Force-induced color developing material, preparation method thereof and intelligent bolt based on force-induced color developing material

Abstract

The invention discloses a force-induced color developing material, a preparation method thereof and an intelligent bolt based on the material, and the force-induced color developing material comprises the following components in percentage by mass: 65.00% of epoxy resin, 24.00% of a curing agent, 0.5% of spiropyrane and 0.5% of ethanol, and the mass percentage of each component is as follows: the mass percentage of the epoxy resin is 65.00%, the mass percentage of the curing agent is 24.00%, and the mass percentage of the spiropyrane is 0.5%. The mass percent of spiropyrane is 1.00%, and the mass percent of ethanol is 10.00%; the sum of the mass percent of the epoxy resin, the curing agent, the spiropyrane and the ethanol is 100%. The intelligent bolt is convenient to use, the stress condition of the bolt can be judged without connection of other electronic equipment and the bolt, and the problem that traditional bolt monitoring equipment is complex and tedious can be solved. The intelligent bolt can be manufactured into different types of intelligent bolts according to actual application scenes or stress environments of the bolt, so that different working environments are met.

Description

Technical Field

[0001] The present invention relates to the technical field of infrastructure stress structure monitoring, and particularly relates to a force-induced chromogenic material containing spiropyran, a preparation method thereof, and an intelligent bolt based on the material, which can present corresponding color changes according to the loosening-tightening of the bolt, and provide intuitive and reliable technical support for the loosening detection of the bolt. Background Art

[0002] As one of the most commonly used fasteners in steel structures and steel-concrete composite structures, high-strength bolts are widely used in engineering practice. During the use of bolts, the fastening force loss will occur due to the influence of harsh environments such as complex stress, fatigue load, temperature change, elastic stiffness change of joint components, and corrosion. However, the loosening of bolt connections is not easy to be detected and monitored, and the loosening and falling off of bolts will cause the failure of key structural parts or the whole, and even trigger major engineering accidents, resulting in huge economic losses and casualties. In summary, how to accurately obtain the loaded state of bolts is an urgent problem to be solved in bolt detection.

[0003] At present, bolt loosening detection methods are mainly divided into three categories: direct detection methods, indirect detection methods, and intelligent bolt detection methods, which are commonly used in engineering practices (such as "Vision-based autonomous bolt-looseness detection method for splice connections: Design, lab-scale evaluation, and field application", Thanh-Canh et al., page 103591, Automation in Construction, 2021). Direct detection methods include visual inspection, torque method, and ultrasonic detection method. Such methods have disadvantages such as being greatly affected by human factors, having strong subjectivity, and limited application scope ("An ultrasmall bolt defect detection method for transmission line inspection", Luo et al., page 79, Ieee Transactions on Instrumentation and Measurement, 2023); Indirect detection methods include vibration analysis method, fiber Bragg grating sensing method ("Development and application of intelligent bolts based on fiber Bragg grating sensors", Ren Liang et al., page 10, Instrument Technique and Sensor, 2020), etc. Such methods have high detection costs, complex operations, and are easily affected by the environment. It is difficult to achieve full coverage of a huge number of bolts and is not suitable for simultaneous detection of the loosening of multiple bolts ("Study on inspection of high-temperature bolts of 600MW supercritical unit", Wang et al., page 79, Hot Working Technology, 2012); Intelligent bolt detection methods include piezoresistive impedance intelligent bolt method and force-induced color change intelligent bolt method. The piezoresistive bolt method has disadvantages such as complex installation, high cost, and possible fatigue or aging during long-term use, which affects the measurement accuracy. The force-induced color change bolt undergoes a chemical reaction and produces a color change when subjected to an external force through a special coating or material on the bolt surface. The force-induced color change intelligent bolt method relies on chemical reactions and has disadvantages such as high cost and low reuse rate.

[0004] Resins with good color display characteristics include epoxy resin, polyurethane resin, polycarbonate resin, and polyimide resin, etc. Different resin molecular structures have different absorption and reflection characteristics of light, thus affecting their color display performance. Among such resins with optical color display properties, epoxy resin is selected as the color display base material for bolts in this patent because it meets the optical characteristics of the birefringence effect and has a certain strength after curing to meet the deformation requirements when the bolt is stressed.

[0005] Compared with the patent No. CN109780029A, the differences of this patent are as follows: 1) The color - developing material used in the patent No. CN109780029A is a rare - earth force - induced luminescence material. The manufacturing and processing technology of this kind of material is complex and the material is scarce. While the material used in this patent is an epoxy resin with birefringence effect and other materials, which are easier to obtain and still have good color - developing effects; 2) This patent does not use a color - developing material coating. Instead, without damaging the stress structure of the bolt, a certain depth of hole is drilled from the nut to the inside of the screw rod of the bolt, and the color - developing material is filled into the bolt. In this way, the color - developing material can bear force synergistically with the bolt, and the force on the material can be evenly distributed when working with the bolt synergistically, so that the color change is more uniform; 3) This patent judges the stress condition of the bolt according to the color change of the material, while the patent No. CN109780029A judges the stress condition of the bolt according to the radius of the luminescence ring of the rare - earth material. Compared with the patent No. CN109780029A, this patent can use optical simulation to analyze and quantify the color change of the material, and can more accurately reflect the stress state of the bolt. 4) In order to obtain better color - developing effects, this patent adds a spiropyran material, and through RGB three - primary - color analysis, better force - color - developing sensitivity is obtained.

[0006] Based on the resin color - developing material and spiropyran, this patent designs an intelligent bolt with obvious color - developing effects, which can solve the problem that traditional bolt detection is time - consuming and labor - intensive, and can be widely applied to the loosening detection of all bolts. Summary of the Invention

[0007] The purpose of the present invention is to solve the problems that common bolt detection technologies are complex and cumbersome, the engineering quantity is relatively large, and the cost of other types of intelligent bolts is relatively high at present, and most of them require a lot of auxiliary devices such as optical fibers or wiring during detection. By comparing the color - developing effects of pure resin color - developing materials and color - developing materials added with spiropyran, a force - induced color - developing material, its preparation method and an intelligent bolt based on this material are provided. The color - developing effect of the intelligent bolt is obvious with the change of force, which is intuitive and economical.

[0008] The present invention adopts the following technical scheme: A force - induced color - developing material, comprising the following components: epoxy resin, curing agent, spiropyran (1,3,3 - trimethylindole o - phenylthiophenol) and ethanol. The mass percentages of each component are as follows:

[0009] The mass percentage of the epoxy resin is 65.00%, the mass percentage of the curing agent is 24.00%, the mass percentage of the spiropyran is 1.00%, and the mass percentage of the ethanol is 10.00%;

[0010] The sum of the mass percentages of the epoxy resin, curing agent, spiropyran and ethanol is 100%.

[0011] The preparation method of the above-mentioned force-induced chromogenic material comprises the following steps:

[0012] 1) Take epoxy resin and put it into a dryer, set the temperature to 70 °C and soften it for no less than 30 minutes. Without affecting the performance of the epoxy resin, reduce the viscosity of the epoxy resin and increase its fluidity;

[0013] 2) Take spiropyran and add it to ethanol, and stir until it is completely dissolved;

[0014] 3) Slowly add the spiropyran / ethanol solution to the softened epoxy resin, and continuously stir until it is evenly mixed;

[0015] 4) Mix the mixture from the previous step with a curing agent in proportion, and perform ultrasonic dispersion and magnetic stirring;

[0016] 5) Vacuumize the mixture from the previous step to remove the bubbles in the epoxy resin and the curing agent;

[0017] 6) After standing, put the prepared material into a drying oven for curing to complete the production of the spiropyran-containing resin chromogenic material.

[0018] An intelligent bolt based on the above-mentioned force-induced chromogenic material comprises a bolt, a force-induced chromogenic material, a bolt gasket, a polarizer and a reflective material;

[0019] The force-induced chromogenic material is cylindrical. The force-induced chromogenic material is filled inside the bolt rod of the bolt. A bolt gasket is provided on the bolt. A reflective material is provided at the bottom of the force-induced chromogenic material, and a polarizer is provided on the reflective material;

[0020] When the force-induced chromogenic material is subjected to external forces such as extrusion force, obvious color changes will occur when observed through the polarizer. When the external forces such as extrusion force become smaller or the external force is removed, the force-induced chromogenic material returns to the colorless state.

[0021] Advantages of the present invention:

[0022] 1) Simple operation

[0023] The intelligent bolt of this patent is convenient to use. Without connecting other electronic devices to the bolt, the stress condition of the bolt can be judged, and the problem of complex and cumbersome traditional bolt monitoring equipment can be solved.

[0024] 2) Strong designability

[0025] This intelligent bolt can be made into different types of intelligent bolts according to the actual application scenario or stress environment of the bolt, so as to meet different working environments.

[0026] 3) Low manufacturing cost

[0027] The materials used in the intelligent bolt of this patent are epoxy resin and curing agent, and the costs of these materials are relatively low, so that they can be produced and used on a large scale. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the tensile specimen of the present invention;

[0029] Figure 2 It is a diagram of the tensile interference test of the whole process of epoxy resin of the present invention;

[0030] Figure 3 It is a diagram of the tensile interference test of the whole process of polycarbonate of the present invention;

[0031] Figure 4 It is a diagram of the tensile interference test of the whole process of polyurethane of the present invention;

[0032] Figure 5 It is a diagram of the stress-optical coefficient of the present invention;

[0033] Figure 6 It is a schematic structural diagram of the intelligent bolt with a cylindrical chromogenic material inside the present invention;

[0034] Figure 7 is Figure 6 cross-sectional view of. Detailed Description of the Invention

[0035] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0036] A method for selecting a force-induced chromogenic material of the present invention specifically includes the following materials and their performance ranges: the viscosity range of epoxy resin is 200-300 mPa·s; the epoxy resin curing agent is applicable to the epoxy resin within the above viscosity range; polycarbonate and its curing agent are applicable to application scenarios requiring high transparency and impact resistance; polyurethane and its curing agent are applicable to application scenarios requiring high wear resistance and chemical resistance; 1,3,3-trimethylindole o-phenylthiophenol (spiropyran) is used as a chromogenic material additive and is applicable to application scenarios indicating stress or temperature changes through color changes.

[0037] 1) The mass percentage of polycarbonate is 9.10%, the mass percentage of the curing agent is 90.91%, and the sum of the mass percentages of polycarbonate and the curing agent is 100%. There is no other solvent in the resin.

[0038] 2) The mass percentage of polyurethane is 83.33%, the mass percentage of the curing agent is 16.67%, and the sum of the mass percentages of polyurethane and the curing agent is 100%. There is no other solvent in the resin.

[0039] 3) The mass percentage of pure epoxy resin is 75.00%, and the mass percentage of the curing agent is 25%.

[0040] The sum of the mass percentages of epoxy resin and curing agent is 100%. There are no other solvents in the resin.

[0041] 4) When adding the spiropyran chromogenic material, the proportion of epoxy resin is 65.00%, the mass percentage of the curing agent is 24.00%, the mass percentage of spiropyran is 1.00%, and the mass percentage of ethanol is 10.00%.

[0042] The sum of the mass percentages of epoxy resin, curing agent, spiropyran and ethanol is 100%.

[0043] Interference test during the whole tensile process:

[0044] Prepare samples of the above three resin materials and conduct an interference test during the whole tensile process. The sample preparation and test plan for the tensile specimens are as follows.

[0045] 1) Put the epoxy resin into a dryer and set the temperature to 70°C to soften it for 30 minutes. Without affecting the performance of the epoxy resin, reduce the viscosity of the epoxy resin to increase its fluidity.

[0046] 2) Mix the softened epoxy resin and the epoxy resin curing agent in proportion, disperse them ultrasonically for 10 minutes (the instrument model is not limited), and stir magnetically at 400 rpm for 5 minutes.

[0047] 3) Evacuate the mixture to remove the bubbles in the epoxy resin and the curing agent, and let it stand for 10 minutes.

[0048] 4) After standing, pour the prepared material into a dog-bone-shaped mold and put it into a drying oven (the model of the vacuum drying oven is not limited) to cure at 70°C for 5 hours to complete the production of the epoxy resin tensile specimen.

[0049] The universal testing machine used in the test has a maximum load of 2.5 kN. According to the existing resin performance test "Experimental Scheme for Tensile Properties of Resin Castings" (GB / T 2568-1995) and "Experimental Scheme for Tensile Properties of Resin Castings" (GB / T 2568-1995), the tensile specimens are as Figure 1 shown, and conduct a tensile test on them. Place the prepared tensile specimens on the tensile tester, align the central axis of the specimens with the alignment center line of the upper and lower clamps, continuously load at a tensile speed of 2 mm / min until failure, obtain the failure strength of 3 groups of specimens, and take the average value of the three groups of specimens as the tensile strength of the material.

[0050] After obtaining the ultimate failure deformation of the test piece, place the prepared tensile test piece on the tensile tester and simulate the natural light incident through the LED lamp. The load amplitudes are respectively 30%, 50%, 70%, 80%, 85%, 90%, 95% and 100% of the maximum strain in the linear segment. When loaded to the predetermined strain, hold for 2 minutes. Wait for the test piece to stabilize and show obvious color changes, and record with a camera until the test piece fails. Since the detection light source interferes successively through the polarizer, the tensile sample and the analyzer, and then is recorded by the camera, the stress state of the color display element can be obtained by observing the polarization interference color sequence. Figure 2 , Figure 3 , Figure 4 are the tensile interference test pictures of epoxy resin, polycarbonate and polyurethane respectively.

[0051] After the test, according to λN / h(×10 -6 ) and σ 1 -σ 2 to obtain a straight line passing through the origin as shown in Figure 5 . The slope of the straight line is the required stress-optical coefficient C value. The larger the stress-optical coefficient C, the greater the influence of the internal stress on the optical properties and the more obvious the color. According to Figure 5 , the C value of epoxy resin can be obtained as 113.76, the C value of polycarbonate is 84.55, and the C value of polyurethane is 71.648. The stress-optical coefficient of epoxy resin is the highest and the color display effect is the best ("Data storage containing transparent photoelastic", Ramesh H et al., 2003). Therefore, this patent uses epoxy resin as the color display material of the smart bolt.

[0052] Confining pressure interference test:

[0053] Make samples of the above two color display materials and conduct confining pressure interference tests. The preparation of the pure epoxy resin confining pressure test piece is as follows.

[0054] 1) Take epoxy resin and put it into a dryer, set the temperature to 70°C and soften for at least 30 minutes. Without affecting the performance of epoxy resin, reduce the viscosity of epoxy resin and increase its fluidity;

[0055] 2) Mix the softened epoxy resin with the epoxy resin curing agent in proportion, and conduct ultrasonic dispersion and magnetic stirring;

[0056] 3) Evacuate the mixture to remove the bubbles in the epoxy resin and the curing agent;

[0057] 4) After standing, pour the prepared material into a mold and place it in a drying oven for curing to complete the production of the pure resin confining pressure test piece.

[0058] The preparation of the confined pressure specimen of the spiropyran-containing resin is as follows:

[0059] 1) Take the epoxy resin and put it into a dryer. Set the temperature to 70°C and soften it for no less than 30 minutes. Without affecting the performance of the epoxy resin, reduce the viscosity of the epoxy resin to increase its fluidity.

[0060] 2) Take spiropyran and add it to ethanol, and stir until it is completely dissolved.

[0061] 3) Slowly add the spiropyran / ethanol solution to the softened epoxy resin and keep stirring until it is evenly mixed.

[0062] 4) Mix the mixture with the epoxy resin curing agent in proportion, and disperse it evenly by ultrasonic dispersion and magnetic stirring;

[0063] 5) Evacuate the mixture to remove the bubbles in the mixture;

[0064] 6) After standing, pour the prepared material into a cylindrical mold and put it into a drying oven for curing to complete the production of the confined pressure specimen of the spiropyran-containing resin.

[0065] Confined pressure interference test:

[0066] 1) Determination of the polarization angle between polarizers: In order to avoid the influence of the angle difference between polarizers on the observation of the color change of the bolt chromogenic material prepared in this patent during the tensile interference test and the confined pressure interference test, set the angle of the polarizer to zero, rotate the analyzer until no obvious color appears between the two polarizers, and at this time, set the angle difference between the two polarizers as the angle difference between the two polarizers during the test;

[0067] 2) Conduct a confined pressure test on the selected type of epoxy resin to explore the chromogenic performance of the material: Prepare samples for the selected epoxy resin. The sample preparation method is the same as steps 1) to 3) of the preparation method of the intelligent bolt chromogenic material above. After pouring the prepared material into the mold, put it into a drying oven for curing to obtain the confined pressure sample.

[0068] 3) Use a special confined pressure device to apply pressure to the material gradually. It is found that as the pressure increases, the color change of the epoxy resin chromogenic material becomes more and more obvious. The color change of the chromogenic material occurs during the process of the confined pressure from 0 N to 700 N; To quantify the color change of the chromogenic material, introduce the RGB analysis method for analysis. Use an image processing software (such as OpenCV or ImageJ of Python) to extract the RGB values on the surface of the material, and calculate the error E between the stressed and unstressed states through the weighted RGB value formula to judge the color discrimination. The error ΔE calculation formula is as follows:

[0069]

[0070] Table 1 RGB analysis results of the added spiropyran colorimetric material

[0071]

[0072] As shown in Table 1, the RGB values of the epoxy resin added with spiropyran change significantly after being stressed, indicating that it has obvious force-induced color change characteristics and is suitable for stress visualization monitoring.

[0073] The preparation method of the above-mentioned intelligent bolt colorimetric material includes the following steps:

[0074] 1) Take the epoxy resin and put it into a dryer, set the temperature to 70°C and soften it for no less than 30 minutes. Without affecting the performance of the epoxy resin, reduce its viscosity and increase its fluidity.

[0075] 2) Take spiropyran and add it to ethanol, and stir until it is completely dissolved.

[0076] 3) Slowly add the spiropyran / ethanol solution to the softened epoxy resin and continuously stir until it is evenly mixed.

[0077] 4) Mix the mixture with the epoxy resin curing agent in proportion, and disperse it evenly by ultrasonic dispersion and magnetic stirring.

[0078] 5) Vacuumize the mixture to remove the bubbles in the epoxy resin and the curing agent.

[0079] 6) After standing, put the prepared material into a drying oven for curing to complete the production of the spiropyran-containing resin colorimetric material.

[0080] The key of the intelligent bolt of the present invention lies in the experimental optimization of the bolt colorimetric material, the confining pressure interference test, and the design of the intelligent bolt.

[0081] Such as Figure 6 and Figure 7 shown, an intelligent bolt based on the above-mentioned force-induced colorimetric material includes a bolt 1, a force-induced colorimetric material 2, a bolt gasket 3, a polarizer 4, and a reflective material 5;

[0082] The force-induced colorimetric material 2 is cylindrical. The force-induced colorimetric material 2 is filled inside the bolt rod of the bolt 1. A bolt gasket 3 is provided on the bolt 1. A reflective material 5 is provided at the bottom of the force-induced colorimetric material 2, and a polarizer 4 is provided on the reflective material 5;

[0083] When the force-induced colorimetric material 2 is subjected to external forces such as extrusion force, obvious color changes will occur when observed through the polarizer 4. When the external forces such as extrusion force become smaller or the external force is removed, the force-induced colorimetric material 2 returns to the colorless state.

[0084] During the use process, a polarizer is used to observe the color change of the bolt. Due to factors such as vibration and temperature, the pre-tightening force of the bolt will continuously decrease. At this time, the color display effect of the force-induced color-changing material gradually decays until it decays to the set minimum value. The minimum value can be used as the pre-tightening force value when the color display effect disappears. At this time, the bolt needs to be inspected and re-tightened.

[0085] It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this example can be implemented by the prior art.

Claims

1. A mechanochromic material, characterized in that: The invention comprises the following components: epoxy resin, curing agent, spiropyran and ethanol, and the mass percentage of each component is: The mass percentage of the epoxy resin is 65.00%, the mass percentage of the curing agent is 24.00%, the mass percentage of spiropyran is 1.00%, and the mass percentage of ethanol is 10.00%; The sum of the mass percentages of the epoxy resin, the curing agent, the spiropyran and the ethanol is 100%.

2. The method for preparing a mechanochromic material according to claim 1, characterized in that: The following steps are involved: 1) Put the epoxy resin into a dryer and set the temperature to 70°C to soften for no less than 30 minutes. Under the premise of not affecting the performance of the epoxy resin, reduce the viscosity of the epoxy resin and increase its fluidity; 2) Add spiropyran to ethanol and stir until completely dissolved; 3) Slowly add the spiropyran / ethanol solution into the softened epoxy resin and stir continuously until the mixture is uniformly mixed; 4) Mix the mixed solution in the previous step with the curing agent in proportion, and perform ultrasonic dispersion and magnetic stirring; 5) Vacuum the mixture from the previous step to remove bubbles in the epoxy resin and curing agent; 6) After standing, the prepared material is placed in a drying oven for solidification, thereby completing the preparation of the spiropyran resin-containing color-developing material.

3. A smart bolt based on the mechanochromic material according to claim 1, characterized in that: Includes bolts, mechanochromic materials, bolt washers, polarizing films and reflective materials; The mechanochromic material is cylindrical, and is filled inside the bolt rod of the bolt. A bolt gasket is provided on the bolt, and a reflective material is provided at the bottom of the mechanochromic material, and a polarizer is provided on the reflective material. When the mechanochromic material is subjected to an external force, an obvious color change will occur when it is observed through a polarizing plate. When the external force becomes smaller or the external force is removed, the mechanochromic material returns to a colorless state.

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