Fluorescent pressure-sensitive coating applicable to underwater large-curvature model as well as preparation method and application of fluorescent pressure-sensitive coating

Abstract

The invention relates to a fluorescent pressure-sensitive coating suitable for an underwater large-curvature model and a preparation method and application thereof. The coating comprises a bonding layer used for fixing the coating as a bottom layer, a sensitive layer used for realizing pressure response as a middle layer and a flat layer used for reducing the influence of the coating on flow as a surface layer. The preparation method comprises the following steps: preparing a bonding layer raw material, a sensitive layer raw material and a leveling layer raw material, then spraying the bonding layer, spraying the sensitive layer before the bonding layer is completely cured, and preparing the leveling layer after the bonding layer is cured. The obtained fluorescent pressure sensitive coating can be used for underwater pressure and pressure distribution detection of parts. Compared with the prior art, the method has the advantages that the coating is directly sprayed and prepared on the surface of the measured model, pressure response unit deformation caused by pressure is converted into fluorescence signal change on the basis of the micron-sized pressure response unit in the sensitive layer, and the problem of low spatial resolution of underwater large-curvature model surface pressure measurement is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluid mechanics testing, and relates to a fluorescent pressure-sensitive coating suitable for an underwater large-curvature model, and a preparation method and application thereof. Background Art

[0002] Surfaces of high curvature are common on various surface and underwater vehicles, such as propellers, hydrofoils, and various corner joints. The flow conditions on these surfaces are often complex and have significant implications for the vehicle's navigation performance and structural stability. Pressure on these surfaces is also a crucial physical parameter for understanding complex flow mechanisms such as transition, separation, and cavitation. Therefore, measuring pressure distribution on surfaces of high curvature structures is crucial in fluid dynamics experiments.

[0003] In current hydrodynamic experiments, surface pressure load measurements rely on single-point contact pressure sensors. These sensors have a low density of measurement points, and the data provided by these scattered points cannot accurately reflect the overall pressure distribution. Therefore, in hydrodynamic experiments, when measuring underwater surface pressure, the following requirements are imposed on surface pressure sensors to meet these demands:

[0004] 1) The sensor can respond to changes in water pressure;

[0005] 2) The sensor can be placed on the surface of the underwater model with large curvature;

[0006] 3) The sensor can provide pressure measurement results with high spatial resolution over a large range.

[0007] Pressure-sensitive paint (PSP) is a widely used non-contact sensor for measuring surface pressure distribution. According to the book "Pressure and Temperature Sensitive Paints" by Tianshu Liu et al., this sensor uses fluorescent molecules sprayed on the surface of the model being measured as pressure-responsive units. These fluorescent molecules are actually sensitive to oxygen concentration, and the "oxygen quenching" effect is used to establish a quantitative relationship between oxygen concentration and fluorescence intensity. Due to the compressibility of air, the oxygen partial pressure changes proportionally with changes in air pressure. When using PSP, the air pressure is calculated by measuring the oxygen partial pressure. However, due to the incompressibility of water and its slight solubility in oxygen, changes in water pressure hardly cause changes in the oxygen partial pressure, making PSP unusable in water.

[0008] Chinese patent application CN109141731A discloses a flexible-based microsensor that can be used for underwater turbulent boundary layer wall pulsating pressure testing and its manufacturing method. The flexible-based pulsating pressure microsensor uses a standard MEMS manufacturing process, has high time resolution, and high resonant frequency, meets the requirements of broadband testing of underwater turbulent boundary layer pulsating pressure, is easy to array, and is suitable for attachment to the curved surface of underwater vehicles. The pressure sensor array processed based on MEMS technology has small and dense measuring points. However, its pressure response principle is the same as that of a single-point contact pressure sensor, which converts pressure changes into changes in electrical signals and transmits them outward. This is completely different from the principle of the sensor mentioned in the present invention. Since the data of each measuring point needs to be transmitted outward through wires, it is difficult for such sensors to be simultaneously arranged over a large area and to collect high-spatial-resolution pressure fields.

[0009] Chinese patent CN110307929B discloses a fluid pressure measurement system and method based on a pressure-sensitive film. The pressure response principle of this invention is to measure the change in fluorescence intensity caused by the compressive deformation of fluorescent elastic microspheres to obtain the pressure exerted on the microspheres. The pressure measurement method based on compressive deformation responds to pressure changes caused by different media such as air and water. Since the size of the microspheres is very small, the spatial resolution of the pressure field measured in this invention is very high, usually less than 1mm. When this technical solution is applied to the pressure measurement of underwater large-curvature surfaces, since the pressure-sensitive film is obtained by coating and is a flat film, it cannot be attached to the surface of the underwater large-curvature model to be measured. The large-scale wrinkles caused by forced attachment cause the flow to be seriously disturbed, and the large-curvature deformation will also cause the internal structure of the film to change. The compressive deformation is different from that of the plane, and the measurement results are distorted.

[0010] Chinese patent application CN115537054A discloses a polymer coating with enhanced dynamic response to force-induced fluorescence, and its preparation method and application. The polymer coating of the present invention is made of the following components in a mass ratio: a nitro-aggregation-induced luminescence dye and a polymer matrix in a mass ratio of 1:10 to 10,000; the polymer matrix is ​​a polymer resin. Its preparation method is as follows: 1) mixing the nitro-aggregation-induced luminescence dye with the polymer resin and a solvent to obtain a mixed liquid; 2) applying the mixed liquid to a substrate by the following method to obtain the polymer coating with enhanced dynamic response to force-induced fluorescence; the method includes at least one of a casting method, a coating method, a template method, a spraying method, a brushing method, and a scraping method. This patent application combines a nitro-containing dye with a polymer matrix to achieve a highly sensitive and reversible stress response. Chinese patent application CN115537054A differs from the technical solution described herein in two aspects.

[0011] The first is the applicability of the measurement object. In order to achieve the pressure sensitivity of Chinese patent application CN115537054A, two measures are mainly taken in the application example: the first is to add patterns or fillers to create an uneven surface, so that the coating has an area with large local deformation; the second is to heat the coating to reduce the basic light intensity. Untreated millimeter-level patterns or micron-level fillers are not suitable for fine underwater model testing, because their uneven surfaces will destroy the model boundary layer and interfere with the flow. The second method requires heating and stabilizing the bottom plate at 50-80°C during the experiment to enhance the thermal quenching (inward rotation) of the AIE molecules, which cannot be achieved in underwater experiments. Because a large amount of water at room temperature flows over the surface of the model, the heated model surface undergoes heat exchange related to the flow, resulting in the inability to maintain the surface temperature of the model. Subsequently, the light intensity of the coating is affected by the dual effects of temperature change and pressure, causing the experimental results to lose reference significance. That is, because this patent application uses AIE molecules as pressure-sensitive elements, in order to achieve changes in the aggregation state of AIE dyes in the polymer network, adjustments must be made to the coating structure or usage method, resulting in its inability to measure pressure on the surface of underwater large-curvature models.

[0012] The second is the complexity of the manufacturing process. The spraying method is also mentioned in the Chinese patent application CN115537054A, but because the material to be sprayed is relatively uniform in mechanics, it is not necessary to describe the specific process of spraying in detail. If the material to be sprayed is mixed with other substances in addition to the polymer prepolymer, especially some substances with a large density difference from the polymer prepolymer (such as hundreds of micron-level hollow microspheres), the situation is different. If it is sprayed directly onto a surface with large curvature according to the general method, the coating will be affected by gravity and obvious stratification, accumulation, etc. will occur, resulting in extremely uneven pressure sensitivity of the coating. Therefore, it is necessary to develop new and more complex technical solutions to solve this problem. Summary of the Invention

[0013] The purpose of the present invention is to provide a fluorescent pressure-sensitive coating suitable for underwater large-curvature models, as well as its preparation method and application. By directly spraying the coating on the surface of the model to be measured, based on the micron-level pressure response units in the sensitive layer, the deformation of the pressure response units caused by pressure is converted into fluorescent signal changes, thereby solving the problem of low spatial resolution of surface pressure measurement of underwater large-curvature models.

[0014] The purpose of the present invention can be achieved by the following technical solutions:

[0015] A first aspect of the present invention provides a fluorescent pressure-sensitive coating suitable for an underwater large-curvature model, comprising a bottom layer, which is an adhesive layer that serves to fix the coating;

[0016] The middle layer is the sensitive layer for achieving pressure response;

[0017] The surface layer is a smooth layer that reduces the effect of the coating on flow.

[0018] The second aspect of the present invention provides a method for preparing a fluorescent pressure-sensitive coating, comprising: preparing bonding layer raw materials, sensitive layer raw materials and planarizing layer raw materials, then spraying the bonding layer, spraying the sensitive layer before the bonding layer is completely cured, and preparing the planarizing layer after the bonding layer is cured.

[0019] Furthermore, the preparation method of the bonding layer raw material includes: mixing a polymer monomer and a curing agent to obtain a liquid viscous prepolymer, adding a non-polar solvent, and mixing uniformly to obtain.

[0020] Furthermore, the liquid viscous prepolymer is selected from one of transparent polyurethane prepolymer, transparent epoxy resin prepolymer or transparent organic silicone prepolymer, and the polymer monomer and curing agent are selected accordingly.

[0021] This type of prepolymer is liquid at room temperature and requires mixing the monomer components and curing agent before polymerization begins at a certain temperature, making it highly manipulable. The polymer exhibits high transparency and good light transmittance, along with certain temperature tolerance, water resistance, good chemical stability, and excellent adhesion to materials such as metal and wood. It also exhibits no fluorescence under UV light.

[0022] The non-polar organic solvent is a solvent whose solvent molecules are non-polar organic molecules and is highly volatile, including but not limited to benzene, carbon tetrachloride, n-hexane, etc.

[0023] The mass ratio of the polymer monomer to the curing agent is 1:(0.2-1); the volume ratio of the liquid viscous prepolymer to the non-polar solvent is 0.5:(1-10).

[0024] Furthermore, the preparation method of the sensitive layer raw material includes:

[0025] Mixing expandable microspheres with a polar fluorescent agent at or above the foaming temperature of the expandable microspheres to obtain fluorescent expanded microspheres;

[0026] Preferably, the expandable microspheres and the polar fluorescent agent are continuously stirred until the volume of the mixture no longer changes.

[0027] Furthermore, the mass ratio of the expandable microspheres to the polar fluorescent agent is 1:(0.05-0.001); and the mass ratio of the liquid viscous solvent to the fluorescent expandable microspheres is 1:(0.01-0.1).

[0028] Furthermore, the expandable microspheres are dry, unexpanded expandable foam microspheres, white thermoplastic core-shell microspheres composed of a polymer shell encapsulating a volatile solvent, originally intended to act as a physical foaming agent. The foam microspheres have a core-shell structure, with the shell being a thermoplastic polymer and the core being a low-boiling-point hydrocarbon. Although thin, the shell possesses excellent structural strength and elasticity, maintaining its integrity even after the low-boiling-point hydrocarbon expands upon heating. When the foam microspheres are heated, the shell softens, the volatile solvent vaporizes, and the internal air pressure increases dramatically, causing the volume of the foam microspheres to expand several times. During the expansion process, the internal pressure of the foam microspheres, the tension of the polymer shell, and the external pressure reach equilibrium, and the spheres remain in the expanded state. At a reasonable expansion temperature, the gas in the core does not escape into the environment. After expansion, the foam microspheres retain excellent elasticity and are easily compressed; after the pressure is removed, the microspheres return to their original shape under the action of the internal pressure. This method does not involve the preparation of expandable microspheres. Expandable microspheres have a fixed foaming temperature range: below this temperature range, the microspheres cannot foam; above this temperature range, the microspheres burst. For example, Akzo Nobel's Expancel 920DU 80 has a foaming temperature of 121-178°C, and Matsumoto Yushi Pharmaceutical Co., Ltd.'s FN-100S has a foaming temperature of 125-160°C. As a preferred technical solution, the expandable microspheres have a diameter of 10 μm to 300 μm.

[0029] Furthermore, the polar fluorescent agent is a type of fluorescent agent that exhibits polar fluorescent properties and is largely soluble in polar organic solvents, insoluble or slightly soluble in non-polar organic solvents, and retains its fluorescent properties after solvent evaporation. Such fluorescent agents should have a difference of at least 50 nm between their excitation and emission peaks, including but not limited to Nile Red, Rhodamine-B, and Coumarin-6 (which is not temperature-sensitive).

[0030] Furthermore, the preparation method of the planarization layer raw material includes: mixing a polymer monomer and a curing agent to obtain a liquid viscous prepolymer, adding a non-polar solvent, and mixing them uniformly to obtain.

[0031] Furthermore, the liquid viscous prepolymer is selected from one of transparent polyurethane prepolymer, transparent epoxy resin prepolymer or transparent organic silicone prepolymer, and the polymer monomer and curing agent are selected accordingly.

[0032] This type of prepolymer is liquid at room temperature and requires mixing the monomer components and curing agent before polymerization begins at a certain temperature, making it highly manipulable. The polymer exhibits high transparency and good light transmittance, along with certain temperature tolerance, water resistance, good chemical stability, and excellent adhesion to materials such as metal and wood. It also exhibits no fluorescence under UV light.

[0033] The non-polar organic solvent is a solvent whose solvent molecules are non-polar organic molecules and is highly volatile, including but not limited to benzene, carbon tetrachloride, n-hexane, etc.

[0034] The mass ratio of the polymer monomer to the curing agent is 1:(0.02-1); the volume ratio of the liquid viscous prepolymer to the non-polar solvent is 0.5:(1-10).

[0035] Furthermore, the adhesive layer, sensitive layer, and smoothing layer are sprayed using a spray gun. The spray gun utilizes a high-speed airflow generated by the expansion of compressed air to atomize the liquid material flowing out of the nozzle and spray it onto the surface of the sprayed component. The amount of liquid discharged is determined by the diameter of the spray gun.

[0036] The spraying process conditions include: air supply pressure of 0.04-0.08 MPa, spray gun diameter of 0.01-1 mm, spray gun distance of 30-100 cm, and layer thickness of 0.05-0.15 mm.

[0037] The bonding layer material is cured after spraying, and the curing conditions include: curing temperature of 40-60° C. and curing time of 5-15 minutes;

[0038] The sensitive layer material is cured after spraying, and the curing conditions include: vacuum heating curing, pressure 0.4-0.6 bar, curing temperature 60-140° C., and curing time 2-4 hours;

[0039] The planarization layer material is cured after spraying, and the curing process includes: first heating and curing at 60-90° C. for 1-2 hours, and then heating and curing at 100-150° C. for 1-2 hours.

[0040] A third aspect of the present invention provides an application of a fluorescent pressure-sensitive coating, including using the fluorescent pressure-sensitive coating for underwater pressure and pressure distribution detection of components, particularly for underwater pressure and pressure distribution detection of curved components.

[0041] Detection methods include:

[0042] The sample with the fluorescent pressure-sensitive coating is placed in water, the fluorescent pressure-sensitive coating is illuminated, the water pressure is adjusted, the fluorescence intensity of the coating under different water pressures is obtained, and the quantitative relationship between the pressure change and the coating light intensity change is obtained;

[0043] The component to be tested with a fluorescent pressure-sensitive coating is placed in a test environment, and the fluorescent pressure-sensitive coating is illuminated to obtain the fluorescence intensity of the coating. Based on the quantitative relationship between the pressure change and the coating light intensity change, the pressure condition or pressure distribution of the component to be tested is obtained.

[0044] Compared with the prior art, the present invention has the following characteristics:

[0045] 1) The present invention provides a method for directly applying a fluorescent pressure-sensitive coating to the surface of a model to be measured, capable of meeting the requirements for pressure measurement on large-curvature underwater models. The coating consists of three layers: a bottom adhesive layer that contacts the model and secures the coating; a middle sensitive layer that achieves pressure response; and a top smoothing layer that contacts water and reduces the impact on flow. All three functional layers are formulated in liquid form and spray-cured directly onto the model surface. The adhesive layer, primarily composed of a polymer, secures the coating's upper structure to the model surface. The sensitive layer, primarily composed of fluorescent elastic microspheres, emits a corresponding change in fluorescence intensity when deformed by pressure. To ensure the sensitive layer's attachment to the adhesive layer, it is spray-applied before the adhesive layer is fully cured. Due to the presence of the fluorescent elastic microspheres in the sensitive layer, its surface is uneven. Therefore, a smoothing layer is sprayed onto the sensitive layer to restore the coating's surface roughness to a level comparable to that of the model surface, thereby controlling the coating's effect on flow conditions.

[0046] 2) In the present invention, the fluorescent dye is present only in the pressure-sensitive layer and serves solely to emit light. Variations in light intensity are unrelated to the type of fluorescent dye. Therefore, when selecting a fluorescent dye, one can choose the appropriate fluorescent dye based on the actual lighting and temperature conditions of the intended use environment. This, in principle, avoids significant temperature fluctuations affecting light intensity. Furthermore, heating is not required during use, while maintaining a smooth surface.

[0047] 3) This invention solves the problem of low spatial resolution in surface pressure measurement of large-curvature underwater models by directly applying a coating to the surface of the model being measured. Based on the micron-scale pressure-responsive elements in the sensitive layer, the deformation of the pressure-responsive elements caused by pressure is converted into a change in fluorescence signal. By spraying an adhesive layer and then spraying the sensitive layer before the adhesive layer is fully cured, the problem of evenly fixing the micron-scale pressure-responsive elements on the surface of the large-curvature model is solved. By spraying a flattening layer to control the surface roughness of the coating, the problem of the coating affecting flow is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the structure of the fluorescent pressure-sensitive coating of the present invention;

[0049] Figure 2 It is a structural diagram of the calibration box in the present invention;

[0050] Figure 3 This is a photo of the experimental platform, light source, and camera in Example 1;

[0051] Figure 4 This is the calibration result diagram in Example 1;

[0052] Figure 5This is a physical picture of the calibration box and the measurement results in Example 1.

[0053] Description of the marks in the figure:

[0054] 1-adhesive layer, 2-bottom of adhesive layer, 3-sensitive layer, 4-flat layer, 5-underwater large curvature model, 6-fluorescent pressure-sensitive coating area, 7-water storage box, 8-vertical water pipe, 9-water pump, 10-water pressure sensor, 11-LED light, 12-camera. DETAILED DESCRIPTION

[0055] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0056] The calibration box used in the following examples is as follows Figure 2 As shown, there is a transparent water storage box and a device for changing the water pressure in the box, including a transparent water storage box 7, a vertical water pipe 8 connected to one end of the transparent water storage box 7 and extending upward by bending, a three-way valve connected to the other end of the transparent water storage box 7, and a water pressure sensor 10 and a water pump 9 respectively connected to the three-way valve. The pressure sensor 10 is also electrically connected to a computer. The water storage box 7 has a detachable cover for putting in and taking out samples. One end of the water storage box 7 is connected to the vertical water pipe 8, and the water level in the water pipe determines the water pressure in the box. The other end of the water storage box 7 is connected to the water pump 9 and the water pressure sensor 10. The water pump 9 can supply and pump water into the box, and the water pressure sensor 10 and the collection device can measure the real-time water pressure in the box. As shown Figure 3 As shown, the water storage box 7 is provided with an LED lamp 11 (UHP-TLED, 385nm, Prizmatix) and a camera 12 facing the sample.

[0057] Example 1:

[0058] A fluorescent pressure-sensitive coating suitable for underwater large-curvature models and its preparation method. The coating consists of three functional layers: a bottom adhesive layer (1) that secures the coating, a middle sensitive layer (3) that achieves pressure response, and a surface smoothing layer (4) that reduces the coating's impact on flow. The coating is applied directly to the surface of the model being tested by spraying.

[0059] like Figure 1 The fluorescent pressure-sensitive coating suitable for underwater large-curvature models is prepared by preparing bonding layer materials, sensitive layer materials, and flattening layer materials, then spraying bonding layer 1, spraying sensitive layer 3 before the bonding layer is completely cured, and preparing flattening layer 4 after the bonding layer is cured. The specific steps are as follows:

[0060] S1: Prepare the bonding layer raw materials. Prepare 500 mL of liquid epoxy resin prepolymer (JC6002C, Zhongshan Jiecheng Silicone) at a polymer monomer:curing agent ratio of 1 / 0.2 g / g. Add benzene at a ratio of 0.5 / 1 mL liquid epoxy resin prepolymer / mL benzene. Place in an ultrasonic disperser and oscillate.

[0061] S2: Prepare fluorescent pressure-sensitive microspheres. Place an appropriate amount of dry, unexpanded expandable microspheres (Expancel 920DU 80) in a beaker at a ratio of 1 / 0.001g expandable microspheres / g rhodamine-B. Add rhodamine-B to the microspheres and mix thoroughly in a vibrator. Place the glass container on a preheated hot plate at 150°C and stir continuously until the mixture no longer changes volume. This yields fluorescent expandable microspheres.

[0062] S3: Prepare the raw materials for the sensitive layer. Prepare a liquid viscous solvent with a ratio of 1 / 0.001 g / g water and 1 / 0.01 g / g isopropyl alcohol. Add the fluorescent pressure-sensitive microspheres obtained in step S2 at a ratio of 1 / 0.01 g / g and stir until evenly combined.

[0063] S4: Prepare the leveling layer raw material. Prepare a liquid epoxy resin prepolymer (HASUNCAST 3016LV) at a polymer monomer:curing agent ratio of 1 / 0.02 g / g. Add benzene at a ratio of 0.5 / 1 mL liquid epoxy resin prepolymer / mL benzene. Place in an ultrasonic disperser and shake.

[0064] S5: The model under test is an aluminum hydrofoil model with the following structure: Figure 3 As shown, the measured area is the pressure surface. Wash and dry the model to be measured, and prepare a 10mm*10mm*1mm aluminum plate for calibration. Put the bonding layer raw material into the spray gun, the air supply pressure is 0.04MPa, the spray gun diameter is 0.01mm, the spray gun is 30cm away from the model to be measured, and move the spray gun back and forth so that the material sprayed on the surface of the model to be measured is evenly distributed with a thickness of 0.05mm. Place the model in a preheated oven, heat the bonding layer at 40℃ for 5min, because it takes more than 0.5 hours for the bonding layer to fully cure at this temperature, and it is not fully cured at this time. Perform the same operation on the aluminum plate;

[0065] S6: Spray the sensitive layer material onto the uncured adhesive layer using the spraying method from step S5. Place the model in a preheated vacuum oven at 60°C for 2 hours to cure the sensitive layer. Repeat the same process on the aluminum plate.

[0066] S7: Spray the flattening layer material onto the sensitive layer using the same method as in step S5. Place the model in an oven and heat-cure the flattening layer at 60°C / 1 hour followed by 100°C / 1 hour. Repeat the same process on the aluminum plate.

[0067] A fluorescent pressure-sensitive coating suitable for underwater large-curvature models is calibrated by placing a prepared aluminum plate sample in a calibration chamber and stimulating the sample with a stable-intensity LED (UHP-TLED, 385nm, Prizmatix). The water pressure in the calibration chamber is gradually increased from normal pressure to 10kPa, and the sample is photographed using a high-resolution camera. The light intensity of the sample under normal pressure is compared with the light intensity of the sample under normal pressure to obtain a quantitative relationship between the pressure change and the coating light intensity change, such as Figure 4 shown.

[0068] A fluorescent pressure-sensitive coating suitable for underwater large-curvature models is used as follows: the model to be tested, with the fluorescent pressure-sensitive coating prepared on the surface, is placed in a water tunnel, and the sample is excited by an LED lamp with stable luminous intensity. A camera is arranged to collect the reference light intensity of the coating when there is no flow. The flow is adjusted to the experimental working conditions, and the experimental light intensity of the coating is collected. The two are compared to obtain a light intensity ratio distribution diagram of the coating surface (such as Figure 5 As shown, the flow direction is from right to left), and the high spatial resolution pressure distribution on the surface of the model to be tested can be calculated by combining the calibration results.

[0069] Example 2:

[0070] A fluorescent pressure-sensitive coating suitable for underwater large-curvature models and its preparation method. The coating consists of three functional layers: a bottom adhesive layer (1) that secures the coating, a middle sensitive layer (3) that achieves pressure response, and a surface smoothing layer (4) that reduces the coating's impact on flow. The coating is applied directly to the surface of the model being tested by spraying.

[0071] A fluorescent pressure-sensitive coating suitable for underwater large-curvature models is prepared by preparing bonding layer materials, sensitive layer materials, and flattening layer materials, then spraying bonding layer 1, spraying sensitive layer 3 before the bonding layer is completely cured, and preparing flattening layer 4 after the bonding layer is cured. The specific steps are as follows:

[0072] S1: Prepare the bonding layer raw materials. Prepare a liquid epoxy resin prepolymer (Shenzhen Chengxinkang T6308) at a polymer monomer:curing agent ratio of 1 / 1g / g. Add n-hexane at a ratio of 0.5 / 10mL n-hexane / mL liquid polyurethane prepolymer (Femiao Chemical FS-7). Place in an ultrasonic disperser and shake.

[0073] S2: Prepare fluorescent pressure-sensitive microspheres. Place an appropriate amount of dry, unexpanded expandable microspheres (FN-100S) in a beaker at a ratio of 1 / 0.05g expandable microspheres / g coumarin-6. Add coumarin-6 to the microspheres and mix thoroughly in a vibrator. Place the glass container on a preheated hot plate at 145°C and stir continuously until the mixture no longer changes volume. This yields fluorescent expandable microspheres.

[0074] S3: Prepare the raw materials for the sensitive layer. Prepare a liquid viscous solvent with a ratio of 1 / 0.5g / g water and methylcyclohexanol. Add the fluorescent pressure-sensitive microspheres obtained in step S2 at a ratio of 1 / 0.1g / g and stir until evenly combined.

[0075] S4: Prepare the planarization layer raw materials. Prepare a liquid epoxy resin prepolymer (Shenzhen Chengxinkang T6308) at a polymer monomer:curing agent ratio of 1 / 1g / g. Add n-hexane at a ratio of 0.5 / 1mL benzene / mL liquid polyurethane prepolymer (Femiao Chemical FS-7). Place in an ultrasonic disperser and shake.

[0076] S5: The model to be tested is an aluminum propeller model, and the area to be tested is the pressure surface. Wash and dry the model to be tested, and prepare a 10mm*10mm*1mm aluminum plate for calibration. Put the bonding layer raw material into the spray gun, the air supply pressure is 0.08MPa, the spray gun diameter is 1mm, the spray gun is 100cm away from the model to be tested, and move the spray gun back and forth so that the material sprayed on the surface of the model to be tested is evenly distributed with a thickness of 0.1mm. Place the model in a preheated oven, heat the bonding layer at 60℃ for 15min, because it takes more than 0.5 hours for the bonding layer to fully cure at this temperature, and it is not fully cured at this time. Perform the same operation on the aluminum plate;

[0077] S6: Spray the sensitive layer material onto the uncured adhesive layer using the same spraying method as in step S5. Place the model in a preheated vacuum oven and heat at 140°C for 2 hours at 0.6 bar to cure the sensitive layer, to a thickness of 0.12 mm. After curing, use an empty spray gun to purge the sensitive layer with air. Repeat the same process on the aluminum plate.

[0078] S7: Spray a 0.15mm thick flattening layer onto the sensitive layer using the same method as in S5. Place the model in an oven and heat-cure the flattening layer at 90°C / 2h followed by 150°C / 2h. Repeat the same process on the aluminum plate.

[0079] A fluorescent pressure-sensitive coating suitable for underwater large-curvature models is calibrated by placing a prepared aluminum plate sample in a calibration chamber and stimulating it with a stable-intensity LED (UHP-TLED, 405nm, Prizmatix). The water pressure in the calibration chamber is gradually increased from atmospheric pressure to 100 kPa, and the sample is photographed using a high-resolution camera. The light intensity of the sample under extraordinary pressure is compared with that under atmospheric pressure, yielding a quantitative relationship between the pressure change and the coating's light intensity change.

[0080] A fluorescent pressure-sensitive coating suitable for underwater models with large curvature is used. The model to be tested, coated with the fluorescent pressure-sensitive coating, is placed in a water tunnel and excited with a stable LED light. A camera is positioned to capture the reference light intensity of the coating when there is no flow. The flow is adjusted to experimental conditions, and the experimental light intensity of the coating is captured. The two light intensity ratios are compared to obtain a distribution map of the coating surface. Combined with the calibration results, the pressure distribution on the surface of the model to be tested can be calculated.

[0081] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A fluorescent pressure-sensitive coating suitable for underwater large curvature models, characterized in that: include The bottom layer is a bonding layer that fixes the coating; The middle layer is the sensitive layer for achieving pressure response; The surface layer is a smooth layer that reduces the effect of the coating on flow.

2. A method for preparing a fluorescent pressure-sensitive coating according to claim 1, characterized in that: The method comprises: preparing bonding layer raw materials, sensitive layer raw materials and flattening layer raw materials, then spraying the bonding layer, spraying the sensitive layer before the bonding layer is completely cured, and preparing the flattening layer after the bonding layer is cured.

3. The method for preparing a fluorescent pressure-sensitive coating according to claim 2, wherein: The preparation method of the bonding layer raw material comprises: mixing a polymer monomer and a curing agent to obtain a liquid viscous prepolymer, adding a non-polar solvent, and mixing them uniformly to obtain.

4. The method for preparing a fluorescent pressure-sensitive coating according to claim 3, wherein: The liquid viscous prepolymer is selected from one of transparent polyurethane prepolymer, transparent epoxy resin prepolymer or transparent organic silicone prepolymer; The mass ratio of the polymer monomer to the curing agent is 1:(0.2-1); the volume ratio of the liquid viscous prepolymer to the non-polar solvent is 0.5:(1-10).

5. The method for preparing a fluorescent pressure-sensitive coating according to claim 2, wherein: The preparation method of the sensitive layer raw material includes: The expandable microspheres are mixed with a polar fluorescent agent at or above the foaming temperature of the expandable microspheres to obtain fluorescent expanded microspheres.

6. The method for preparing a fluorescent pressure-sensitive coating according to claim 5, wherein: The mass ratio of the expandable microspheres to the polar fluorescent agent is 1:(0.05-0.001).

7. The method for preparing a fluorescent pressure-sensitive coating according to claim 2, wherein: The preparation method of the flattening layer raw material comprises: mixing a polymer monomer and a curing agent to obtain a liquid viscous prepolymer, adding a non-polar solvent, and mixing them uniformly to obtain.

8. The method for preparing a fluorescent pressure-sensitive coating according to claim 7, wherein: The liquid viscous prepolymer is selected from one of transparent polyurethane prepolymer, transparent epoxy resin prepolymer or transparent organic silicone prepolymer; The mass ratio of the polymer monomer to the curing agent is 1:(0.02-1); the volume ratio of the liquid viscous prepolymer to the non-polar solvent is 0.5:(1-10).

9. The method for preparing a fluorescent pressure-sensitive coating according to claim 2, wherein: The spraying process of the bonding layer, sensitive layer and flattening layer respectively includes: air supply pressure of 4-8 bar, spray gun diameter of 0.01-1 mm, spray gun distance of 30-100 cm, and layer thickness of 0.05-0.15 mm; The bonding layer material is cured after spraying, and the curing conditions include: curing temperature of 40-60° C. and curing time of 5-15 minutes; The sensitive layer material is cured after spraying, and the curing conditions include: vacuum heating curing, pressure 0.4-0.6 bar, curing temperature 60-140° C., and curing time 2-4 hours; The planarization layer material is cured after spraying, and the curing process includes: first heating and curing at 60-90° C. for 1-2 hours, and then heating and curing at 100-150° C. for 1-2 hours.

10. An application of the fluorescent pressure-sensitive coating according to claim 1, characterized in that: The fluorescent pressure-sensitive coating is used for detecting underwater pressure and pressure distribution of components.

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