Flexible strain sensor material for monitoring of seismic isolation bearings and method of preparation and use thereof

Abstract

The application discloses a flexible strain sensor material for monitoring an isolation bearing, and a preparation method and application thereof, and comprises the following steps: S1, sodium dodecyl sulfate, tetradecyl trimethyl ammonium bromide and conductive fillers are mixed in an organic solvent, the organic solvent is removed by volatilization after being sufficiently mixed and uniformly distributed, and conductive nano fillers are obtained; S2, mixing: the conductive nano fillers, methyl vinyl silicone rubber, silicon dioxide and vulcanizing agents are mixed according to a mass ratio, and are mixed to obtain a mixed material; S3, vulcanization: the mixed material is vulcanized in two stages, and the vulcanization temperature in the second stage is 20-30 DEG C higher than that in the first stage, and the flexible strain sensor material is obtained. The sensor material prepared by the application is stretchable, has high sensitivity, good mechanical properties, fast response time, stable resistance / response signal, and is especially suitable for real-time structural health monitoring of the isolation bearing under large deformation.

Description

Technical Field

[0001] The present invention relates to the field of rubber materials and strain sensing technology, and in particular to a flexible strain sensor material for monitoring a seismic isolation support, a preparation method thereof, and applications thereof. Background Art

[0002] Earthquakes are natural disasters that pose a serious threat to human life and property. Therefore, countries around the world are committed to improving earthquake mitigation and disaster reduction in engineering projects, enhancing the seismic fortification and resilience of construction projects. The use of seismic isolation technology and seismic bearings can isolate or dissipate seismic wave energy and is currently the most effective earthquake mitigation measure. Base isolation technology employs a flexible connection between the building superstructure and the foundation, creating a sufficiently safe seismic isolation system. Due to the isolation and shock absorption properties of the isolation layer, the superstructure undergoes approximately translational motion during an earthquake, with the structural response reduced to only 1 / 4-1 / 8 of that in a non-isolated environment, thereby effectively isolating the earthquake. Among the various seismic isolation systems, rubber bearings are the mainstream in global research and application. Seismic isolation bearings are devices used to isolate building structures. Their primary function is to reduce the impact of earthquakes on buildings by adding an isolation layer between the foundation and superstructure. The operating principles of seismic isolation bearings are based on two main principles: first, absorbing seismic energy through deformation of the elastic material; second, dissipating seismic energy through sliding or damping mechanisms. Specifically, when an earthquake occurs, the energy generated by the ground motion is first absorbed and dissipated by the isolation layer. Only a small portion of this energy is transferred to the superstructure via the isolation bearings, significantly reducing the seismic effects on the building. Currently, various laminated rubber bearing isolation houses used both domestically and internationally have proven effective isolation and significant seismic performance after numerous strong earthquake tests.

[0003] However, when the seismic isolation bearings are often in a high-load working environment of "continuous small earthquakes and occasional strong earthquakes", the bearings will be severely damaged and have a short service life; plus, the seismic isolation bearings are mainly made of rubber materials, and the aging and failure of rubber will also accelerate the fatigue and damage of the bearings. It can be said that the service performance of the seismic isolation bearings in high-intensity earthquake zones directly determines the health of the engineering structure. Therefore, regular inspections of seismic isolation bearings are very important to ensure their normal performance. Inspection items include seismic isolation bearings, isolation joints, flexible connections, tensile devices, etc.; inspection content includes instrumental measurement of the horizontal deformation and vertical compression deformation of the bearings, as well as observation and inspection of other items.

[0004] However, most experimental testing methods, both domestically and internationally, focus only on pre-use isolation bearings. Real-time performance and damage analysis of bearings during service relies solely on theoretical simulations, which lack accuracy and reliability. In cases where simulations are inadequate, the bearings must be removed from the building for testing. This requires extensive engineering effort, is inefficient, and extremely costly, and does not yield real-time data. For example, the isolation bearings of a large building, which had been in service for over 10 years, experienced six earthquakes below magnitude 5 on the Richter scale. The damage to some bearings urgently required assessment. However, the cost of disassembling and inspecting a single bearing exceeded 50,000 yuan, and the extent of damage varied from bearing to bearing, making disassembly and inspection of all bearings unnecessary. If real-time monitoring of isolation bearing performance while in service were possible, capturing dynamic stress and strain information, the extent of damage to each bearing could be accurately and promptly determined, allowing for service life assessment. Furthermore, the extent of earthquake damage to the building could be analyzed, enabling comprehensive analysis and early warning of the structural safety status. Therefore, real-time monitoring of bearing performance has become a bottleneck in the development of seismic isolation technology and a pressing issue in the current disaster prevention and mitigation field.

[0005] One of the core issues in structural health monitoring technology for seismic isolation bearings is intelligent sensing technology. Currently, widely used structural health monitoring sensors are mainly made of inorganic non-metallic materials such as fiber gratings and piezoelectric ceramics. These materials are brittle, have weak damage resistance, poor durability and processability, high maintenance costs, and a relatively short service life. The structural and functional characteristics of rubber seismic isolation bearings determine that the sensing material must have the characteristics of large deformation, damage resistance, long life, and high sensitivity. Ordinary inorganic non-metallic intelligent materials are no longer applicable. This problem is more prominent in high-intensity earthquake zones, which is why real-time monitoring of seismic isolation bearings has not yet been achieved. Therefore, the research and development of new intelligent sensing materials is urgent.

[0006] Multi-walled carbon nanotubes (MWCNTs) possess excellent physical and chemical properties, and their unique microstructure offers significant advantages for constructing molecular conductive networks. Ultrasonic mixing of MWCNTs with cationic and anionic dispersants such as sodium dodecyl sulfate and tetradecyltrimethylammonium bromide creates a stable charge layer on the MWCNT surface. This generates electrostatic repulsion, preventing aggregation of the MWCNTs and promoting the uniform dispersion of the conductive nanofillers within the rubber matrix, ultimately building a conductive network with high deformation capacity within the material. Based on the tunneling effect, the resistivity of the conductive network changes synchronously with deformation, enabling load and deformation response monitoring. This resistance / strain-responsive material has been extensively researched in the biomedical and mechanical manufacturing fields due to its excellent resistance to damage and processability. The core material of seismic isolation bearings is rubber. Designing and preparing intelligent sensing materials suitable for load and deformation monitoring in seismic isolation bearings would completely resolve the compatibility issue between sensors and isolation materials, making it an ideal choice for new sensing materials and of great significance to the development of structural health monitoring technology. Summary of the Invention

[0007] The object of the present invention is to address the above-mentioned problems and provide a flexible strain sensor material for monitoring seismic isolation bearings, a preparation method thereof, and an application thereof.

[0008] In order to achieve its purpose, the present invention adopts the following technical solutions:

[0009] A first aspect of the present invention provides a method for preparing a flexible strain sensor material for monitoring a seismic isolation bearing, comprising the following steps:

[0010] S1. Preparation of conductive nanofillers:

[0011] Sodium lauryl sulfate, tetradecyltrimethylammonium bromide and a conductive filler are mixed in an organic solvent, mixed thoroughly, and then heated to evaporate and remove the organic solvent to obtain a conductive nanofiller;

[0012] The mass ratio of sodium lauryl sulfate, tetradecyltrimethylammonium bromide and conductive filler is 0-5:0-1.2:0.8-1.2;

[0013] S2. Mixing

[0014] The conductive nanofiller prepared in step S1 is mixed with methyl vinyl silicone rubber, silicon dioxide, and a vulcanizing agent in a mass ratio of 12-16:350-450:6-10:3-5, and kneaded to obtain a mixture;

[0015] S3, vulcanization:

[0016] The mixed material prepared in step S2 is vulcanized in two stages, with the vulcanization temperature in the second stage being 20 to 30° C. higher than that in the first stage, to obtain the flexible strain sensor material.

[0017] Preferably, the organic solvent is ethyl acetate, tetrahydrofuran or acetone;

[0018] The conductive filler is selected from multi-walled carbon nanotubes or conductive carbon black;

[0019] The vulcanizing agent is selected from one or more of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl perbenzoate, and dibenzoyl peroxide.

[0020] In step S1, the mass ratio of sodium lauryl sulfate, tetradecyltrimethylammonium bromide and conductive filler is 1-4:0.8-1.2:0.8-1.2 or 1-3:0.9-1.1:0.9-1.1;

[0021] In step S1, sodium lauryl sulfate, tetradecyltrimethylammonium bromide, and a conductive filler are mixed in an organic solvent, ultrasonically stirred to uniformly mix, and heated to volatilize and remove the organic solvent to obtain a conductive nanofiller; wherein the volume ratio of the sum of the mass of sodium lauryl sulfate, tetradecyltrimethylammonium bromide, and the conductive filler to the organic solvent is 0.1-1 g:100-1000 ml;

[0022] The ultrasonic stirring conditions are as follows: an ultrasonic frequency of 100 to 150 Hz, a stirring rate of 450 to 600 rpm, and ultrasonic stirring and mixing for 2 to 4 hours;

[0023] Preferably, magnetic stirring is performed before ultrasonic stirring, and the magnetic stirring condition is stirring at a stirring rate of 450-600 rpm for 30-60 min;

[0024] The organic solvent is ethyl acetate, and the temperature is raised to 50-70° C. to remove the ethyl acetate and obtain a conductive nanofiller.

[0025] In step S2, the conductive nanofiller is mixed with methyl vinyl silicone rubber, silicon dioxide, and a vulcanizing agent in a mass ratio of 13-15:380-420:7-9:3-5 or 14:400:8:4;

[0026] The mixing temperature is 40-60° C., the roller distance is 0.5-1 mm, the speed is 20-35 rpm, and the mixing process is 40-60 min.

[0027] In step S3, the first stage of vulcanization is performed at a vulcanization temperature of 150-170°C, a time of 10-20 min, and a pressure of 10-20 MPa. Preferably, the vulcanization temperature is 160-170°C, a time of 10-15 min, and a pressure of 10-15 MPa.

[0028] Then the second stage vulcanization treatment is carried out, the vulcanization temperature is 180-200°C, and the time is 2-4 hours.

[0029] In step S3, the first stage of vulcanization is carried out on a flat plate vulcanizer, and the second stage of vulcanization is carried out in an oven.

[0030] The vinyl content of the methyl vinyl silicone rubber is 0.18%, and the molecular weight is 6.2×10 5 g / mol;

[0031] The multi-walled carbon nanotubes are 10-20 μm long, 4-6 nm in diameter, and have a specific surface area of ​​500-700 m 2 / g.

[0032] The nano-silicon dioxide has a particle size of 7-40 nm and a specific surface area of ​​300 m 2 / g.

[0033] A second aspect of the present invention provides a flexible strain sensor material, which is prepared by any of the preparation methods described above.

[0034] A third aspect of the present invention provides use of the above-mentioned flexible strain sensor material in preparing a flexible strain sensor.

[0035] Preferably, the flexible strain sensor material is prepared into a flexible sensor for structural health monitoring of seismic isolation bearings.

[0036] The beneficial effects of the present invention are:

[0037] (1) By assembling the flexible strain sensor material of the present invention with the seismic isolation support, the compatibility of the flexible strain sensor material with the rubber seismic isolation material and the resistance / strain response characteristics are fully utilized, so that the support has both the seismic isolation function and the strain signal acquisition function, the seismic isolation support is realized to be intelligent, and the development of seismic isolation support structural health monitoring technology is promoted.

[0038] (2) Although there are many research reports on smart sensors, their application in civil engineering and seismic isolation technology is still blank. This project aims to realize the service performance monitoring of rubber isolation bearings, and to innovate the preparation and application of flexible smart sensors in a targeted manner, thus opening up new areas for the application of nanocarbon materials.

[0039] (3) Compared with traditional commercial conductive fillers, the present invention uses self-assembled anionic and cationic dispersants to modify multi-walled carbon nanotubes. The conductive fillers modified with anionic and cationic dispersants can be evenly dispersed in the rubber matrix and can form a stable charge layer on the surface of the multi-walled carbon nanotubes, thereby generating a significant electrostatic repulsion effect and effectively inhibiting the agglomeration of the multi-walled carbon nanotubes. This self-assembly method not only significantly improves the uniform dispersion of the conductive nanofiller in the rubber matrix, but also promotes the reconstruction and stability of the conductive network inside the material, thereby giving the rubber composite material excellent deformation ability, mechanical properties and conductive properties. The rubber composite material prepared by the method of the present invention is used as a sensor material and has lower volume conductivity and more stable resistance / strain response signal acquisition capabilities than flexible sensors prepared from commercial multi-walled carbon nanotubes.

[0040] (4) The appropriate ratio of anionic and cationic dispersants can make multi-walled carbon nanotubes more compatible with the rubber matrix, enhance the interfacial bonding strength of the composite material, and thus have good dispersion in the rubber matrix, thereby achieving a significant improvement in the performance of the final product.

[0041] The present invention prepares a flexible strain sensor material that is stretchable, highly sensitive, has good mechanical properties, fast response time, and stable resistance / response signal in a low-cost, high-efficiency, and pollution-free manner. The material can undergo synchronous deformation and coordination with the isolation bearing to output a response monitoring signal, and thus can be suitable for real-time structural health monitoring of the isolation bearing under large deformation, providing strong technical support for the structural health monitoring of large components using intelligent sensing monitoring technology, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flow chart of the preparation process of the flexible strain sensor material of the present invention.

[0043] Figure 2 This is a diagram showing the actual conditions of the flexible strain sensor material of Example 4 under tension, torsion, and bending.

[0044] Figure 3 These are SEM micromorphology images of the flexible strain sensors of Comparative Example 2 and Example 4.

[0045] Figure 4 is the response time of the flexible strain sensor material of Example 4.

[0046] Figure 5 This is the monitoring response signal of the flexible strain sensor material of Example 4 to the seismic isolation support. DETAILED DESCRIPTION

[0047] The present invention will be further described below with reference to the embodiments, but the present invention is not limited thereto.

[0048] The experimental methods in the following examples are conventional methods unless otherwise specified.

[0049] Example

[0050] The raw materials are:

[0051] Anionic dispersant sodium dodecyl sulfate (SDS, CAS No. 151-21-3), cationic dispersant tetradecyltrimethylammonium bromide (TTAB, CAS No. 1119-97-7), multi-walled carbon nanotubes (MWCNT), ethyl acetate, methyl vinyl silicone rubber (VMQ), nano-silica, dicumyl peroxide (curing agent DCP).

[0052] Among them, the vinyl content of methyl vinyl silicone rubber is 0.18%, and the molecular weight is 6.2×10 5 g / mol. Multi-walled carbon nanotubes are 10-20 μm long, 4-6 nm in diameter, and have a specific surface area of ​​500-700 m 2 / g.

[0053] Nano-silicon dioxide particle size 7-40nm, specific surface area 300m 2 / g.

[0054] The preparation method of the flexible strain sensor material for monitoring the seismic isolation support of the present invention (process flow chart as shown in FIG Figure 1 As shown), follow the steps below:

[0055] S1. Preparation of conductive nanofillers:

[0056] Anionic and cationic dispersants (sodium lauryl sulfate and tetradecyltrimethylammonium bromide) and multi-walled carbon nanotubes were mixed in ethyl acetate using a magnetic stirrer and stirred at 450 rpm for 30 minutes at room temperature to obtain a conductive filler suspension. The beaker containing the conductive filler suspension was then placed in an ultrasonic cleaner. A stirrer was installed above the beaker, with the stirring head inserted into the beaker. Ultrasonic stirring was performed at a frequency of 100 Hz, a temperature of 20°C, and a stirring rate of 450 rpm for 2 hours. The mixture was then heated to 50°C to remove the ethyl acetate, resulting in the conductive nanofiller (black powder).

[0057] This process can form a stable charge layer on the surface of multi-walled carbon nanotubes, resulting in significant electrostatic repulsion and effectively inhibiting the aggregation of multi-walled carbon nanotubes. In the next step, they can be evenly dispersed in methyl vinyl silicone rubber.

[0058] S2. Mixing to prepare a conductive nanocomposite:

[0059] The conductive nanofiller prepared in step S1 was uniformly mixed with methyl vinyl silicone rubber, silicon dioxide, and dicumyl peroxide in a two-roll mill at a mixing temperature of 60° C., a roller distance of 1 mm, a speed of 20 rpm, and a mixing process of 40 min to obtain an unvulcanized conductive nanomixture.

[0060] This process uses the shear force generated by the double-roll mill to evenly disperse the filler in the methyl vinyl silicone rubber to form a three-dimensional conductive network, enabling it to have the ability to collect signals for monitoring seismic isolation bearings under large deformations.

[0061] S3, vulcanization

[0062] S3.1. First stage vulcanization: The conductive nanocomposite prepared in step S2 is placed in a flat plate vulcanizer and vulcanized at a temperature of 170° C., a pressure of 10 MPa, and a time of 10 min to obtain a product after the first stage vulcanization.

[0063] In the first stage of vulcanization, dicumyl peroxide is decomposed into free radicals through high temperature, which triggers the rupture of the vinyl double bonds in the methyl vinyl silicone rubber. New free radicals are generated to cross-link the molecular chains in the rubber to form a cross-linked structure.

[0064] S3.2. Second stage vulcanization: Place the conductive nano-rubber composite material that has completed the first stage vulcanization into an oven and vulcanize it at a temperature of 200°C for 4 hours to obtain a block-shaped conductive nano-rubber composite material, which is the flexible strain sensor material.

[0065] The second stage of vulcanization at high temperature further increases the degree of cross-linking through cross-linking points initiated by free radicals, thereby improving the mechanical properties, high temperature resistance, elasticity and chemical stability of the flexible smart sensor.

[0066] According to the above method, the conductive nano-rubber composite materials of Examples 1-4 were prepared. The specific raw material ratios of each example are shown in Table 1:

[0067] Table 1

[0068] Example / Raw Materials Example 1 Example 2 Example 3 Example 4 SDS / g 0 0.16 0.32 0.48 TTAB / g 0 0.16 0.16 0.16 MWCNT / g 0.16 0.16 0.16 0.16 Ethyl acetate / ml 500 500 500 500 Conductive nanofiller / g 0.14 0.14 0.14 0.14 VMQ / g 4 4 4 4 Silicon dioxide / g 0.08 0.08 0.08 0.08 Curing agent DCP / g 0.04 0.04 0.04 0.04

[0069] Comparative Example 1 (using the same raw materials as the present invention, different processes)

[0070] The raw materials and dosages of Example 4 of the present invention were used, but the preparation process adopted the existing technology: methyl vinyl silicone rubber, commercial multi-walled carbon nanotubes, sodium lauryl sulfate, tetradecyltrimethylammonium bromide, silicon dioxide, and diisopropyl peroxide were directly placed in an internal mixer and mixed at a temperature of 70°C, a speed of 80 rpm, a roller gap of 1 mm, and a mixing time of 30 minutes. Subsequently, the mixture was placed in a flat plate vulcanizer and vulcanized at a pressure of 15 MPa, a temperature of 160°C, and a mixing time of 15 minutes.

[0071] Comparative Example 2 (using different raw materials and the same process as the present invention)

[0072] Different raw materials were used from those in Example 4. Specifically, the filler included 100 parts of methyl vinyl silicone rubber, 10 parts of conductive carbon black, 300 ml of tetrahydrofuran, 5 parts of silicon dioxide, and 2 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (curing agent bis-25). A flexible strain sensor material was prepared according to the preparation process of Example 4.

[0073] The preparation process is as follows: Conductive carbon black and tetrahydrofuran are mixed and stirred at room temperature using a magnetic stirrer at a stirring rate of 450 rpm for 30 minutes to obtain a conductive filler suspension. The conductive filler suspension is then placed in an ultrasonic cleaner and ultrasonically stirred at a frequency of 100 Hz, a temperature of 20°C, and a stirring rate of 450 rpm for 2 hours. The tetrahydrofuran is then removed by heating to 50°C to obtain a conductive black powder filler. Methyl vinyl silicone rubber is then thinly passed through a two-roll mill, followed by the addition of the conductive black powder filler, silica, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane. The mixture is then kneaded uniformly at a temperature of 60°C, a roll gap of 1 mm, a speed of 20 rpm, and a time of 40 minutes to obtain an uncured conductive nanocomposite. The uncured conductive nano-mixture was placed in a flat-plate curing instrument for the first stage of curing. The curing conditions were temperature 170°C, pressure 10 MPa, and time 10 min to obtain the product after the first stage of curing. The product was then placed in an oven at 200°C for 4 hours of second stage curing to obtain a flexible strain sensor material.

[0074] Performance testing

[0075] The performance of the prepared flexible strain sensor material was tested.

[0076] (1) Volume conductivity: The volume conductivity of the conductive nano-rubber material was tested according to the GT / T1692-2008 standard. First, the sample was cut into a standard sample with a size of 40 mm × 10 mm × 1 mm (the surface was cleaned with anhydrous ethanol). The resistance value of the sample in the unstrained state was measured using a Keysight 34465A digital multimeter. The average resistance value within 1 second of the digital multimeter was collected. Three test specimens were tested in each group, and the average value was taken. The volume conductivity formula is defined as:

[0077]

[0078] In formula (1), σ is the volume conductivity (S / m), ρ is the volume resistivity of the material (Ω·m), R is the volume resistance (Ω), L is the length of the sample (m), and S is the cross-sectional area (m 2 ).

[0079] (2) Sensitivity test: Clamp the two ends of the conductive nano-rubber material on an electronic universal testing machine, take a wire, connect one end of the wire to the conductive nano-rubber material, and connect the other end of the wire to a digital multimeter. Set the strain through the universal testing machine. After a single stretching cycle, the maximum resistance value is transmitted to the computer through the digital multimeter. Then, calculate the sensitivity through the resistance and strain according to formula (2).

[0080] Sensitivity calculation method: Use formula (2) to evaluate the sensitivity of the composite material:

[0081] GF=(ΔR / R0) / ε Formula (2)

[0082] In formula (2), ε is the strain. ΔR / R0, ΔR=R-R0, where R0 is the initial resistance and R is the test resistance.

[0083] (3) Resistance / strain response signal test method: The conductive nano-rubber material was cut into strips of 40 mm × 40 mm × 1 mm. The sample was fixed on an electronic universal testing machine for a cyclic loading-unloading test, and the resistance / strain response signal changes were recorded using a digital multimeter.

[0084] (4) Mechanical properties test method: According to GB / T528-2009, the mechanical properties of dumbbell-shaped standard conductive nano-rubber material specimens were measured using an electronic universal testing machine (DDL10) at a tensile rate of 200 mm / min. -1 , test 3 groups of experimental data and take the average value.

[0085] The performance test results are shown in Table 2.

[0086] Table 2: Flexible strain sensor material performance results

[0087] Examples / Comparative Examples Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 Volume conductivity (S / m) 0.42 0.18 0.07 0.04 <![CDATA[5.37×10 -5 ]]> <![CDATA[6.48×10 -6 ]]> Sensitivity 13.06 48.69 57.69 87.28 210.61 397.21 Tensile strength (MPa) 1.62 4.68 2.33 3.55 5.47 8.17 Elongation at break (%) 221.45 363.42 298.11 321.78 426.79 544.77

[0088] (5) Response time detection

[0089] The flexible strain sensor material of Example 4 was fixed on an electronic universal testing machine. Cyclic stretching-unloading was set on the electronic universal testing machine. The two ends of the wire were connected to the sensor and a digital multimeter respectively. The cyclic stretching-unloading output signal of the sensor was transmitted to the computer to obtain a cyclic resistance / strain signal graph. The time between two adjacent cycles was the response time. The test results are shown in Figure 2. Figure 4 As shown, the flexible strain sensor material of the present invention can be used as a sensor to quickly reflect the deformation state and collect deformation characteristics in a timely manner, and is very suitable for use in seismic isolation bearing structure health monitoring.

[0090] Figure 2 This is a diagram showing the actual conditions of the flexible strain sensor material of Example 4 under stretching, torsion, and bending.

[0091] From the various embodiments and comparative examples, it can be seen that the volume conductivity of each embodiment is significantly reduced compared with comparative example 1 or comparative example 2. In particular, the volume conductivity of embodiment 4 using the same filler is more significantly reduced compared with comparative example 1. Comparative example 1 directly mixes all the raw materials and kneads them, while embodiment 4 first mixes the conductive nanofiller raw materials and performs self-assembly by magnetic stirring and ultrasonic mixing. This process can form a stable charge layer on the surface of multi-walled carbon nanotubes, thereby producing a significant electrostatic repulsion effect, effectively suppressing the agglomeration of multi-walled carbon nanotubes, and then in the next step, it can be evenly dispersed in methyl vinyl silicone rubber to prepare conductive nanofillers. Self-assembly not only significantly improves the uniform dispersion of conductive nanofillers in the rubber matrix, but also promotes the reconstruction and stability of the conductive network inside the material, thereby giving the composite material excellent deformation ability and conductive properties. The rubber composite material product finally obtained can reduce the volume conductivity to the greatest extent.

[0092] All examples can achieve good sensitivity, and compared with Comparative Example 1 or Comparative Example 2, the sensitivity is improved to varying degrees.

[0093] Tensile strength and elongation at break are primarily related to the dispersion of the conductive nanofillers in the matrix. Comparative Example 1, which did not use self-assembled conductive nanofillers, yielded a rubber composite with lower tensile strength and elongation at break. However, Example 4 exhibited significantly improved tensile strength and elongation at break.

[0094] The appropriate ratio of anionic and cationic dispersants can make multi-walled carbon nanotubes more compatible with the rubber matrix, enhance the interfacial bonding strength of the composite material, and thus achieve good dispersion in the rubber matrix. In Examples 1-4, the mass ratio of sodium lauryl sulfate to tetradecyltrimethylammonium bromide in Example 4 is 3:1, which is greater than the mass ratio of sodium lauryl sulfate to tetradecyltrimethylammonium bromide in Examples 1-3. The product performance of Example 4 is superior to that of Examples 1-3.

[0095] The SEM micromorphology of the materials of Comparative Example 2 and Example 5 ( Figure 3 ) As can be seen, the conductive filler in Comparative Example 2 exhibits severe agglomeration within the rubber matrix, hindering its continuity within the rubber matrix. The self-assembled conductive filler in Example 5 exhibits good dispersion within the rubber matrix, which is a key factor in achieving low volume conductivity, high sensitivity, good mechanical properties, and a stable resistance / strain response signal.

[0096] Through the method of the present invention, combined with a specific mass ratio of anionic and cationic dispersants and the combination of multi-walled carbon nanotubes and methyl vinyl silicone rubber, a flexible strain sensor material with low volume conductivity, high sensitivity, and good mechanical properties can be produced. In addition, the innovative ratio of the raw materials of the present invention enables the flexible strain sensor material itself to have a good resistance / response signal, which is more conducive to real-time structural health monitoring of the isolation bearing. At the same time, the flexible intelligent sensor can overcome the defects of traditional strain sensors such as brittleness, low sensitivity, and narrow monitoring range. During the monitoring process, the resistance / response signal output cooperates with the perfect deformation of the isolation bearing to obtain the health status of the isolation bearing in real time.

[0097] Application Example 1

[0098] The flexible strain sensor material prepared in Example 4 was cut into 40×10×1mm blocks. Silicone rubber glue was used to attach the cut flexible strain sensor to a lead-core seismic isolation rubber bearing in the research team's laboratory. One end of a wire was taped to the sensor material with strong tape, and the other end was connected to a digital multimeter. Deformation of the lead-core rubber bearing caused the sensor to deform, which in turn caused a change in resistance. A real-time resistance / strain response signal was output on a computer, thereby assessing the deformation of the lead-core rubber bearing and enabling monitoring of the bearing. Under certain experimental conditions, significant deformation of the bearing, which in turn caused significant deformation of the sensor and led to a significant change in the resistance / response signal, indicated damage or aging of the bearing.

[0099] The entire experimental process was carried out on a shear press with the working conditions of frequency: 0.05-0.1Hz, deformation displacement: 20-80mm, pressure: 10MPa-25MPa. Deformation direction: bidirectional shear deformation. The test results are as follows Figure 5 As shown, as the rubber bearing deforms, the sensor can capture it with high sensitivity and stably output resistance / strain response signals, and the detection results are accurate and reliable.

[0100] Most of the isolation bearings currently on the market are rubber bearings. The flexible strain sensor material prepared by the present invention has a rubber matrix, which can solve the compatibility problem with rubber isolation bearings. At the same time, the flexible strain sensor has high sensitivity, the output resistance / strain response signal of the isolation bearing deformation is stable, and the excellent deformation ability can achieve perfect coordinated deformation with the isolation bearing. In addition, since the isolation bearing is often in a harsh environment, compared with the fragility, low sensitivity, and poor aging resistance of traditional strain sensors, which cannot perform real-time monitoring of the isolation bearing under large deformation, the flexible strain sensor material of the present invention is particularly suitable for real-time monitoring of the structural health of the isolation bearing. The application of the sensor of the present invention to the real-time monitoring of the isolation bearing does not require each bearing to be disassembled and taken back to the laboratory for testing, which greatly saves manpower, material resources and testing costs.

Claims

1. A method for preparing a flexible strain sensor material for monitoring a seismic isolation support, characterized in that: The steps include: S1. Preparation of conductive nanofillers: Sodium lauryl sulfate, tetradecyltrimethylammonium bromide and a conductive filler are mixed in an organic solvent, mixed thoroughly, and then heated to volatilize and remove the organic solvent to obtain a conductive nanofiller; the organic solvent is ethyl acetate, tetrahydrofuran or acetone; and the conductive filler is selected from multi-walled carbon nanotubes or conductive carbon black; The mass ratio of sodium lauryl sulfate, tetradecyltrimethylammonium bromide and conductive filler is 1-4:0.8-1.2:0.8-1.2; S2. Mixing The conductive nanofiller prepared in step S1 is mixed with methyl vinyl silicone rubber, silicon dioxide, and a vulcanizing agent in a mass ratio of 12-16:350-450:6-10:3-5, and kneaded at a kneading temperature of 40-60° C. to obtain a mixture; S3, vulcanization: The mixture prepared in step S2 is vulcanized in two stages. The vulcanization temperature of the first stage is 150-170°C, and the vulcanization temperature of the second stage is 180-200°C. The second stage vulcanization temperature is 20-30°C higher than the first stage vulcanization temperature to obtain the flexible strain sensor material.

2. The preparation method according to claim 1, wherein: The vulcanizing agent is selected from one or more of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl perbenzoate, and dibenzoyl peroxide.

3. The preparation method according to claim 1, wherein: In step S1, the mass ratio of sodium lauryl sulfate, tetradecyltrimethylammonium bromide and conductive filler is 1-3:0.9-1.1:0.9-1.1; In step S1, sodium lauryl sulfate, tetradecyltrimethylammonium bromide, and a conductive filler are mixed in an organic solvent, ultrasonically stirred to uniformly mix, and heated to volatilize and remove the organic solvent to obtain a conductive nanofiller; wherein the volume ratio of the sum of the mass of sodium lauryl sulfate, tetradecyltrimethylammonium bromide, and the conductive filler to the organic solvent is 0.1-1 g:100-1000 ml; The ultrasonic stirring conditions are as follows: an ultrasonic frequency of 100 to 150 Hz, a stirring rate of 450 to 600 rpm, and ultrasonic stirring and mixing for 2 to 4 hours; The organic solvent is ethyl acetate, and the temperature is raised to 50-70° C. to remove the ethyl acetate and obtain a conductive nanofiller.

4. The preparation method according to claim 3, wherein: Magnetic stirring is performed before ultrasonic stirring. The magnetic stirring condition is stirring at a stirring rate of 450-600 rpm for 30-60 min.

5. The preparation method according to claim 1, wherein: In step S2, the conductive nanofiller is mixed with methyl vinyl silicone rubber, silicon dioxide, and a vulcanizing agent in a mass ratio of 13-15:380-420:7-9:3-5 or 14:400:8:4; The mixing roller distance is 0.5-1 mm, the speed is 20-35 rpm, and the mixing process is 40-60 min.

6. The preparation method according to claim 1, wherein: In step S3, The first stage of vulcanization is at a vulcanization temperature of 160-170°C, a time of 10-20 min, and a pressure of 10-20 MPa; Then the second stage vulcanization treatment is carried out, and the vulcanization time is 2 to 4 hours.

7. The preparation method according to claim 6, characterized in that: In step S3, the first stage of vulcanization is carried out on a flat plate vulcanizer, and the second stage of vulcanization is carried out in an oven.

8. The preparation method according to claim 1, wherein: The vinyl content of the methyl vinyl silicone rubber is 0.18%, and the molecular weight is 6.2×10 5 g / mol; The multi-walled carbon nanotubes are 10-20 μm long, 4-6 nm in diameter, and have a specific surface area of ​​500-700 m 2 / g; The silica particle size is 7-40nm and the specific surface area is 300m 2 / g.

9. A flexible strain sensor material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the flexible strain sensor material according to claim 9 in preparing a flexible strain sensor.

11. The use according to claim 10, characterized in that: The flexible strain sensor material is prepared into a flexible sensor for structural health monitoring of seismic isolation bearings.

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