A device and method for testing the pull-pull fatigue performance of materials in a water environment

Abstract

The application discloses a device and method for realizing tensile-tensile fatigue performance test in a material water environment, and belongs to the technical field of material fatigue performance evaluation. The device comprises a test bin body which is sleeved outside a test section of a test piece to construct a local fluid test environment, a bottom sealing piece which is arranged at a bottom opening of the test bin body to seal a gap, a top splash-proof shielding piece which covers a top opening and keeps an active gap with the test piece, and a spraying assembly which is arranged inside the bin body and sprays fluid to the surface of the test piece to form a flowing environment. The application realizes semi-closed and lightweight fluid environment simulation, reduces additional mass interference, and improves the accuracy and reliability of water environment fatigue test.

Description

Technical Field

[0001] This invention belongs to the field of material fatigue performance evaluation technology, specifically relating to an apparatus and method for testing the tensile fatigue performance of materials in an aqueous environment. Background Technology

[0002] Polymer-based composite materials are widely used in underwater structures and equipment due to their advantages such as lightweight, high strength, and corrosion resistance. These materials are subjected to long-term fatigue loads in underwater environments, which can easily lead to performance degradation, crack propagation, and eventual failure. Therefore, accurately simulating the fatigue process of composite materials in underwater environments is crucial for material selection, structural design, and life prediction.

[0003] Currently, fatigue performance testing of polymer-based composite materials in fields such as marine platforms, ship structures, and underwater pipelines is difficult to conduct underwater fatigue testing due to limitations in material fatigue testing equipment. Therefore, most fatigue tests are performed in air, which cannot accurately reflect the impact of water on the fatigue performance of composite materials. Water affects the fatigue performance of composite materials in two ways: first, polymer-based composite materials have a certain degree of water absorption, and the basic mechanical properties of polymer-based composite materials decrease to some extent after water absorption; second, during fatigue testing, once cracks appear in polymer-based composite materials, water will seep into the cracks, and under the coupled effect of fatigue loads, the cracks will propagate rapidly, reducing fatigue performance. For example, Chinese patent application CN112147010A discloses a fatigue performance testing system for composite pressure-resistant shells, which forms a closed space through a high-pressure autoclave cylinder and end caps, and uses a hydrostatic testing machine to apply alternating pressure to simulate the hydrostatic pressure environment of the deep sea. However, such devices typically employ fully enclosed heavy metal pressure vessels, which are quite heavy and prone to introducing additional inertial loads and vibration interference during high-frequency fatigue loading, affecting the accuracy of test data. Furthermore, they simulate static or quasi-static deep-water hydrostatic environments, making it difficult to reproduce the surface water erosion, dynamic wetting, and fluid-medium coupled fatigue conditions faced by materials in actual service. In addition, while large-scale water tank immersion methods can simulate aquatic environments, they also suffer from problems such as bulky equipment, poor compatibility with testing machines, and inability to precisely control local flow fields and temperatures. Therefore, there is an urgent need for a compact device and method that can realistically simulate the flowing water environment on material surfaces and achieve stable fatigue testing with low added mass interference. Summary of the Invention

[0004] This invention provides an apparatus and method for testing the tensile fatigue performance of materials in an aqueous environment. It enables the construction of a semi-closed local fluid environment and the synergy of fatigue loading without affecting the normal operation of the fatigue testing machine. This effectively reduces the interference of the device's own weight on the test and improves the realism of the environmental simulation.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An apparatus for testing the tensile fatigue properties of materials in an aqueous environment includes: a test chamber, a bottom seal, a top splash shield, and a spray assembly; wherein, the test chamber is fitted over the test section of the specimen to create a localized fluid testing environment; the bottom seal is located at the bottom opening of the test chamber to seal the gap between the bottom of the test chamber and the specimen to prevent fluid leakage downwards; the top splash shield covers the top opening of the test chamber and maintains a clearance with the specimen to prevent fluid from splashing upwards and to allow the specimen to undergo axial deformation during fatigue loading; the spray assembly is located inside the test chamber to spray fluid onto the surface of the specimen to create a flowing fluid environment on the specimen surface.

[0007] The aforementioned device constructs a localized test area by housing the test specimen within the test chamber. Combined with a bottom seal to prevent fluid leakage and contamination of the testing machine, and a top splash shield that provides splash protection while allowing for movement to accommodate specimen deformation, it forms a semi-enclosed, lightweight fluid environment simulation chamber. In addition, the internal spray assembly directly sprays fluid onto the surface of the specimen, replacing the traditional full immersion or high-pressure static water mode. This significantly reduces the added mass while ensuring the authenticity of the water environment and avoids interference with the load applied to the fatigue testing machine.

[0008] In the above-described structure, the spray assembly includes multiple fluid spraying units, which are distributed on opposite sides of the test chamber and arranged at equal intervals along the axial direction of the specimen, so that the sprayed fluid uniformly covers the surface of the specimen.

[0009] The top splash shield has a through hole in the middle for the test piece to pass through, and the diameter of the through hole is larger than the outer diameter of the test piece to form a movable gap;

[0010] The bottom seal is a flexible seal that fits against the surface of the specimen to allow for slight vibration of the specimen while sealing the fluid.

[0011] The test chamber is made of a lightweight, transparent polymer material, preferably polycarbonate (PC) or modified acrylic material. The wall thickness of the test chamber is 2 mm to 4 mm to reduce the weight of the test chamber while accommodating the test section of the specimen.

[0012] The device also includes a water inlet pipe and a diverter. One end of the water inlet pipe is connected to a fluid supply device, and the other end is connected to the diverter. The diverter is configured to distribute the fluid in the water inlet pipe to multiple fluid injection units located on the same side of the test chamber, avoiding the risk of entanglement and weight increase caused by multiple independent water inlet pipes, while ensuring the consistency of flow rate and pressure of each injection unit on the same side, and improving the stability of flow field control.

[0013] The device also includes a fluid circulation pipeline and a temperature control module. The fluid circulation pipeline connects the bottom of the test chamber to the fluid supply device, and is used to guide the outflowing fluid from the bottom of the test chamber back to the fluid supply device to form a closed-loop circulation system. The temperature control module includes a temperature sensor and a temperature regulating device. The temperature sensor is used to monitor the temperature of the circulating fluid in real time, and the temperature regulating device is configured to heat or cool the fluid according to the monitored temperature to maintain a constant temperature of the circulating fluid. The closed-loop fluid circulation system enables the reuse of the test medium, saves water resources, and maintains stable water quality. The integrated temperature control module regulates the fluid temperature through closed-loop feedback, which can accurately simulate the water temperature conditions of different sea areas or seasons, expands the environmental simulation dimension of the device, and supports the study of material fatigue performance under the coupling effect of temperature and water environment.

[0014] The device also includes a control unit and a pump body; the pump body is disposed in the fluid supply device, and the control unit is communicatively connected to the pump body; the control unit is configured to change the fluid jet intensity of the spray assembly by adjusting the flow rate and pressure of the pump body, so as to simulate the water flow conditions under different water environment conditions.

[0015] The present invention also provides a method for testing the tensile fatigue properties of materials in an aqueous environment, using the aforementioned apparatus for testing the tensile fatigue properties of materials in an aqueous environment, comprising the following steps:

[0016] The test chamber is fitted over the test section of the specimen. The gap between the bottom of the test chamber and the specimen is sealed with a bottom seal, and the top of the test chamber is covered with a top splash shield to create a semi-closed local fluid test environment. The fluid supply device is activated, and the fluid is sprayed onto the surface of the specimen through the spray assembly, creating a flowing fluid environment on the surface of the specimen. At the same time, the outflowing fluid is returned to the fluid supply device through the fluid circulation pipeline. In the flowing fluid environment, the specimen is subjected to cyclic load by a fatigue testing machine to conduct a water environment fatigue performance test.

[0017] The above method ensures that the specimen is always in a stable flowing water environment when subjected to fatigue load by first constructing a semi-closed local fluid environment and then starting the coordinated process of fluid circulation and loading. Moreover, the environment construction process does not interfere with the mechanical boundary conditions of the specimen, thus realizing the organic integration of environmental simulation and mechanical testing.

[0018] In the method described above, during the application of cyclic loads to the specimen using a fatigue testing machine, the strain data and crack propagation of the specimen are monitored in real time. Combined with environmental parameters of the flowing fluid environment, the fatigue performance of the specimen in the water environment is evaluated. By linking mechanical response monitoring with environmental parameters, a multi-dimensional data mapping relationship of "environment-load-damage" is established, which helps to reveal the influence of the water environment on the fatigue failure mechanism of materials and improves the depth and scientific nature of performance evaluation.

[0019] Based on the set aquatic environment conditions, the control unit synchronously adjusts the fluid jet intensity, fluid temperature, and cyclic load parameters of the fatigue testing machine. Specifically, the flow rate and pressure of the pump body of the fluid supply device are adjusted to change the fluid jet intensity, and the fluid temperature is adjusted by the temperature control module to simulate coupled fatigue environments at different water depths or flow velocities. This achieves synchronous and coordinated adjustment of fluid jet intensity, temperature, and mechanical load parameters, enabling high-fidelity reproduction of complex and variable underwater service conditions. It supports advanced testing such as multi-factor coupled accelerated aging and fatigue interruption points, meeting the needs of high-end equipment material research and development for refined environmental simulation.

[0020] Beneficial effects: This invention provides an apparatus and method for testing the tensile fatigue properties of materials in an aqueous environment, which has the following advantages compared with the prior art:

[0021] This invention fundamentally solves the technical problems of traditional fully immersion tanks or autoclaves being heavy and easily interfering with the load application of fatigue testing machines by constructing a semi-closed local fluid environment using a lightweight test chamber fitted over the test section of the specimen. The coordinated design of the bottom seal and the top splash shield effectively prevents fluid leakage and splashes, protecting the test equipment. Meanwhile, the reserved movement gaps and flexible contact methods ensure that the axial deformation and micro-vibrations of the specimen during fatigue loading are unrestrained, guaranteeing the authenticity of mechanical transmission. The internal spray assembly, combined with the fluid circulation and temperature control system, can form a uniform, stable, and temperature-controlled flowing fluid environment on the specimen surface, realistically simulating the dynamic wetting and water scouring conditions faced by materials in actual underwater service, overcoming the limitations of existing technologies that can only simulate hydrostatic pressure or static immersion. Furthermore, the transparent chamber design supports visual observation throughout the entire test process, and combined with the ability to adjust multiple parameters simultaneously, it significantly improves the accuracy, reliability, and environmental adaptability of fatigue performance testing of polymer-based composite materials and other materials in water environments. Attached Figure Description

[0022] Figure 1 This is a perspective view of the apparatus for testing the tensile fatigue properties of materials in an aqueous environment, as described in this embodiment of the invention.

[0023] Figure 2This is a schematic diagram of the overall structure of the device for testing the tensile-tensile fatigue performance of materials in an aqueous environment, as described in this embodiment of the invention.

[0024] Figure 3 This is a schematic diagram of the main working area of ​​the device for testing the tensile-tensile fatigue performance of materials in an aqueous environment, as described in this embodiment of the invention.

[0025] Figure 4 This is a microscopic schematic diagram of the tensile fatigue crack propagation in a polymer-based composite laminate according to an embodiment of the present invention;

[0026] Figure 5 This is a SN fitting curve of the material in a specific water environment in an embodiment of the present invention;

[0027] In the figure, 1-test chamber, 2-fluid jetting unit, 3-water inlet pipe, 4-pump body, 5-fluid supply device, 6-fluid circulation pipe, 7-test piece, 8-fatigue testing machine, 9-diverter, 10-pumping pipe, 11-bottom seal, 12-tee connector, 13-top splash shield. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments: Example 1

[0029] like Figure 1 and Figure 2 As shown, this embodiment provides a device for testing the tensile fatigue performance of materials in an aqueous environment. It aims to solve the technical problems of traditional fully immersion testing equipment being heavy and easily interfering with the application of fatigue testing machine loads. It achieves high-fidelity fatigue testing in an aqueous environment by constructing a semi-closed local fluid environment. The device includes a test chamber 1, a bottom seal 11, a top splash shield 13, and a spray assembly.

[0030] Test chamber 1 is fitted over the test section of specimen 7 to create a localized fluid testing environment. Specifically, instead of immersing the entire specimen 7 or fatigue testing machine 8 in a large water tank, test chamber 1 only partially encloses the critical test section of specimen 7 subjected to alternating loads. This encasing structure confines the fluid medium to a small area on the surface of specimen 7, rather than filling the entire container, thus significantly reducing the mass of water involved in the vibration. It should be understood that although test chamber 1 is cubic in shape as shown in the figure, in other embodiments, it can also be designed as a cylindrical, ellipsoidal, or other hollow cavity structure adapted to the geometry of specimen 7, as long as it can accommodate the test section of specimen 7 and form a relatively independent fluid space. Through this localized environment construction method, the device ensures that the surface of specimen 7 is in a realistic water environment while minimizing additional mass interference to the dynamic response of fatigue testing machine 8, ensuring the accuracy of mechanical test data.

[0031] A bottom seal 11 is located at the bottom opening of the test chamber 1 to seal the gap between the bottom of the test chamber 1 and the specimen 7, preventing fluid leakage downwards. Figure 1 and Figure 2 In the structure shown, the bottom seal 11 is located at the interface between the lower end of the test chamber 1 and the specimen 7, forming the lower boundary of the fluid environment. Since the fatigue testing machine 8 typically contains high-precision force sensors, actuators, and electrical components, any fluid leakage could lead to equipment corrosion, short circuits, or measurement drift. The bottom seal 11, through physical barrier function, strictly confines the test fluid inside the test chamber 1, effectively preventing fluid from leaking down the surface of the specimen 7 and contaminating the fatigue testing machine 8 below. For example, the bottom seal 11 can take various forms such as an elastic annular sealing ring, flexible tape, or injection sealing layer; as long as it can achieve a dynamic sealing function between the specimen 7 and the bottom of the test chamber 1, it is within the protection scope of this invention.

[0032] A top splash shield 13 covers the top opening of the test chamber 1, and a movable gap is maintained between the top splash shield 13 and the specimen 7 to prevent fluid from splashing upwards and to allow the specimen 7 to undergo axial deformation during fatigue loading. This is the key structural design for decoupling "environmental simulation" and "mechanical testing" in this embodiment. Specifically, during the tensile fatigue test, the specimen 7 will experience periodic axial elongation and shortening. If the top uses rigid contact or interference fit, it will generate additional frictional resistance or constraint stress on the movement of the specimen 7, severely distorting the fatigue life data. In this embodiment, the top splash shield 13 has a through hole in the middle for the specimen 7 to pass through. The diameter of the through hole is larger than the outer diameter of the specimen 7, thereby forming a non-contact movable gap between them. This gap serves two purposes: firstly, it provides a free channel for the axial movement of specimen 7, completely eliminating mechanical interference from the top structure on the deformation of specimen 7; secondly, in conjunction with the fluid dynamics design inside the chamber, it effectively prevents atomized droplets generated by high-speed jet fluid from escaping upwards, protecting the upper clamping mechanism and loading unit of the fatigue testing machine 8 from water mist corrosion. It should be understood that the size of this movable gap should be reasonably set according to the maximum axial deformation of specimen 7 and the splash prevention requirements, ensuring sufficient freedom of movement while avoiding excessive fluid splashing due to an excessively large gap.

[0033] The spray assembly is located inside the test chamber 1 and is configured to spray fluid onto the surface of the specimen 7 to create a flowing fluid environment on the surface of the specimen 7. Unlike static immersion testing, this embodiment actively delivers fluid with a certain kinetic energy to the surface of the specimen 7 through the spray assembly, simulating the water flow erosion and dynamic wetting conditions experienced by the material surface in marine engineering structures. The spray assembly may include one or more fluid jetting units 2, which are arranged on the inner wall of the test chamber 1 or on independent supports, and spray directionally toward the test section surface of the specimen 7. After the fluid impacts the surface of the specimen 7, it forms a turbulent or laminar boundary layer and flows along the surface of the specimen 7, eventually converging at the bottom of the chamber. This actively sprayed flowing fluid environment not only more realistically reproduces underwater service conditions but also accelerates the penetration of the fluid medium into the microcracks or damaged areas of the material, which helps to study the coupling effect mechanism of the water environment on the fatigue performance of materials. Furthermore, the specific layout, spray angle, and flow rate parameters of the spray assembly can be flexibly adjusted according to actual test requirements to adapt to environmental simulation requirements under different flow velocities and erosion intensities.

[0034] This embodiment constructs a complete semi-closed local fluid testing system by partially fitting the test chamber 1, implementing a leak-proof design for the bottom seal 11, using a non-contact gap for the top splash shield 13, and employing dynamic flow generation from the spray assembly. The system achieves lightweight integration and functional decoupling of the environmental simulation unit and the mechanical loading unit in its physical structure. This ensures the authenticity of the water environment fatigue test while avoiding interference from additional mass and mechanical constraints on the test results, providing reliable basic hardware support for the water environment fatigue performance evaluation of various engineering materials, such as polymer-based composite materials.

[0035] Example 2

[0036] like Figure 3 As shown, this embodiment, based on Embodiment 1, further refines the flow field construction structure and low-interference design of the device, aiming to solve the technical challenge of ensuring that uniform water environment simulation and mechanical testing do not interfere with each other. In this embodiment, the spray assembly includes multiple fluid spray units 2, which are distributed on opposite sides of the test chamber 1 and arranged at equal intervals along the axial direction of the specimen 7, so that the sprayed fluid uniformly covers the surface of the specimen 7. Specifically, this bilaterally symmetrical and axially equally spaced layout eliminates the problem of uneven load on the specimen 7 that may be caused by unilateral spraying, and avoids the introduction of additional bending moments due to asymmetrical water flow impact forces, thereby ensuring the purity of fatigue test load transfer. At the same time, the equal-interval arrangement ensures that the fluid boundary layer thickness on the entire test section surface of the specimen 7 tends to be consistent, preventing local drying or excessive scouring, and improving the spatial uniformity of environmental simulation. For example, in this embodiment, a set of three fluid spray units 2 is set on each of the left and right sides of the test chamber 1, and the spacing between adjacent fluid spray units 2 can be adaptively adjusted according to the height of the test chamber 1 and the effective test length of the specimen 7. It should be understood that although the figure shows an arrangement of three fluid jet units 2 on each side, in other embodiments, the number of fluid jet units 2 can be increased or decreased according to the length of the specimen 7, or a non-equal spacing gradient arrangement can be adopted to adapt to specific flow field requirements, as long as the fluid can achieve uniform coverage of the surface of the specimen 7.

[0037] The top splash shield 13 has a through hole in the middle for the specimen 7 to pass through. The diameter of the through hole is larger than the outer diameter of the specimen 7 to form a movable gap. The bottom seal 11 is a flexible seal that fits against the surface of the specimen 7 to allow the specimen 7 to vibrate slightly while sealing the fluid. Specifically, the dimensional difference between the top through hole and the outer diameter of the specimen 7 constitutes a non-contact movement channel. The size of this movable gap should be at least greater than the sum of the axial deformation and radial oscillation amplitude of the specimen 7 under the maximum fatigue load, thereby completely removing the mechanical constraints of the top structure on the degrees of freedom of the specimen 7. For example, for a standard tensile specimen, the width of one side of this movable gap can be set to 1 mm to 3 mm, which effectively blocks the splashing of atomized droplets and provides sufficient safety space for the high-frequency vibration of the specimen 7. At the same time, the bottom seal 11 is made of a flexible material with elasticity, such as vacuum sealing tape, silicone sealing ring, or polyurethane elastomer, which fits tightly against the surface of the specimen 7 through its own flexible deformation. This flexible contact mechanism can not only adapt to the slight axial displacement and radial runout of the specimen 7 during fatigue loading, maintaining the effectiveness of the dynamic seal, but also absorb some vibration energy, avoiding stress concentration or wear and leakage of the sealing surface caused by rigid sealing connections. It should be understood that the specific material and cross-sectional shape of the bottom seal 11 are not limited to the above examples. Any flexible connection method that can ensure sealing performance while allowing relative movement of the specimen 7 is within the protection scope of this invention.

[0038] The test chamber 1 is made of a lightweight, transparent polymer material with a wall thickness of 2mm to 4mm to reduce its weight while accommodating the test section of specimen 7. Specifically, lightweight, transparent polymer materials such as polycarbonate (PC), modified acrylic resin, or polymethyl methacrylate (PMMA) are selected. Their low density significantly reduces the overall mass of the device, minimizing the impact of added mass on the high-frequency dynamic response of the fatigue testing machine 8. Simultaneously, their excellent optical transmittance facilitates real-time observation of crack initiation and propagation behavior on the surface of specimen 7 during the test. Controlling the wall thickness within the range of 2mm to 4mm is based on a balance between structural strength and weight reduction requirements: if the wall thickness is less than 2mm, the chamber may not be able to withstand the internal spray water pressure and installation stress, easily leading to deformation or cracking; if the wall thickness is greater than 4mm, it will result in excessive weight, weakening the advantages of the lightweight design. For example, in this embodiment, the test chamber 1 is a cubic structure with a side length of 60mm and a wall thickness of 3mm. This size can accommodate standard composite material specimens while providing sufficient internal flow space. It should be understood that the shape of the test chamber 1 is not limited to a cube, and can also be designed as a cylinder, ellipsoid or other irregular cavity according to the geometric characteristics of the specimen 7; the wall thickness parameter can also be adaptively adjusted according to the mechanical properties of the selected material and the test pressure level, as long as the basic requirements of lightweight and visualization are met.

[0039] The device in this embodiment also includes an inlet pipe 3 and a diverter 9. One end of the inlet pipe 3 is connected to the fluid supply device 5, and the other end is connected to the diverter 9. The diverter 9 distributes the fluid in the inlet pipe 3 to multiple fluid jet units 2 located on the same side of the test chamber 1. Specifically, the diverter 9, as the core node for fluid distribution, evenly distributes the single main fluid from the fluid supply device 5 to each fluid jet unit 2 on the same side, ensuring the consistency of inlet pressure and flow rate of each jet unit, thereby achieving a uniform and stable flow field. Compared with configuring an inlet pipe separately for each fluid jet unit 2, this integrated diverter design greatly simplifies the external pipeline layout, reduces the risk of pipeline entanglement and overall weight, and also reduces the leakage risks caused by multiple interface connections. For example, the diverter 9 can be in the form of a four-way connector, a water distributor, or a multi-hole distribution block, and its material can be the same as that of the test chamber 1 to further reduce weight, or it can be made of corrosion-resistant metal material to improve pressure resistance. In this embodiment, the diversion connector 9 is made of the same lightweight, transparent polymer material as the test chamber 1 and is integrally formed by 3D printing. This ensures the diversion function while minimizing the added mass. It should be understood that the specific structural form and manufacturing process of the diversion connector 9 are not limited to this. Any fluid connector capable of uniformly distributing water from a single inlet to multiple spray units can be used as an equivalent alternative.

[0040] Example 3

[0041] like Figure 1 and Figure 2As shown, this embodiment, based on Embodiment 1, further constructs a fluid circulation temperature control and spray intensity dynamic adjustment subsystem to achieve precise control of water environment parameters and multi-condition simulation. Based on Embodiment 1 or Embodiment 2, the device in this embodiment also includes a fluid circulation pipeline and a temperature control module; the fluid circulation pipeline connects the bottom of the test chamber 1 to the fluid supply device 5, guiding the outflowing fluid from the bottom of the test chamber 1 back to the fluid supply device 5 to form a closed-loop system. Specifically, the fluid circulation pipeline 6 in this embodiment mainly consists of an outlet pipe, one end of which is connected to the drain outlet at the bottom of the test chamber 1, and the other end is connected to the return port of the fluid supply device 5 (such as a water tank). This closed-loop design not only enables the reuse of the test medium and significantly reduces water consumption during long-term fatigue testing, but more importantly, it maintains the stability of the water quality in the test environment. Compared to open discharge or periodic water changes, closed-loop circulation avoids water quality fluctuations (such as changes in dissolved oxygen content, pH value, ion concentration, etc.) caused by water source changes, thereby eliminating the interference of non-target variables on the material fatigue performance test results and ensuring the repeatability and scientific validity of the test data. It should be understood that the specific routing and connection method of the fluid circulation pipeline 6 can be flexibly adjusted according to the laboratory space layout. For example, a filtration device or a degassing device can be added to further improve the purity of the water quality, as long as reliable return of the fluid from the test chamber 1 to the fluid supply device 5 can be achieved.

[0042] The temperature control module includes a temperature sensor and a temperature regulating device. The temperature sensor monitors the temperature of the circulating fluid in real time, and the temperature regulating device is configured to heat or cool the fluid based on the monitored temperature to maintain a constant temperature in the circulating fluid. Specifically, the temperature sensor is immersed inside the fluid supply device 5 or at a key node in the fluid circulation pipeline, acquiring fluid temperature signals in real time and feeding them back to the control system. The temperature regulating device includes heating elements (such as stainless steel heating rods or ceramic heating elements) and / or cooling elements (such as compressor refrigeration units or semiconductor refrigeration chips), performing corresponding heat exchange actions based on the feedback signals. For example, when simulating deep-sea low-temperature environments, the cooling device continuously operates to maintain the water temperature at around 4°C; while when studying the effect of temperature on the hydrolytic aging of polymer-based composite materials, the heating device can precisely control the water temperature at 60°C or even higher.

[0043] The device in this embodiment also includes a control unit and a pump body 4. The pump body 4 is disposed on the fluid supply device 5, and the control unit is communicatively connected to the pump body 4. The control unit is configured to change the fluid jet intensity of the spray assembly by adjusting the flow rate and pressure of the pump body 4 to simulate water flow conditions under different water environment conditions. Specifically, the control unit establishes a bidirectional data link with the drive unit of the pump body 4 through a digital communication interface. The pump body 4 is preferably a variable frequency pump or a servo metering pump, and its motor speed can be precisely adjusted by a frequency signal or pulse signal issued by the control unit. Compared with traditional valve throttling regulation, it has significant advantages such as fast response speed, low energy consumption, and small flow pulsation, and can more realistically and stably reproduce complex and variable underwater flow velocity fields. It should be understood that the communication protocol and control strategy between the control unit and the pump body 4 are not limited to the above example. Any technical means that can change the output characteristics of the pump body through electrical signals to achieve jet intensity adjustment is within the protection scope of this application.

[0044] Example 4

[0045] This embodiment provides a method for testing the tensile-tensile fatigue performance of materials in an aqueous environment. Using the material aqueous environment fatigue performance testing device described in the previous embodiment, precise coupling of environmental simulation and mechanical loading is achieved. Unlike conventional equipment operation procedures, this method emphasizes actively constructing a stable semi-closed fluid environment before applying the load to ensure the authenticity and repeatability of the fatigue test data. The main steps include:

[0046] S1: The test chamber 1 is fitted over the test section of the specimen 7. The gap between the bottom of the test chamber 1 and the specimen 7 is sealed using the bottom seal 11, and the top splash shield 13 is used to cover the top of the test chamber 1 to create a semi-closed local fluid test environment. Specifically, this step is the physical basis of the test method and must be completed before any cyclic load is applied to the fatigue testing machine 8. During operation, the specimen 7 is first installed between the upper and lower clamps of the fatigue testing machine 8, and then the test chamber 1 is moved axially along the specimen 7 to the preset test section position. During this process, the bottom seal 11 acts as a flexible interface, closely adhering to the surface of the specimen 7, blocking the downward leakage path of the fluid, and its flexibility does not restrict the subsequent small displacement of the specimen 7; the top splash shield 13 covers the top of the chamber, and the reserved movable gap between it and the specimen 7 ensures that the specimen 7 has sufficient axial freedom during the upcoming tensile fatigue motion and will not be subject to mechanical interference.

[0047] S2: Activate the fluid supply device 5, causing fluid to be sprayed onto the surface of the specimen 7 through the spray assembly, creating a flowing fluid environment on the surface of the specimen 7. Simultaneously, the outflowing fluid is returned to the fluid supply device 5 through the fluid circulation pipeline. Specifically, after the physical construction of the semi-closed environment is completed, mechanical testing does not begin immediately. Instead, the fluid supply device 5 (e.g., water pump 4) is activated first to establish a stable fluid dynamic state. Fluid enters the spray assembly (including multiple fluid jet units 2) inside the test chamber 1 through the inlet pipe 3, impacting the surface of the specimen 7 at a set pressure and flow rate, forming a flowing water film or turbulent boundary layer covering the entire test section. At the same time, the fluid collected at the bottom of the chamber is returned to the fluid supply device 5 in real time through the fluid circulation pipeline 6 (e.g., outlet pipe).

[0048] S3: In a flowing fluid environment, cyclic loads are applied to specimen 7 using a fatigue testing machine 8 to conduct fatigue performance tests in a water environment. Specifically, after the flowing fluid environment established in S2 stabilizes, the fatigue testing machine 8 is controlled to apply alternating tensile loads to specimen 7 according to preset loads. At this time, starting from the first fatigue cycle, the surface crack initiation and propagation zones of specimen 7 are under the real, continuous, and parameter-controllable scouring and wetting action of the water medium. Throughout the test, the bottom seal 11 elastically deforms with the slight vibration of specimen 7, maintaining a dynamic seal; the top splash shield 13, while allowing significant axial expansion and contraction of specimen 7, continuously blocks the escape of atomized droplets, ensuring the safe operation of the fatigue testing machine 8 and the long-term stability of environmental parameters. It should be understood that the cyclic load parameters (frequency, stress ratio, maximum load, etc.) in this step should be set according to the specific material's test standards, while the parameters of the flowing fluid environment (flow rate, temperature, etc.) are set independently or coupled according to the simulated service conditions. The two remain synchronized on the time axis until specimen 7 fails or the predetermined number of cycles is reached.

[0049] Example 5

[0050] Based on Example 4, this embodiment further provides a specific application of the testing method. By using multi-dimensional data fusion evaluation and multi-parameter synchronous coupling adjustment, the depth of testing and the realism of the working condition simulation are improved.

[0051] During the test of applying cyclic load to specimen 7 through fatigue testing machine 8, the damage evolution process of specimen surface (such as matrix microcrack initiation, crack propagation, fiber / matrix interface debonding, etc.) is observed in real time through transparent test chamber or recorded in combination with external optical equipment. The strain data and crack propagation of specimen 7 are monitored in real time, and the water environment fatigue performance of specimen 7 is evaluated in combination with the environmental parameters of the flowing fluid environment.

[0052] Taking the tensile-tensile fatigue test process of polymer-based composite laminates as an example, such as Figure 4As shown, the crack propagation process on the specimen surface was observed in real time through a transparent test chamber combined with external optical equipment. Based on the observed damage changes, the subsequent treatments included:

[0053] (1) Multi-source data synchronization and labeling: The macroscopic damage morphology nodes on the specimen surface are synchronized with the real-time mechanical data (such as cycle number, transient strain, dynamic stiffness, etc.) collected by the fatigue testing machine to establish the correspondence between damage state and mechanical response. Specifically, the macroscopic morphological features such as the initiation density and crack propagation length of microcracks on the specimen surface are mapped with the percentage decrease in dynamic stiffness and the increase in transient strain collected by the testing machine under the specific fatigue cycle to clarify the three-stage evolution law of underwater fatigue of materials: "crack initiation-initial stiffness decay", "matrix cracking and stable crack propagation-linear stiffness degradation" and "fiber fracture failure-sudden stiffness drop".

[0054] (2) Dynamic environmental condition adjustment: If a crack propagates rapidly in a specific area, the spray flow rate or fluid temperature of the spray assembly can be adjusted in real time by the control unit to further explore the accelerated coupling mechanism of extreme fluid impact on crack propagation rate.

[0055] (3) Failure determination and test termination: When macroscopic fracture is observed in the specimen, or when the dynamic stiffness of the specimen is monitored to drop to the set threshold of the initial stiffness (such as fracture or stiffness drop of a specified percentage), the specimen is determined to be in failure. The current fatigue test is automatically or manually terminated by the system and the environmental and mechanical coupling data is saved.

[0056] Regarding the acquisition of fatigue properties of polymer-based composite laminates, this method follows relevant national / international standards for tensile fatigue testing of composite materials (such as GB / T 35465), and emphasizes the environmental simulation characteristics of this apparatus. The specific steps are as follows:

[0057] (1) Plotting the SN curve (stress-life curve): Under different stress levels (maximum cyclic stress), multiple sets of fatigue tests were conducted using this device in the same underwater flowing fluid environment. The number of fatigue cycles (N) at the failure of each specimen was recorded, thereby fitting the SN curve of the material in a specific water environment and evaluating its environmental fatigue life; combined with Figure 5 By comparing the fatigue cycle number change gradient under high stress level and low stress level, the fitting curve in the model can effectively evaluate the reduction of material fatigue limit and service life evolution trend caused by the coupling effect of water flow scouring and interface penetration.

[0058] (2) Stiffness degradation assessment: Extract the load-displacement data recorded by the testing machine and calculate the attenuation law of the dynamic stiffness of the specimen during the fatigue cycle. The specific calculation process is as follows: extract the maximum load during the i-th fatigue cycle. With minimum load and the corresponding maximum displacement With minimum displacement Using the formula The dynamic stiffness of the i-th cycle is calculated. By analyzing the degradation ratio of dynamic stiffness with the number of cycles, the degree of progressive weakening of material mechanical properties after fluid intrusion into microcracks (such as water-induced swelling and resin plasticization) can be characterized.

[0059] (3) Environmental Effect Comparison Analysis: A control group experiment was set up, and the fatigue test data (life, stiffness degradation rate) obtained by this device in the underwater flowing environment were compared with the fatigue test results of the same specimen in a standard air environment. By calculating the environmental reduction factor, the accelerated reduction effect of the flowing water environment (scouring, seepage) on the fatigue life of the laminate was quantitatively evaluated. The specific calculation process is as follows: using the formula Calculate the environmental reduction factor ,in This refers to the fatigue life under a specific load in a flowing water environment, as tested by this device. This represents the fatigue life under the same specific load in a comparative example of an air environment.

[0060] Compared to the comparative test data in an air environment, the specimens in a flowing water environment experience accelerated internal structural damage and a significantly faster rate of dynamic stiffness decay due to water molecule penetration along the composite material interface and the water wedge effect within microcracks. This results in a shorter fatigue life under the same stress level. Significantly lower than in air. (i.e., environmental reduction factor) < 1), thus highlighting the necessity and core role of this device in simulating real service conditions assessment.

[0061] According to the set water environment conditions, the fluid jet intensity, fluid temperature and cyclic load parameters of the fatigue testing machine 8 are synchronously adjusted by the control unit; wherein, the flow rate and pressure of the pump body 4 of the fluid supply device 5 are adjusted to change the fluid jet intensity, and the fluid temperature is adjusted by the temperature control module to simulate the coupled fatigue environment under different water depths or flow velocities.

[0062] In summary, the testing apparatus and method provided by this invention have the following advantages:

[0063] 1. High Realism of Environmental Simulation: Existing technologies mostly use static water tank immersion or simple spraying, which cannot simulate the uniformly moist underwater flow environment. This invention, through multiple direct-shot nozzles arranged vertically on the left and right sides, can form a uniform and stable water flow on the surface of the specimen, which can more realistically simulate the interface conditions of materials when they are actually in underwater service, greatly improving the accuracy and reliability of test data.

[0064] 2. Minimal interference with testing and high reliability: Existing technologies often employ large water tanks or rigid sealed structures with significant self-weight. This added mass can affect the dynamic response of the specimen under high-frequency fatigue loads, introducing testing errors. This invention creatively uses lightweight, transparent polycarbonate or modified acrylic materials to construct the water tank and optimizes the wall thickness. While ensuring structural strength, it minimizes the device's self-weight, effectively avoiding interference with fatigue testing. Furthermore, the semi-sealed structure of the water tank prevents water leakage from damaging the experimental instruments.

[0065] 3. Excellent system integration and operability: In traditional methods, the components are relatively scattered, and the circulation control is imprecise. This invention highly integrates the atomizing spray system with a closed circulating water circuit, resulting in a compact structure and simple operation.

[0066] 4. Convenient observation: Compared with closed devices made of metal or opaque materials, the present invention uses a transparent chamber throughout the process, allowing researchers to observe the water wetting status, damage evolution, and even crack initiation and propagation behavior of the test specimen surface in real time and intuitively during the experiment, providing key technical support for in-depth research on the underwater fatigue failure mechanism of materials.

[0067] 5. Energy-saving and environmentally friendly circulating water system: The water pump draws water from the water tank and supplies it to three direct-spray nozzles on each side of the chamber through the inlet pipe and four-way connector. The nozzles spray water evenly on the surface of the specimen and form a stable water flow on the surface of the specimen. The water flowing down the surface of the specimen flows back to the water tank through the outlet pipe connected to the lower surface of the chamber. It is recycled and used to save water resources and maintain the stability of water temperature and water quality.

[0068] 6. Wide applicability: The number and position of the nozzles can be adjusted, and the water flow intensity and flow rate can be adjusted to simulate different underwater working conditions. It is suitable for fatigue testing of polymer-based composite materials under various underwater working conditions.

[0069] 7. Wide Dimensions of Environmental Simulation: This invention integrates a temperature control module into the water circulation system, enabling wide-range water temperature adjustment from low to high temperatures. By simulating underwater environments at different temperatures, it studies the accelerated aging and fatigue failure points of composite materials under the combined effects of temperature and water environment, overcoming the limitation of existing devices that can only perform room temperature tests.

[0070] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A device for testing the tensile fatigue properties of materials in an aqueous environment, characterized in that, include: The test chamber comprises a test chamber body, a bottom seal, a top splash shield, and a spray assembly. The test chamber body is fitted over the test section of the specimen to create a localized fluid testing environment. The bottom seal is located at the bottom opening of the test chamber body to seal the gap between the bottom of the test chamber body and the specimen, preventing downward fluid leakage. The top splash shield covers the top opening of the test chamber body and maintains a clearance with the specimen to prevent upward fluid splashing and allow axial deformation of the specimen during fatigue loading. The spray assembly is located inside the test chamber body and sprays fluid onto the surface of the specimen to create a flowing fluid environment on the specimen surface.

2. The apparatus for testing the tensile-tensile fatigue properties of materials in an aqueous environment according to claim 1, characterized in that, The spray assembly includes multiple fluid spraying units, which are distributed on opposite sides of the test chamber and arranged at equal intervals along the axial direction of the specimen, so that the sprayed fluid uniformly covers the surface of the specimen.

3. The apparatus for testing the tensile-tensile fatigue properties of materials in an aqueous environment according to claim 1, characterized in that, The top splash shield has a through hole in the middle for the test specimen to pass through. The diameter of the through hole is larger than the outer diameter of the test specimen to form a movable gap. The bottom seal is a flexible seal that fits the surface of the test specimen to allow the test specimen to vibrate slightly while sealing the fluid.

4. The apparatus for testing the tensile-tensile fatigue properties of materials in an aqueous environment according to claim 1, characterized in that, The test chamber is made of a lightweight, transparent polymer material, and the wall thickness of the test chamber is 2mm-4mm, so as to reduce the weight of the test chamber while accommodating the test section of the specimen.

5. The apparatus for testing the tensile fatigue properties of materials in an aqueous environment according to claim 2, characterized in that, The device also includes a water inlet pipe and a diverter; one end of the water inlet pipe is connected to a fluid supply device, and the other end is connected to the diverter; the diverter distributes the fluid in the water inlet pipe to a plurality of fluid injection units located on the same side of the test chamber.

6. The apparatus for testing the tensile-tensile fatigue properties of materials in an aqueous environment according to claim 1 or 5, characterized in that, The device also includes a fluid circulation pipeline and a temperature control module; the fluid circulation pipeline connects the bottom of the test chamber to the fluid supply device, guiding the outflowing fluid from the bottom of the test chamber back to the fluid supply device to form a closed-loop system; the temperature control module includes a temperature sensor and a temperature regulating device, the temperature sensor is used to monitor the temperature of the circulating fluid in real time, and the temperature regulating device heats or cools the fluid according to the monitored temperature to maintain a constant temperature of the circulating fluid.

7. The apparatus for testing the tensile-tensile fatigue properties of materials in an aqueous environment according to claim 6, characterized in that, The device also includes a control unit and a pump body; the pump body is disposed on the fluid supply device, and the control unit is communicatively connected to the pump body; the control unit adjusts the flow rate and pressure of the pump body to change the fluid jet intensity of the spray assembly, so as to simulate water flow conditions under different water environment conditions.

8. A method for testing the tensile fatigue properties of materials in an aqueous environment, characterized in that, The apparatus for testing the tensile fatigue properties of materials in an aqueous environment, as described in any one of claims 1-7, comprises the following steps: The test chamber is fitted over the test section of the specimen, the bottom seal is used to seal the gap between the bottom of the test chamber and the specimen, and the top splash shield is used to cover the top of the test chamber to create a semi-closed local fluid test environment. Start the fluid supply device to spray fluid onto the surface of the specimen through the spray assembly and create a flowing fluid environment on the surface of the specimen. At the same time, the outflowing fluid is returned to the fluid supply device through the fluid circulation pipeline. In the flowing fluid environment, the specimen is subjected to cyclic loads using a fatigue testing machine to perform fatigue performance tests in an aquatic environment.

9. The method for testing the tensile-tensile fatigue properties of materials in an aqueous environment according to claim 8, characterized in that, During the process of applying cyclic loads to the specimen using the fatigue testing machine, the strain data and crack propagation of the specimen are monitored in real time, and the water environment fatigue performance of the specimen is evaluated in conjunction with the environmental parameters of the flowing fluid environment.

10. The method for testing the tensile-tensile fatigue properties of materials in an aqueous environment according to claim 8, characterized in that, Based on the set water environment conditions, the fluid jet intensity, fluid temperature, and cyclic load parameters of the fatigue testing machine are synchronously adjusted by the control unit. Specifically, the fluid jet intensity is changed by adjusting the flow rate and pressure of the pump body of the fluid supply device, and the fluid temperature is adjusted by the temperature control module to simulate coupled fatigue environments under different water depths or flow velocities.

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