250 mm), and electrodes were installed on both ends thereof. A method of fixing the lead wire with a conductive paste was adopted for this electrode. An insulating resin molding was coated around the conductive composite material. A glass fiber was impregnated with a resin, adhered to the periphery of the conductive composite material, and cured by heating (130 ° C., 90 minutes). Thus, the maximum strain sensor 1 was obtained.
[0042]
Although the maximum strain sensor 1 is obtained as described above, in this embodiment, a grip portion as shown in the photograph of FIG. 3 was installed in order to perform a tensile test on the composite material. This grip part is made of steel and has a hollow shape. The maximum strain sensor 1 was introduced into this, and a cement-based expansion material was poured into the gap and cured, thereby firmly fixing the steel pipe and the composite material.
[0043]
[Performance verification test by tensile test of maximum strain sensor]
The composite material 1 as the produced maximum strain sensor was repeatedly subjected to tensile strain under the condition of applying a pretension, the change in conductivity was measured, and the maximum strain memory function was evaluated.
[0044]
[Test method]
A tensile test was performed on the produced maximum strain sensor for a tensile test using a hydraulic fatigue test apparatus. A schematic diagram of this tensile test system is shown in FIG. In this tensile test, the maximum strain sensor is fixed by applying a compressive force to the grip portion. After grip-fixing the maximum strain sensor, a constant current is applied to the two electrodes from the conductive composite material, and the voltage drop between the electrodes is measured, that is, the conductivity of the conductive composite material is determined by the two-terminal method. Measured. In this tensile test, the load acting on the maximum strain sensor was measured with a load cell, and the acting tensile strain was measured with an extensometer. In all experimental results shown in this example, this change in conductivity is the initial resistance value R. ₀ Resistance change during stress action ΔR = RR ₀ Resistance change rate ΔR / R ₀ As shown. Furthermore, the tensile resistance was not applied to the composite material in the steel pipe of the grip part, and the measured resistance change rate was corrected on the premise that the tensile strain acts only on the composite material between the grips.
[0045]
In this tensile test, two types of loading patterns were applied as loading methods. First, as a monotonic tensile test, the tensile strain was gradually increased at a constant speed by displacement control from the time of zero load and tensile strain to the final fracture. As a result, the relationship between the tensile strain and the change in electrical conductivity and the relationship between the tensile strain and the stress were grasped, and the basic data for determining the introduction amount of the pretension was obtained while optimizing the volume ratio of the carbon fiber. Next, with the pre-tension applied as a reference, a test was performed in which repeated tensile stress was applied with the peak load increased stepwise, and the applied tensile strain and conductivity change were measured as a function of time, The response to the maximum value of tensile strain was evaluated.
[0046]
[Test results]
First, the result of the monotonic tensile test is shown in FIG. In this test, evaluation was performed on a maximum strain sensor with a volume ratio of 7.5 vol.% And 22.5 vol.%. In the stress-strain diagram shown in (a), there is a linear relationship between tensile stress and tensile strain, and the tensile strength at break and the elastic modulus corresponding to the slope of the carbon fiber volume fraction decrease. However, the fracture strain is almost the same. On the other hand, a nonlinear relationship was obtained in the tensile strain dependence of the resistance change rate shown in (b). This behavior reflects the phenomenon of transition from elastic deformation of the carbon fiber to fiber breakage as the tensile strain increases. That is, up to about 1.0% tensile strain, the carbon fiber is elastically stretched and its resistance change is linear. When the pulling strain is further increased, the carbon fiber starts to be partially broken, and the resistance value greatly increases at the broken portion, so that the resistance change of the composite material as a whole increases nonlinearly. Since the rupture of the carbon fiber brings about an irreversible resistance change corresponding to the maximum strain, the higher the resistance change rate in this non-linear region, the more noticeable the residual resistance phenomenon for the maximum strain memory function appears. I can expect. From this result, a non-linear region showing a high resistance change rate when the volume ratio of the carbon fiber is low was obtained. The reason for this is considered to be that the contact between the carbon fibers decreases as the volume ratio of the carbon fibers decreases, and the influence of the fiber breakage at one place on the resistance change rate of the entire composite material increases.
[0047]
From the above results, a composite material having a low volume ratio of carbon fibers was selected as the maximum strain sensor. The composite material was subjected to a repeated tensile test under a condition where a pretension was applied. The results are shown in FIGS. From the results shown in FIG. 5, the amount of pre-tension introduced was about 540 MPa, and a condition in which a tensile strain of about 1.2% at which a nonlinear behavior began to appear in the resistance change rate was applied was used as a reference. After introducing the pre-tension, a holding time of about 10000 s was provided, and after confirming its stability, a tensile strain with a stepwise increase in the peak value was applied. It shows elastic deformation behavior, and after the unloading, the tensile strain has recovered up to the pre-tension, but its resistance change rate increases step by step, and the resistance change rate under load almost returns after unloading. Excellent residual resistance phenomenon was exhibited. As is clear from the results summarized as the relationship between tensile strain and resistance change rate, about 90% or more of the resistance change rate during loading remains even after unloading, and this residual resistance phenomenon is about 0.05% or more. It is clearly expressed with respect to the tensile strain. From the above results, it was demonstrated that an excellent maximum strain memory function can be achieved by introducing a pretension into a conductive composite material composed of carbon fibers.
[0048]
In order to quantitatively evaluate the storage accuracy of the maximum strain in this maximum strain sensor, the rate of change in resistance (ΔR _max ) And the rate of change in residual resistance after unloading (ΔR _res ) As a function of the maximum strain applied. For example, it is assumed that 35% is measured as the resistance change rate of the maximum strain sensor due to some deformation acting on the structure. In that case, the range of the tensile strain that can take the resistance change rate is limited to 0.717 to 0.742%. Therefore, the maximum distortion storage accuracy can be estimated to be about ± 1.7%. It is important to note that even if the structure remains deformed, this accuracy can be guaranteed regardless of the amount of residual stress and residual strain. When the residual rate is low as in the conventional technology, that is, this ΔR _max And ΔR _res When the interval is wide, the storage accuracy of the maximum distortion is greatly reduced. The high storage accuracy for the maximum strain demonstrated here is obtained by the high residual rate in the maximum strain sensor.
[0049]
(Example 2: Conductive composite material in which carbon particles are dispersed)
[Fabrication of maximum strain sensor]
A schematic diagram of the structure of the maximum strain sensor 7 produced in this example is shown in FIG.
The maximum strain sensor 2 has a rod shape as a whole, and a composite material composed of insulating glass fibers 10 and a polymer material 11 is used as a basic structure, and carbon particles 12 are dispersed in the polymer material 11. It has a structure in which the periphery is covered with an insulating composite material 9 around the conductive composite material 8.
[0050]
Hereinafter, the manufacturing process of the maximum strain sensor 2 will be described.
As a method for producing the conductive composite material 8, first, conductive particles 12 are dispersed in a liquid polymer material 11. As the conductive particles, carbon black having a particle size of 50 nm and high structure was adopted, and dispersed in a thermosetting epoxy resin using a stirring defoaming apparatus. In general, since the viscosity of an epoxy resin is high, it is difficult to disperse fine particles such as carbon black at a high concentration. Therefore, in this example, methyl ethyl ketone was added as an organic solvent to the epoxy resin to suppress an increase in resin viscosity due to particle dispersion. This combination of resin and organic solvent is used when producing an anti-cured long fiber reinforced composite material called a prepreg. This organic solvent is premised on volatilization in the heat curing process. In this example, the volume ratio of the carbon particles was 5 to 100 vol.%. Here, a composite material with a volume fraction of carbon particles of 100 vol.% Is a material in which carbon black is dispersed only in an organic solvent and cured (dried), and is brittle because it does not contain a resin. It is presumed to show fracture behavior. The polymer material in which the conductive particles were dispersed was impregnated into glass fiber and cured under heat treatment conditions of 160 ° C. and 90 minutes. The resin molded body was cut into a predetermined length (250 mm), and electrodes were installed on both ends thereof. A method of fixing the lead wire with a conductive paste was adopted for this electrode. An insulating resin molding was coated around the conductive composite material. The glass fiber was impregnated with a resin not containing carbon particles, adhered to the periphery of the conductive composite material, and cured by heating (160 ° C., 90 minutes). Thus, the maximum strain sensor 2 was obtained.
[0051]
The maximum strain sensor 2 is obtained as described above. In this example, a grip portion as shown in the photograph of FIG. 3 was installed in order to perform a tensile test on this composite material. This grip part is made of steel and has a hollow shape. In this, the maximum strain sensor 2 was introduced, and a cement-type expansion material was poured into the void and hardened to firmly fix the steel pipe and the composite material.
[0052]
[Performance verification test by tensile test of maximum strain sensor]
The composite material 2 as the produced maximum strain sensor was repeatedly subjected to tensile strain, the change in conductivity was measured, and the maximum strain memory function was evaluated. In this embodiment, no pretension is applied to the composite material 2.
[0053]
[Test method]
A tensile test was performed in the same manner as in Example 1 on the produced maximum strain sensor for tensile test. After gripping the maximum strain sensor, the conductivity of the conductive composite material was measured by the two-terminal method. Further, the load acting on the composite material was measured with a load cell, and the acting tensile strain was measured with an extensometer. In the experimental results shown in this example, this conductivity change is the resistance change rate ΔR / R. ₀ The measured resistance change rate was corrected on the assumption that tensile strain acts only on the composite material between the grips. In this tensile test, as a loading method, a test was applied with repeated tensile stress with the peak load increased stepwise, and the applied tensile strain and conductivity change were measured as a function of time, and the maximum tensile strain was measured. Responsiveness to the value was evaluated.
[0054]
[Test results]
9 and 10 show the results of repeated tensile tests on composite materials having a volume ratio of 5%, 30% and 100% of the dispersed conductive particles. FIG. 9 shows the tensile strain applied to each composite material and the measured resistance change rate as a function of time. Further, the relationship between the applied tensile strain and the rate of change in resistance is shown in FIG. From this result, when the volume ratio of carbon particles is low, most of the resistance change rate at the time of loading returns to the initial value after unloading, whereas the volume ratio of carbon particles increases. Residual resistance phenomenon began to appear, and in the composite material having a volume ratio of 100 vol.%, The residual resistance phenomenon having an extremely high residual ratio was developed. From the result of (b), the residual resistance phenomenon appeared corresponding to the maximum value of tensile strain of about 0.02% or more, and the residual ratio reached 99% at the maximum.
[0055]
In order to grasp the relationship between the volume ratio of the dispersed particles and the residual resistance phenomenon in more detail, a repeated tensile test was performed on the composite material in which the volume ratio was further finely set and the action was performed as shown in FIG. The dependence of the residual rate on the maximum strain is summarized. From this result, it is possible to more clearly grasp the increase in the residual rate accompanying the increase in the volume ratio of the dispersed particles in the entire maximum strain range. It is inferred that this remarkable phenomenon is greatly influenced by the brittleness of the particle-dispersed matrix resin forming the conductive composite material. In addition, the embrittlement of the matrix is considered to be related to the particle morphology in addition to the high concentration dispersion. The carbon black dispersed here forms a structure called a structure in which fine particles having a particle diameter of 50 nm are chemically bonded to form an aggregate. DBP (Dibutyl Phtalate) absorption (JIS K6217) can be cited as an index indicating the degree of this structure (aggregation). The DBP absorption of the particles used in this example is 175 cm. ^Three / 100g. Since this chain structure is brittlely broken by the action of maximum strain, it may be possible to achieve this extremely high residual rate. From the above results, it was demonstrated that an excellent maximum strain memory function can be achieved by increasing the volume ratio of the conductive composite material in which carbon particles are dispersed in a matrix resin. It should be noted here that, unlike the case of the first embodiment, the maximum strain storage function can be achieved without surplus tension. Furthermore, the fact that the residual resistance phenomenon can be adjusted by adjusting the particle dispersion amount is very interesting from the viewpoint of monitoring technology. This is because it is possible to control the function of increasing the particle dispersion ratio when it is desired to store the maximum strain and decreasing the particle dispersion ratio when it is desired to reduce the residual resistance phenomenon for constant monitoring.
[0056]
In order to quantitatively evaluate the storage accuracy of the maximum strain in this maximum strain sensor, the rate of change in resistance (ΔR _max ) And the rate of change in residual resistance after unloading (ΔR _res ) As a function of the maximum strain applied. For example, it is assumed that 75% is measured as the resistance change rate of the maximum strain sensor due to some deformation acting on the structure. In that case, the range of the tensile strain that can take the rate of resistance change is limited to 0.912 to 0.931%. Therefore, the maximum distortion storage accuracy can be estimated to be about ± 1.0%. As described in the first embodiment, even when the structure remains deformed, it is important that this accuracy can be guaranteed regardless of the amount of residual stress and residual strain. Based on the above results, in the conductive composite material in which the carbon particles are dispersed in the matrix resin, the function of storing the maximum strain with high accuracy by operating from the low strain region by increasing the volume ratio of the particles is reserved. It has been demonstrated that it can be realized under conditions that do not require the introduction of tension.
[0057]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the sensor which enables the advanced soundness diagnosis of measuring the maximum value of the distortion which acted on the structure can be provided. As a result, whether or not the maximum strain applied exceeds the design tolerance of the structure for a structure in which damage or destruction of the steel structure or the fuselage constituting the aircraft in a social infrastructure structure is a problem. It is possible to show one of the indicators that make this determination, which not only greatly contributes to the improvement of its safety, but can also extend the life by accurate life judgment, so it is possible to make a huge amount of efficient structure operation Enables cost reduction and resource saving.
[0058]
Further, since this sensor has a feature that the sensor itself can store information on the maximum strain, it is possible to perform monitoring by regular or necessary measurement instead of constant monitoring in general structures requiring safety. Thereby, a simple and versatile monitoring system can be provided at low cost.
[Brief description of the drawings]
FIG. 1 is a structural schematic diagram of a maximum strain sensor made of a composite material composed of carbon fibers.
FIG. 2 is a structural schematic diagram of a maximum strain sensor composed of a composite material in which carbon particles are dispersed.
FIG. 3 is a diagram showing the entire maximum strain sensor for a tensile test.
4 is a schematic diagram of an evaluation system used for testing in Examples 1 and 2. FIG.
5 is a diagram (a) and (b) showing the results of a simple tensile test among the test results carried out in Example 1. FIG.
6 is a result of a repeated tensile test in which the peak load is gradually increased among the test results performed in Example 1, where the horizontal axis represents time and the vertical axis represents ΔR / R. ₀ It is the graph which took the stress and distortion.
7 is a result of a repeated tensile test in which the peak load is gradually increased among the test results performed in Example 1, where the horizontal axis indicates strain and the vertical axis indicates ΔR / R. ₀ It is the graph figure which took.
8 is a result for quantitatively evaluating the storage accuracy of the maximum strain among the test results performed in Example 1. FIG.
9 is a result of a repeated tensile test in which the peak load is gradually increased among the test results performed in Example 2, where the horizontal axis represents time and the vertical axis represents ΔR / R. ₀ It is the graph figure which took and distortion.
10 is a result of a repeated tensile test in which the peak load is gradually increased among the test results performed in Example 2, in which the horizontal axis indicates strain and the vertical axis indicates ΔR / R. ₀ It is the graph figure which took.
FIG. 11 is a result showing the influence of the dispersed particle volume ratio on the maximum strain dependence of the residual ratio among the test results carried out in Example 2.
12 is a result for quantitatively evaluating the storage accuracy of the maximum strain among the test results performed in Example 2. FIG.
[Explanation of symbols]
1 Maximum strain sensor made of composite material composed of carbon fiber
2 Sensing materials composed of carbon fiber
3 Insulating composite material composed of glass fiber
4 Glass fiber
5 Resin (polymer material)
6 Carbon fiber
7 Maximum strain sensor composed of composite material with dispersed carbon particles
8 Sensing materials with carbon particles dispersed
9 Insulating composite material composed of glass fiber
10 Glass fiber
11 Resin (polymer material)
12 Carbon particles (carbon black)

Claims (8)

A sensing material having a conductive path by a percolation structure of conductive particles, and a coating layer made of an insulating material and covering the sensing material,
The sensing material has a composition in which the volume ratio of conductive particles: polymer material is 80:20 to 100: 0,
The conductive particles are aggregates formed by aggregation of conductive fine particles,
The conductivity changes due to the tensile strain acting on the conductive path, and after the strain is removed, information on the maximum residual strain is obtained by permanently retaining 80% or more of the changed amount of conductivity before the strain is removed. A maximum strain memory type sensor that can be stored in itself and is configured to increase the amount of change in conductivity that is retained according to the maximum value of tensile strain. A sensing material having a conductive path by a conductive fiber, and a coating layer made of an insulating material and covering the sensing material,
In the sensing material, the volume ratio of the conductive fibers in the total amount of the polymer material and the conductive fibers is 7.5 to 30 vol% ,
The sensing material is maintained in a tensioned state,
The conductivity changes due to the tensile strain acting on the conductive path, and after the strain is removed, information on the maximum residual strain is obtained by permanently retaining 60% or more of the changed amount of conductivity before the strain is removed. A maximum strain memory type sensor that can be stored in itself and is configured to increase the amount of change in conductivity that is retained according to the maximum value of tensile strain.   The maximum strain memory type sensor according to claim 1 or 2, wherein the sensing material and / or the coating layer contains an electrically insulating fiber along the conductive path.   The maximum strain memory type sensor according to any one of claims 1 to 3, which is a sheet-like body.   The maximum strain memory type sensor according to any one of claims 1 to 3, which is a rod-shaped body. A method for producing a maximum strain memory type sensor comprising: a sensing material having a conductive path by a conductive fiber; and a covering layer made of an insulating material and covering the sensing material ,
A method for producing a maximum strain memory type sensor , comprising a step of producing the conductive fiber in a state in which tension is applied. The manufacturing method of the maximum strain memory type sensor according to claim 6, wherein the sensing material is molded by a hot press method in a state where tension is applied only to the conductive fibers. Mounting the maximum strain memory type sensor according to any one of claims 2 to 5 in a state where tension is applied to the maximum strain memory type sensor;
Detecting a change in conductivity in the maximum strain memory type sensor.

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