Piezoelectric composite material applied to seabed sensor

Abstract

The invention discloses a multi-protection material for a seabed sensor, belongs to the technical field of composite functional materials and ocean sensing, is mainly used for monitoring scouring of offshore wind power pile foundations, and can also be expanded to other seabed monitoring scenes. Aiming at the pain points that a traditional material is high in rigidity and poor in toughness, metal is easy to corrode and heavy, a carrier and a piezoelectric unit interface are weak in bonding and easy to strip and the like, the material adopts a structure customization design, reinforced fiber-epoxy resin is used as a matrix, a polyaniline coating is coated outside the matrix, a three-layer composite protection structure is constructed, and the material is adaptive to a complex seabed environment with high salt, high pressure and biological attachment. The composite material carrier integrates rigidity and toughness, reduces self weight, improves interface compatibility and bonding strength with a BTO / PVDF piezoelectric unit, inhibits seawater corrosion and biological fouling, prolongs the service life of a sensor, can support the PVDF unit to realize'scouring sensing-energy self-sufficiency 'integration, and provides a high-adaptability and high-reliability composite material carrier scheme for underwater structure scouring monitoring.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite material sensor carrier, and particularly relates to a composite material sensor integrating piezoelectric sensing function and marine protection characteristics, which is mainly applied to real-time monitoring of seabed scour pits of offshore wind pile foundations. BACKGROUND

[0002] In the fields of marine engineering and structural health monitoring, piezoelectric sensors are widely used due to their high mechanical energy-electric energy conversion efficiency and fast response speed. However, the long-term stability and reliability of existing piezoelectric sensors in complex environments still face significant challenges.

[0003] 1. Interface compatibility problem between base material and piezoelectric unit

[0004] The interface bonding force between traditional sensor base (such as metal, ordinary polymer) and PVDF / BTO composite piezoelectric film is insufficient, leading to broken charge transmission path or signal attenuation. For example, due to the large difference in thermal expansion coefficient between the metal base and the piezoelectric film, interface debonding is easily generated under temperature fluctuation or long-term load, which makes the sensor sensitivity decrease by more than 30%. Carbon fiber has high strength and corrosion resistance, but its surface is inert, and the interface hydrogen bond is weak when directly combined with PVDF / BTO, limiting the charge conduction efficiency.

[0005] 2. Functional limitations of corrosion-resistant coating

[0006] Existing corrosion prevention solutions cannot balance conductivity and corrosion resistance. Traditional insulating coatings such as epoxy resin can effectively isolate seawater corrosion, but they hinder the export of piezoelectric signals, causing the signal-to-noise ratio (SNR) to drop below 15 dB. Conductive coatings have corrosion resistance defects, such as zinc-nickel alloy with a corrosion rate of 0.1 mm / year in seawater, and are prone to cracking in deep-sea high-pressure environments. Conductive polymer polypyrrole has a conductivity decay of more than 60% in seawater within six months, and its anti-biofouling ability is significantly insufficient.

[0007] 3. Integration process bottleneck of multi-layer structure

[0008] Traditional composite material sensors often use a multi-step preparation process for multi-layer structure, which has weak interface bonding and long preparation cycle. For example, the curing shrinkage rate difference between the epoxy resin encapsulation layer and the PVDF / BTO composite piezoelectric film easily leads to micro-cracks, and the bonding strength of the polyaniline coating layer to the base is usually less than 3 MPa if traditional electrochemical polymerization method is used, which cannot withstand deep-sea high-pressure environments.

[0009] 4. Special challenges of marine environment

[0010] In marine engineering applications, sensors also face the following three technical bottlenecks:

[0011] 1. High-salt corrosion: In a 3.5% NaCl solution, metal electrodes are prone to oxygen absorption corrosion, and the impedance rises to more than 10 times the initial value;

[0012] 2. Biofouling: Marine microorganisms adhere to form a biofilm, resulting in a 30%-50% annual decline in sensor sensitivity;

[0013] 3. Signal interference: The ionic conductivity of seawater and fluid dynamic noise easily introduce background interference, and the signal-to-noise ratio of traditional sensors is difficult to meet the needs of high-precision monitoring.

[0014] In summary, the existing piezoelectric sensor has obvious shortcomings in the design of multi-layer composite material structure, optimization of interface bonding, integration of corrosion-resistant and conductive functions, etc. Therefore, it is urgent to develop a new type of composite material sensor with high strength interface bonding, excellent corrosion resistance and signal transmission efficiency. SUMMARY

[0015] I. Invention purpose

[0016] In view of the problems of weak interface bonding, split of corrosion-resistant and conductive functions, and complex integration process of existing piezoelectric sensors in complex environments, the present application provides a piezoelectric sensor with a multi-layer composite structure. Through the material design of hydroxylation treatment of the surface of the carbon fiber substrate and hot pressing of the PVDF / BTO composite piezoelectric film, and the synergistic process optimization of the polyaniline corrosion-resistant coating and the epoxy resin packaging layer, the interface bonding force between the carbon fiber substrate and the PVDF / BTO composite piezoelectric unit is enhanced to improve the charge transmission efficiency, the polyaniline coating with corrosion-resistant and conductive properties is constructed to solve the problems of seawater corrosion and signal attenuation, and the integrated process is adopted to simplify the preparation process and improve the long-term stability of the sensor.

[0017] II. Technical scheme (1) Structure design of composite piezoelectric sensor

[0018] Carbon fiber reinforced epoxy resin / PVDF-BTO composite matrix layer: carbon fiber woven cloth is used as the reinforcing framework, and the epoxy resin system with uniformly dispersed PVDF / BTO piezoelectric functional filler is used as the matrix, and the resin transfer molding process is used for integrated composite forming. The mass ratio of PVDF to BTO is 85:15, and the addition amount of PVDF / BTO composite powder is 15% of the mass of the epoxy resin. The composite matrix layer is formed under the condition of 80°C for 12 hours, and has the characteristics of structure bearing and piezoelectric response.

[0019] Polyaniline corrosion-resistant coating: polyaniline paint and matching curing agent are mixed according to a mass ratio of 7:1 to prepare a polyaniline coating, which is applied to the outer surface of the composite matrix layer by a solution coating process, and is cured at room temperature for 5 hours to form a dense corrosion-resistant layer with a thickness of 10-30 microns.

[0020] (ii) Preparation method

[0021] Carbon fiber pretreatment and layering: Carbon fiber woven cloth is cut to a predetermined size, layering design (12 layers) and necessary drilling pretreatment are performed.

[0022] Mold preparation and vacuum preparation: uniformly coat the mold surface with release agent, then lay the release cloth, flow guide net and pretreated carbon fiber layer in turn, and vacuum after sealing.

[0023] Resin mixing and injection molding: mix the epoxy resin and PVDF / BTO powder (PVDF:BTO=85:15) in proportion, ensuring that the PVDF / BTO addition amount is 15% of the mass of the epoxy resin. After vacuum degassing treatment of the mixed system, inject the sealed mold cavity through the resin transfer molding process. Curing and post-processing: place the resin injected mold in an oven at 80°C for 12 hours to complete the molding of the composite body. Then demold and cut the cured composite plate into sensor samples of a predetermined size.

[0024] Surface coating preparation: mix the polyaniline paint and curing agent in a mass ratio of 7:1 to form a mixed solution, uniformly brush it on the outer surface of the composite body, and cure it at room temperature for 5 hours to form a polyaniline corrosion-resistant coating.

[0025] III. Beneficial effects

[0026] 1. Integrated structure realizes intrinsic interface strengthening: by uniformly dispersing PVDF / BTO piezoelectric fillers in the epoxy resin matrix and integrating them with the carbon fiber skeleton through RTM process, the physical interface in the traditional layered structure is fundamentally eliminated. The composite body is formed by the three-dimensional interwoven fiber skeleton and the micro combination of resin-filler, which forms a stable whole, ensures the continuity and reliability of the force-electricity conversion path, and effectively avoids the risk of interlayer peeling.

[0027] 2. Synergistic multiple protection mechanism: the outer polyaniline coating and the inner epoxy resin matrix form a highly efficient synergistic protection system. The polyaniline coating forms a dense protective film on the metal surface through its unique passivation mechanism, effectively blocking the penetration of Cl - and other corrosive media; even if the polyaniline coating is partially damaged, the epoxy resin matrix below can still provide excellent physical barrier effect, significantly delaying the corrosion of the material inside.

[0028] 3. Durable antifouling properties: Polyaniline material itself has certain antibacterial properties, and the coating it forms has a low surface energy, significantly reducing the adhesion strength and probability of marine organisms (such as barnacles and algae). This results in a significantly lower accumulation of biofouling on the sensor surface after long-term immersion compared to traditional coatings, maintaining the long-term stability of the sensor's function.

[0029] 4. Optimized signal generation and transmission efficiency: The PVDF / BTO filler forms a piezoelectric functional network within the epoxy resin matrix, enabling it to directly generate electrical charges under external mechanical loads (such as water pressure and vibration). The integrated structure minimizes signal transmission loss and charge recombination between multi-layer interfaces, resulting in a sensor with high output sensitivity and a signal-to-noise ratio (SNR exceeding 28dB), allowing for precise capture of subtle changes in scouring conditions.

[0030] 5. Excellent process applicability and environmental durability: The resin transfer molding (RTM) process used is mature and stable, making it easy to achieve consistency and large-scale manufacturing of complex-shaped sensors. The integrated composite material sensor has a dense structure and good compatibility between its components, enabling it to maintain long-term structural integrity and functional stability in extreme environments such as high pressure, high salinity, and low temperature at a depth of 5000 meters in the ocean.

[0031] IV. Application Scenarios

[0032] The composite material piezoelectric sensor described in this invention is suitable for monitoring the health of marine engineering structures, especially for monitoring the scouring, vibration and corrosion status of underwater facilities such as offshore wind turbine piles and submarine pipelines. It can achieve long-term real-time data acquisition and early warning under self-powered conditions. Attached Figure Description

[0033] Figure 1 Functional and schematic diagram of a piezoelectric composite material for use in seabed sensors

[0034] Figure 2 Image of composite material sample prepared by RTM process

[0035] Figure 3 Image of composite material coating cured sample prepared by RTM process Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1: Fabrication of a composite material piezoelectric sensor

[0038] 1. Carbon fiber pretreatment and layup

[0039] Material Preparation: 3K carbon fiber woven fabric, 80 micrometers thick; anhydrous ethanol and deionized water with a resistivity ≥18.2 MΩ·cm are required. Processing Steps: Cut the carbon fiber fabric into 5cm × 25cm pieces, preparing 12 layers in total. Immerse the carbon fiber fabric in ethanol and ultrasonically clean for 20 minutes to remove surface oil and contaminants; then rinse three times with deionized water and dry the surface with nitrogen gas for later use.

[0040] 2. Mold preparation and resin mixing

[0041] A release agent is evenly coated onto the surface of the mold's aluminum plate. The pre-treated 12 layers of carbon fiber cloth are then laid flat in the mold, followed by the release cloth and a flow guide mesh. The entire assembly structure is sealed and connected to a vacuum system, evacuating to -0.1 MPa and maintaining this vacuum level.

[0042] Accurately weigh 100g of low-viscosity epoxy resin, then weigh 15g of PVDF / BTO composite powder (PVDF to BTO mass ratio of 85:15). Thoroughly mix the powder and epoxy resin using mechanical stirring. Place the mixture in a vacuum degassing machine for 10 minutes until the adhesive solution is free of obvious bubbles.

[0043] 3. Resin infusion and curing molding

[0044] The degassed epoxy resin / PVDF / BTO mixture was injected into a vacuum-sealed mold cavity using an RTM process, ensuring that the resin fully impregnates the carbon fiber layup. Maintaining negative vacuum, the entire mold was moved to a forced-air drying oven and cured at 80°C for 12 hours.

[0045] 4. Post-treatment and coating preparation

[0046] After curing, the sensor component is removed from the mold. The composite plate is then precisely cut according to the design dimensions to obtain the sensor sample.

[0047] To prepare the polyaniline anti-corrosion coating, mix polyaniline and the matching curing agent at a mass ratio of 7:1 according to the component requirements. Apply the mixture evenly to the outer surface of the sensor sample and cure at room temperature for 5 hours to form a complete polyaniline anti-corrosion coating.

Claims

1. A piezoelectric composite material for use in seabed sensors, characterized in that, The sensor comprises a matrix made of carbon fiber reinforced epoxy resin composite, wherein PVDF / BTO piezoelectric functional filler is uniformly dispersed in the epoxy resin matrix to form a composite material body with piezoelectric response; a polyaniline anti-corrosion coating is bonded to the outer surface of the composite material body.

2. The composite material piezoelectric sensor according to claim 1, characterized in that, The carbon fiber reinforced epoxy resin matrix is ​​integrally formed by resin transfer molding, wherein carbon fiber is the reinforcing phase and epoxy resin is the matrix phase.

3. The composite material piezoelectric sensor according to claim 2, characterized in that, Before being injected into the epoxy resin, the PVDF / BTO piezoelectric functional filler is first mixed with the epoxy resin matrix and then degassed. It is then injected into the mold cavity with carbon fiber through the RTM process.

4. The composite material piezoelectric sensor according to claim 1, characterized in that, The composite material body is cured at 80°C for 12 hours to form a sensor sample after demolding and cutting.

5. The composite material piezoelectric sensor according to claim 1, characterized in that, The carbon fiber reinforced material is cut, drilled and laid up before molding, with 12 layers.

6. A method for preparing a composite material piezoelectric sensor as described in any one of claims 1-5, characterized in that, Includes the following steps: The carbon fiber is cut to a predetermined size and pre-treated by lay-up and drilling. A release agent is applied to the surface of the mold, and a release cloth and a flow guide net are laid in sequence. The pre-treated carbon fiber layup is then placed inside, and the mold is sealed and vacuumed. Epoxy resin is mixed with PVDF / BTO powder, and after degassing, it is injected into the mold cavity through resin transfer molding process. The composite material body is formed by curing at 80°C for 12 hours. Demolding and cutting are performed to obtain sensor samples; A polyaniline anti-corrosion coating is prepared on the outer surface of the composite material body.

7. The preparation method according to claim 6, characterized in that, In the PVDF / BTO powder, the mass ratio of PVDF to BTO is 85:15, and the amount of the composite powder added is 15% of the mass of the epoxy resin.

8. The preparation method according to claim 6, characterized in that, The polyaniline anti-corrosion coating is applied to the surface of the composite material body by in-situ polymerization or solution coating, and the coating thickness is 10-30 micrometers.

9. An application of a composite material piezoelectric sensor as described in any one of claims 1-5, characterized in that, This sensor is applied in the field of marine engineering structural health monitoring, and is suitable for real-time monitoring of the scour status of offshore wind power pile foundations, enabling long-term stable data acquisition and scour early warning under self-powered conditions.

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