In-situ testing device and method for mechanical properties of composite materials in seawater environment

Abstract

The present application relates to the manufacturing detection technology of marine pressure equipment, and aims to provide a kind of in-situ testing device and method for mechanical properties of composite material in seawater environment.The device includes seawater preparation and storage system, pretreatment system, test system, delivery circulation system, heating system and control system;In the water bath of pretreatment system, a plurality of traction tooling are provided, for continuously applying stress to the sample during pretreatment;Test system includes tensile test system and environmental chamber, and the environmental chamber is installed between the two traction mechanisms of tensile test system;Delivery circulation system includes pipeline for connecting various container equipment, for delivering seawater for circulation use.The composite material laminate sample of the present application is immersed in seawater environment from installation to final fracture failure, and the problem of in-situ testing of mechanical properties of composite material in seawater environment is solved.The structure of the device is simple, easy to install, and can be used for composite material performance testing in different temperature conditions and different salinity seawater environment.

Description

Technical Field

[0001] This invention relates to manufacturing and testing technology for marine pressure equipment, specifically to an in-situ testing device and method for the mechanical properties of composite materials in a seawater environment. Background Technology

[0002] The ocean plays an increasingly important role in social development due to its abundant resources. Composite materials, with their high specific strength and stiffness, designable properties, and simple manufacturing processes, have seen rapid development in marine applications. However, the marine environment, compared to air, is characterized by high humidity and high salinity, making composite materials susceptible to hygroscopic corrosion aging, leading to performance degradation and even destruction. Studies have shown that hygroscopic aging is more severe when samples are subjected to stress. Therefore, to ensure the long-term, safe, and reliable application of composite materials in marine environments, it is necessary to evaluate and test their mechanical properties under marine conditions.

[0003] To study the impact of the marine environment on the mechanical properties of composite materials, it is necessary to conduct mechanical property tests on composite materials in a marine environment. Currently, research mainly focuses on influencing factors such as material modification, seawater salinity, ambient temperature, and immersion time. A common method for mechanical property testing is non-in-situ pre-immersion, which involves immersing the sample in seawater for a period of time, then removing it and placing it in air for mechanical property testing.

[0004] Compared to non-in-situ testing, in-situ testing is conducted with the sample completely immersed in seawater, providing a more accurate reflection of the material's mechanical properties in a seawater environment. In recent years, researchers have successively developed marine in-situ testing devices and methods. For example, Chinese invention application CN201910695976.8 proposes a method for processing seabed in-situ test data, and Chinese invention application CN202010644965.X proposes a mounted underwater multifunctional in-situ testing machine for rock and soil. These devices are primarily designed for the analysis of rock, soil, or sediments during seabed exploration, rather than for conducting in-situ mechanical property tests on composite materials used in marine environments. Regarding in-situ mechanical performance testing devices, Chinese invention application CN202110266968.9 proposes an in-situ mechanical testing device for lead-bismuth environments. This device adopts a horizontal structure, occupies a large space, and has a complex sealing structure. Chinese invention application CN202210715775.1 proposes an in-situ mechanical testing device, system, and testing method for humidity-controlled or liquid environments. However, this device does not consider the control of liquid salinity and temperature, cannot provide a seawater environment with specific salinity and temperature, and adopts a low-stress clamping method, which is prone to pull-out when testing composite materials.

[0005] In addition to the technical features mentioned in the literature, existing testing equipment suffers from several drawbacks. It cannot provide the necessary testing conditions or allow the specimens to be fully immersed in seawater and subjected to continuous stress before mechanical property testing. Therefore, subsequent tests cannot accurately reflect the process of composite materials under continuous stress until failure in real-world applications, nor the changes in their mechanical properties. To address this, some technicians have proposed directly applying continuous stress to the specimens using the testing system for an extended period before conducting mechanical property tests. However, this approach suffers from the problem that the pre-treatment tensile process occupies the testing system for a long time, resulting in low equipment utilization. Furthermore, existing testing systems require draining the liquid from the environmental chamber used in the previous test before changing specimens, which also reduces testing efficiency during batch testing.

[0006] Given the current lack of in-situ mechanical performance testing devices and methods in seawater environments, this invention aims to propose a solution to provide a new approach for testing the performance of composite materials in seawater environments. Summary of the Invention

[0007] The key problem to be solved by this invention is to overcome the shortcomings of the prior art and propose an in-situ testing device and method for the mechanical properties of composite materials in a seawater environment.

[0008] To address the key issues, the solution of this invention is:

[0009] An in-situ testing device for the mechanical properties of composite materials in a seawater environment is provided, comprising: a seawater preparation and storage system, a pretreatment system, a testing system, a transport and circulation system, a heating system, and a control system; wherein,

[0010] The seawater production and storage system includes a seawater tank, a distilled water tank, a seawater premixing tank, and a seawater recovery tank. An agitator is installed inside the seawater premixing tank.

[0011] The pretreatment system includes a water bath, which is equipped with multiple sets of traction fixtures for continuously applying stress to the sample during pretreatment.

[0012] The test system includes a tensile testing system and an environmental chamber; the environmental chamber is installed between two traction mechanisms of the tensile testing system, and an extensometer and two loading heads arranged opposite each other are provided inside the environmental chamber. The loading heads are respectively connected to the corresponding traction mechanisms through traction shafts.

[0013] The heating system includes heating elements located in the environmental chamber and the water bath.

[0014] The conveying and circulation system includes pipelines for connecting various container devices, with two water pumps and multiple valves installed on the pipelines; the seawater tank and the distilled water tank are connected to the top of the seawater premixing tank via pipelines; the bottom outlet of the seawater premixing tank is connected to the first water pump, and the outlet of the first water pump is connected to the top of the seawater premixing tank, the inlet of the water bath tank, and the inlet of the environmental tank via pipelines; the bottom outlet of the environmental tank is connected to the top of the seawater recovery tank via pipelines, and the bottom outlet of the seawater recovery tank is connected to the second water pump, and the outlet of the second water pump is connected to the inlet of the environmental tank via pipelines;

[0015] The control system includes a host industrial computer, which is connected to sensors and power equipment in each system via signal lines.

[0016] As a preferred embodiment of the present invention, the traction fixture includes an upper clamp and a lower clamp arranged in parallel, which are connected by at least two sets of traction screws; each clamp consists of two clamping parts that are joined together, and the end of the sample to be tested is located between the clamping parts and is fastened with fastening screws; the traction fixture is also equipped with a load sensor and connected to a host computer via a signal line to monitor the traction force applied to the sample.

[0017] As a preferred embodiment of the present invention, the extensometer is fixed inside the environmental chamber by an extensometer bracket; sealing components are respectively provided between the traction shaft and the environmental chamber body, and between the extensometer bracket and the environmental chamber body.

[0018] As a preferred embodiment of the present invention, an online salinity detector is provided in the seawater tank, the seawater premixing tank, and the environmental tank, respectively; a level gauge is provided in the seawater premixing tank, the environmental tank, and the seawater recovery tank, respectively; the online salinity detector and the level gauge are connected to the host computer via signal lines.

[0019] As a preferred embodiment of the present invention, the heating element is an electric heater; or, the heating system further includes a heating unit, wherein the heating element is a heating coil, and the heating unit and the heating coil are connected by a pipeline to form a circulation loop for the heating medium.

[0020] As a preferred embodiment of the present invention, a flow control valve or gate valve is provided on the pipeline connecting each container device; a flow control valve is provided on the pipeline at the outlet of the water pump; a filter is provided on the pipeline at the inlet of the seawater recovery tank; and vent valves are provided at the bottom of the water bath and the seawater recovery tank respectively.

[0021] As a preferred embodiment of the present invention, a manual operation window and a glass observation window are provided on the door on the front of the environmental chamber, with the manual operation window located in the upper middle part of the door; and a vent is provided on the top of the environmental chamber and the seawater premixing tank to balance the pressure.

[0022] As a preferred embodiment of the present invention, the tensile testing system is provided with a horizontal guide rail, and the bottom of the environmental chamber is movably mounted on the guide rail.

[0023] This invention further provides a method for testing the mechanical properties of composite materials in a seawater environment using the aforementioned in-situ testing device, comprising the following steps:

[0024] S1. Add real seawater to the seawater tank and distilled water to the distilled water tank; introduce seawater into the seawater premixing tank, or add distilled water according to the test plan to control salinity; start the first water pump for self-circulation, and start the agitator to mix the seawater evenly.

[0025] S2. Fix the test sample on the traction fixture, adjust the traction force to the preset range, and then fix it in the water bath.

[0026] S3. Use the first water pump to inject seawater into the water bath; control the heating conditions in the water bath according to the test plan, so that the test sample is pretreated under the preset conditions in a fully submerged seawater environment.

[0027] S4. Install the two loading heads inside the environmental chamber, tighten the sealing components, close the chamber door, and fix the traction shaft connected to the loading heads onto the tensile testing system.

[0028] S5. The test operator puts on heat-insulating and corrosion-resistant gloves, takes out the pretreated test sample from the water bath, clamps the sample onto the loading head through the manual operation window, and then closes the window.

[0029] S6. Use the first water pump to inject seawater into the environmental chamber and monitor the liquid level until it meets the test requirements; use the heating system to control the internal temperature of the environmental chamber and maintain it within the set temperature ±0.1℃ range for at least 20 minutes.

[0030] S7. After inputting the parameters of specimen width, specimen thickness, and test speed on the industrial control computer, start the tensile testing system to load the specimen until the specimen breaks; record the force-displacement and stress-strain curves during the test in real time, and calculate the elastic modulus of the specimen.

[0031] S8. After the test, turn off the heating inside the environmental chamber and drain the liquid in the environmental chamber into the recovery tank;

[0032] S9. Open the door of the environmental chamber, take out the broken sample, and clean the inside of the environmental chamber.

[0033] As a preferred embodiment of the present invention, it further includes:

[0034] (1) When it is necessary to conduct continuous testing on a batch of samples, multiple samples are pretreated simultaneously in step S2.

[0035] (2) After step S7, without turning off the heating inside the environmental chamber, drain the seawater into the seawater recovery tank and control the liquid level to be lower than the lower edge of the manual operation window; after replacing the sample, start the second water pump to send the recovered seawater into the environmental chamber; and according to the decrease in liquid level in the environmental chamber and the monitoring data of the online salinity detector, use the seawater tank, distilled water tank and seawater premixing tank to replenish an appropriate amount of new seawater.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) In this invention, when conducting mechanical property tests on composite laminate samples, the samples are immersed in seawater from installation to final fracture failure, thus solving the problem of in-situ testing of the mechanical properties of composite materials in seawater environment.

[0038] (2) This invention can meet the mechanical property testing needs of composite materials under various test conditions in seawater environment; real seawater or artificial seawater with different salinity can be selected; long-term temperature and salinity control of the environmental chamber is realized through heating unit and online salinity detector on environmental chamber.

[0039] (3) The present invention achieves seawater immersion pretreatment of the sample under stress by applying a traction fixture that applies continuous stress. By circulating the environmental chamber and the seawater recovery tank, the sample can be replaced without draining the seawater in the environmental chamber, which reduces the test cost and improves the test efficiency.

[0040] (4) The present invention has a simple structure and is easy to install. It can be used for rapid screening of the properties of composite materials under room temperature and high temperature conditions and seawater with different salinity.

[0041] (5) All equipment, pipelines and valves in this invention are made of corrosion-resistant stainless steel (such as S31603 austenitic), which can avoid corrosion problems under seawater test conditions with varying temperatures. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention;

[0043] Figure 2 This is a three-dimensional (left), top (middle), and bottom (right) schematic diagram of the environmental chamber;

[0044] Figure 3 This is a schematic diagram of the traction tooling.

[0045] Figure 4 for Figure 3 Top view of the traction fixture;

[0046] Figure 5 for Figure 3 Longitudinal sectional view of the traction tool.

[0047] The attached figures are labeled as follows: 1 Industrial control computer; 2 First online salinity meter; 3 Seawater tank; 4 Distilled water tank; 5 Seawater premixing tank; 6 Heating unit; 7 Environmental chamber; 8 Heating coil; 9 Third online salinity meter; 10 Tensile testing system; 11 Loading head; 12 Composite laminate specimen to be tested; 13 Extensometer; 14 Seawater recovery tank; 15 Second water pump; 16 Water bath; 17 Traction fixture; 18 First water pump; 19 Agitator; 20 Second online salinity meter; 21 Glass observation window; 22 Manual operation window; 23 First sealing component; 24 Vent; 25 Second sealing component; 26 Third sealing component; 27 Traction screw; 28 Upper clamp; 29 Fastening screw; 30 Test specimen; 31 Fastening screw; 32 Lower clamp; 33 Load sensor. Detailed Implementation

[0048] The serial numbers assigned to components in this application, such as "first" and "second," are merely for distinguishing the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages). It should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing this application and for simplification, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0049] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0050] The implementation of the present invention will now be described with reference to the accompanying drawings:

[0051] like Figure 1 As shown, the in-situ testing device for the mechanical properties of composite materials in a seawater environment according to the present invention includes: a seawater preparation and storage system, a pretreatment system, a testing system, a transport and circulation system, a heating system, and a control system; wherein,

[0052] The seawater production and storage system includes a seawater tank 3, a distilled water tank 4, a seawater premixing tank 5, and a seawater recovery tank 14. The seawater tank 3 and the distilled water tank 4 are used to provide high-salinity seawater and distilled water, respectively; the seawater premixing tank 5 is equipped with a stirring paddle 19 for mixing when preparing seawater for testing.

[0053] The pretreatment system includes a water bath 16, the temperature of which is adjustable from room temperature to 100°C, to provide the high-temperature seawater environment required for sample pretreatment. Multiple sets of traction fixtures 17 are installed inside the water bath 16 to continuously apply stress to the sample during pretreatment.

[0054] like Figure 3 As shown, the traction fixture 17 includes an upper chuck 28 and a lower chuck 32 arranged in parallel, connected by at least two sets of traction screws 27. Figure 4 As shown, both chucks consist of two mating clamping components, each with two lead screw holes. The end of the test sample 30 is located between the clamping components, and the chucks are secured with fastening screws 29 and 31. (See reference...) Figure 5 The traction screw 27 passes through the screw hole of the upper chuck 28 and abuts against the lower chuck 32. Rotating the traction screw 27 causes the upper and lower chucks to move in opposite directions, thereby continuously applying stress to the sample. The entire traction fixture 17 continuously applies stress to the clamped sample through four traction screws 27. A load sensor 33 is installed on the traction fixture and is connected to the host computer 1 via a signal line to monitor the traction force applied to the sample.

[0055] The testing system includes a tensile testing system 10 and an environmental chamber 7. A horizontal guide rail is provided between the two traction mechanisms of the tensile testing system 10, and the bottom of the environmental chamber 7 is movably mounted on the guide rail. The guide rail allows the tensile testing system 10 to be switched between using the environmental chamber 7 and not using it, thereby obtaining control group data through testing under normal air conditions.

[0056] like Figure 2As shown, two loading heads 11 are arranged opposite each other inside the environmental chamber 7. Each loading head 11 is connected to its corresponding traction mechanism via a traction shaft. A first sealing component 23 and a third sealing component 26 seal the traction shafts from the environmental chamber body. An extensometer 13 is fixed inside the environmental chamber 7 via an extensometer bracket, and a second sealing component 25 seals the extensometer bracket from the environmental chamber body. A manual operation window 22 (150mm × 150mm) and a transparent, colorless glass observation window 21 are provided on the front door of the environmental chamber 7. The manual operation window 22 is located in the upper middle part of the door, allowing the test personnel to install or replace samples with the environmental chamber door closed. Ventilation ports 24 are provided on the top of both the environmental chamber 7 and the seawater premixing tank 5 to balance internal and external pressures. The temperature control range inside the environmental chamber is room temperature to 100℃, with a temperature control accuracy of ±0.1℃.

[0057] The heating system includes heating elements located in the environmental chamber and water bath, which can be electric heaters. Alternatively, the heating system may also include a heating unit 6, in which case the heating element is replaced by a heating coil 8, and the heating unit 6 and the heating coil 8 form a circulation loop for the heating medium through piping. The heating temperature of the heating system does not exceed 100℃, ensuring that the seawater in the water bath and environmental chamber does not boil and remains in a liquid state throughout the entire test.

[0058] The conveying and circulation system includes piping for connecting various containers, with two water pumps and multiple valves installed on the piping. Seawater tank 3 and distilled water tank 4 are connected to the top of seawater premixing tank 5 via piping. The bottom outlet of seawater premixing tank 5 is connected to a first water pump 18, whose outlet is connected via piping to the top of seawater premixing tank 5, the inlet of water bath 16, and the inlet of environmental chamber 7. The bottom outlet of environmental chamber 7 is connected via piping to the top of seawater recovery tank 14, whose bottom outlet is connected to a second water pump 15, whose outlet is connected via piping to the inlet of environmental chamber 7. Flow control valves or gate valves are installed on the piping connecting the containers. A flow control valve on the water pump outlet piping controls the seawater delivery rate. A filter is installed on the seawater recovery tank inlet piping for collecting sample debris. Vent valves are installed at the bottom of the water bath and seawater recovery tank for facilitating seawater discharge. A base is installed at the bottom of seawater premixing tank 5.

[0059] The control system includes a host industrial computer 1, which is connected to sensors and power equipment in each system via signal lines. For example, online salinity detectors 2 are installed in the seawater tank 3, seawater premixing tank 5, and environmental chamber 7, respectively; level gauges are installed in the seawater premixing tank 5, environmental chamber 7, and seawater recovery tank 14, respectively. The online salinity detectors 2 and level gauges are connected to the host computer via signal lines, and electrically controlled valves are installed on the pipelines. Based on the above setup, the industrial computer 1 can be used to automate the testing process. For example, it can control the transport and circulation of seawater by driving valves and water pump motors, and realize seawater mixing, salinity control, temperature control, and level control by receiving signals from the seawater tank 3, seawater premixing tank 5 and its agitator 19, heating unit 6, environmental chamber 7, and water bath 16. It can also control the test loading and record test data by connecting to the tensile testing system 10.

[0060] The tensile testing system 10 described in this invention is a conventional device for testing the mechanical properties of materials, and this invention does not impose any special limitations on it. All materials in the testing device that come into contact with seawater should be resistant to high temperatures and corrosion (e.g., S31603 austenitic stainless steel) to ensure the service life of the device.

[0061] This in-situ testing device enables the testing of the mechanical properties of composite materials in a seawater environment, specifically including the following steps:

[0062] S1. Add real seawater (or high-salinity seawater) to the seawater tank 3 and add distilled water to the distilled water tank 4; open the valve to introduce seawater into the seawater premixing tank 5, or add distilled water according to the test plan to control the salinity. Then start the first water pump 18 for self-circulation, and at the same time start the agitator 19 to mix the seawater evenly;

[0063] S2. Fix the test sample 30 on the traction fixture 17, adjust the traction force to the preset range, and then fix the traction fixture 17 in the water bath 16.

[0064] S3. Use the first water pump 18 to inject seawater into the water bath 16; control the heating conditions in the water bath 16 according to the test plan, so that the test sample 30 is pretreated in the seawater full immersion environment according to the preset conditions.

[0065] S4. Install the two loading heads 11 inside the environmental chamber 7, tighten the sealing components and close the chamber door, and fix the traction shaft connected to the loading head 11 to the traction mechanism of the tensile testing system 10.

[0066] S5. The test operator puts on heat-insulating and corrosion-resistant gloves, takes out the pretreated test sample 30 from the water bath 16, clamps the sample onto the loading head 11 through the manual operation window 22, and then closes the window.

[0067] S6. Use the first water pump 18 to inject seawater into the environmental chamber 7, monitor the liquid level until it meets the test requirements; use the heating system to control the internal temperature of the environmental chamber and maintain it within the set temperature ±0.1℃ range for at least 20 minutes.

[0068] S7. After inputting the parameters of specimen width, specimen thickness and test speed on the industrial control computer 1, start the tensile test system 10 to load the specimen until it breaks; based on the deformation of the specimen measured in real time by the extensometer 13, obtain the force-displacement and stress-strain curves of the test process, and calculate the elastic modulus of the specimen.

[0069] S8. After the test, turn off the heating inside the environmental chamber and drain the liquid in the environmental chamber into the recovery tank;

[0070] S10. Open the door of the environmental chamber, take out the broken sample, and clean the inside of the environmental chamber.

[0071] Based on the design of this invention, the device enables sample replacement without completely draining the seawater from the environmental chamber 7, allowing for repeated testing and thus improving the efficiency of repeated testing. Furthermore, the circulation between the seawater recovery tank 14 and the environmental chamber 7 conserves seawater and reduces testing costs. An example of this operation method is as follows:

[0072] (1) After the first tensile test, do not turn off the internal heating of the environmental chamber. Open the valve on the pipeline connecting the outlet of the environmental chamber 7 and the inlet of the seawater recovery tank 14 to drain some of the liquid into the seawater recovery tank 14. This pipeline is equipped with a filter to filter out sample debris and prevent it from entering the seawater recovery tank 14. Use a level gauge to monitor the drop in the liquid level in the environmental chamber 7. When the liquid level in the environmental chamber is lower than the lower edge of the manual operation window 22, close the valve to retain as much seawater as possible in the chamber.

[0073] (2) Open the manual operation window 22, and the test operator puts on heat-insulating and corrosion-resistant gloves and takes out the fractured composite laminate sample from the environmental chamber 7.

[0074] (3) Take out the next test sample 30 from the batch pre-treated samples in the water bath 16. Control the loading head 11 to move through the industrial control computer 1, clamp the sample between the two loading heads 11, and then close the manual operation window 22.

[0075] (4) Start the second water pump 15, open the valve on the pipeline connecting the inlet of the environmental tank 7 and the outlet of the seawater recovery tank 14, and pump the seawater in the seawater recovery tank 14 into the environmental tank 7.

[0076] (5) Since the seawater recycling process may cause liquid loss in the environmental tank 7, and the previous high temperature test will also cause water evaporation and seawater salinity to rise, it is necessary to adjust new seawater using the seawater tank 3, distilled water tank 4 and seawater premixing tank 5 according to the liquid level drop in the environmental tank 7 and the monitoring data of the third online salinity detector 9, and replenish it through the first water pump 18 until the seawater level and salinity in the tank meet the test conditions.

[0077] (6) After keeping it warm for about 20 minutes, conduct the second tensile test.

[0078] Following this method, the mechanical properties of a large number of composite laminate samples can be tested in a short time.

[0079] The apparatus of this invention can be used to prepare artificial seawater solutions with different salinities, facilitating experiments.

[0080] The preparation steps for artificial seawater solutions with different salinities are as follows:

[0081] (1) Add distilled water to distilled water tank 4; add high salinity seawater solution to seawater tank 3, with a salinity of x%.

[0082] (2) If it is to prepare a seawater solution with a salinity of y% by αL in the seawater premixing tank 5, then open the flow control valves connecting the seawater tank 3, the distilled water tank 4 and the seawater premixing tank 5 respectively, and send in (α·y / x)L of x% high salinity seawater solution and α(1-y / x)L of distilled water, and then close the valves.

[0083] (3) Start the stirring paddle 19 to stir the mixed solution, and then use the second online salinity detector 20 to measure the salinity of the mixed solution in the seawater premixing tank 5; if the set seawater solution salinity requirements are not met, adjust the salinity of the mixed solution according to the measurement results until the salinity of the mixed solution in the tank meets the test conditions.

[0084] Based on the above operations, the present invention can also conduct mechanical property tests on samples after accelerated corrosion and aging at high salinity.

[0085] The above description is merely one embodiment of the present invention and is not intended to limit the invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make certain modifications or alterations to the disclosed structure and technical content without departing from the scope of the present invention to create equivalent embodiments. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An in-situ testing device for the mechanical properties of composite materials in a seawater environment, characterized in that, include: Seawater production and storage system, pretreatment system, testing system, conveying and circulation system, heating system, and control system; among which, The seawater production and storage system includes a seawater tank, a distilled water tank, a seawater premixing tank, and a seawater recovery tank. A stirring paddle is installed inside the seawater premixing tank. Online salinity detectors are installed in the seawater tank, the seawater premixing tank, and the environmental tank, respectively. Level gauges are installed in the seawater premixing tank, the environmental tank, and the seawater recovery tank, respectively. The pretreatment system includes a water bath containing multiple sets of traction fixtures for continuously applying stress during sample pretreatment. Each traction fixture includes an upper and lower clamp arranged in parallel, connected by at least two sets of traction screws. Each clamp consists of two opposing clamping components, with the end of the sample to be tested positioned between the clamping components and secured with fastening screws. A load sensor is also installed on the traction fixture and connected to the control system via a signal line to monitor the applied traction force on the sample. The testing system includes a tensile testing system and an environmental chamber. The environmental chamber is installed between two traction mechanisms of the tensile testing system. Inside the environmental chamber, there is an extensometer and two loading heads arranged opposite each other. The loading heads are connected to the corresponding traction mechanisms via traction shafts. The extensometer is fixed inside the environmental chamber by an extensometer bracket. Sealing components are provided between the traction shaft and the environmental chamber body, and between the extensometer bracket and the environmental chamber body. A manual operation window and a glass observation window are provided on the front door of the environmental chamber. The manual operation window is located in the upper middle part of the door. The heating system includes heating elements located in the environmental chamber and the water bath. The conveying and circulation system includes pipelines for connecting various container devices, with two water pumps and multiple valves installed on the pipelines; the seawater tank and the distilled water tank are connected to the top of the seawater premixing tank via pipelines; the bottom outlet of the seawater premixing tank is connected to the first water pump, and the outlet of the first water pump is connected to the top of the seawater premixing tank, the inlet of the water bath tank, and the inlet of the environmental tank via pipelines; the bottom outlet of the environmental tank is connected to the top of the seawater recovery tank via pipelines, and the bottom outlet of the seawater recovery tank is connected to the second water pump, and the outlet of the second water pump is connected to the inlet of the environmental tank via pipelines; The control system includes a host industrial computer, which is connected to sensors and power equipment in each system via signal lines.

2. The apparatus according to claim 1, characterized in that, The heating element is an electric heater; or, the heating system further includes a heating unit, the heating element being a heating coil, and the heating unit and the heating coil forming a circulation loop for the heating medium via pipelines.

3. The apparatus according to claim 1, characterized in that, Flow control valves or gate valves are installed on the pipelines connecting each container; a flow control valve is installed on the pipeline at the water pump outlet; a filter is installed on the pipeline at the inlet of the seawater recovery tank; and vent valves are installed at the bottom of the water bath and the seawater recovery tank.

4. The apparatus according to claim 1, characterized in that, Vents are provided on the top of the environmental tank and the seawater premixing tank to balance the pressure.

5. The apparatus according to claim 1, characterized in that, The tensile testing system is equipped with a horizontal guide rail, and the bottom of the environmental chamber is movably mounted on the guide rail.

6. A method for testing the mechanical properties of composite materials in a seawater environment using the in-situ testing device described in claim 1, characterized in that, Includes the following steps: S1. Add real seawater to the seawater tank and distilled water to the distilled water tank; introduce seawater into the seawater premixing tank, or add distilled water according to the test plan to control salinity; start the first water pump for self-circulation, and start the agitator to mix the seawater evenly. S2. Fix the test sample on the traction fixture, adjust the traction force to the preset range, and then fix it in the water bath. S3. Use the first water pump to inject seawater into the water bath; control the heating conditions in the water bath according to the test plan, so that the test sample is pretreated under the preset conditions in a fully submerged seawater environment. S4. Install the two loading heads inside the environmental chamber, tighten the sealing components, close the chamber door, and fix the traction shaft connected to the loading heads onto the tensile testing system. S5. The test operator puts on heat-insulating and corrosion-resistant gloves, takes out the pretreated test sample from the water bath, clamps the sample onto the loading head through the manual operation window, and then closes the window. S6. Use the first water pump to inject seawater into the environmental chamber and monitor the liquid level until it meets the test requirements; use the heating system to control the internal temperature of the environmental chamber and maintain it within the set temperature ±0.1℃ range for at least 20 minutes. S7. After inputting the parameters of specimen width, specimen thickness, and test speed on the industrial control computer, start the tensile testing system to load the specimen until the specimen breaks; record the force-displacement and stress-strain curves during the test in real time, and calculate the elastic modulus of the specimen. S8. After the test, turn off the heating inside the environmental chamber and drain the liquid in the environmental chamber into the recovery tank; S9. Open the door of the environmental chamber, take out the broken sample, and clean the inside of the environmental chamber.

7. The method according to claim 6, characterized in that, Also includes: (1) When it is necessary to conduct continuous testing on a batch of samples, multiple samples are pretreated simultaneously in step S2; (2) After step S7, without turning off the heating inside the environmental chamber, drain the seawater into the seawater recovery tank and control the liquid level to be lower than the lower edge of the manual operation window; after replacing the sample, start the second water pump to send the recovered seawater into the environmental chamber; and according to the decrease in liquid level in the environmental chamber and the monitoring data of the online salinity detector, use the seawater tank, distilled water tank and seawater premixing tank to replenish an appropriate amount of new seawater.

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