JP2005337819A - Strain sensor, its manufacturing method, and strain detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a strain sensor capable of measuring the maximum value of a strain working to a structure in a required strain range. <P>SOLUTION: This strain sensor 2 is equipped with insulating fibers 12 arranged with a fixed directivity, an organic phase 10 acquired by heat treatment of an organic polymer material and arranged at least along the insulating fibers, and a conductor phase 14 having the organic phase 10 at least on a part. Since having the organic phase 10 acquired by heat treatment of the organic polymer material, a conductivity change of a conductive conductor is shown from an extremely small strain domain, and a remaining phenomenon of the conductivity variation corresponding to the working maximum strain is expressed, and a high resistance remaining rate can be attained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a strain sensor for detecting a deformation or damage state and a strain detection method for a structure, and more particularly to a strain sensor suitable for detecting a maximum strain, a manufacturing method thereof, a strain sensing material, a strain detection method, and a structure.

  In recent years, rapid deterioration of social infrastructure structures such as railways and roads has become apparent. In the event of a disaster such as a collapse of a concrete structure or an earthquake, it is important to accurately evaluate the damage given to these structures in order to prepare a more healthy structure and prepare for future accidents and disasters. is there. Under such circumstances, there is a strong demand for a soundness monitoring technique that can detect the maximum strain for diagnosing damage, destruction, and deterioration in these important structures that require high safety.

As an intelligent material capable of diagnosing the maximum strain acting on a single material, a composite material composed of carbon fibers has been proposed (Patent Document 1). This composite material applies a phenomenon (residual resistance phenomenon) in which long-fiber reinforced plastics composed of carbon fibers retain their electrical conductivity changes by breaking the carbon fibers corresponding to the maximum strain. . In addition, in a composite material in which conductive carbon particles are dispersed in an organic phase resin made of glass fiber reinforced plastics, and the conductivity is maintained by the continuous contact structure of the particles, the structural change of the conductive path corresponding to the maximum strain There is also proposed a composite material that applies the phenomenon that the change in conductivity remains (Patent Document 2). Furthermore, conductive carbon particles are dispersed in an organic phase resin on a metal base material having a low yield point, and a material having conductivity due to the continuous contact structure of the particles is combined, and plastic deformation of the metal base material is performed. There has also been proposed a strain sensor that applies the phenomenon that a change in conductivity remains corresponding to the maximum strain (Patent Document 3).
JP-A-6-50830 JP-A-9-1003006 JP 2001-153603 A

  Usually, the diagnostic strain region required in many structures to be monitored is, for example, an elastic strain range of a steel material of 0.2% or less and a crack generation strain in concrete of 0.1% or less. On the other hand, in the case of a composite material using carbon fiber, since the tensile strain of about 0.5% or more is required for breaking the carbon fiber, the memory function of the maximum strain is also limited to a strain region beyond that. End up. Further, although a residual resistance phenomenon is observed by forming a continuous contact structure of conductive particles in the organic phase resin, it is difficult to obtain a sufficient residual resistance phenomenon by itself. Further, in the case of utilizing the plastic deformation of the metal base material, 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 addition, when a metal base material is used, if the stress or strain of compression as well as tension acts on the structure to be monitored, the plastic deformation amount of the base material also changes following the compressive deformation. There is a possibility that the memory function of the maximum strain may not be exhibited.

  It is an object of the present invention to provide a strain sensor capable of measuring the maximum value of strain applied to a structure in a required strain region, a manufacturing method thereof, a strain sensing material, a strain detection method, and a structure. Objective. Another object of the present invention is to provide a strain sensor capable of accurately measuring the maximum value of strain acting on the structure, a manufacturing method thereof, a strain sensing material, a strain detection method, and a structure. To do.

  In order to solve at least a part of the above problems, the inventors of the present invention have proposed a composite material in which a continuous conductor phase is formed in an organic phase resin of a fiber reinforced composite material, and the destruction corresponding to the maximum strain of the conductive path is made. We focused on applying behavior. And by applying heat treatment to the organic polymer material in which conductive particles are dispersed as the conductor phase, or by applying heat treatment until the organic polymer material not containing conductive particles shows conductivity, The present inventors have found a method in which the conductivity change of the conductive conductor is exhibited from an extremely low strain region, and the phenomenon of remaining in accordance with the maximum strain on which the amount of change in conductivity acts is exhibited, thereby achieving a high resistance residual ratio. Furthermore, as a result, the present inventors have found that this composite material enables diagnosis of the maximum strain in a desired strain region, and completed the present invention. That is, according to the present invention, the following means are provided.

  According to one embodiment of the present invention, the strain sensor is an organic fiber obtained by heat-treating an organic polymer material along the insulating fiber and at least the insulating fiber arranged with a certain direction. There is provided a strain sensor comprising a phase and a conductor phase comprising at least a portion of the organic phase. In this embodiment, it is preferable that the conductor phase has a conductive path with a continuous contact structure of a large number of conductive particles. In addition, it is preferable that the conductive phase has the organic phase having conductivity, and it is preferable that the conductive phase consists only of the organic phase. In addition, it is preferable that residual stress due to heat treatment of the organic polymer material acts on the organic phase, and the organic phase is obtained by heat-treating the organic polymer material in an inert atmosphere. In another preferred embodiment, the heat treatment is preferably performed at a temperature at which the organic polymer material is thermally decomposed or higher.

  Furthermore, in these forms, it is a preferable aspect that an insulating coating layer is provided on the surface layer side, and it is also a preferable aspect that at least 80% or more of the conductivity change amount is retained and acts on the strain sensor. It is also a preferable aspect to maintain the conductivity change amount corresponding to the maximum strain. Such a strain sensor is preferably in the form of a sheet or rod.

  According to another aspect of the present invention, there is provided a method for manufacturing a strain sensor, which is a molded body of an organic polymer material including conductive particles and insulating fibers arranged with a certain direction. A process of forming a conductor phase having an organic phase obtained by heat-treating the organic polymer material and a conductive path by a continuous contact structure of the conductive particles. Is provided. Further, according to another embodiment, there is provided a method for manufacturing a strain sensor, comprising a step of heat-treating a molded body of an organic polymer material in which insulating fibers are arranged with a certain direction. In the heat treatment step, there is also provided a production method for forming a conductor phase composed of a part or the whole of an organic phase obtained by heat-treating the organic polymer material. In these forms, the heat treatment is preferably performed in an inert atmosphere. Furthermore, according to the other one form of this invention, the strain sensor obtained by the method of either of these forms is also provided.

  According to another embodiment of the present invention, the strain sensing material is an insulating fiber arranged with a certain directionality, and at least the organic polymer material along the insulating fiber is heat-treated. There is provided a strain sensing material comprising the obtained organic phase and a conductor phase comprising at least a portion of the organic phase.

  According to another aspect of the present invention, there is provided a method for detecting strain, the method comprising detecting a conductivity in the strain sensor in a structure to which any one of the strain sensors is mounted. Is provided. According to yet another embodiment, a structure equipped with the strain sensing material is provided.

  The strain sensor of the present invention comprises insulating fibers arranged with a certain directionality, an organic phase obtained by heat-treating an organic polymer material, and a conductor phase having at least a part of the organic phase. It is characterized by providing. According to this strain sensor, by having an organic phase obtained by heat-treating an organic polymer material, the conductivity of the conductor phase changes due to the strain, and the strain is generated even after the strain is removed. In addition, at least a part of the changed amount of conductivity remains and is retained. Further, by having an organic phase obtained by heat-treating an organic polymer material, the residual ratio of the conductivity change amount of the conductor is increased, and the conductivity change is expressed in a low strain region. For this reason, according to this strain sensor, strain can be detected in a required low strain region, and maximum strain can be monitored with high accuracy. Although the present invention is not theoretically constrained, the improvement of the residual ratio and the decrease of the strain region where the residual phenomenon is manifested are caused by the tensile residual stress in the organic phase obtained by the heat treatment of the organic polymer material. It is inferred that, even if a part of the conductor is separated by tensile deformation, the residual tensile stress is originally acting, so that the once separated continuous structure is suppressed from being restored to the initial state. can do. Hereinafter, as the best mode for carrying out the present invention, a strain sensor will be described, and a manufacturing method thereof, a strain detection method using the strain sensor, and the like will be described in detail.

  FIG. 1 shows a schematic diagram of an example of the structure of a sensing material provided in the strain sensor of the present invention, and FIG. 2 shows a schematic diagram of an example of a strain sensor used in a tensile test. The strain sensor 2 includes a sensing material 3 and an electrode 20. The sensing material 3 is a conductor phase having an organic phase 10 obtained by heat-treating insulating fibers 12 and an organic polymer material and a conductive path 6 by a continuous contact structure (also referred to as a percolation structure) of the conductive particles 4. 14 is provided. The conductive path 6 is bonded or held by the organic phase 10 to hold the contact structure. A sensing material 3 that is a conductive composite material including the insulating fiber 12 and the conductor phase 14 constitutes a sensing portion that is the core of the strain sensor 2.

(Insulating fiber)
The strain sensor 2 can include an insulating fiber 12. By providing the insulating fiber 12, the organic phase 10 can be reinforced. As an insulating fiber, 1 type, or 2 or more types, such as glass fiber, a vinylon fiber, an aramid fiber, a silicon carbide fiber, an alumina fiber, can be used, for example.

  The insulating fibers 12 are preferably provided with a certain direction. By forming the conductor phase along the insulating fiber 12 having a certain direction, it is possible to easily detect the strain having the direction. In addition, by supplying heat along the insulating fibers 12 arranged with a certain direction and heat treating the organic polymer material, the resistance against shrinkage in the shrinkage process accompanying this heat treatment along the insulating fibers 12 By applying a force, the residual tensile stress along the direction of the insulating fiber can be applied to the organic phase 10, and as a result, the strain range where the change in conductivity is exhibited can be reduced. The insulating fiber 12 preferably has continuity corresponding to the formation length of the conductive path 6. For example, a filament-like fiber bundle corresponding to the length of the conductive path 6 is used, or a plurality of fibers not individually having the length of the conductive path 6 are bundled, entangled, or twisted. Or a fiber bundle formed to have a predetermined length.

  Insulating fiber 12 can also be made to intersect, for example, approximately perpendicular to the strain direction to be measured. Such an arrangement direction mainly contributes to strengthening the organic phase 10 and maintaining the shape. As an arrangement form of such insulating fibers 12, a cloth material in which fibers oriented in a direction along a strain direction to be measured and a direction orthogonal to the direction can be used.

(Organic phase)
The organic phase 10 is disposed along at least the insulating fiber 12. As long as the organic phase 10 is provided along the insulating fiber 12, the organic phase 10 may exist even in a portion where the insulating fiber 12 is not disposed. Therefore, even if the organic phase 10 is provided along the insulating fiber 12 and the organic phase 10 is provided in a region not along the insulating fiber 12, the organic phase 10 is provided along the insulating fiber 12. I can say that. Further, the organic phase 10 may be dispersed along the insulating fiber 12 as long as it is present as a part of the conductor phase 14 along the insulating fiber 12, or exists as a continuous phase. May be. The organic phase 10 is a phase obtained by heat-treating an organic polymer material. The organic phase 10 will be described in detail in the manufacturing method of the sensing material 3.

(Conductor phase)
The conductor phase 14 includes at least a part of the organic phase 10. The conductor phase 14 partially includes the organic phase 10 when the conductor phase 14 includes the organic phase 10 and the conductive path 6 formed by components other than the components of the organic phase 10 (first form) It means at least two types of forms when the phase 14 has only the organic phase 10 (second form). This is because the organic phase 10 can maintain its insulating properties depending on the degree of heat treatment, and can impart conductivity by advancing carbonization or graphitization. Among these forms, when the conductive path of the conductive particles 4 is provided, high conductivity and a large amount of change in conductivity with respect to strain can be easily expressed. Sensitive and highly accurate detection of maximum distortion is possible. In the first embodiment, in order for the conductive path 6 to function effectively, the organic phase 10 is preferably sufficiently higher in resistance than the conductive path 6 compared to the conductive path 6, but the organic phase 10 itself May have conductivity, and the conductive phase 14 may be formed from the conductive organic phase 10 and the conductive path 6 formed of conductive particles. In this case, the conductor phase 14 has cooperative conductivity between the organic phase 10 and the conductive path 6. In the second embodiment, the conductor phase 14 is composed only of the organic phase 10 having conductivity. When the organic phase 10 is the conductor phase 14, the organic phase 10 has both the functions of the conductor phase 14 and the organic phase 10 as a medium for developing a high residual resistance. Since the organic phase 10 can be made porous by heat treatment conditions, it is possible to control the expression of various conductivity.

  The conductive path 6 in the first form can include the conductive path 6 by a continuous contact structure of a large number of conductive particles existing together with the organic phase 10. The conductive particles 4 preferably have a contact structure formed by the organic phase 10 or are dispersed in the organic phase 10 to form a contact structure. The conductive particles 4 can be used without any 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 4 can be used alone or in combination of two or more.

The form of the conductive particles 4 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) -like 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, DBP is an index indicating the degree of the structure (aggregation) (Dibutyl Phthalate) absorption (JIS K6217) is preferably 10~1000cm ³ / 100g. More preferably, it is 100-500 cm < ³ > / 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.

(Coating layer)
The sensing material 3 can include an insulating coating layer 16 that covers the outer periphery of the conductive path 6 and the organic phase 10. According to the insulating coating layer 16, a stable sensing function can be achieved by electrically insulating the sensing material 3 which is a conductive composite material from the structure to be applied or its surrounding environment. . For example, in application to steel-based structures, it is essential 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.

  The covering layer 16 is preferably formed of an insulating polymer material. If the coating layer is made of such a material, it is possible to easily ensure water resistance as well as insulation. Examples of the insulating polymer material 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, a vinyl ester resin, a phenol resin, and a furan resin can be used. The insulating coating layer 16 can include insulating fibers 18 such as glass fibers, vinylon fibers, aramid fibers, silicon carbide fibers, alumina fibers, etc., as in the organic phase 8, for example. It is preferable that the insulating fiber 18 is provided along the insulating fiber 12 in the organic phase 10.

  As with the organic phase 10, the insulating coating layer 16 may be formed by heat-treating these insulating polymer materials. In addition, when it is formed by heat treatment, a thermal decomposition product of the polymer material, a condensate thereof, a polymerization product thereof, or the like is generated, and the composition change occurs, but the same polymer as the organic phase 10 is formed. When the material is used, it is formed in a layer having the same composition as the organic phase 10. When the insulating coating layer 16 is thus formed by heat treatment, it may have the same composition as the organic phase 10 except that it does not contain the conductive particles 4. When the insulating coating layer 16 is formed by heat treatment, it is preferable to provide an insulating coating layer that is not further heat-treated on the surface layer side in order to ensure water resistance.

  The sensing material 3 is provided with various forms by the form of the conductor phase 14 and the insulating fiber 12 and further by the coating layer 16. The form of the sensing material 3 is not particularly limited. According to the embodiment illustrated in FIGS. 1 and 2, the cross-sectional shape is circular, but the cross-sectional shape is not limited to this. The sensing material 3 can take, for example, a linear shape, a rod shape, a plate shape, a film (sheet) shape, a tube shape, or a designed two-dimensional or three-dimensional shape.

  Thus, the insulating fiber 12 and the conductor phase 14 constitute a sensing material 3 that is a conductive composite material having a sensing function of maximum strain. Therefore, according to another form of this invention, the electroconductive composite material which has a sensing function provided with the insulating fiber 12 and the conductor phase 14, or the coating layer 16 in addition to these is also provided.

(Sensing material manufacturing method)
Next, a method for manufacturing the sensing material 3 will be described. The sensing material 3 is obtained by heat-treating a molded body of an organic polymer material that includes or does not include conductive particles and in which the insulating fibers 12 are arranged with a certain direction. Here, the organic polymer material constitutes the organic phase 10 after the heat treatment, and the conductive particles 4 constitute the conductive path 6. The conductive particles 4 to be used are as already described. The organic polymer material constituting the organic polymer material is preferably an insulating organic polymer material, for example, polyester, polypropylene, acrylic, nylon, polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol. , Polysulfone, polyacetal, polyurethane, polyformal, polybutyral, polyamide, polycarbonate, polyvinyl acetate, copolymer of two or more of the above polymers, fluorine resin, silicone resin, epoxy resin, vinyl ester resin, phenol resin, furan resin These can be used alone or in combination of two or more.

  A molded body of an organic polymer material including or not including the conductive particles 4 can be obtained as a normal resin molded body. For example, a known resin 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 employed.

  In order to dispose the insulating fiber 12 in the organic polymer material, for example, a slurry in which the conductive particles 4 are dispersed in an uncured organic polymer material is prepared, and the slurry is used as the fiber of the insulating fiber 12. It can be obtained by supplying to a bundle or the like by dipping or other known method and impregnating and holding it, followed by curing under conditions according to the type of the organic polymer material. According to this method, the precursor can be obtained with a simple configuration, and there is an advantage that the degree of freedom in molding such as a molding shape is high. Moreover, according to this method, the precursor which provided the organic polymer material and the electroconductive particle 4 along the insulating fiber 12 can be produced easily.

  In order to adjust the compounding ratio of the conductive particles 4 in the conductor phase 14, it can be adjusted by the concentration of the conductive particles 4 in the molding raw material such as slurry. In order to increase the blending ratio of the conductive particles 4 in the conductor phase 14, it is necessary to disperse the particles in a high concentration in the uncured organic polymer material. An organic solvent can be used to suppress an increase in viscosity of the molecular material. The organic solvent only needs to be compatible with the uncured polymer material. For example, methyl ethyl ketone, acetone, styrene monomer, and the like can be selected. On the other hand, when the blending ratio of the conductive particles 4 in the organic phase 10 is low, it is not necessary to use an organic solvent.

  When the conductive path 6 is formed by the conductive particles in the conductor phase 14, the blending ratio of the organic polymer material and the conductive particles 4 in the molding raw material is the conductive particles 4 with respect to the total amount (volume) thereof. Of 1 vol. % Or more is preferable. 1 vol. If it is less than%, it is difficult to obtain a continuous contact structure with the conductive particles 4, and the occurrence of the residual resistance phenomenon cannot be expected. More preferably, 3 vol. % Or more. In the case where the insulating coating layer 16 is formed of an organic polymer material together with the conductor phase 14, the blending ratio of the conductive particles 4 may be increased to 100 vol%. Although this molding raw material itself does not contain an organic polymer material, the conductive particles 4 become porous at the time of heat treatment, and the organic polymer material of the outer peripheral coating layer 16 provided after the heat treatment penetrates part or all of the material. As a result, they form the coating layer 16 and the organic phase 10 around the conductive particles 4 to hold the conductive paths 6 of the conductive particles 4. As described above, when increasing the blending ratio of the conductive particles, it is necessary to add an organic solvent. However, from the viewpoint of reducing the amount of the organic solvent added, more preferably 3 vol. % To 60 vol. %, More preferably 3 vol. % -30 vol. %.

  Next, this molded body is heat-treated. By thermally decomposing the organic polymer material in the heat treatment, the organic phase 10 is formed and the conductor phase 14 is formed. The conditions for the heat treatment are preferably a temperature and a time at which the organic polymer material is thermally decomposed. While the organic polymer material is thermally decomposed, the pyrolyzate undergoes carbonization, grafting, cyclization, aromatization, condensation, polymerization, and the like, resulting in a change in composition and simultaneously a residual tensile stress. According to the present inventors, it is inferred that the change due to the heat treatment contributes to the expression of the residual resistance phenomenon in the conductive path 6 in the low strain region.

  In addition, when the precursor provided with the organic polymer material and the conductive particles 4 along the insulating fiber 12 is heat-treated, tensile stress may remain in the organic phase 10 along the direction of the insulating fiber 12. It can be assumed that such residual tensile stress contributes to the expression of the residual resistance phenomenon in the low strain region.

  In this heat treatment, when the molded body includes the conductive particles 4, the conductor phase 14 having the conductive path 6 by the continuous contact structure of the conductive particles 4 can be formed together with the organic phase 10. On the other hand, when the molded body does not include the conductive particles 4, the conductor phase 14 composed of a part or the whole of the organic phase 10 can be formed.

  In the heat treatment, the conductivity of the organic phase 10 can be adjusted. If the progress of carbonization or graphitization is promoted in the organic phase 10, the organic phase 10 can be made into a conductor, and by suppressing the progress of graphitization, the formation of the conductor can be suppressed and the insulation can be maintained. As described above, in order for the conductive path 6 by the conductive particles 4 to function effectively, it is preferable that the organic phase 10 has high resistance, that is, is insulating. The heat treatment conditions for this vary depending on the organic polymer material used, but the heat treatment temperature is preferably 2000 ° C. or lower, more preferably 1000 ° C. or lower, and even more preferably 600 ° C. or lower. On the other hand, in order to convert the organic phase 10 into a conductor, the heat treatment temperature is preferably 600 ° C. or higher, more preferably 1000 ° C. or higher, even more preferably 2000 ° C., although it depends on the organic polymer material used. That's it.

  In the heat treatment, an atmosphere in which oxygen is present or an inert atmosphere from which oxygen is excluded may be used. However, if an inert atmosphere is obtained by heat treatment in an inert atmosphere such as nitrogen or argon, an organic polymer material is used. The disappearance of carbon in the organic phase 10 can also be suppressed, and the organic phase 10 having a stable composition and form can be obtained. On the other hand, by conducting a heat treatment in an atmosphere in which oxygen is present, a part of carbon is eliminated from the organic phase 10 to change the composition and form of the organic phase 10 to obtain a preferable conductive form.

  In the case where the sensing material 3 includes the insulating coating layer 16, the insulating coating layer 16 can be formed on the surface of the sensing material 3. As described above, the insulating coating layer 16 can be obtained by supplying an insulating polymer material to the surface of the sensing material 3 and curing it. When applying the insulating coating layer 16, it is possible to employ a 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. However, the same dipping method as in the precursor molding can also be adopted. When the insulating fiber 16 is included in the insulating coating layer 16, for example, after the fiber bundle or cloth of the insulating fiber 16 is dipped on the polymer material to hold the polymer material, the insulating material 16 is surrounded by the surroundings of the sensing material 3. And then heat-cured.

  In the case of forming the heat-insulating insulating coating layer 16, after the molded body is formed and before the heat treatment, the polymer material of the insulating coating layer 16 is supplied to the outer periphery of the molded body and cured, and then the coating is applied. The molded body comprising the layer 16 can also be heat treated as described above. By doing so, the organic polymer material phase of the molded body and the coating layer 16 can be heat-treated simultaneously. However, in this case, it is preferable to form an insulating coating layer 16 that is not heat-treated on the surface layer side so as to ensure water resistance. In this case, as already described, the organic phase 10 is formed around the conductive particles 4 even when the molded body is composed of only the conductive particles 4 without containing the organic polymer material. Can do.

  According to such a precursor heat treatment step, a conductor phase 14 including an organic phase obtained by heat-treating an organic polymer material phase can be formed, and a sensing material 3 having a sensing function for detecting a maximum strain can be obtained. Can do. Moreover, a structure to which such a sensing material 3 is attached can be obtained.

(Strain sensor)
As shown in FIG. 2, the strain sensor 2 can be obtained by installing the electrode 20 on the sensing material 3. The electrode 20 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 can be selected as the fixing method. It is possible to fix by using a crimping terminal. In addition, 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 may include a polymer material, a method that can be fixed at a temperature lower than the heat resistant temperature is preferable.

  The strain sensor 2 generates a change in conductivity according to the magnitude of the strain applied to the conductor phase 14 and can retain at least a part of the change in conductivity generated by the applied strain. For this reason, it can be said that the strain sensor 2 has a function in which the conductor phase 14 permanently retains the change in conductivity with respect to the maximum strain and the sensor itself stores information on the maximum strain. Therefore, the maximum strain that has acted on the structure is stored and stored in the installed strain sensor 2 itself, and it is necessary to perform continuous measurement, data storage and analysis with a measurement device always connected to this sensor. Therefore, the maximum strain that the strain sensor 2 has received so far can be known by accessing the strain sensor 2 and measuring the conductivity of the strain sensor and the like at appropriate times.

In the strain sensor 2, since the conductor phase 14 including the organic phase 10 obtained by heat-treating the organic polymer material phase is retained, the residual rate of the amount of change in conductivity is increased. The maximum strain can be stored in the area. That is, the closer the numerical value of the change in conductivity after strain removal is to the value of the change in conductivity at the time of strain action, the more accurately the maximum strain can be detected regardless of the strain action state. As an index indicating the storage performance of the maximum strain, a residual ratio and a strain detection lower limit are defined. This residual ratio is the ratio of the amount of change in conductivity (ΔR _res ) remaining after strain removal to the amount of change in conductivity (ΔR _max ) at the time when the maximum strain is applied to the strain sensor 2, and ΔR _res / ΔR _max It is defined that the storage accuracy is higher as the residual ratio is closer to 100%. The strain detection lower limit is defined as the minimum limit of strain necessary to show this residual resistance phenomenon, and the lower the strain detection lower limit, the higher the sensitivity to strain. In the strain sensor 2, the residual ratio of the amount of change in conductivity is preferably 60% or more, more preferably 80% or more, and further preferably 90% or more. Most preferably, it is 95% or more. Further, the strain detection lower limit of the strain sensor 2 can detect and store a strain from a strain region of preferably 0.05% or less. The strain detection lower limit is more preferably 0.02% or less.

  The strain sensor 2 can take various forms based on the form of the sensing material 3 and the like. For example, a rod shape, a plate shape, a film (sheet) shape, a tube shape, or a designed two-dimensional or three-dimensional shape can be adopted. One preferred form is a sheet-like body. By constructing a sheet-shaped strain sensor 2, not only can it be attached to the surface of a steel structure or a concrete structure when constructing a new structure, but it can also be attached to the surface of an existing structure. The maximum strain of the structure can be measured. For surface mounting on the structure, a method using an adhesive or a method using a mechanical jig such as a screw can be selected. The sheet-like strain sensor 2 is a preferable form particularly in application to an existing structure.

  Moreover, a rod-shaped body can be mentioned as another preferable form of the strain sensor 2. By using the strain sensor 2 of a rod-shaped body, it can be easily embedded in the structure. That is, when constructing a new structure, for example, a strain that can be embedded in a concrete structure and also has a reinforcing function of the structure by using high-elasticity and high-strength long fiber reinforced plastics for the insulating coating layer 16. The sensor 2 can be provided.

(Distortion detection method)
In order to detect the strain of the structure, the strain sensor 2 is installed on the structure to be measured. Thereby, a structure provided with the sensor is provided. Although the material of the structure used as object is not specifically limited, Steel structure structures, such as a concrete structure and a steel frame structure, are mentioned as an example in a social infrastructure structure. The structure to be measured is not limited to a building, and is not limited as long as it has utility such as safety and function confirmation by measuring strain. Therefore, it is a preferable measurement target structure not only for metal materials and composite materials constituting the fuselage and tail of an aircraft, but also for drive-related members in moving bodies such as ships and vehicles, and for drive-related members in various industrial devices.

  When embedding in concrete, it can also be applied to a structure with a pretension applied to the sensing material. This pretension may lead to improvement of the maximum strain memory function and contributes to improvement of the strength characteristics of the concrete structure. A concrete structure has a high strength against compressive deformation but a low strength against tensile deformation. Generally, the tensile strength is improved by introducing a reinforcing bar into the concrete structure, but it is embedded with a pre-tension applied to the reinforcing bar and the tension is released after the concrete is hardened. As a result, compressive stress acts on the concrete, and the strength against tensile deformation can be improved.

  The direction in which the strain sensor 2 is installed on the measurement target can be measured with higher sensitivity by matching the measurement direction of the conductivity of the conductive composite material with the strain direction assumed to act on the structure. Can be expected to do.

  A method for measuring the conductivity or resistivity of the strain sensor 2 is not particularly limited, and examples thereof include a two-terminal method and a four-terminal method. The resistivity of the sensing material 3 varies depending on the material and heat treatment conditions. However, when the resistivity is relatively high, measurement by the two-terminal method is possible, and when the resistivity is relatively low, the four-terminal method is used. In some cases, it may be necessary to measure this.

  As an embodiment of monitoring in the structure in which the strain sensor 2 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 memory type sensor is installed, since the sensor itself has a function of storing information on the maximum strain, there is nothing other than this sensor such as a measurement system and a data storage device. It is not necessary to always install it, and monitoring is possible by carrying a measuring instrument regularly 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.

  Therefore, according to the strain sensor 2, it is possible to obtain information on the maximum value of the strain that has acted in the past only by measuring the conductivity of the sensor periodically or as necessary. 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.

  The best mode for carrying out the present invention has been described with reference to the embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention. Of course, it can be implemented in the form.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below 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.

  In the following examples, a strain sensor having a sensing material having a conductive path made of conductive particles and heat-treating a polymer material constituting the organic phase thereof is manufactured, and a verification test by a tensile test of the strain sensor is performed. It was.

(1) Fabrication of strain sensor and performance verification test by tensile test [fabrication of strain sensor]
The structural schematic diagram of the strain sensor 2 produced in this example is as shown in FIG.
The strain sensor 2 has a rod shape as a whole, and has an electrode 20 on a sensing material 3 composed of a conductive path 6 of carbon particles, an organic phase 10 and an insulating coating layer 16.

  Hereinafter, the manufacturing process of the strain sensor 2 will be described. First, the conductive particles 3 are dispersed in a liquid organic polymer molding material. 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, which is an organic polymer molding material, using a stirring deaerator. The volume ratio of carbon to be dispersed is 5, 30, 60 and 100 vol. %. 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, except for the case of 5 vol.% Or less, 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 organic solvent is premised on volatilization in the heat curing process. The organic polymer molding material in which the conductive particles are dispersed is impregnated and held in glass fibers (fiber diameter: 16 μm, number: about 2000), and cured under the conditions of 160 ° C. and 90 minutes. A precursor was obtained.

  Furthermore, the coating layer is impregnated with the same liquid thermosetting epoxy resin as that used to form the precursor, except that the glass fiber (fiber diameter: 16 μm, number: about 2000) does not contain carbon particles. It was adhered to the periphery of the composite material and cured by heating (160 ° C., 90 minutes). Note that the precursor in which the dispersion ratio of carbon particles is 100 vol.% Is composed of carbon whose organic phase contains many voids, and the epoxy resin component penetrates into the voids during the formation process of this coating layer. It is thought that.

  The molded body in which the precursor is further coated with the resin layer is introduced into a degreasing furnace, and kept in a nitrogen atmosphere at temperatures of 300 ° C. and 500 ° C. for 5 hours, respectively, and subjected to heat treatment to obtain conductive particle concentration and Various sensing materials with different heat treatment conditions were prepared. In addition, the sensing material operated similarly to the sensing material 3 of these Examples was also produced except not heat-processing as a comparative example.

  These various sensing materials 3 were cut into a predetermined length (250 mm), and then electrodes 20 were installed at both ends thereof to obtain a strain sensor 2. A method of fixing the lead wire with a conductive paste was adopted for this electrode.

  In the present embodiment, in order to perform a tensile test on the strain sensor 2, as shown in FIG. The grip portion 30 is made of steel and has a hollow shape. The steel pipe and the composite material were firmly fixed by introducing the strain sensor 2 into this and pouring and hardening a cement-type expansion material into the gap.

(2) Performance demonstration test by tensile test of strain sensor A tensile strain was repeatedly applied to the produced strain sensors of Examples and Comparative Examples, and the change in conductivity was measured to evaluate the maximum strain memory function.

[Test method]
A tensile test was performed on the produced 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 strain sensor is fixed by applying a compressive force to the grip portion. After the strain sensor is gripped, 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 measured by the two-terminal method. did. In this tensile test, the load applied to the maximum strain memory type sensor was measured with a load cell, and the applied tensile strain was measured with an extensometer. In all the experimental results shown in this example, this change in conductivity is shown as a resistance change rate ΔR / R ₀ obtained by dividing the resistance change ΔR = RR ₀ at the time of stress by the initial resistance value R ₀ . 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. 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.

[Test results]
The dispersion ratio of the carbon particles is 5 vol. Three types of composite materials, those not heat-treated and those heat-treated at 300 ° C. and 500 ° C., were synthesized and subjected to repeated tensile tests. The results are shown in FIGS. In each of these figures, the tensile strain applied to each composite material and the measured resistance change rate are shown as a function of time in (a), and the relationship between the applied tensile strain and the resistance change rate is shown as (b) )Pointing out toungue. From this result, in the case where heat treatment is not performed, although the resistance change is shown according to the action of the tensile strain, the resistance change reversibly returns to the initial value in the unloading process, and in FIG. It has become. That is, the phenomenon that brings about the function of the maximum strain memory is not shown. On the other hand, when heat treatment at 300 ° C. is performed, a residual resistance phenomenon in which a resistance change remains after unloading is developed. Further, by increasing the heat treatment temperature to 500 ° C., extremely remarkable residual resistance is exhibited. The phenomenon was successfully expressed. Thereby, in the function of time shown in (a), the resistance change changes stepwise according to the magnitude of the maximum strain applied, and in the relationship with the tensile strain shown in (b), the increased resistance change rate. However, the change in resistance remained almost unchanged even when the strain recovered elastically. When this residual rate (residual resistance change rate after unloading / maximum resistance change rate at the time of loading) is obtained, it can be seen that it has reached about 94%. This very high residual rate makes it possible to store and measure the maximum strain that has been applied with high accuracy regardless of the presence or absence of residual deformation (strain).

  Further, FIG. 7 shows the result of expanding the response in the low strain region based on the result of FIG. 6 (heat treatment temperature 500 ° C.). From this result, the residual resistance phenomenon can be exhibited even for a very low strain peak value of 0.02% (200 με) or less, and it has extremely excellent characteristics from the viewpoint of the strain detection sensitivity. It became clear to have. This is important as a result showing the possibility of storing and diagnosing the strain history before the occurrence of cracking, for example, since the cracking strain in concrete is several hundred με. From the above results, it was found that the polymer material constituting the organic phase including the continuous path of the conductive particles can be subjected to heat treatment, so that a remarkable residual resistance phenomenon can be exhibited, and an excellent maximum strain memory function is achieved. It was clarified that it could be achieved.

  FIG. 8 shows the volume ratio of the conductive particles to be dispersed as 5, 30, 60 and 100 vol. The heat treatment is performed on the composite material in%, and the result of the repeated tensile test is shown for the composite material after the heat treatment. The relationship between the tensile strain applied to each composite material and the rate of resistance change is shown. From this result, a remarkable residual resistance phenomenon was obtained at each particle volume ratio. As a point to be noted here, when the respective residual ratios are compared, 5 vol. In the case of%, it is 94%, whereas 30 vol. %, 84%, 60 vol. %, It is slightly reduced to 84% and 100 vol. % Recovered slightly to 91%, but as a result, 5 vol. % Indicates that the memory function is the highest. This 5 vol. The volume ratio of% is a limit ratio that can be dispersed in the resin without adding a solvent, and the fact that a solvent-free synthesis process can be applied is important for stabilizing the characteristics in the actual production process. The result. The volume ratio of the conductive particles is 3 vol. Attempts were made to synthesize composite materials reduced to less than or equal to%, but good electrical conductivity could not be obtained, and a stable residual resistance phenomenon could not be obtained even in the results of tensile tests.

It is a structure schematic diagram of a strain sensor. It is a schematic diagram of the strain sensor for tensile tests. It is a schematic diagram of the evaluation system used for the test. The figure which shows the result of having evaluated the presence or absence of heat processing, and the dependence of temperature, as a result of the repeated tensile test which increased the peak load among the test results implemented about the sensor which is not heat-treated. The figure which shows the result of having evaluated the presence or absence of heat processing, and the dependence of temperature which is a result of the repeated tensile test which increased the peak load among the test results implemented about the sensor of heat processing temperature 300 degreeC. The figure which shows the result of having evaluated the presence or absence of heat processing, and the dependence of temperature which is a result of the repeated tensile test which increased the peak load among the test results implemented about the sensor of heat processing temperature 500 degreeC. The figure which shows the result of having expanded the low strain area | region in the repeated tension test result which increased the peak load about the sensor heat-processed at the heat processing temperature of 500 degreeC of FIG. The figure which shows the result of having evaluated the dependence of the volume ratio of the electroconductive particle to disperse | distribute as a result of the repeated tensile test which increased the peak load gradually among the test results implemented in the Example.

Explanation of symbols

2 Strain sensor, 3 Sensing material, 4 Conductive particle, 6 Conductive path, 10 Organic phase, 12 Insulating fiber, 14 Conductor phase, 16 Coating layer, 18 Insulating fiber, 20 Electrode, 30 Grip part

Claims (18)

A strain sensor,
Insulating fibers arranged with a certain directionality;
An organic phase obtained by heat-treating an organic polymer material at least along the insulating fiber; and
A conductor phase comprising at least a portion of the organic phase;
A strain sensor.   The strain sensor according to claim 1, wherein the conductor phase has a conductive path having a continuous contact structure of a large number of conductive particles.   The strain sensor according to claim 1, wherein the conductor phase includes the organic phase having conductivity.   The strain sensor according to claim 1, wherein the conductor phase includes only the organic phase.   The strain sensor according to claim 1, wherein residual stress due to heat treatment of the organic polymer material acts on the organic phase.   The strain sensor according to claim 1, wherein the organic phase is obtained by heat-treating the organic polymer material in an inert atmosphere.   The strain sensor according to claim 1, wherein the heat treatment is performed at a temperature equal to or higher than a temperature at which the organic polymer material is thermally decomposed.   The strain sensor according to claim 1, further comprising an insulating coating layer on a surface layer side.   The strain sensor according to claim 1, wherein at least 80% or more of the change in conductivity is retained.   The strain sensor according to claim 1, wherein the strain change amount corresponding to the maximum strain applied to the strain sensor is retained.   The strain sensor according to any one of claims 1 to 10, which is a sheet-like body or a rod-like body. A strain sensing material,
Insulating fibers arranged with a certain directionality;
An organic phase obtained by heat-treating an organic polymer material at least along the insulating fiber; and
A conductor phase comprising at least a portion of the organic phase;
A strain sensing material comprising: A method for manufacturing a strain sensor, comprising:
Comprising a step of heat-treating a molded body of an organic polymer material containing conductive particles and having insulating fibers arranged in a certain direction,
In the heat treatment step, a conductor phase having an organic phase obtained by heat-treating the organic polymer material and a conductive path by a continuous contact structure of the conductive particles is formed. A method for manufacturing a strain sensor, comprising:
It includes a step of heat-treating a molded body of an organic polymer material in which insulating fibers are arranged with a certain direction,
A manufacturing method, wherein in the heat treatment step, a conductor phase comprising a part or the whole of an organic phase obtained by heat-treating the organic polymer material is formed.   The method for manufacturing a strain sensor according to claim 13 or 14, wherein the heat treatment is performed in an inert atmosphere.   A strain sensor obtained by the method according to claim 13. A distortion detection method,
A structure provided with the strain sensor according to any one of claims 1 to 11, comprising a step of detecting conductivity in the strain sensor.   A structure equipped with the strain sensing material according to claim 12.

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