KR102776130B1 - composition for fiber reinforced composite materials having crack detection using color changeableness, fiber reinforced composite comprising the same and method of crack detection of structures using the same - Google Patents

Abstract

The present invention relates to a composition for a fiber-reinforced composite material capable of damage detection, a structural safety diagnosis system comprising the same, and an analysis method for a structural safety diagnosis system using the same. The fiber-reinforced composite material of the present invention provides excellent mechanical properties, and at a desired inspection point in time for a structure using the same, the state of damage and the degree of cracking of the structure caused by external force can be easily and accurately confirmed in an effective, economical, and easy manner by monitoring color changes through photographs using the same or a drone.

Description

Composition for fiber reinforced composite materials having crack detection using color changeableness, fiber reinforced composite comprising the same and method of crack detection of structures using the same

The present invention relates to a composition for a fiber-reinforced composite material, a fiber-reinforced composite material comprising the same, and a damage diagnosis method for a structure using the same. More specifically, the present invention relates to a system for structural safety diagnosis using a fiber-reinforced composite material that exhibits color change when damaged or broken by an external force, and a method for analyzing the same.

Fiber-reinforced plastics (hereinafter referred to as "FRP") composites are composite materials that are hardened by mixing fibers and thermosetting resins. FRP composites have excellent corrosion resistance, are lighter than aluminum, and have higher specific strength than steel. In advanced countries, they are widely used in processes in almost all industrial fields, including construction, petrochemicals, leisure, automobiles, environmental industries, and even high-tech industries. In particular, their use in the manufacture of large structures such as automobiles and wind turbine blades is also increasing.

These fiber-reinforced composite materials are manufactured by continuously impregnating thermosetting resin and reinforcing fibers to produce a prepreg in order to secure high strength. However, although the prepreg has a high flexural modulus, when applied to large structures, it has a problem in that it does not properly absorb external impact and instead transmits it, making it easily damaged or broken.

In particular, among large structures, the blades of wind turbines are rotating structures, so they are highly susceptible to damage from external environmental conditions. If the damage/cracks caused by various external environmental conditions are left as they are, the cracked portion may fall off, causing secondary damage to nearby houses or people. In addition to the reduction in efficiency of wind power generation due to blade damage, in severe cases, the wind turbine itself may have to be replaced, resulting in a large loss.

In order to maintain such large structures, it is most important to accurately diagnose the damaged area, but most existing technologies are only interested in how to repair blades or how to reinforce the strength of fiber-reinforced composite materials so that they are not easily damaged, and do not focus on how to diagnose the damage. Therefore, the present invention has tried to develop a new technology that can easily and conveniently measure whether a structure is damaged when an external load is applied to the structure, and has completed a method that can easily diagnose and monitor the safety of the structure by observing the color change.

Patent Document 1. Republic of Korea Patent Publication No. 10-2013-0011774

The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a composition for a fiber-reinforced composite material capable of damage detection.

Another object of the present invention is to provide a fiber-reinforced composite material having improved mechanical properties and capable of diagnosing damage through color changes.

Another object of the present invention is to provide a system for structural safety diagnosis that can easily and conveniently diagnose damage through color changes and an analysis method of the system for structural safety diagnosis using the same.

In order to achieve the above-mentioned purpose, the present invention provides a composition for a fiber-reinforced composite material, which comprises 10 to 40 parts by weight of a curing agent per 100 parts by weight of a thermosetting resin; and 0.1 to 4 parts by weight of a red pigment or red disperse dye; and which enables the presence of damage to be determined through a change in color when physical damage occurs due to an external force.

The composition for the above fiber-reinforced composite material may include 25 to 35 parts by weight of a curing agent per 100 parts by weight of a thermosetting resin; and 0.13 parts by weight of a red pigment or a red disperse dye.

The above thermosetting resin may be a bisphenol A type epoxy resin.

The above curing agent may be at least one selected from the group consisting of an aliphatic amine curing agent, an amidoamine curing agent, and a phenalkamine curing agent.

The above pigment may be a high chroma magenta pigment (Cinquasia® Magenta D 4570).

In order to achieve the above-mentioned purpose, the present invention provides a fiber-reinforced composite material capable of damage detection, including reinforcing fibers; and a composition for the fiber-reinforced composite material.

The above fiber-reinforced composite material may be manufactured by impregnating the reinforcing fiber into the composition for the fiber-reinforced composite material.

The above reinforcing fiber may be at least one selected from the group consisting of glass fiber, natural fiber, metal fiber, ultra-high molecular weight polyethylene fiber, polyacrylonitrile fiber, arylate fiber, polyetheretherketone fiber, rayon fiber, basalt fiber, aromatic polyamide fiber, polyaramid fiber, alumina fiber, and boron fiber.

The above fiber-reinforced composite material may experience color change in the affected area when physically damaged by external force.

The above color change may be a decrease of 40% to 50% in CMYK chromaticity values or RGB chromaticity values.

In order to achieve the above-mentioned purpose, the present invention provides a structural safety diagnosis system including the fiber-reinforced composite material, wherein a color change occurs when force, stress or deformation is applied to the fiber-reinforced composite material, and the color change is measured by examining RGB chromaticity values or CMYK chromaticity values from an optical image of the fiber-reinforced composite material.

In order to achieve the above-mentioned object, the present invention provides a method for analyzing a structural safety diagnosis system including the fiber-reinforced composite material, the method comprising: i) a step of capturing an image of a structural safety diagnosis system including the fiber-reinforced composite material of claim 11 by using a camera; ii) a step of extracting an RGB chromaticity value or a CMYK (Cyan, Magenta, Yellow, Key) chromaticity value from the image; and iii) a step of deriving damage information of the structural safety diagnosis system based on the extracted chromaticity value.

In step i) above, the distance between the system for structural safety diagnosis and the camera can be 15 cm to 1 m.

In the above step ⅲ), if the color value decreases by 30 to 50% or more compared to the initial color value, it may be judged to be damaged.

The composition for a fiber-reinforced composite material according to the present invention has superior strength to a prepreg in which a conventional thermosetting resin is used as a matrix and reinforcing fibers are impregnated, and can induce color change depending on damage.

Therefore, the fiber-reinforced composite material of the present invention provides excellent mechanical properties, and at the desired inspection point in a structure using the same, the color change can be monitored with the naked eye or through photographs taken by a drone, thereby enabling the damage status and degree of cracking of the structure caused by external force to be easily and accurately confirmed, effectively, economically, and easily.

In addition, structures constructed with the fiber-reinforced composite material of the present invention can be easily diagnosed for damage and cracks by visual inspection or RGB/CMYK numerical change measurements, thereby providing an economical damage detection method for a wide area along with high strength.

Figure 1 shows the results of CMYK analysis before (Wetted) and after (Cured) curing for fiber-reinforced composite materials (base, red, green, blue, black).
Figure 2 is a photograph of the compositions for fiber-reinforced composite materials of Examples 1-3 to 2-3 and Comparative Examples 1 to 3.
Figure 3 shows FT-IR graphs (a) and chemical structures (be) of three dyes (Dispersion Dye Red 1, Acid Red 299, Remazol Red RB-133) and a pigment (Cinquasia® Magenta D4570).
FIG. 4 is a photograph (top) of the compositions for fiber-reinforced composite materials of Examples 1-1 to 1-5 and Examples 2-1 to 2-5 and the results of analysis of each using an optical microscope (bottom).
Figure 5 is an FT-IR analysis graph of the fiber-reinforced composite material compositions of Comparative Example 1 (Neat) and Examples 1-1 and 2-1 before curing and after curing.
Figure 6 is a graph showing changes in the glass transition temperature (T _g ) of fiber-reinforced composite materials of Comparative Example 1 (Neat), Examples 1-1 to 1-5, and Examples 2-1 to 2-5.
FIG. 7a is a graph showing the tensile strength and yield strength of a single film manufactured from the compositions for fiber-reinforced composite materials of Examples 1-1 to 1-5, and FIG. 7b is a graph showing the tensile strength and yield strength of a single film manufactured from the compositions for fiber-reinforced composite materials of Examples 2-1 to 2-5.
FIG. 8 is a graph showing the bending strength and impact strength (Izod impact strength) of a single film manufactured from the composition for fiber-reinforced composite materials of Examples 1-1 to 1-5 and Examples 2-1 to 2-5.
FIGS. 9a to 9d are optical microscope photographs of the fiber-reinforced composite material (GF/P-epoxy) of Example 3 (a), the fiber-reinforced composite material (GF/D-epoxy) of Example 4 (b), the fiber-reinforced composite material (CF/P-epoxy) of Example 5 (c), and the fiber-reinforced composite material (CF/D-epoxy) of Example 6 (d).
Figure 9e is a graph of tensile strength and flexural strength for the fiber-reinforced composite material (GF/P-epoxy) of Example 3, the fiber-reinforced composite material (GF/D-epoxy) of Example 4, and the fiber-reinforced composite material (GF/epoxy) of Comparative Example 4.
FIG. 9f is a graph of tensile strength and flexural strength for the fiber-reinforced composite material (CF/P-epoxy) of Example 5, the fiber-reinforced composite material (CF/D-epoxy) of Example 6, and the fiber-reinforced composite material (CF/epoxy) of Comparative Example 5.
Figure 10 shows a photograph (left) and an enlarged image (right) of the fiber-reinforced composite material (GF/p-epoxy) of Example 3 and the fiber-reinforced composite material (GF/epoxy) of Comparative Example 4 to which a bending load of 400 N was applied.
Figure 11a is a drawing schematically illustrating the principle of observing color change when a fiber-reinforced composite material according to the present invention is damaged by an external force (load).
FIG. 11b is a fiber-reinforced composite material of Example 3 before being damaged, FIG. 11c is a fiber-reinforced composite material of Comparative Example 4 before being damaged, FIG. 11d is a fiber-reinforced composite material of Example 3 that has been torsionally damaged, FIG. 11e is a fiber-reinforced composite material of Comparative Example 4 that has been torsionally damaged, FIG. 11f is a fiber-reinforced composite material of Example 3 that has been bending damaged, and FIG. 11g is a photograph of a fiber-reinforced composite material of Comparative Example 4 that has been bending damaged.
Figure 12 is a photograph taken to compare color changes when the fiber-reinforced composite material of Example 3 and the fiber-reinforced composite material of Comparative Example 4 were subjected to ⅱ bending damage, ⅲ tensile damage, and ⅳ wear damage.
Figure 13 is a photograph of the fiber-reinforced composite material of Example 3 taken at various shooting distances.
Figure 14 is a graph showing the results of RGB analysis from photographs of the fiber-reinforced composite material of Example 3 taken at various shooting distances.
Figure 15 is a graph showing the change in CMYK values according to the type of damage in the fiber-reinforced composite material of Comparative Example 4 (left) and the fiber-reinforced composite material of Example 3 (right).
Fig. 16 is a graph visually dataifying the color change at a defective portion of a fiber-reinforced composite material of Example 3 after the fiber-reinforced composite material of Example 3 is damaged by various flexural stresses. The lower left of Fig. 16 is the result of converting the image to black and white to check the degree of damage in contrast.
Figure 17 is a graph and photograph visually dataifying the color change at a defective site after a pure fiber-reinforced composite material (Comparative Example 4) without pigment was damaged by various flexural stresses.
Figure 18 is a schematic diagram illustrating a method for analyzing damage in a structure using fiber-reinforced composite materials.

Below, various aspects and various implementation examples of the present invention are described in more detail.

One aspect of the present invention provides a composition for a fiber-reinforced composite material capable of damage detection, comprising 10 to 50 parts by weight of a curing agent per 100 parts by weight of a thermosetting resin; and 0.1 to 4 parts by weight of a red pigment or red disperse dye.

According to one embodiment of the present invention, when the composition for the fiber-reinforced composite material includes 25 to 35 parts by weight of a curing agent and 0.13 parts by weight of a red pigment or a red disperse dye per 100 parts by weight of a thermosetting resin, the mechanical properties of the fiber-reinforced composite material are improved, so that the tensile strength and impact strength, etc. are improved, and the color expression is excellent, so that color change can be easily diagnosed in a damaged state, which is preferable.

The thermosetting resin may be at least one selected from among nylon resin, polyethylene resin, polypropylene resin, polybutylene resin, polyester resin, polyurethane resin, polyacrylic resin, styrene butadiene resin, vinyl resin, polycarbonate resin, polysulfone resin, polyethersulfone resin, polyvinyl butyral resin, polyvinyl formal resin, polyvinylacetate resin, polystyrene resin, styrene divinylbenzene resin, fluorine resin, acrylic resin, silicone resin, epoxy resin, amino resin, and phenol resin, but is preferably an epoxy resin.

The above epoxy resin may be used without limitation as long as it is a conventional thermosetting resin, and preferably may be selected from biphenyl-based epoxy resin, bisphenol A epoxy resin, bisphenol F epoxy resin, cresol novolac epoxy resin, phenol novolac epoxy resin, tetrafunctional epoxy resin, triphenolmethane-type epoxy resin, alkyl-modified triphenolmethane-type epoxy resin, naphthalene-type epoxy resin, dicyclopentadiene-type epoxy resin, and dicyclopentadiene-modified phenol-type epoxy resin, and more preferably, bisphenol A-type epoxy resin.

Examples of commercially available products related to the above epoxy resin include KFR140 or KFR 120V from Kukdo Chemical.

The curing agent usable in the composition for the above fiber-reinforced composite material may be at least one selected from the group consisting of an amine-based curing agent, an acid anhydride-based curing agent, an amide-based curing agent, and a phenol-based curing agent, but it is preferable to use an amine-based curing agent that has the effects of low linear expansion and improved heat resistance when mixed with an epoxy resin and a red pigment/dispersant.

Examples of commercially available products related to the above hardener include Kukdo Chemical's KFH180 or KFH163.

The pigment or disperse dye in the present invention may have an average diameter of 1 to 10 ㎛, preferably 1 to 5 ㎛. If the average diameter is outside the above range, problems such as agglomeration or inability to secure uniform dispersion may occur, and therefore it is preferable that the average diameter satisfies the above range.

The pigment in the present invention is intended to mean red particles of any shape, and the particles may be uniformly dispersed by mixing with an epoxy resin in a composition in which the particles exist.

The above pigment may be appropriately selected from organic pigments and mineral pigments known in the art as long as it is a red pigment, and is not particularly limited thereto.

The red pigment according to the present invention may be an organic pigment. The organic pigment may be selected in particular from nitroso, nitro, azo, xanthene, pyrene, quinoline, anthraquinone, triphenylmethane, fluorane, phthalocyanine, metal complexes, isoindolinone, isoindoline, quinacridone, perinone, perylene, diketopyrrolopyrrole, indigo, thioindigo, dioxazine, triphenylmethane and quinophthalone compounds.

In particular, the organic pigment may preferably be at least one selected from the group consisting of red pigments coded in the color index with the names CI 12085, 12120, 12370, 12420, 12490, 14700, 15525, 15580, 15620, 15630, 15800, 15850, 15865, 15880, 17200, 26100, 45380, 45410, 58000, 73360, 73915 and 75470, more preferably, the product Cinquasia® Magenta D4570 sold by BASF may be used.

The above red dye is preferably a dispersion dye because it has excellent miscibility with epoxy resin and can implement an excellent red color without precipitation. The above disperse dye may be at least one selected from the group consisting of benzene azo, heterocyclic azo, azothraquinone, and condensed disperse dyes, more preferably a heterocyclic azo disperse dye can be used, and most preferably a Dispersion Dye Red 1 (DIANIX Red S-G) product sold by DyStar.

The composition for the above fiber-reinforced composite material can be mixed according to a conventional mixing method, and each component can be melt-mixed to produce a pellet form.

In addition, the present invention can provide a cured product manufactured using the composition for a fiber-reinforced composite material described above. The cured product according to the present invention exhibits excellent flexibility such as tensile strength along with improved impact resistance.

In addition, the cured product according to one embodiment of the present invention has a significantly higher increase rate in tensile strength, yield strength, flexural strength, and impact strength when a red pigment is used than when a disperse dye is used. Specifically, when a disperse dye is used, almost no improvement in mechanical properties is observed, but when a red pigment is used, the mechanical properties significantly increase by about 10% or more, while having the advantage of excellent color implementation and easy observation of color change due to damage. Therefore, it is more preferable that the cured product of the present invention be produced using a composition for a fiber-reinforced composite material comprising 10 to 50 parts by weight of a curing agent and 0.1 to 4 parts by weight of a red pigment or red disperse dye per 100 parts by weight of a thermosetting resin, preferably 25 to 35 parts by weight of a curing agent and 0.1 to 0.2 parts by weight of a red pigment or red disperse dye per 100 parts by weight of a thermosetting resin, and it is most preferable that it comprises 25 to 35 parts by weight of a curing agent and 0.13 parts by weight of a red pigment or red disperse dye per 100 parts by weight of a thermosetting resin.

The glass transition temperature (Tg) of the cured product of the above fiber-reinforced composite material is 90 to 100°C. Since the glass transition temperature exists within the above range, there is an advantage in that it can be applied to not only aircraft parts or automobile materials requiring heat resistance, but also composite materials for rotary blades of wind turbines.

The above-mentioned cured product may have a tensile strength of 2500 MPa or more as measured according to the method of ASTM D638. Specifically, the tensile strength of the above-mentioned cured product may be 2600 MPa or more, more specifically, 2600 to 2700 MPa.

The above-mentioned cured product may have a flexural strength of 90 to 100 MPa as measured according to the method of ASTM D790 and an impact strength of 100 J/m or more as measured according to the method of ASTM D256. Specifically, the impact strength of the above-mentioned cured product may be 110 J/m or more, more specifically, 110 to 120 J/m.

The cured product according to the present invention has excellent mechanical properties and excellent durability to withstand external or internal impacts, and therefore can be usefully utilized as a material for various types of structures that require not only excellent impact performance but also easy diagnosis/detection of damage in real time. Specifically, it can be used as a material for interior and exterior of automobiles, interior and exterior of railways, aircraft, ships, and spacecraft, as well as a material for a rotor blade of a wind turbine. In particular, when utilized as a material for a rotor blade of a wind turbine, which is a large structure that is difficult to repair, maintain, and manage, it is preferable because it has excellent mechanical properties and allows for accurate and easy diagnosis of damaged areas through photographs or the naked eye.

In addition, another aspect of the present invention provides a damage-detectable fiber-reinforced composite material comprising reinforcing fibers; and a composition for the fiber-reinforced composite material.

The term "fiber-reinforced composite material" used in the present invention refers to a composite material in which a liquid synthetic resin, such as epoxy resin, is impregnated into a fiber reinforcing material, such as carbon fiber or glass fiber, and the final product can be manufactured through a single molding, or the final product can be manufactured through secondary molding after making an intermediate material, such as prepreg.

The above fiber-reinforced composite material is manufactured by impregnating reinforcing fibers into the composition for the fiber-reinforced composite material, and may contain 40 to 60 wt% of the reinforcing fibers and 40 to 60 wt% of the composition for the fiber-reinforced composite material with respect to 100 wt% of the composite material. If the wt% of the reinforcing fibers exceeds the above range, the mechanical properties of the composite material increase, but the instability of the red pigment or red disperse dye may increase, which may cause a problem. Therefore, it is preferable that the blending ratio of the reinforcing fibers and the composition for the fiber-reinforced composite material is appropriately selected within the above range.

The above reinforcing fiber is not particularly limited, but may be at least one selected from the group consisting of glass fiber, natural fiber, metal fiber, ultra-high molecular weight polyethylene fiber, polyacrylonitrile fiber, arylate fiber, polyetheretherketone fiber, rayon fiber, basalt fiber, aromatic polyamide fiber, polyaramid fiber, alumina fiber, and boron fiber, and is preferably not limited thereto as long as it is a transparent or white reinforcing fiber without a specific color, and for example, may be at least one selected from the group consisting of glass fiber, natural fiber, ultra-high molecular weight polyethylene fiber, polyacrylonitrile fiber, arylate fiber, polyetheretherketone fiber, rayon fiber, aromatic polyamide fiber, polyaramid fiber, alumina fiber, and boron fiber, and more preferably, may be glass fiber.

The above reinforcing fibers preferably have an average diameter of 0.3 to 300 μm. However, if the diameter is less than the lower limit, there is a concern that the physical property reinforcing effect may not be sufficient due to the diameter being too thin, and the fibers may become entangled, which is not preferable. If the diameter exceeds the upper limit, there is a concern that the reinforcing fibers may not be sufficiently impregnated into the fiber-reinforced composite material composition of the present invention, which is not preferable.

The above reinforcing fibers may be in the form of fiber structures such as short fibers, long fibers, continuous fibers, fabrics, knits, non-woven fabrics, braids, and mats, which are clearly known in the field of fiber-reinforced composite material technology, but are not limited thereto.

The reinforcing fibers in the form of the above fiber structure may be laminated in at least one layer, and it is preferable to laminate in two or more layers to improve physical properties, but is not particularly limited thereto.

Any specific method for impregnating reinforcing fibers into the above fiber-reinforced composite material composition may be used as long as it is known in the art.

Since the above fiber-reinforced composite material causes a color change in the affected area when it is physically damaged by an external force, the damaged area can be identified with the naked eye or through an image using a camera, and the presence or absence of damage can be easily, conveniently, and accurately determined.

In this regard, FIGS. 10, 11, 12, and 16 are images showing an example of color change due to stress or deformation of a fiber-reinforced composite material. The fiber-reinforced composite material was discolored from red to transparent by an external stimulus, and it was confirmed that the CMYK chromaticity value in the area of the discolored fiber-reinforced composite material was reduced by more than 50% compared to the original state.

Another aspect of the present invention provides a structural safety diagnosis system including the fiber-reinforced composite material, wherein a color change occurs when force, stress or strain is applied to the fiber-reinforced composite material, and the color change is measured by examining CMYK chromaticity values from an optical image of the fiber-reinforced composite material.

Since the above fiber-reinforced composite material can refer to the contents of the fiber-reinforced composite material described above, duplicate explanation will be omitted.

The above fiber-reinforced composite material requires a process in which red pigment or red disperse dye molecules are uniformly dispersed in a thermosetting resin. Within the chemical structure of the thermosetting resin, the red pigment molecules form strong interactions with neighboring molecules, while also having excellent dispersibility in the epoxy resin. Therefore, when an external force, stress, or strain (displacement) is applied, the physical structure of the thermosetting resin changes, and the light is scattered by the thermosetting resin before the red pigment absorbs the light, so that the red color is not displayed.

That is, when the system for structural safety diagnosis according to the present invention is physically damaged by an external force, it displays a red color in its original state and then changes color to transparent, and the degree of the change can be analyzed by extracting the RGB color value. This can be confirmed through the experiment described below.

In particular, although not explicitly described in the examples or comparative examples below, in the case of a structural safety diagnosis system using a fiber-reinforced composite material according to the present invention, the fiber-reinforced composite material was manufactured by varying the composition content, type, and number of layers, and then left under sunlight for 100 days, after which the CMYK chromaticity value changes were analyzed.

In addition, after leaving it under sunlight for 100 days, damaging it with a 400 N bending load, and repeating it 100 times, the change in CMYK color value was analyzed, and it was confirmed that there was almost no error range even after repeating it 100 times.

As a result, it was confirmed that when all of the following conditions are satisfied, the color change is stably maintained for a long period of time even under sunlight, and quantitative and qualitative measurements are possible for damage caused only by external force.

The above fiber-reinforced composite material is manufactured by impregnating glass fiber into a composition for a fiber-reinforced composite material containing 25 to 35 parts by weight of a hardener and 0.13 parts by weight of a red pigment of the product Cinquasia® Magenta D4570 sold by BASF per 100 parts by weight of a thermosetting resin; wherein the glass fiber is a glass fiber sheet laminated in 2 to 10 layers, and when an external force is applied and damaged, the red color lightens and changes to transparent, so that the presence and degree of damage can be analyzed by extracting the CMYK chromaticity values from the image of this color change.

Another aspect of the present invention provides a method for analyzing a structural safety diagnosis system, including: i) a step of capturing an image of a structural safety diagnosis system including the above-described fiber-reinforced composite material by a camera; ii) a step of extracting CMYK values from the image; and iii) a step of deriving damage information of the structural safety diagnosis system based on the extracted CMYK values.

In the case of structures, especially large structures, if damage is left untreated, it can cause an unexpected disaster or secondary damage, so it is necessary to diagnose the damage easily and accurately in advance. Since structures or large structures are large and tall, it is difficult to diagnose damage using electrical resistance or using the human five senses. Therefore, a method is needed that can accurately diagnose at a desired time when physical changes occur on the outside and inside of the material (i.e., damage, cracks, abrasion, fractures, etc.) due to external force (force/stress/displacement). In the case of a structure including the fiber-reinforced composite described above, when damage occurs due to an external force, the bonding relationship between the thermosetting resin and the red pigment/red disperse dye present in the fiber-reinforced composite changes, and by detecting and quantifying the visible color change caused by this from the outside, the location of the damage to the material can be measured/analyzed and the degree of damage can be diagnosed.

For the above color change, light is incident on the thermosetting resin, the red pigment/red disperse dye absorbs the light, and only the red light is reflected or scattered to produce a red color. The light source for this can be a sunlight or a light source already installed where the structure is located, or it can selectively irradiate light of a specific wavelength band using a filter or a monochromator. In cases where the light is insufficient or the light characteristics of the incident light source need to be controlled, light can be irradiated through an additional light source.

A system for structural safety diagnosis including a fiber-reinforced composite material according to the present invention can easily measure color changes due to damage using only sunlight without supplying a separate light source, and can clearly confirm the color changes qualitatively or quantitatively by comparing them with the records of CMYK chromaticity values before damage, making it easy to detect color changes due to damage.

In order to measure color changes to diagnose damage from the above structural safety diagnosis system, first, the above structural safety diagnosis system can be photographed with a camera to obtain an image.

At this time, it is preferable that the distance between the system for structural safety diagnosis and the camera be 15 cm to 1 m. If it is less than 15 cm, color change measurement is unclear, and if it exceeds 1 m, the color value may decrease due to absorption/scattering by the measurement path, which may cause a problem in that it is impossible to accurately measure whether there is damage.

Next, RGB chromaticity values or CMYK (Cyan, Magenta, Yellow, Key) chromaticity values can be extracted or calculated from the image above, but since CMYK (Cyan, Magenta, Yellow, Key) chromaticity values clearly show changes due to damage, it is significantly better in terms of accuracy to use CMYK chromaticity values than RGB chromaticity values.

In order to extract or calculate the above color value, data can be received from the image using an RGB sensor and converted into CMYK color value for use.

Finally, based on the extracted chromaticity value, damage information of the structural safety diagnosis system can be derived, and if the chromaticity value decreases by 30 to 50% or more compared to the initial chromaticity value, it can be determined to be damaged, and the degree of damage can also be quantitatively analyzed through the difference in the chromaticity value. Preferably, if the CMYK chromaticity value decreases by 30 to 50% or more compared to the initial chromaticity value, it can be determined to be damaged, and more preferably, if the K value among the CMYK chromaticity values decreases by 30 to 50% compared to the initial K value, it can be determined to be damaged or broken.

The above image can be used to determine the presence and degree of damage by location by calculating or extracting color values by location.

In addition, by converting the image to a black and white image, the color change of the damaged area can be clearly shown, allowing immediate confirmation without comparing the CMYK color values.

By connecting the above camera to a drone, it is possible to easily take pictures of various locations of a target structure for diagnosis and provide data, and by connecting the camera-equipped drone to a color value extraction program or a device equipped with the above program, an analysis interface can be implemented, and by quantitatively analyzing the color of the images from the camera taken at each location into color value and displaying them, an interface can be constructed where even non-experts can easily diagnose and determine whether or not a structure is damaged and the degree of damage. This concept is illustrated in Fig. 18.

For example, after obtaining images at different points of a structure including the fiber-reinforced composite material of the present invention, the color value can be calculated or extracted from a connected device, thereby diagramming the change in the color value according to the position of the structure, and easily and conveniently monitoring a desired part at a desired time and diagnosing the presence and degree of damage. FIG. 18 shows a system that photographs a structure manufactured from the fiber-reinforced composite material according to the present invention through a camera mounted on a drone, calculates or extracts the change in the color value in each image, and displays the results to check the distribution, diagnose, and interpret whether there is physical damage due to an external force and the degree of damage.

Hereinafter, the present invention will be described in more detail through examples and the like. However, the scope and content of the present invention cannot be reduced or limited by the examples and the like. In addition, based on the disclosure of the present invention including the examples below, it is obvious that those skilled in the art can easily practice the present invention, even though specific experimental results are not presented, and it is natural that such modifications and variations fall within the scope of the appended patent claims.

Experimental materials

KFR140 (epoxy resin) and KFH180 (curing agent) were purchased from Kukdo Chemical. Non-compressed glass fabric (SE1500) was purchased from Owens Corning, and carbon fiber fabric (T700SC 24K) was purchased from Toray. The above fabrics were used as reinforcing materials for reinforced composite materials.

Cinquasia® Magenta D4570 pigment was purchased from BASF (Pigment Red 202). Disperse dyes (DIANIX Red S-G, Dispersion Dye Red 1), acid dyes (Telon Red AFG, Acid Red 299), and reactive dyes (Remazol Red RB-133) were purchased from DyStar.

Examples 1 to 2 and Comparative Examples 1 to 3: Preparation of compositions for fiber-reinforced composite materials

A composition for fiber-reinforced composite materials was prepared by adding dye or pigment to epoxy monomer (KFR140, Kukdo Chemical) and dispersing and dissolving using an ultrasonic homogenizer (0.5 cycle, 60% amplitude, 1 hour). At this time, the epoxy resin, hardener, and pigment were mixed as shown in Table 1. A separate dispersion solvent was not used. Since heat of up to 50℃ is generated during the ultrasonic treatment process, the composition mixed by ultrasonic treatment was cooled to room temperature and then used.

division Epoxy Hardener coloring agent type g type g type g Example 1 Example 1-1
(P-epoxy) KFR140 76.9 KFH180 23 Cinquasia® Magenta D4570 0.1 Example 1-2
(P-epoxy) KFR140 76.9 KFH180 23 0.2 Example 1-3
(P-epoxy) KFR140 76.9 KFH180 23 0.5 Example 1-4
(P-epoxy) KFR140 76.9 KFH180 23 1 Example 1-5
(P-epoxy) KFR140 76.9 KFH180 23 3 Example 2 Example 2-1
(D-epoxy) KFR140 76.9 KFH180 23 Dispersion Dye Red 1 0.1 Example 2-2
(D-epoxy) KFR140 76.9 KFH180 23 0.2 Example 2-3
(D-epoxy) KFR140 76.9 KFH180 23 0.5 Example 2-4
(D-epoxy) KFR140 76.9 KFH180 23 1 Example 2-5
(D-epoxy) KFR140 76.9 KFH180 23 3 Comparative example Comparative Example 1
(neat) KFR140 76.9 KFH180 23 - - Comparative Example 2
(A-epoxy) KFR140 76.9 KFH180 23 Acid Red 299 0.5 Comparative Example 3
(R-epoxy) KFR140 76.9 KFH180 23 Remazol Red RB-133 0.5

Example 3: Preparation of fiber-reinforced composite material (GF/p-epoxy) capable of crack detection

In order to manufacture a fiber-reinforced composite material capable of crack detection, a laminate in which two layers of non-compressed glass fabric (SE1500) (GF) were laminated was manufactured. After the laminate was placed in a mold, the fiber-reinforced composite material composition of Example 1-1 was impregnated under high pressure using an RTM method to obtain a fiber-reinforced composite material of Example 3 capable of crack detection.

Specifically, when a sufficient amount of fiber reinforcement and a composition for fiber reinforced composite material are impregnated in the mold, a fiber reinforced composite material capable of crack detection can be obtained through a curing process. The curing process can be performed at room temperature for 24 hours, but considering the curing speed, in this example, it was performed at 80° C. for 1 hour to obtain a fiber reinforced composite material.

Example 4: Preparation of fiber-reinforced composite material (GF/D-epoxy) capable of crack detection

A fiber-reinforced composite material of Example 4 was manufactured in the same manner as in Example 3, except that the fiber-reinforced composite material composition of Example 2-1 was used instead of the fiber-reinforced composite material composition of Example 1-1.

Example 5: Preparation of fiber-reinforced composite material (CF/p-epoxy) capable of crack detection

A fiber-reinforced composite material was manufactured in the same manner as in Example 3, except that carbon fiber fabric (T700SC 24K) (CF) was used instead of non-compressed glass fabric (SE1500) (GF).

Example 6: Preparation of fiber-reinforced composite material (CF/D-epoxy) capable of crack detection

A fiber-reinforced composite material was manufactured in the same manner as in Example 4, except that carbon fiber fabric (T700SC 24K) (CF) was used instead of non-compressed glass fabric (SE1500) (GF).

Comparative Example 4: Manufacturing of Fiber-Reinforced Composite Material (CF/epoxy)

A fiber-reinforced composite material of Comparative Example 4 was manufactured in the same manner as in Example 3, except that the fiber-reinforced composite material composition of Comparative Example 1 was used instead of the fiber-reinforced composite material composition of Example 1-1.

Comparative Example 5: Manufacturing of Fiber-Reinforced Composite Material (CF/epoxy)

A fiber-reinforced composite material was manufactured in the same manner as in Comparative Example 4, except that carbon fiber fabric (T700SC 24K) (CF) was used instead of non-compressed glass fabric (SE1500) (GF).

Experimental Example 1: Comparative Analysis of Fiber-Reinforced Composite Materials Colored in Various Colors

A. Fiber-reinforced composite materials manufactured using various colorants

Fiber-reinforced composites colored in different colors (red, green, blue, black) were prepared in the same manner as in Examples 1-3, except that sigma aldrich Anthracene, ReagentPlus®, 99% (green), sigma aldrich solvent blue 59 (blue), CM-95, carbon nanotube (black) dye, or red pigment of Cinquasia® Magenta D4570 was added to epoxy monomer (KFR140, Kukdo Chemical). For the control, basic fiber-reinforced composites (neat) were prepared in the same manner without adding any colorant.

B. Analysis

When dyes or pigments are dispersed in epoxy resin, colors can be implemented in the epoxy resin. When pigments are used as colorants, opaque colors are implemented, and when dyes are used as colorants, transparent colors are implemented. Each color can be identified by CMYK values. The CMYK before (Wetted) and after (Cured) curing of each fiber-reinforced composite material (basic, red, green, blue, and black) manufactured through the above-described process were analyzed and shown in Fig. 1.

Figure 1 shows the results of CMYK analysis before (Wetted) and after (Cured) curing for fiber-reinforced composite materials (base, red, green, blue, black).

As shown in Figure 1, the color is clearly distinguished when the dye is mixed with pigment in the epoxy resin solution, but it can be seen that the color changes significantly after curing.

It was confirmed that color realization was not properly achieved in fiber-reinforced composites when green, blue, and black dyes, rather than red pigments, were used. Therefore, in order to be able to detect damage to fiber-reinforced composites, perfect color realization must be achieved, and for this purpose, red is preferable, and it is most preferable to use pigments rather than dyes.

Experimental Example 2: Optical Evaluation

A composition for fiber-reinforced composite materials was prepared by selecting a red pigment and dye, and the dispersion/dissolution thereof in epoxy resin was evaluated. Specifically, the compositions for fiber-reinforced composite materials of Examples 1-3 to 2-3 and Comparative Examples 1 to 3 were photographed using a microscope to analyze the degree of dispersion of the dye or pigment in the epoxy resin.

FIG. 2 is a photograph of the compositions for fiber-reinforced composite materials of Examples 1-3 to 2-3 and Comparative Examples 1 to 3. According to the photographs, no precipitation of pigment or dye particles was observed in the compositions for fiber-reinforced composite materials of Examples 1-3 and 2-3.

On the other hand, it was confirmed that the composition for fiber-reinforced composite materials (A-epoxy) of Comparative Example 2 did not completely dissolve the dye particles and formed precipitates, and it was confirmed that the composition for fiber-reinforced composite materials (R-epoxy) of Comparative Example 3 did not dissolve and formed precipitates entirely.

Since the dispersion/dissolution of dyes and pigments in epoxy monomers is due to the chemical structure and/or functional groups of the molecules, FT-IR analysis was performed on the compositions for fiber-reinforced composite materials of Examples 1-3 to 2-3 and Comparative Examples 2 to 3 according to the present invention to confirm this.

Experimental Example 3: Analysis of the dissolution/dispersion of three dyes (Dispersion Dye Red 1, Acid Red 299, Remazol Red RB-133), pigment (Cinquasia® Magenta D4570) and epoxy monomer

Figure 3 shows FT-IR graphs (a) and chemical structures (b-e) of three dyes (Dispersion Dye Red 1, Acid Red 299, Remazol Red RB-133) and a pigment (Cinquasia® Magenta D4570).

Looking at Fig. 3a, in the pigment (pigment, Cinquasia® Magenta D4570) used in Example 1, peaks at about 1643 cm ^-1 and 1600 cm ^-1 , which are characteristic peaks of quinacridone derivatives, were confirmed. These correspond to the C=O and C=C vibrations in the carbonyl and benzene groups of the quinacridone skeleton, respectively. Looking at the molecular structure of the pigment (pigment, Cinquasia® Magenta D4570) shown in Fig. 3b, it can be seen that the pigment forms an excellent mixture with the epoxy monomer due to the presence of the functional group and chlorine (823 cm ^-1 ) and amine (3265 cm ^-1 and 3230 cm ^-1 ) groups. In particular, the pigment (pigment, Cinquasia® Magenta D4570) used in Example 1 shows a significant bathochromic shift of ~200 cm ^-1 when examining the NH vibration peak of the amine group, which means that a strong interaction is formed between pigment molecules.

Furthermore, the pigment (pigment, Cinquasia® Magenta D4570) used in Example 1 was confirmed to have an IR peak at 1625 cm ^-1 that occurs when the secondary amine group and the carbonyl group of adjacent pigment molecules interact (NH···O). That is, the pigment used in Example 1 forms an intermolecular interaction, which can also be seen by other IR peaks observed at about 3161 cm ^-1 and 3139 cm ^-1 . The IR peaks indicate the interaction of the carbonyl group and the NH group of adjacent pigment molecules. Therefore, as shown in the composition for a fiber-reinforced composite material of Example 1, it can be seen that the pigment (Cinquasia® Magenta D4570) has a high molecular interaction, and therefore has low solubility in solvents but excellent dispersion characteristics in epoxy monomers.

Looking at Figs. 3a and 3c, the disperse dye (Dispersion Dye Red 1) used in Example 2 was confirmed to have strong peaks at ~1509 cm ^-1 and ~1334 cm ^-1 for the asymmetric and symmetric stretches of the nitro group (-NO ₂ ) of the aromatic compound. The nitro group causes N…O interactions between the disperse dye molecules and the epoxy monomer, which helps the compound to dissolve in the epoxy monomer. The hydroxyl group observed at about 3438 cm ^-1 in the disperse dye (Dispersion Dye Red 1) forms O…H interactions with the epoxy groups of the epoxy monomer, which allows the disperse dye molecules to dissolve in the epoxy monomer.

The disperse dye (Dispersion Dye Red 1) used in Example 2 is based on an azo group and therefore has a higher degree of freedom than a pigment having a rigid and planar quinacridone skeleton, and the nitro and hydroxyl groups present in the flexible skeleton increase the solubility with the epoxy monomer.

Looking at FIGS. 3a and 3d, the acid dye (Acid Red 299) used in Comparative Example 2 had a hydroxyl group observed at 3438 cm ^-1 , which can enhance the dissolution with the epoxy monomer. However, the acid dye (Acid Red 299) had a sodium sulfonate group at ~1035 cm ^-1 , which hinders the dissolution with the epoxy monomer. In other words, it can be seen that the acid dye (Acid Red 299) has functional groups with different characteristics, so it has poor solubility in the epoxy monomer and cannot be properly dissolved or dispersed.

Looking at FIGS. 3a and 3e, it can be seen that the reactive dye (Remazol Red RB-133) used in Comparative Example 3 has four sodium sulfate groups on the outside, which block the approach of the amine group of the reactive dye and the epoxy monomer, so it does not dissolve or disperse, but rather completely precipitates.

Based on the above results, a pigment and a disperse dye (Dispersion Dye Red 1) were selected as colorants for the epoxy resin composition, and an experiment was conducted.

Experimental Example 4: Analysis of Coagulation in Compositions for Fiber-Reinforced Composite Materials of Examples 1 to 2

In order to analyze the degree of dissolution/dispersion of each pigment or dye with an epoxy monomer, compositions for fiber-reinforced composite materials of Examples 1-1 to 1-5 and Examples 2-1 to 2-5 were prepared by mixing different contents, and analyzed using a microscope eyepiece and objective lens. At this time, the eyepiece was photographed at a magnification of 10 times, and the objective lens was photographed at a magnification of 5 to 40 times to analyze the presence of aggregation.

FIG. 4 is a photograph (top) of the compositions for fiber-reinforced composite materials of Examples 1-1 to 1-5 and Examples 2-1 to 2-5 and the results of analysis of each using an optical microscope (bottom). According to the photographs, it can be confirmed that as the pigment content increases, the color of the composition for fiber-reinforced composite materials becomes darker and particles of several hundred micrometers in size are generated. On the other hand, in the composition for fiber-reinforced composite materials of Example 2 in which a disperse dye was used, although the formation of agglomerates was relatively low even when the dye content increased, it was confirmed that some agglomerations occurred starting from the composition for fiber-reinforced composite materials of Example 2-2.

Through the results described above, it was confirmed that the composition for fiber-reinforced composite materials of Examples 1-1 and 2-1 using 0.1 wt% pigment or dye had a desirable condition in which no agglomerates were formed in the liquid phase.

When a pigment is used as a coloring agent for a composition for a fiber-reinforced composite material as in Example 1, it exhibits an opaque color, but since the size of the pigment molecules is large, it is preferable to use a small amount of 0.1 wt% or less so that it can be evenly and completely dispersed. In the case of a disperse dye, it exhibits a transparent color, so it is easy to implement color, but there is a risk of deteriorating the epoxy resin itself, so it is most preferable to use a pigment rather than a disperse dye.

Experimental Example 5: Analysis of chemical structural changes in compositions for fiber-reinforced composite materials

In order to examine the chemical structural changes before and after curing of the fiber-reinforced composite material compositions of Examples 1-1 and 2-1, the fiber-reinforced composite material compositions of Examples 1-1 and 2-1 were each poured into a mold having a predetermined shape (e.g., a stainless steel mold), and cured by heating at 80° C. for 1 hour to produce a single film having a thickness of 4 mm.

The film of the above-mentioned cured Example 1-1 or Example 1-2 was separated from the mold and analyzed according to the ATR method.

FIG. 5 is an FT-IR analysis graph of the fiber-reinforced composite material compositions of Comparative Example 1 (Neat) and Examples 1-1 and 2-1 before curing and after curing (Cured). The right side of FIG. 5 is an optical microscope photograph of a film cured with the fiber-reinforced composite material compositions of Comparative Example 1 (Neat) and Examples 1-1 and 2-1. According to FIG. 5, since no new peaks are found after curing in the fiber-reinforced composite material compositions of Examples 1-1 and 2-1, it is expected that no new chemical bonds are formed between the epoxy resin and the pigment and dye.

Experimental Example 6: Analysis of Glass Transition Temperature of Fiber-Reinforced Composite Materials

The glass transition temperature (T _g ) of the fiber-reinforced composite material compositions of Examples 1-1 to 1-5 and Examples 2-1 to 2-5 was measured by a double scanned curve of differential scanning calorimetry (DSC) (temperature condition: 40 to 200°C). At this time, the analysis was performed under a heating/cooling rate condition of 5°C/min.

Figure 6 is a graph showing changes in the glass transition temperature (T _g ) of fiber-reinforced composite material compositions of Comparative Example 1 (Neat), Examples 1-1 to 1-5, and Examples 2-1 to 2-5.

According to FIG. 6, it can be seen that the glass transition temperature (T _g ) of the fiber-reinforced composite material compositions manufactured from Examples 1-1 to 1-5 rapidly increases with an increase in the pigment content and then gradually increases under the condition of a pigment content of 1 to 3 wt%. It was confirmed that the fiber-reinforced composite material composition manufactured from Example 1-5 had a glass transition temperature (T _g ) (~84° C.) that was about 10% higher than that of the fiber-reinforced composite material of Comparative Example 1 (neat). That is, since the pigment is evenly dispersed in the epoxy resin in the form of reinforcing particles having a size of tens to hundreds of micrometers, not only does it not interfere with the crystallization of the epoxy resin, but also reduces the free volume of the epoxy resin to improve the mechanical properties.

According to FIG. 6, in the fiber-reinforced composite material compositions manufactured from Examples 2-1 to 2-5, the dye molecules are positioned between the epoxy resin monomer and the oligomer and act as a plasticizer in the epoxy resin matrix, thereby reducing the free volume of the epoxy resin. That is, the disperse dye inhibits the formation and/or growth of epoxy crystals, thereby reducing T _g as in the fiber-reinforced composite material compositions manufactured from Examples 2-1 to 2-5.

Experimental Example 7: Analysis of mechanical properties of composition for fiber-reinforced composite materials

The purpose of this invention was to analyze the mechanical properties of a single film manufactured only with the composition for a fiber-reinforced composite material according to the present invention. Specifically, the compositions for a fiber-reinforced composite material of Examples 1-1 to 1-5 and Examples 2-1 to 2-5 were each poured into a mold having a predetermined shape (e.g., a stainless steel mold), and heated at 80° C. for 1 hour to harden, thereby manufacturing a single film having a thickness of 3 mm. In order to evaluate the tensile strength, yield strength, flexural strength, and impact strength, specimens measuring 200 mm × 200 mm (width × height) were manufactured.

For each of the above single films, tensile strength, flexural strength, impact strength, and yield strength were evaluated using a Universal Testing Machine (UTM). The tensile, flexural, and Izod impact strength tests were evaluated according to ASTM D638, ASTM D790, and ASTM D256 standards, respectively, and each experiment was repeated 10 times, which were expressed as the mean ± standard deviation.

FIG. 7a is a graph showing the tensile strength and yield strength of a single film manufactured from the compositions for fiber-reinforced composite materials of Examples 1-1 to 1-5, and FIG. 7b is a graph showing the tensile strength and yield strength of a single film manufactured from the compositions for fiber-reinforced composite materials of Examples 2-1 to 2-5.

FIG. 8 is a graph showing the bending strength and impact strength (Izod impact strength) of a single film manufactured from the composition for fiber-reinforced composite materials of Examples 1-1 to 1-5 and Examples 2-1 to 2-5.

According to FIG. 7, it was confirmed that the single film manufactured with the composition for fiber-reinforced composite material of Example 1-1 containing 0.1 wt% of pigment had the highest tensile strength and yield strength, and as the pigment content increased, the tensile strength and yield strength gradually decreased.

In the case of disperse dyes, it was confirmed that the tensile strength and yield strength increased as the dye content decreased. It was confirmed that the tensile strength and yield strength of the single film manufactured by Example 1-1 were ~100 MPa higher than that of the single film manufactured by Example 2-1, so adding 0.1 wt% of pigment is most preferable for enhancing mechanical properties.

According to Fig. 8, the addition of dye or pigment improved the bending strength and impact strength by 40 MPa, but it could be confirmed that the bending strength and impact strength decreased rapidly when the content of dye or pigment exceeded 0.2 wt%. In summary, among the red-colored colorants, mixing a pigment with an epoxy resin is preferable because it can obtain the effect of reinforcing the mechanical properties, and mixing 0.1 wt% of pigment based on the total weight of the epoxy resin is most preferable because it can achieve excellent mechanical properties along with clear color implementation.

Experimental Example 8: Mechanical Properties Analysis for Fiber-Reinforced Composite Materials

The fiber-reinforced composite materials of Comparative Example 4 or 5, the fiber-reinforced composite materials of Examples 3 and 5, and the fiber-reinforced composite materials of Examples 4 and 6 were prepared, and the tensile strength and bending strength thereof were evaluated as in Experimental Example 7.

FIGS. 9a to 9d are optical microscope photographs of the fiber-reinforced composite material (GF/P-epoxy) of Example 3 (a), the fiber-reinforced composite material (GF/D-epoxy) of Example 4 (b), the fiber-reinforced composite material (CF/P-epoxy) of Example 5 (c), and the fiber-reinforced composite material (CF/D-epoxy) of Example 6 (d). FIG. 9e is a graph of tensile strength and flexural strength for the fiber-reinforced composite material (GF/P-epoxy) of Example 3, the fiber-reinforced composite material (GF/D-epoxy) of Example 4, and the fiber-reinforced composite material (GF/epoxy) of Comparative Example 4, and FIG. 9f is a graph of tensile strength and flexural strength for the fiber-reinforced composite material (CF/P-epoxy) of Example 5, the fiber-reinforced composite material (CF/D-epoxy) of Example 6, and the fiber-reinforced composite material (CF/epoxy) of Comparative Example 5.

Looking at FIGS. 9a to 9d, it can be seen that the fiber-reinforced composite material (GF/P-epoxy) of Example 3 and the fiber-reinforced composite material (GF/D-epoxy) of Example 4 are both uniformly colored. On the other hand, the fiber-reinforced composite material (CF/P-epoxy) of Example 5 and the fiber-reinforced composite material (CF/D-epoxy) of Example 6 are not properly colored because the carbon fibers are black, which absorbs the entire range of visible light.

According to FIG. 9e, it can be confirmed that the fiber-reinforced composite material (GF/P-epoxy) of Example 3 has significantly higher tensile strength and flexural strength by ~20 MPa and ~60 MPa, respectively, compared to the fiber-reinforced composite materials of Comparative Example 4 and Example 4.

In addition, it can be confirmed that the fiber-reinforced composite material (CF/p-epoxy) of Example 5 has significantly higher tensile strength and flexural strength of ~30 MPa and ~50 MPa, respectively, compared to the fiber-reinforced composite materials of Comparative Example 5 and Example 6. It can be seen that it is most desirable to use a pigment even for the same red color.

Experimental Example 9: Color Change Analysis of Fiber-Reinforced Composite Materials

The purpose was to analyze whether damage detection was possible for the fiber-reinforced composite material (GF/p-epoxy) of Example 3 and the fiber-reinforced composite material (GF/epoxy) of Comparative Example 4.

The fiber-reinforced composite material (GF/p-epoxy) of Example 3 and the fiber-reinforced composite material (GF/epoxy) of Comparative Example 4 were prepared, and a bending load of 400 N was applied thereto. Then, an image file was obtained through a general smart phone (LG Q92), and the RGB chromaticity values were measured from the image through a PPT program, and the RGB chromaticity values were converted to CMYK values and analyzed. CMYK (Cyan, Magenta, Yellow, and Black) measurement was performed using an RGB conversion program. The CMYK chromaticity values were derived at 10 points each in the area where the color did not change and the area where the color changed, and their average value is shown.

Figure 10 shows a photograph (left) and an enlarged image (right) of the fiber-reinforced composite material (GF/p-epoxy) of Example 3 and the fiber-reinforced composite material (GF/epoxy) of Comparative Example 4 to which a bending load of 400 N was applied.

As shown in Fig. 10, it can be confirmed that the color of the area damaged by the bending load of the fiber-reinforced composite material (GF/p-epoxy) of Example 3 has faded, and damage caused by external force can be easily confirmed with the naked eye through the color change without separate equipment.

In the fiber-reinforced composite material of Example 3, the portion damaged by external force is deformed by epoxy crystallization, and this scatters light before the pigment absorbs it, so that the red color does not appear. The color change of the fiber-reinforced composite material of Example 3 can be clearly observed even from 1 m away (Fig. 10, left).

As a result of quantifying the color change of the fiber-reinforced composite material of Example 3 (right side of Fig. 10), it was confirmed that the M value and the K value significantly decreased by more than 35, respectively, compared to before damage. On the other hand, no significant change was observed in the fiber-reinforced composite material of Comparative Example 4 before and after curing.

Experimental Example 10: Analysis of color change in fiber-reinforced composite materials according to damage

When the fiber-reinforced composite material according to the present invention is damaged in various ways, the occurrence of color change was observed and the principle thereof was analyzed. Specifically, the fiber-reinforced composite material of Example 3 and the fiber-reinforced composite material of Comparative Example 4 were prepared, and the color change was observed after causing different types of damage to each of the fiber-reinforced composite materials.

i) Twist damage using jig equipment

ⅱ) Flexural damage with 400N bending load applied

ⅲ) Tensile damage due to tensile force pulling from both sides (yield flexural strength)

ⅳ) Wear damage due to repeated friction

After obtaining image files from each of the above specimens through a general smart phone (LG Q92), RGB chromaticity values were measured from the images through a PPT program, and the RGB chromaticity values were converted to CMYK values and analyzed. CMYK (Cyan, Magenta, Yellow, and Black) measurement was performed using an RGB conversion program. CMYK chromaticity values were derived from 10 points each in the area where the color did not change and the area where the color changed, and their average value was presented.

FIG. 11a is a drawing schematically showing the principle of observing color change when a fiber-reinforced composite material according to the present invention is damaged by an external force (load). FIG. 11b is a fiber-reinforced composite material of Example 3 before being damaged, FIG. 11c is a fiber-reinforced composite material of Comparative Example 4 before being damaged, FIG. 11d is a fiber-reinforced composite material of Example 3 that has been torsionally damaged, FIG. 11e is a fiber-reinforced composite material of Comparative Example 4 that has been torsionally damaged, FIG. 11f is a fiber-reinforced composite material of Example 3 that has been bending damaged, and FIG. 11g is a photograph of a fiber-reinforced composite material of Comparative Example 4 that has been bending damaged.

Figure 12 is a photograph taken to compare color changes when the fiber-reinforced composite material of Example 3 and the fiber-reinforced composite material of Comparative Example 4 were subjected to ⅱ bending damage, ⅲ tensile damage, and ⅳ wear damage.

As shown in Fig. 11, the fiber-reinforced composite material of Example 3 clearly shows a color change at the damaged area, so it can be seen that accurate detection of the damaged area is easy. On the other hand, the fiber-reinforced composite material of Comparative Example 4 shows no significant change at the damaged area, so it is difficult to detect the damaged area.

In the fiber-reinforced composite material of Example 3, not only is a color change clearly observed only at the damaged area, but damage of up to 1 mm can also be quantitatively evaluated by comparing CMYK values.

The photograph in Fig. 11 was taken using a Q92 smartphone camera at a distance of 15 cm from the sample, demonstrating that effective damage detection is possible even with a low-cost camera.

According to Fig. 12, it was confirmed that the fiber-reinforced composite material of Example 3 had a damaged area expressed differently depending on the damage, and that there was a difference in color, such as being completely transparent or slightly reddish depending on the depth of damage. On the other hand, it was confirmed that the fiber-reinforced composite material of Comparative Example 4 had an insignificant color difference between the damaged area and the undamaged area.

Experimental Example 11: Analysis of color change of fiber-reinforced composite material according to shooting distance

When observing damage to the fiber-reinforced composite material according to the present invention, it was attempted to determine whether it was affected by the shooting distance. Specifically, the fiber-reinforced composite material of Example 3 was photographed at different shooting distances using a general smart phone (LG Q92) to obtain image files, and RGB color values were extracted from the images using a PPT program. The image file was divided into 16 equal areas, and the average RGB values derived from each divided surface are shown in Fig. 14.

Fig. 13 is a photograph of the fiber-reinforced composite material of Example 3 taken at various shooting distances, and Fig. 14 is a graph of the results of analyzing RGB from the photographs of the fiber-reinforced composite material of Example 3 taken at various shooting distances.

According to FIGS. 13 and 14, when the same specimen (fiber-reinforced composite material of Example 3) was photographed at different shooting distances, the RGB values were different, but the R value was measured uniformly when the shooting distance was 15 cm or more. Based on the above results, it was confirmed that the shooting distance is preferably 15 cm or more. When measuring with CMYK, discrimination is possible up to 1 m, so a shooting distance of 15 cm to 1 m is preferable. In addition, it was confirmed that using CMYK chromaticity values rather than RGB chromaticity values more accurately shows the difference between damaged and undamaged areas, so it is most preferable to use CMYK chromaticity values.

Experimental Example 12: Quantitative Analysis by CMYK

When observing damage of the fiber-reinforced composite material according to the present invention, a quantitative evaluation of CMYK values according to the type of damage was performed. Specifically, the fiber-reinforced composite material of Example 3 and the fiber-reinforced composite material of Comparative Example 4 were image files obtained at 15 cm using a general smart phone (LG Q92), and then the RGB chromaticity values were measured from the images using a PPT program, and the RGB chromaticity values were converted to CMYK values and analyzed. CMYK (Cyan, Magenta, Yellow, and Black) measurement was performed using an RGB conversion program. The CMYK chromaticity values were derived at 10 points each from the part where the color did not change (pristine) and the part where the color changed (crack), and their average value was presented.

Figure 15 is a graph showing the change in CMYK values according to the type of damage in the fiber-reinforced composite material of Comparative Example 4 (left) and the fiber-reinforced composite material of Example 3 (right).

According to Figure 15, the fiber-reinforced composite material (pristine) of Comparative Example 4 before damage had very low C and M values to begin with, so no significant color difference was observed in the area where crack damage occurred, making it difficult to confirm damage using CMYK values.

On the other hand, the fiber-reinforced composite material of Example 3 has high CMYK values before damage, and when significant damage occurs, the M, Y, and K values all decrease significantly, so that easy and accurate confirmation is possible with the naked eye and numerically. Since the fiber-reinforced composite material of Example 3 has different CMYK values depending on the degree of damage, it can be seen that both qualitative and quantitative evaluations of the degree of damage are possible.

Experimental Example 13: Damage Analysis of Fiber-Reinforced Composite Materials

When a 400 N bending stress is applied to the fiber-reinforced composite material according to the present invention, it was analyzed whether the damaged portion can be observed with the naked eye and whether it can be evaluated through quantitative evaluation of CMYK values and conversion to a black and white image. Specifically, the fiber-reinforced composite material of Example 3 and the fiber-reinforced composite material of Comparative Example 4 were image files obtained at 15 cm using a general smart phone (LG Q92), and then the RGB chromaticity values were measured from the images using a PPT program, and the RGB chromaticity values were converted to CMYK values for analysis. CMYK (Cyan, Magenta, Yellow, and Black) measurement was performed using an RGB conversion program. The CMYK chromaticity values were derived at 10 points each from the part where the color did not change (pristine) and the part where the color changed (crack), and their average value was presented.

Fig. 16 is a graph visually dataifying the color change at a defective portion of a fiber-reinforced composite material of Example 3 after the fiber-reinforced composite material of Example 3 is damaged by various flexural stresses. The lower left of Fig. 16 is the result of converting the image to black and white to check the degree of damage in contrast.

Figure 17 is a graph and photograph visually dataifying the color change at a defective site after a pure fiber-reinforced composite material (Comparative Example 4) without pigment was damaged by various flexural stresses.

As shown in Fig. 16, when a bending stress is applied to a fiber-reinforced composite material, the red color in the damaged area becomes lighter and the color of the reinforcing fiber (transparent or white glass fiber) appears, so the contrast of the changed color in the damaged area becomes distinct, and the degree and location of the damage or crack can be confirmed with the naked eye.

In order to quantitatively analyze the damaged area through specific data, the color value can be used, but in the case of the RGB color value, it is not easy to recognize the color according to the damage, so it is preferable to utilize the CMYK factor. That is, the fiber-reinforced composite material according to the present invention has a clear red color when there is no damage, and when damaged by an external force, the red color becomes lighter in the area where the damage, damage, or crack occurred, so that the degree and location can be qualitatively diagnosed and judged with the naked eye. In addition, the color value can be extracted by creating an image file using a general camera for the above-mentioned damage, damage, or crack, and it can be easily compared numerically. Since the above analysis process does not require expensive equipment or a separate program, it has the advantage of being very economical.

As shown in Fig. 17, the fiber-reinforced composite material of Comparative Example 4 has a color difference between the damaged and undamaged areas that is not clear, making it difficult to confirm with the naked eye, and it is also not easy to extract the color value.

In addition, conventional fiber-reinforced composite materials have been used with pigments or dyes as additives, or have been painted. Through the experimental examples of the present invention, it was confirmed that when a color other than red is used, the difference in color change due to damage cannot be confirmed, and when a colorant other than a pigment or disperse dye is used in excess of 0.13 parts by weight, not only is the color not properly implemented, but there is also a problem that the color change due to damage is not significant, making it difficult to easily diagnose with only the chromaticity value.

In contrast, the fiber-reinforced composite material according to the present invention can provide a fiber-reinforced composite material having not only excellent mechanical properties but also a new functionality that can diagnose the presence/degree of damage by using a very small amount of red pigment (0.13 parts by weight).

Claims (14)

Reinforcing fibers; and
A damage-detectable fiber-reinforced composite material comprising a composition for a fiber-reinforced composite material;
The composition for the above fiber-reinforced composite material contains 25 to 35 parts by weight of a hardener and 0.13 parts by weight of a high-chroma magenta pigment (Cinquasia® Magenta D 4570) per 100 parts by weight of a thermosetting resin.
The above fiber-reinforced composite material is a damage-detectable fiber-reinforced composite material, characterized in that when physical damage occurs due to an external force, the CMYK chromaticity value or RGB chromaticity value in the relevant area decreases by 40% to 50%. delete In the first paragraph,
A fiber-reinforced composite material, characterized in that the thermosetting resin is a bisphenol A type epoxy resin. In the first paragraph,
A fiber-reinforced composite material, characterized in that the curing agent is at least one selected from the group consisting of an aliphatic amine-based curing agent, an amidoamine-based curing agent, and a phenalkamine-based curing agent. delete delete In the first paragraph,
The above fiber-reinforced composite material is a fiber-reinforced composite material characterized in that it is manufactured by impregnating the reinforcing fiber into the composition for the fiber-reinforced composite material. In the first paragraph,
A fiber-reinforced composite material, characterized in that the reinforcing fiber is at least one selected from the group consisting of glass fiber, natural fiber, metal fiber, ultra-high molecular weight polyethylene fiber, polyacrylonitrile fiber, arylate fiber, polyether ether ketone fiber, rayon fiber, basalt fiber, aromatic polyamide fiber, polyaramid fiber, alumina fiber, and boron fiber. delete delete A system for structural safety diagnosis comprising a fiber-reinforced composite material according to Article 1,
When force, stress or strain is applied to the above fiber-reinforced composite material, a color change occurs.
A system for structural safety diagnosis, characterized in that the color change is measured by examining CMYK chromaticity values from an optical image of the fiber-reinforced composite material. In the analysis method of a system for structural safety diagnosis including a fiber-reinforced composite material of Article 11,
i) A step of obtaining an image by photographing a system for structural safety diagnosis including a fiber-reinforced composite material of Article 11 with a camera;
ⅱ) a step of extracting CMYK (Cyan, Magenta, Yellow, Key) color values from the image; and
ⅲ) A method for analyzing a structural safety diagnosis system, comprising: a step of deriving damage information of the structural safety diagnosis system based on the extracted color value. In Article 12,
An analysis method of a structural safety diagnosis system, characterized in that the distance between the structural safety diagnosis system and the camera in the step i) above is 15 cm to 1 m. In Article 12,
An analysis method for a system for structural safety diagnosis, characterized in that if the color value in step ⅲ) above decreases by 30 to 50% or more compared to the initial color value, it is judged to be damaged.