Bamboo charcoal / ultra-high molecular weight polyethylene composite material substrate type fiber grating sensor and preparation method thereof

Abstract

The invention relates to the field of sensors, in particular to a bamboo charcoal / ultra-high molecular weight polyethylene composite material substrate type fiber bragg grating sensor which comprises a substrate, a covering layer covering the substrate and a fiber bragg grating packaged between the substrate and the covering layer, and the substrate is mainly formed by compounding ultra-high molecular weight polyethylene and bamboo charcoal particles. Compared with the prior art, the substrate of the substrate type fiber grating sensor is made of the mixed material of the bamboo charcoal particles and the ultra-high molecular weight polyethylene, so that the temperature measurement precision, repeatability and strain measurement repeatability of the sensor are improved, and the strain loss is lower.

Description

Technical Field

[0001] This invention relates to the field of sensors, and in particular to a bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber optic grating sensor and its preparation method. Background Technology

[0002] Fiber Bragg grating (FBG) sensors are highly sensitive sensors, with substrate-type FBG sensors commonly used in engineering inspections for strain and temperature measurement of structural surfaces. For example... Figure 1 As shown, a substrate-type fiber Bragg grating sensor generally includes a substrate 1, a cover layer 3 covering the substrate 1, and a fiber Bragg grating 2 sandwiched between the substrate 1 and the cover layer 3. The fiber Bragg grating 2 is protected by being encapsulated in the middle by the substrate 1 and the cover layer 3. At the same time, the substrate 1 and the cover layer 3 can also transmit temperature and stress changes to the fiber Bragg grating 2 for strain and temperature measurement.

[0003] The substrate 1 can be made of metal or organic polymers. While fiber Bragg grating sensors using metal substrates 1 have the advantages of simple structure and easy installation, they are prone to strain transfer loss and corrosion, resulting in poor durability. Therefore, currently, substrates 1 are often made of high-molecular organic polymers such as epoxy resin, polyimide, and polyethylene, or composite materials based on organic polymers, to balance stiffness and toughness, reduce strain loss, and improve corrosion resistance. Correspondingly, the capping layer 3 is often made of materials such as silicone or polyurethane, taking into account optical transparency, mechanical compatibility, chemical stability, and adhesion to the substrate 1. It can be encapsulated by bonding with the substrate through secondary potting.

[0004] However, current substrate-based fiber Bragg grating sensors using organic polymers as substrates still suffer from significant problems such as high strain transfer loss, poor testing accuracy, and poor test repeatability. In recent years, some research teams have focused on using composite materials to encapsulate fiber Bragg grating sensors to address these issues, but no solutions have been found to date. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to overcome the defects or deficiencies of the prior art and provide a fiber optic grating sensor.

[0006] A bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber Bragg grating sensor includes a substrate, a cover layer covering the substrate, and a fiber Bragg grating encapsulated between the substrate and the cover layer. The substrate is mainly composed of ultra-high molecular weight polyethylene and bamboo charcoal particles.

[0007] Compared with existing technologies, the substrate of the substrate fiber optic grating sensor of the present invention is made of a mixture of bamboo charcoal particles and ultra-high molecular weight polyethylene. The sensor has improved temperature measurement accuracy, repeatability, and strain measurement repeatability, and has lower strain loss.

[0008] In one embodiment, the bamboo charcoal particles have a mass fraction of 5-50% in the substrate. At this mass fraction, the properties of the blended material are superior.

[0009] In one embodiment, the bamboo charcoal particles have a particle size of less than or equal to 4.7 μm and greater than or equal to 1.3 μm. Under these parameters, the properties of the mixed material are superior, and it is easier to mix uniformly.

[0010] In one embodiment, the material of the cover layer is the same as the material of the substrate layer.

[0011] In addition, the present invention also provides a method for preparing a bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber Bragg grating sensor, comprising the steps of forming a substrate: mixing bamboo charcoal particles with ultra-high molecular weight polyethylene and cooling to form a substrate; placing a fiber Bragg grating on the substrate; and forming a capping layer to cover the substrate and the fiber Bragg grating.

[0012] In one embodiment, the bamboo charcoal particles have a mass fraction of 5-50% in the substrate.

[0013] In one embodiment, the bamboo charcoal particles have a particle size of less than or equal to 4.7 μm and greater than or equal to 1.3 μm.

[0014] In one embodiment, the specific steps for mixing the bamboo charcoal particles with ultra-high molecular weight polyethylene are as follows: the bamboo charcoal particles and ultra-high molecular weight polyethylene are melt-blended at 180-200°C to obtain a masterbatch; the masterbatch and ultra-high molecular weight polyethylene are melt-blended at 180-200°C.

[0015] In one embodiment, the mass fraction of bamboo charcoal particles in the masterbatch is 50-80%.

[0016] In one embodiment, bamboo charcoal particles are mixed with ultra-high molecular weight polyethylene and cooled to 150±10°C to pre-cur them to form a substrate; a fiber grating is then placed on the pre-cured substrate.

[0017] In one embodiment, the specific steps for forming the capping layer are as follows: using a mixture of bamboo charcoal particles and ultra-high molecular weight polyethylene (UHMWPE) prepared during the substrate preparation, the mixture is applied to the substrate and the fiber Bragg grating, and then cooled and solidified. After the capping layer and the substrate have completely cooled and solidified, the substrate and the capping layer are bonded and fixed together, thereby encapsulating the fiber Bragg grating between the substrate and the capping layer.

[0018] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0019] Figure 1This is a schematic diagram of the exploded structure of a grating sensor in the background art;

[0020] Figure 2 The method flowchart provided by the present invention. Detailed Implementation

[0021] This invention analyzes the causes of poor testing accuracy and repeatability in substrate-type fiber Bragg grating sensors, revealing that creep is prone to occur in the substrate material of the sensor and at its interface with the fiber Bragg grating 2 / capsule 3. Creep increases the strain transmission loss of the sensor, affecting its accuracy and causing distortion. Furthermore, creep affects the encapsulation effect between the substrate 1 and the capsule 3, accelerating sensor deformation and aging, further leading to measurement inaccuracies.

[0022] Therefore, in order to enhance the creep resistance of various parts of the fiber Bragg grating sensor, this invention, through extensive experiments and testing, discovered that adding bamboo charcoal particles to organic polymer materials can improve the creep resistance of the organic polymer materials. Thus, the composite material formed by mixing bamboo charcoal particles and organic polymers has the potential to prepare substrate 1 with better creep resistance.

[0023] In subsequent research, this invention used polyethylene, a commonly used substrate material, as the specific experimental object for further analysis and improvement. Firstly, this invention selected ultra-high molecular weight polyethylene (a linear polyethylene with a relative molecular mass of over 1.5 million) as the base material for testing, as it possesses stronger wear resistance, higher strength, more stable chemical properties, and superior anti-aging performance.

[0024] Furthermore, during the preparation of the substrate, the problem of the difficulty in fully mixing ultra-high molecular weight polyethylene with bamboo charcoal powder was encountered. To solve this problem, the present invention adopts a two-stage mixing method: first, bamboo charcoal powder and ultra-high molecular weight polyethylene are mixed into a masterbatch, and then mixed with the remaining ultra-high molecular weight polyethylene to form a composite material, so that the two are fully mixed.

[0025] Furthermore, this invention reveals that the composite material formed by mixing bamboo charcoal powder and ultra-high molecular weight polyethylene exhibits isotropic properties and does not affect signal transmission. Therefore, in addition to serving as a rigid support substrate, it can also be used as a capping layer. This results in both the substrate and the capping layer possessing excellent creep resistance, meaning the overall fiber Bragg grating sensor exhibits superior creep resistance. Simultaneously, to reduce interfacial anisotropy between the substrate and the capping layer, this invention employs a two-stage casting and integral molding method: before the substrate is fully cured, the same composite material as the substrate is directly cast onto it to form the capping layer. This allows the composite material to melt and diffuse at the interface between the substrate and the capping layer, forming an integral structure without obvious interfacial delamination. This reduces the number of interfaces between the substrate and the capping layer and minimizes strain loss during interlayer transfer, resulting in superior signal transmission performance and measurement accuracy for the substrate-type fiber Bragg grating sensor.

[0026] The present invention will now be described in detail with reference to the accompanying drawings.

[0027] Please see Figure 2 The specific fabrication steps of the bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber optic grating sensor of the present invention include:

[0028] S1: Preparation of bamboo charcoal granules.

[0029] Bamboo is carbonized at 500-1000℃, then ground using a planetary grinder and sieved to obtain bamboo charcoal powder, or bamboo charcoal granules. The bamboo carbonization method is conventional and can be adjusted according to specific conditions. The particle size of the bamboo charcoal granules can be adjusted by selecting different mesh sizes of sieves.

[0030] S2: Bamboo charcoal particles are mixed with ultra-high molecular weight polyethylene to form a composite material. This includes the following steps S21 and S22:

[0031] S21: Bamboo charcoal granules are melt-blended with ultra-high molecular weight polyethylene to form a masterbatch.

[0032] Ultra-high molecular weight polyethylene (UHMWPE) and bamboo charcoal powder are fed together into a twin-screw extruder. The twin-screw extruder is set to sequentially perform melting, stirring, blending, and extrusion at 180-200°C. After extrusion, the mixture is pelleted at a pelleting temperature of approximately 30°C to obtain masterbatch. The masterbatch is a granular masterbatch, which facilitates further contact with the UHMWPE.

[0033] S22: Masterbatch and ultra-high molecular weight polyethylene are melt-blended to form bamboo charcoal / ultra-high molecular weight polyethylene composite material.

[0034] Masterbatch and new ultra-high molecular weight polyethylene are fed into a twin-screw extruder, and then melted and stirred again at 180°C to obtain a molten bamboo charcoal / ultra-high molecular weight polyethylene composite material (hereinafter referred to as composite material).

[0035] S3: Substrate 10 is prepared using composite materials.

[0036] The bamboo charcoal granule ultra-high molecular weight polyethylene composite material obtained in S22 is extruded from a twin-screw extruder at an extrusion temperature of 180 degrees Celsius and poured into the die-casting mold of the substrate fiber optic grating sensor. Then, it is die-cast using a die-casting machine at a pressure of 8 MPa and a temperature of 200°C to form the substrate 10. The thickness of the substrate is preferably between 2.5 mm and 3.5 mm. The dimensions of the substrate 10 of this invention are 100 mm * 20 mm * 2.5 mm (length * width * height).

[0037] After being molded into substrate 10, substrate 10 is allowed to cool to 150±10℃ to allow it to pre-cur.

[0038] S4: Place the fiber grating 20 onto the pre-cured substrate 10.

[0039] The fiber Bragg grating 20 is placed on the pre-cured substrate 10, with its center positioned within the substrate 10. Preferably, in this embodiment, one end of the fiber Bragg grating 20 is fused to one end of a transmission optical fiber 21 beforehand. When the fiber Bragg grating 20 is placed in the center of the pre-cured substrate 10, the free end of the transmission optical fiber 21 is located outside the substrate 10, not sandwiched between the substrate 10 and the cover layer 30, so that the sensor can subsequently be connected to other devices via the transmission optical fiber 21.

[0040] S5: Prepare the capping layer 30 using the composite material obtained in S22.

[0041] The bamboo charcoal granules and ultra-high molecular weight polyethylene composite material prepared by S22 were extruded into a mold at 180°C using a twin-screw extruder, covering the substrate 10 and fiber optic grating 20. The mixture was then die-cast to form a 100mm*20mm*2.5mm cover layer 30. The mixture was cooled to room temperature to allow the substrate 10 and cover layer 30 to fully solidify. At this point, the fiber optic grating 20 was encapsulated between the substrate 10 and the cover layer 30. Finally, a bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber optic grating sensor with dimensions of 100mm*20mm*5mm was obtained.

[0042] Based on the above preparation steps, the particle size of the bamboo charcoal particles and the mass fraction of bamboo charcoal particles in the substrate were further adjusted to form multiple experimental examples, and their performance was tested and compared. Please refer to Table 1 below for details.

[0043] Comparative Example 1

[0044] Comparative Example 1 follows the same steps as the Example, except that when bamboo charcoal powder is added, an equal amount of ultra-high molecular weight polyethylene is used instead. Therefore, the grating sensor prepared in Comparative Example 2 does not contain any bamboo charcoal; its substrate 10 and cover layer 30 are made solely of ultra-high molecular weight polyethylene, resulting in an ultra-high molecular weight polyethylene substrate-type fiber optic grating sensor. Experimental parameters are shown in Table 1.

[0045] Comparative Example 2

[0046] The difference between Comparative Example 2 and Example 3 is that calcium carbonate particles with the same particle size and proportion as in Example 3 were used instead of bamboo charcoal particles. Specifically, a calcium carbonate / ultra-high molecular weight polyethylene composite material was used as the substrate 10 and the capping layer 30 to prepare a calcium carbonate / ultra-high molecular weight polyethylene composite substrate fiber grating sensor. Experimental parameters are shown in Table 1.

[0047] Comparative Example 3

[0048] The difference between Comparative Example 2 and Example 4 is that titanium dioxide particles with the same particle size and proportion as in Example 4 were used instead of bamboo charcoal particles. Specifically, a titanium dioxide / ultra-high molecular weight polyethylene composite material was used as the substrate 10 and the capping layer 30 to prepare a titanium dioxide / ultra-high molecular weight polyethylene composite substrate fiber grating sensor. Experimental parameters are shown in Table 1.

[0049] Furthermore, the following performance tests were performed on the products of each embodiment and comparative example:

[0050] Testing the temperature measurement accuracy and repeatability of substrate fiber Bragg grating sensors.

[0051] The substrate-type fiber Bragg grating sensors prepared in the examples and comparative examples were placed in a constant temperature chamber. The temperature was gradually increased and then gradually decreased, and the readings of the fiber Bragg grating sensors were collected during the heating and cooling process. This process was repeated three times. Specifically, when heating, 10°C was used as the initial point of temperature change, and each 10°C was considered a unit of temperature change. Once the current temperature display value in the constant temperature chamber was sufficiently stable, the corresponding reading was recorded, until the temperature reached 50°C. When cooling, the same steps were followed, gradually decreasing from 50°C to 10°C, and a reading was collected every 10°C. This cycle of heating and cooling was repeated three times.

[0052] Calculate the range (difference between the maximum and minimum readings) of the readings at the same temperature during each heating and cooling cycle, with six readings for each temperature. Define the maximum extreme value of the readings at the same temperature during three heating and three cooling cycles for each embodiment or comparative example as the temperature measurement repeatability coefficient of that embodiment or comparative example, and record it in Table 1. The smaller the temperature measurement repeatability coefficient, the more similar the sensor readings are at the same temperature, indicating better temperature measurement repeatability of the substrate fiber Bragg grating sensor.

[0053] Meanwhile, using the temperature of the constant temperature chamber as the independent variable and the reading of the substrate fiber optic grating sensor as the dependent variable, the data from each heating and cooling experiment were linearly fitted, and the linear correlation coefficient R was calculated. 2 Then, the linear correlation coefficients R of the six fitted lines were calculated. 2 The closer the linear correlation coefficient is to 1, the better the linear relationship between the reading of the substrate fiber Bragg grating sensor and the actual temperature. This allows for a more accurate linear conversion of the sensor reading into temperature. The linear correlation coefficient R is defined for the six fitted lines in each embodiment or comparative example. 2 The average value is the temperature measurement accuracy coefficient, which is recorded in Table 1. The closer the temperature measurement accuracy coefficient is to 1, the better the temperature measurement accuracy.

[0054] Repeatability of strain testing and detection of strain loss of substrate fiber Bragg grating sensors.

[0055] The substrate fiber Bragg grating sensors prepared in the examples and comparative examples were attached parallel and adjacent to each other on the equal-strength beam of a conventional equal-strength beam experimental apparatus (model ADBZ-8002). An unloaded weighing tray was suspended at the end of the equal-strength beam, and the load was recorded as 0, with the readings of the substrate fiber Bragg grating sensors recorded. Subsequently, weights were successively placed on the weighing tray, increasing the load of the weighing tray sequentially to 0.4, 0.8, 1.2, 1.6, 2.0, and 7.1 kg, and the readings under each load were recorded during the weight increase process. Then, the weight was successively decreased, and the readings were recorded. This cycle of increasing and decreasing weight was repeated 3 times.

[0056] The range (difference between the maximum and minimum readings) of the readings under the same load (six readings at one temperature) during each weight increase and decrease process was calculated. The maximum extreme value of the readings under the same load during three weight increases and three weight decreases for each embodiment or comparative example was defined as the strain repeatability coefficient for that embodiment or comparative example, and recorded in Table 1. A smaller strain repeatability coefficient indicates more similar sensor readings under the same load, meaning the strain measurement repeatability of the modified substrate fiber Bragg grating sensor is better.

[0057] Meanwhile, using the load on the weighing tray as the independent variable and the reading of the substrate fiber Bragg grating sensor as the dependent variable, the data from each weight gain and weight loss experiment were linearly fitted, and the linear correlation coefficient R was calculated. 2 Then, the linear correlation coefficients R of the six fitted lines were calculated. 2 The closer the linear correlation coefficient is to 1, the better the linear relationship between the reading of the substrate fiber Bragg grating sensor and the actual strain. The strain of the beam of equal strength under different loads can be transmitted to the substrate fiber Bragg grating sensor with a better linear relationship and reflected by its reading, that is, the lower the strain transmission loss.

[0058] Define the linear correlation coefficient R of the six fitted lines for each embodiment or comparative example. 2 The average value is the strain loss coefficient, which is recorded in Table 1. The closer the strain loss coefficient is to 1, the lower the strain loss of the substrate fiber Bragg grating sensor.

[0059] Table 1. Parameters and test results for each embodiment and comparative example.

[0060]

[0061]

[0062] The results in Table 1 show that the temperature repeatability coefficient and strain repeatability coefficient of the bamboo charcoal / ultra-high molecular weight polyethylene (UHMWPE) composite substrate fiber Bragg grating (FBG) sensors in Examples 1-7 are smaller than those in Comparative Examples 1-3. The temperature accuracy coefficient and strain loss coefficient are also closer to 1 than those of the three FBG sensors in Comparative Examples 1-3. This indicates that the bamboo charcoal / UHMWPE composite substrate FBG sensor has superior temperature accuracy and repeatability, lower strain loss, and better strain measurement repeatability compared to the UHMWPE substrate FBG sensor, calcium carbonate / UHMWPE composite substrate FBG sensor, and titanium dioxide / UHMWPE composite substrate FBG sensor in Comparative Examples 1-3. Furthermore, when the bamboo charcoal particles in the substrate have a mass fraction of 5-50% and a particle size of 1.3-4.7 μm, the above performance is even better.

[0063] Analysis revealed that the bamboo charcoal / ultra-high molecular weight polyethylene (UHMWPE) composite material improves the temperature measurement accuracy and repeatability, strain measurement repeatability, and reduces strain loss in substrate-type fiber Bragg grating sensors because the surface of bamboo charcoal particles possesses a rich porous structure, resulting in a large specific surface area. During the composite material preparation process, UHMWPE molecular chains can flow into the pores on the surface of bamboo charcoal particles, increasing the contact area between them. Van der Waals bonds are formed at the contact surface between bamboo charcoal particles and UHMWPE. Although the bond energy of a single van der Waals bond is relatively small, the large total contact area results in a large total van der Waals force, leading to better interfacial compatibility and facilitating bonding. After curing, this promotes better mechanical interlocking and enhances the material's creep resistance. Simultaneously, the polar groups on the surface of bamboo charcoal particles are significantly reduced or even eliminated, becoming non-polar, which is similarly compatible with the non-polar UHMWPE, greatly enhancing the interfacial bonding and further improving the overall creep resistance and other mechanical properties of the composite material. For substrate-type fiber Bragg grating sensors, improving the creep resistance of the substrate 10 and the capping layer 30 can directly improve the overall temperature measurement repeatability and accuracy, improve the strain measurement repeatability, and reduce strain loss.

[0064] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The term "and / or" as used herein refers to and includes any or all possible combinations of one or more associated listed items. When the above description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of this application, those skilled in the art will understand the specific meaning of the above terms in this application according to the specific circumstances.

[0065] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber Bragg grating sensor, comprising a substrate, a capping layer covering the substrate, and a fiber Bragg grating encapsulated between the substrate and the capping layer, characterized in that, The substrate is mainly composed of ultra-high molecular weight polyethylene and bamboo charcoal particles.

2. The bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber optic grating sensor according to claim 1, characterized in that: The bamboo charcoal particles constitute 5-50% of the substrate by mass.

3. The bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber optic grating sensor according to claim 2, characterized in that: The bamboo charcoal particles have a particle size of less than or equal to 4.7 μm and greater than or equal to 1.3 μm.

4. The bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber optic grating sensor according to any one of claims 1-3, characterized in that: The material of the cover layer is the same as that of the substrate layer.

5. A method for preparing a bamboo charcoal / ultra-high molecular weight polyethylene composite substrate fiber optic grating sensor, characterized in that: Includes the following steps: Substrate formation: Bamboo charcoal particles are mixed with ultra-high molecular weight polyethylene and then cooled to form a substrate; at least one fiber grating is placed on the substrate; A cover layer is formed, which covers the substrate and the fiber grating.

6. The preparation method according to claim 5, characterized in that: The bamboo charcoal particles constitute 5-50% of the substrate by mass.

7. The preparation method according to claim 6, characterized in that: The bamboo charcoal particles have a particle size of less than or equal to 4.7 μm and greater than or equal to 1.3 μm.

8. The preparation method according to any one of claims 5-7, characterized in that: The specific steps for mixing the bamboo charcoal particles with ultra-high molecular weight polyethylene are as follows: Bamboo charcoal granules are melt-blended with ultra-high molecular weight polyethylene at 180-200℃ to obtain a masterbatch; The masterbatch is melt-blended with ultra-high molecular weight polyethylene at 180-200°C.

9. The preparation method according to claim 8, characterized in that: Bamboo charcoal particles are mixed with ultra-high molecular weight polyethylene and cooled to 150±10℃ to pre-cur them to form a substrate; fiber optic gratings are then placed on the pre-cured substrate.

10. The preparation method according to claim 9, characterized in that: The specific steps for forming the covering layer are as follows: using the mixture of bamboo charcoal particles and ultra-high molecular weight polyethylene, which was mixed during the preparation of the substrate, the mixture is applied to the substrate and fiber optic grating and then cooled to form the coating.

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