In-situ testing device and method for carbon fiber reinforced composite adhesive joint

Abstract

This invention relates to the field of tensile shaping technology, specifically disclosing an in-situ testing device and method for carbon fiber reinforced composite adhesive joints. The device includes a split-type heat-insulating chamber, a first mounting mechanism, a second mounting mechanism, a material fixing component, an environmental simulation component, and an in-situ monitoring component. By incorporating a dynamic compensation spring in the mounting mechanism, the expansion displacement of the loading rod caused by heat is absorbed, eliminating the interference of thermal stress on the sensor. A microenvironment chamber formed by the docking of movable sleeves, combined with inlet and outlet pipes, maintains constant humidity through liquid vapor pressure, avoiding interference from condensation mist. Combined with an observation window and camera integrated into the chamber, simultaneous in-situ monitoring of mechanical loading and micro-deformation is achieved. This application can significantly improve the accuracy of test data and directly capture the crack initiation and propagation process at the adhesive interface.

Description

Technical Field

[0001] This invention relates to the field of tensile shaping technology, and in particular to an in-situ testing device and method for adhesive joints of carbon fiber reinforced composite materials. Background Technology

[0002] With the rapid development of aerospace, automotive, and high-end manufacturing industries, carbon fiber reinforced composites have been widely used due to their high specific strength, high specific modulus, and excellent fatigue resistance. In the assembly of composite structures, adhesive bonding, as a connection method that can achieve uniform stress distribution, reduce structural weight, and avoid fiber damage, directly determines the safety of the overall structure through the mechanical properties and reliability of the joints. To accurately evaluate the mechanical behavior of carbon fiber reinforced composite adhesive joints under complex service environments, precise tensile mechanical property testing is typically required.

[0003] Conventional non-in-situ testing usually involves the transfer of samples between an environmental chamber and a testing machine. This process can easily cause rapid loss of temperature and humidity from the sample surface, which can lead to certain deviations in the accuracy of the test data and the capture of performance evolution patterns. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ testing device and method for adhesive joints of carbon fiber reinforced composite materials, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an in-situ testing device for carbon fiber reinforced composite adhesive joints, comprising a split-type heat insulation cavity, a first installation mechanism, a second installation mechanism, a material fixing component, an environmental simulation component, and an in-situ monitoring component. By introducing a mechanical compensation structure in the mechanical loading path and integrating an environmental control unit in the sealed cavity, the in-situ mechanical performance evaluation of the adhesive joints under constant temperature and humidity conditions can be achieved.

[0006] The split-type heat insulation cavity serves as the load-bearing and insulating component of the entire device. It includes a first heat insulation cavity and a second heat insulation cavity, which are hinged together. On the contact surfaces of the first and second heat insulation cavities, circumferentially distributed sealing strip grooves are formed, with high-temperature resistant fluororubber sealing strips embedded within these grooves. Hook-and-loop locking devices are installed on the outer walls of the first and second heat insulation cavities. The locking force of these devices causes the high-temperature resistant fluororubber sealing strips to deform under pressure, thereby forming a sealed space between the two cavities. An observation window is embedded in the front of the second heat insulation cavity, and a camera is fixedly mounted on the outer support of the observation window. The lens axis of the camera points towards the geometric center of the split-type heat insulation cavity.

[0007] The first mounting mechanism, serving as an upper load transfer component, includes an upper loading rod that slides through the top of the split-type heat insulation cavity; the first mounting mechanism also includes a first movable sleeve, with the top of the upper loading rod penetrating the top plate of the first movable sleeve; a first sealing gasket is provided at the contact point between the upper loading rod and the first movable sleeve; a first dynamic compensation spring is connected to one end of the upper loading rod outside the first movable sleeve via a threaded pair, and an upper mechanical connecting rod is fixedly connected to the other end of the first dynamic compensation spring away from the upper loading rod, the end of the upper mechanical connecting rod being mechanically locked to the upper clamp adapter of the testing machine; a first tension spring is connected between the top of the first movable sleeve and the inner top of the first heat insulation cavity; a first side connector is installed on the bottom side of the first movable sleeve, and a first heating chamber is wrapped around its outer periphery, with intelligent heating elements arranged inside the first heating chamber.

[0008] The second mounting mechanism, serving as the lower load transfer component, is centrally symmetrically distributed with the first mounting mechanism. The second mounting mechanism includes a lower loading rod that slides through the bottom of the split-type heat insulation cavity, with the lower loading rod and the upper loading rod on the same vertical axis. The second mounting mechanism also includes a second movable sleeve, through which the lower loading rod passes and is equipped with a second sealing gasket. A second dynamic compensation spring is connected to the bottom of the lower loading rod, and the other end of the second dynamic compensation spring is connected to the lower clamp adapter of the testing machine via a lower mechanical connecting rod. A second heating chamber is fitted around the outer periphery of the second movable sleeve, and intelligent heating elements are also arranged inside it. A first connecting sealing strip at the bottom of the first movable sleeve and a second connecting sealing strip at the top of the second movable sleeve abut against each other in the vertical direction. The first side connecting piece and the second side connecting piece of the second mounting mechanism are rigidly fixed by fixing bolts, thereby combining the first and second movable sleeves inside the first heat insulation cavity to form an independent microenvironment chamber.

[0009] Furthermore, to create a humid and hot environment during testing, a water control component is also installed inside the second installation mechanism; a sealing baffle is horizontally fixed at the lower part of the second movable sleeve, and a through hole for the lower loading rod to pass through is opened in the center of the sealing baffle, with a waterproof sealing strip filling the space between the through hole and the lower loading rod; a water inlet is opened on one side wall of the second movable sleeve, and a drain outlet is opened on the other side wall; a water inlet pipe is inserted into the water inlet, and a drain pipe is connected to the drain outlet through a connecting pipe, the drain pipe extending through the first heat insulation cavity to the outside; a one-way valve is connected in series in both the drain outlet and the water inlet pipes; a liquid medium is injected into the second movable sleeve through the water inlet pipe, so that the liquid medium submerges the sample located on the material fixing component, and the set humidity is maintained in the microenvironment chamber by the vapor pressure of the liquid under heating.

[0010] The material fixing components are respectively installed at the opposite ends of the upper and lower loading rods for clamping the carbon fiber composite sample. The material fixing components include a mounting block fixed to the end of the loading rod. The lower surface of the mounting block is machined with a horizontal groove, and a sliding rod is horizontally fixed in the groove. Two sliders are symmetrically slidably connected on the outer circumference of the sliding rod, and a clamping plate is fixed at the bottom end of each slider. The inner opposite surfaces of the two clamping plates are each covered with a serrated anti-slip pad. A threaded rod is horizontally inserted between the two clamping plates. The threaded rod is machined with two sections of threads with opposite directions, which form a screw-nut pair with the threaded holes inside the two clamping plates. A rotating disk is fixed to the end of the threaded rod. Rotating the rotating disk drives the two clamping plates to move synchronously towards the center or to both sides along the sliding rod.

[0011] Furthermore, both the first and second movable sleeves are equipped with temperature sensors, and the signal output terminals of the temperature sensors are connected to an external control system via wires; the top and bottom of the split-type heat insulation cavity are provided with perforations for the loading rod to pass through, and the inner wall of the perforations is provided with a labyrinth-type sealing structure to reduce internal and external heat exchange.

[0012] This invention also provides a method for using an in-situ testing device for adhesive joints of carbon fiber reinforced composite materials, the specific steps of which are as follows: S1. Open the latch locking device and flip the second heat insulation cavity to expose the inside of the cavity; adjust the relative position of the upper mechanical connecting rod and the lower mechanical connecting rod through the control end of the testing machine; fix the split heat insulation cavity to the frame of the testing machine through the support frame, and use the centering gauge to adjust the axis of the upper loading rod and the lower loading rod to make them coincide with the force center line of the tensile sensor of the testing machine.

[0013] S2. Insert one end of the carbon fiber reinforced composite adhesive joint specimen between the two clamps of the upper material fixing assembly, manually rotate the rotating disk, and use the bidirectional transmission characteristics of the threaded rod to drive the clamps to close, so that the anti-slip pad presses against the specimen surface; repeat the above operation to complete the fixing of the lower end of the specimen; adjust the threaded rod to make the geometric center line of the specimen consistent with the axis of the loading rod.

[0014] S3. Close the second heat insulation chamber and lock the latch locking piece to cause radial compression of the high-temperature fluororubber sealing strip; turn on the heating elements of the first heating chamber and the second heating chamber; the control system adjusts the power according to the feedback data of the first temperature sensor and the second temperature sensor; if a damp heat test is to be performed, inject deionized water into the second movable sleeve through the water inlet pipe until the water level completely covers the adhesive area of ​​the sample; use the heating element to generate saturated steam from the water to create a high humidity environment in the microenvironment chamber.

[0015] S4. After the temperature and humidity inside the chamber reach the preset equilibrium point, start the testing machine to perform tensile loading; the tensile force of the testing machine is transmitted to the upper loading rod through the upper mechanical connecting rod and the first dynamic compensation spring in sequence; when the chamber is heated and the loading rod undergoes thermal expansion and elongation, the first dynamic compensation spring and the second dynamic compensation spring absorb the displacement increment through their own compression changes, thus offsetting the thermally induced stress; at the same time, the camera captures the deformation image of the adhesive interface of the sample in real time through the observation window.

[0016] S5. When the adhesive joint breaks, turn off the heating system and drain the liquid in the cavity through the drain pipe; retrieve the video sequence recorded by the camera and use digital image correlation algorithm to analyze the strain distribution cloud map of the adhesive layer before the breakage; combine the load-displacement data recorded by the testing machine to calculate the fracture toughness and strength parameters of the adhesive joint.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. The present invention constructs a mechanical thermal stress relief system by setting a first dynamic compensation spring and a second dynamic compensation spring in the first installation mechanism and the second installation mechanism respectively; under high temperature environment testing, the thermal expansion displacement generated by the loading rod and cavity assembly is absorbed by the elastic deformation of the compensation spring, avoiding the superposition of non-test loads on the mechanical sensor, and significantly improving the accuracy of the force data acquisition of carbon fiber composite adhesive joints.

[0018] 2. This invention utilizes the docking structure of the first movable sleeve and the second movable sleeve to form a secondary sealed microenvironment chamber inside the split-type heat insulation cavity; by setting a sealing baffle and inlet / outlet pipes at the bottom of the chamber, a humid and hot environment is created by combining direct liquid immersion with vapor pressure maintenance, avoiding the interference of condensation water mist generated by traditional spray systems on the line of sight of the observation window, and ensuring the clarity of the in-situ observation images.

[0019] 3. This invention integrates an observation window and a camera on the second heat insulation cavity, and with the bidirectional screw centering structure of the material fixing component, it realizes the synchronous in-situ monitoring of mechanical loading and micro-deformation. The camera can capture the crack initiation and propagation process of the adhesive interface under load in real time, providing intuitive physical evidence for studying the interface failure mechanism of carbon fiber reinforced composite materials in complex environments. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a structural diagram of the main body of the present invention; Figure 2 This is a schematic diagram of the structure of the first heat insulation cavity in this invention; Figure 3 This is a schematic diagram of the structure of the first mounting mechanism in this invention; Figure 4 This is a schematic cross-sectional view of the first mounting mechanism in this invention; Figure 5 This is a schematic diagram of the structure of the second mounting mechanism in this invention; Figure 6 This is a schematic cross-sectional view of the second mounting mechanism in this invention; Figure 7 For the present invention Figure 4 Enlarged view of point A in the middle.

[0022] Explanation of reference numerals in the attached figures: 1. Split-type heat insulation cavity; 11. First heat insulation cavity; 12. Second heat insulation cavity; 13. Fastener locking component; 14. Observation window; 15. Camera; 16. Hinge; 17. High-temperature resistant fluororubber sealing strip; 18. Sealing strip groove; 19. Perforation; 2. First mounting mechanism; 21. First movable sleeve; 22. First connecting sealing strip; 23. First side connector; 24. Upper loading rod; 25. First tension spring; 26. Upper mechanical connecting rod; 27. First dynamic compensation spring; 28. First heating chamber; 29. ​​First temperature sensor; 210. First sealing gasket; 3. Second mounting mechanism; 31 31. Second movable sleeve; 32. Second connecting sealing strip; 33. Second side connector; 34. Lower loading rod; 35. Second tension spring; 36. Lower mechanical connecting rod; 37. Second dynamic compensation spring; 38. Second heating chamber; 39. Second temperature sensor; 310. Second sealing gasket; 311. Sealing baffle; 312. Drain outlet; 313. Drain pipe; 314. Connecting pipe; 315. Water inlet pipe; 4. Fixing bolt; 5. Material fixing assembly; 51. Mounting block; 52. Slide groove; 53. Sliding rod; 54. Clamping plate; 55. Sliding block; 56. Threaded rod; 57. Rotating disk; 58. Anti-slip pad. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figures 1 to 7 The present invention provides a technical solution: An in-situ testing device and method for carbon fiber reinforced composite adhesive joints includes a core frame composed of a split-type heat-insulating cavity 1. This split-type heat-insulating cavity 1 is spatially divided into a first heat-insulating cavity 11 and a second heat-insulating cavity 12, which are mechanically hinged on the sides by hinges 16, allowing the second heat-insulating cavity 12 to freely flip open or close relative to the first heat-insulating cavity 11. To ensure the stability of the internal environment during testing, the contact surfaces of the first heat-insulating cavity 11 and the second heat-insulating cavity 12 are precisely machined, with the contact surfaces along... A continuous annular sealing strip groove 18 is provided around the perimeter; high-temperature resistant fluororubber sealing strips 17 with excellent temperature resistance and resilience are embedded in these grooves; when the split-type heat insulation cavity 1 is in the closed state, the latch locking member 13 installed on the outer wall of the cavity applies a radial fastening force through the lever principle, causing the high-temperature resistant fluororubber sealing strip 17 to undergo physical deformation, thereby forming a physically isolated space with excellent airtightness between the first heat insulation cavity 11 and the second heat insulation cavity 12; this design effectively blocks the heat exchange and moisture penetration between the internal simulated environment and the outside atmosphere.

[0025] Combination Figure 3 and Figure 4 The first mounting mechanism 2 of this device is located above the split-type heat insulation cavity 1, serving as the main transmission path for tensile loads. The upper loading rod 24 has a cylindrical structure and slides vertically through the top wall of the first heat insulation cavity 11. Inside the first heat insulation cavity 11, a first movable sleeve 21 is provided, with a through hole at the center of the top plate of the sleeve for the upper loading rod 24 to pass through. At the contact point between the upper loading rod 24 and the first movable sleeve 21, a first sealing washer 210 is installed. This washer ensures that the upper loading rod 24 can slide slightly axially while maintaining the sealing of the sleeve. The top end of the upper loading rod 24 extends to the outside of the first movable sleeve 21 and is connected to a first dynamic compensation spring 27 via a high-strength threaded pair. The other end of the first dynamic compensation spring 27... The end is fixedly connected to the upper mechanical connecting rod 26. The end of the upper mechanical connecting rod 26 is machined with an adapter interface for mechanical locking with the upper clamp adapter of the external tensile testing machine. A first tension spring 25 is also connected between the top of the first movable sleeve 21 and the inner top surface of the first heat insulation cavity 11. The function of the first tension spring 25 is to provide an upward preload to the first movable sleeve 21 so that it maintains a stable spatial position when not under force. In addition, a first side connector 23 is installed on the bottom side of the first movable sleeve 21, and a first heating chamber 28 is wrapped around its outer periphery. The first heating chamber 28 is densely packed with intelligent heating elements, which heat the air or medium inside the first movable sleeve 21 to a set temperature through heat radiation and heat conduction.

[0026] refer to Figure 5 and Figure 6 The second mounting mechanism 3 of this device is located below the split-type heat insulation cavity 1, and its structure is centrally symmetrical with the first mounting mechanism 2 on the vertical axis. The lower loading rod 34 slides through the bottom wall of the split-type heat insulation cavity 1 and is on the same vertical center line as the upper loading rod 24. The second movable sleeve 31 is set on the outer periphery of the lower loading rod 34, and the lower loading rod 34 passes through the bottom plate of the second movable sleeve 31 and is equipped with a second sealing gasket 310. The bottom end of the lower loading rod 34 extends to the outside and is connected to a second dynamic compensation spring 37. The other end of the second dynamic compensation spring 37 is connected to the lower clamp adapter of the testing machine through the lower mechanical connecting rod 36. The outer periphery of the second movable sleeve 31 is also fitted with a second heating chamber 38, and the intelligent heating elements arranged inside it are responsible for the temperature control of the lower area.

[0027] Further observation Figure 4 and Figure 6 A key innovation of this invention lies in the construction of the microenvironment chamber. The bottom edge of the first movable sleeve 21 is provided with a first connecting sealing strip 22, while the top edge of the second movable sleeve 31 is provided with a second connecting sealing strip 32. When the device is in operation, the first side connector 23 and the second side connector 33 on the second mounting mechanism 3 are rigidly fixed by fixing bolts 4, so that the first movable sleeve 21 and the second movable sleeve 31 abut against each other in the vertical direction. At this time, the first connecting sealing strip 22 and the second connecting sealing strip 32 are pressed and tightened, so that the first movable sleeve 21 and the second movable sleeve 31 are combined into an independent, smaller microenvironment chamber inside the split-type heat insulation cavity 1. This chamber-within-a-chamber structure design greatly reduces the volume space required for precise environmental control and significantly improves the response speed and uniformity of temperature and humidity control.

[0028] For simulating hot and humid environments, the second installation mechanism 3 integrates a sophisticated water control system; such as... Figure 4As shown, a sealing baffle plate 311 is horizontally fixed at the lower position inside the second movable sleeve 31. The sealing baffle plate 311 has a through hole in its center for the lower loading rod 34 to pass through. A special waterproof sealing strip is filled between the through hole and the lower loading rod 34 to prevent liquid leakage to the lower mechanism. A water inlet is provided on one side wall of the second movable sleeve 31, and a drain outlet 312 is provided on the other side wall. A water inlet pipe 315 is inserted into the water inlet, and a drain pipe 313 is connected to the drain outlet 312 via a connecting pipe 314. 13 extends through the first heat insulation cavity 11 to the outside of the device; one-way valves are connected in series in both the water inlet pipe 315 and the drain pipe 313 to control the one-way flow of the liquid; deionized water or other liquid media are injected into the second movable sleeve 31 through the water inlet pipe 315 so that the liquid media can submerge the sample bonding area located on the material fixing assembly 5; the heating effect of the first heating chamber 28 and the second heating chamber 38 is used to generate saturated vapor at a specific pressure in the liquid, thereby maintaining a constant high humidity environment in the microenvironment chamber.

[0029] refer to Figure 7 The material fixing assembly 5 is crucial for achieving precise sample clamping. The material fixing assembly 5 is symmetrically installed at the opposite ends of the upper loading rod 24 and the lower loading rod 34. Each material fixing assembly 5 includes a mounting block 51 fixed to the end of the loading rod. A precise horizontal groove 52 is machined on the lower surface of the mounting block 51, and a sliding rod 53 is laterally fixed within the groove 52. Two sliders 55 are symmetrically slidably connected on the outer circumference of the sliding rod 53, and clamping plates 54 are fixed to the bottom ends of both sliders 55. To increase friction and protect the surface of the carbon fiber composite sample, anti-slip pads 58 with serrated textures are adhered to the inner opposing surfaces of the two clamping plates 54. A threaded rod 56 is transversely inserted between the two clamping plates 54. The unique feature of this threaded rod 56 is that it has two sections of threads with opposite directions of rotation. These two sections of threads form a screw-nut pair with the threaded holes inside the two clamping plates 54. A rotating disk 57 is fixed to the end of the threaded rod 56. When the experimenter manually rotates the rotating disk 57, the threaded rod 56 rotates accordingly. Utilizing the transmission characteristics of the bidirectional thread, it drives the two clamping plates 54 to move synchronously toward the center or separate to both sides along the sliding rod 53. This bidirectional synchronous centering clamping method ensures that the geometric center line of the sample always coincides with the axis of the loading rod, eliminating the additional bending moment caused by eccentric clamping.

[0030] Furthermore, an observation window 14 is embedded in the front of the second heat insulation cavity 12. The observation window 14 is typically made of high-transmittance tempered quartz glass, which can withstand high temperatures and does not produce optical distortion. A high-resolution camera 15 is fixedly installed on the outer support of the observation window 14. The lens axis of the camera 15 is precisely calibrated and points to the geometric center area of ​​the split heat insulation cavity 1, that is, the location of the sample adhesive joint. Through the camera 15, the microscopic deformation images of the adhesive interface under the combined action of complex environment and mechanical load can be captured in real time, providing a high-quality data source for subsequent digital image correlation analysis. In addition, temperature sensors are installed in the internal spaces of the first movable sleeve 21 and the second movable sleeve 31, respectively. The signal output terminals of these temperature sensors are connected to the external microcomputer control system through high-temperature resistant wires to realize closed-loop regulation of heating power and ensure that the temperature fluctuation of the microenvironment chamber is controlled within a very small range.

[0031] The in-situ testing method for adhesive joints of carbon fiber reinforced composite materials provided by this invention has the following specific operating process and principle: Before the experiment begins, the latch locking device 13 is first opened and the second heat insulation cavity 12 is flipped over to fully expose the internal structure of the split heat insulation cavity 1. The vertical distance between the upper mechanical connecting rod 26 and the lower mechanical connecting rod 36 is adjusted through the control terminal of the testing machine. The entire split heat insulation cavity 1 is then securely installed on the load-bearing frame of the testing machine using a dedicated support frame. At this point, a high-precision centering gauge is used to calibrate the axes of the upper loading rod 24 and the lower loading rod 34 to ensure that their common axis is completely coincident with the force center line of the tensile sensor of the testing machine. This is the physical basis for ensuring the accuracy of the test data.

[0032] Take the prepared carbon fiber reinforced composite adhesive joint sample and insert its upper end between the two clamps 54 of the upper material fixing component 5. By manually rotating the rotating disk 57, the two clamps 54 are closed synchronously using the bidirectional transmission characteristics of the threaded rod 56 until the anti-slip pad 58 firmly presses the sample surface. Then, the lower end of the sample is fixed in the same way. During the clamping process, the position of the clamps 54 on the sliding rod 53 can be observed to visually determine whether the sample is in the centering state. This clamping mechanism is not only easy to operate, but also provides sufficient clamping force to prevent the sample from slipping during the stretching process.

[0033] After the sample is clamped, the second heat insulation chamber 12 is closed and the latch locking piece 13 is locked. At this time, the high-temperature resistant fluororubber sealing strip 17 is radially compressed to form a tight external seal. Then, the heating elements in the first heating chamber 28 and the second heating chamber 38 are turned on through the external control system. The control system will monitor the data fed back by the temperature sensors distributed in the microenvironment chamber in real time and use the PID control algorithm to adjust the power so that the temperature in the chamber rises rapidly to the preset value. If the test plan requires simulating a humid and hot environment, a precise meter of deionized water is injected into the second movable sleeve 31 through the water inlet pipe 315 until the water level completely covers the adhesive overlap area of ​​the sample. As heating proceeds, continuous vapor will be generated on the surface of the liquid medium. Due to the limited volume and good sealing of the microenvironment chamber, the vapor pressure will quickly reach equilibrium, thereby forming a high-humidity saturated environment around the sample.

[0034] Once the temperature and humidity in the microenvironment chamber reach a preset equilibrium point and operate stably for a period of time, the testing machine is started to perform axial tensile loading. The tensile force generated by the testing machine is transmitted sequentially through the upper mechanical connecting rod 26 and the first dynamic compensation spring 27 to the upper loading rod 24, and finally acts on the sample. During this process, due to the high ambient temperature, the upper loading rod 24, the lower loading rod 34, and the metal parts of the cavity will inevitably undergo thermal expansion. In traditional testing devices, the displacement generated by this thermal expansion will be superimposed on the mechanical sensor, resulting in false load readings. However, in this invention, the first dynamic compensation spring 27 and the second dynamic compensation spring 37 play a crucial role in physical compensation. When the loading rod elongates due to heat, the compensation spring absorbs this displacement increment through its own compression deformation, thereby offsetting the interference of thermally induced stress on the mechanical sensor. At the same time, the camera 15 captures the deformation image of the sample adhesive interface under load in real time through the observation window 14 at a preset sampling frequency. Due to the use of the microenvironment chamber structure, the observation window 14 is far away from the water source and is uniformly heated, effectively avoiding the generation of condensation mist and ensuring image clarity.

[0035] When the load increases to the critical value and the adhesive joint fails due to fracture, the testing machine automatically stops loading. At this time, the heating system is turned off, and the liquid medium in the second movable sleeve 31 is drained through the drain pipe 313. The experimenter retrieves the complete video sequence recorded by the camera 15 and processes the video frames using a digital image correlation algorithm. This algorithm can calculate the strain distribution cloud map of the adhesive layer before fracture by tracking the movement trajectory of the speckle pattern on the sample surface, intuitively showing the location of stress concentration and the order of crack initiation. Combined with the load and displacement synchronous data recorded by the testing machine, the key mechanical parameters such as fracture toughness and shear strength of the carbon fiber reinforced composite adhesive joint under specific temperature and humidity conditions can be accurately calculated.

[0036] The operating principle of this device fully utilizes the synergistic effect of mechanical compensation and micro-environment control. The stiffness coefficients of the first dynamic compensation spring 27 and the second dynamic compensation spring 37 are pre-calibrated to enable them to generate sensitive responses under minute thermal expansion displacements. The micro-environment chamber formed by the docking of the first movable sleeve 21 and the second movable sleeve 31 solves the problems of large temperature gradients and severe humidity fluctuations commonly encountered in large-space environment simulations by limiting the physical space. In addition, the bidirectional lead screw structure in the material fixing component 5 is aligned with the axis of the in-situ monitoring component, jointly constructing a three-in-one testing platform, making it possible to record the entire process from macroscopic mechanical response to microscopic failure evolution.

[0037] In practical applications, such as simulating the service environment of carbon fiber composite structures in the aerospace field, the alternation of high temperature and high humidity is often involved. This device can simulate extreme humid and hot conditions through the efficient heat conduction of the first heating chamber 28 and the second heating chamber 38, as well as the precise water injection of the water control component. During the stretching process, the adhesive layer of the bonded joint will swell due to moisture absorption, and the high temperature will cause the modulus of the adhesive to decrease. This device can eliminate measurement errors caused by these environmental interference factors. Through the mechanical adjustment of the compensation spring, every Newton of force measured by the mechanical sensor is a real load acting on the material structure. At the same time, the in-situ monitoring function allows researchers to observe whether debonding has occurred between the carbon fiber bundle and the adhesive layer, or whether cohesive failure has occurred inside the adhesive layer. This has important guiding significance for optimizing the bonding process of composite materials.

[0038] Furthermore, the structural design of the device also takes into account the ease of maintenance; the split-type heat-insulating cavity 1 has an opening angle of up to 100 degrees, which facilitates the cleaning of internal components and the replacement of sensors; the first sealing gasket 210 and the second sealing gasket 310 are made of wear-resistant materials and can withstand the frequent reciprocating motion of the loading rod; the one-way valve design in the drain pipe 313 prevents backflow when injecting liquid and also ensures smooth drainage; the sliding rod 53 and the slider 55 in the material fixing assembly 5 are surface hardened to ensure that they will not rust or jam in long-term high-humidity environments; the coordinated operation of these details ensures the high reliability and long service life of the in-situ testing device under complex experimental conditions.

[0039] The device also demonstrates strong adaptability when handling samples of different specifications. By replacing the clamps 54 of different specifications or adjusting the stroke of the threaded rod 56, it can be adapted to carbon fiber sheet adhesives with thicknesses ranging from a few millimeters to tens of millimeters. The setting of the first tension spring 25 ensures that the upper movable sleeve maintains a tight fit with the lower sleeve at different load stages, maintaining the integrity of the microenvironment chamber. This design concept of achieving environmental adaptive adjustment through mechanical structure avoids the defects of complex electronic control actuators that are easily damaged in harsh environments, reflecting the profound consideration of structural reliability in this invention.

[0040] In the data processing stage of in-situ monitoring, the images captured by camera 15 are not only used for qualitative observation, but can also be synchronized with the timestamp of the testing machine to achieve a one-to-one correspondence between the mechanical curve and the deformation image. For example, when the first inflection point appears on the load-displacement curve, researchers can immediately retrieve the monitoring screen at the corresponding moment to check whether it is because microcracks have appeared at the edge of the adhesive layer. This multi-dimensional information acquisition method greatly enriches the research methods for the bonding performance of carbon fiber reinforced composite materials. By comparing and analyzing the experimental data under different temperature and humidity combinations, a quantitative functional relationship between material properties and environmental factors can be established, providing a scientific basis for predicting the safe life of composite material structures.

[0041] The heating logic of this device has also been optimized; the first heating chamber 28 and the second heating chamber 38 are not simply turned on or off, but are dynamically adjusted according to the temperature rise curve of the microenvironment chamber; in the initial stage of heating, the heating element operates at full power to shorten the preheating time; when it approaches the preset temperature, the control system automatically switches to the duty cycle adjustment mode, using thermal inertia to smoothly transition the temperature to the target value, avoiding overshoot; this refined heat management, combined with the high-efficiency heat insulation material of the split-type heat insulation cavity 1, allows the outer wall of the device to maintain a near-normal temperature even when the internal temperature is at 100 degrees Celsius, which is both energy-saving and ensures the operational safety of the experimental personnel.

[0042] The anti-slip pad 58 of the material fixing component 5 is designed with full consideration of the anisotropic characteristics of carbon fiber composite materials; the direction of the serrated pattern is perpendicular to the direction of tensile load, which can effectively hold the fiber texture on the surface of the composite material and prevent interface slippage under extremely high loads; at the same time, the material of the anti-slip pad 58 has a certain toughness, which can buffer the local pressure damage to the carbon fiber caused by the clamping force and ensure that the failure point occurs at the bonding interface rather than the clamping part; this deep understanding of material properties and its transformation into specific mechanical structure design is the key to the invention's ability to obtain highly repeatable experimental data.

[0043] Finally, from the perspective of overall mechanical collaboration, this invention provides macroscopic protection and isolation through the split-type heat insulation cavity 1, establishes precise load transfer and thermal stress compensation channels through the first and second mounting mechanisms 3, achieves stable centering and clamping of the sample through the material fixing component 5, creates a microscopic humid and hot service environment through the water control component and heating chamber, and completes real-time recording of the deformation process through the in-situ monitoring component. The various structural parts are interlocked, compact and reasonable in physical space, and complementary and enhanced in functional logic, together forming a system platform that can realistically simulate complex working conditions and conduct high-precision in-situ mechanical tests.

[0044] To enable those skilled in the art to fully understand and implement this invention, the following supplements the specific implementation principle of this invention with a specific application scenario (such as in-situ tensile testing of a single lap joint of carbon fiber reinforced composite material in a humid and hot environment of 80°C and 100%RH).

[0045] Step 1, Equipment Initialization and Sample Alignment: First, the upper mechanical connecting rod 26 and the lower mechanical connecting rod 36 are fixed to the upper and lower actuating cylinders of the external electronic universal testing machine via threaded connections. Then, the first insulation cavity 11 and the second insulation cavity 12 are released by operating the latch locking device 13, and the cavities are fully opened using the hinge 16. During this process, the experimenter manually rotates the rotating disk 57, causing the threaded rod 56 with bidirectional threads to rotate within the mounting block 51. Using the screw-nut transmission principle, the two clamping plates 54 are driven to converge synchronously towards the center along the sliding rod 53, thus clamping both ends of the carbon fiber composite sample in the upper and lower material fixing components 5. Due to the symmetrical thread structure of the threaded rod 56, the longitudinal geometric centerline of the sample is ensured to be in the same vertical plane as the axes of the upper loading rod 24 and the lower loading rod 34, effectively eliminating the additional eccentric bending moment caused by asymmetrical clamping, laying a physical alignment foundation for subsequent high-precision mechanical data acquisition.

[0046] Step 2, during the construction and sealing of the microenvironment chamber, after the sample is installed, the mechanical connecting rod 26 is slightly lowered by controlling the testing machine, so that the sealing end face at the bottom of the first movable sleeve 21 and the sealing end face at the top of the second movable sleeve 31 make physical contact. At this time, the connection points between the first side connector 23 and the side of the second movable sleeve 31 are rigidly locked by fasteners, so that the first movable sleeve 21 and the second movable sleeve 31 enclose a volume-limited area in the geometric center region of the split-type heat insulation cavity 1. The microenvironment inner chamber is then inverted and closed. The second heat-insulating cavity 12 is closed, and a pre-tightening force is applied through the snap-locking member 13, causing the high-temperature resistant fluororubber sealing strip 17 to undergo radial elastic deformation at the cavity joint, thereby achieving a large-space airtight seal between the first heat-insulating cavity 11 and the second heat-insulating cavity 12. This double-layer nested sealing structure not only uses the outer cavity to block the convection of outside air, but also reduces the target volume for temperature and humidity control through the inner microenvironment inner chamber, significantly reducing the thermal inertia of environmental fluctuations on test interference.

[0047] Step 3: During the precise simulation and stabilization of the humid and hot environment, deionized water is injected into the second movable sleeve 31 through the water inlet pipe 315 until the water level completely covers the top of the sample. The dynamic sealing structure between the sealing baffle plate 311 and the lower loading rod 34 prevents liquid seepage. At the same time, the controller activates the resistance wire heating elements in the first heating chamber 28 and the second heating chamber 38. Heat penetrates the sleeve wall through thermal radiation and acts on the internal air and moisture. During this process, the temperature sensor collects the temperature signal of the microenvironment chamber in real time and feeds it back to the controller. The heating power is adjusted to make the water evaporate and generate saturated steam. Since the microenvironment chamber is in a closed state, as the steam partial pressure increases, the chamber quickly reaches the preset high temperature and high humidity equilibrium state of 80°C. At this time, the first tension spring 25 provides an upward compensating tension to the first movable sleeve 21 through its own elastic restoring force, ensuring that the sleeve will not compress the sample due to its own weight or thermal expansion displacement during the heating process.

[0048] Step 4: During the in-situ loading process, when the environment stabilizes, the testing machine starts the tensile program. The tensile load is sequentially transferred to the sample through the upper mechanical connecting rod 26, the first dynamic compensation spring 27, and the upper loading rod 24. During the entire loading process, the heat generated by the first heating chamber 28 causes the upper loading rod 24 to undergo axial thermal elongation. If no compensation is made, this elongation displacement will be converted into a pseudo-load acting on the force sensor of the testing machine. This invention absorbs this thermal expansion increment through the physical deformation of the first dynamic compensation spring 27. That is, when the upper loading rod 24 extends downward due to heat, the first dynamic compensation spring 27 is compressed synchronously in the load transmission path, using the linear elastic characteristics of the spring to offset the additional stress generated by the thermally induced displacement. Similarly, the lower second dynamic compensation spring 37 synchronously compensates for the thermal deformation of the lower loading rod 34, ensuring that the data collected by the mechanical sensor is only the real mechanical load borne by the adhesive interface of the sample.

[0049] Step 5, in-situ image acquisition and failure evolution monitoring: As the tensile load continues to increase, the high-resolution camera 15 focuses in real time on the side surface of the adhesive area of ​​the sample through the quartz glass medium of the observation window 14. Due to the design of the microenvironment chamber, the high-temperature steam is confined inside the sleeve, and there is an air insulation layer between the observation window 14 and the heat source, which effectively prevents water vapor from fogging on the inner surface of the observation window 14. The microscopic deformation images of the adhesive layer captured by the camera 15 are transmitted to the back-end processing system through the signal cable. Combined with the load-time curve recorded synchronously by the testing machine, the entire process of the adhesive interface from microcrack initiation and propagation to final brittle fracture or ductile delamination can be clearly captured. After the experiment, the remaining water is drained through the drain pipe 313, thus completing an in-situ performance evaluation under a complete working condition. This process achieves a high degree of synchronization between environmental simulation, load loading, and microscopic monitoring in space and time.

[0050] All contents not described in detail in the specification are existing technologies known to those skilled in the art, and the model parameters of each electrical appliance are not specifically limited; conventional equipment can be used. Electrical control components not mentioned in this technical solution are not shown in the figures because they are existing technologies, and will not be described here.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An in-situ testing device for adhesive joints of carbon fiber reinforced composite materials, characterized in that: The system includes a split-type heat insulation cavity (1), which comprises a first heat insulation cavity (11) and a second heat insulation cavity (12). A first mounting mechanism (2) is provided at the upper part of the interior of the first heat insulation cavity (11), and a second mounting mechanism (3) is provided at the lower part of the interior of the first heat insulation cavity (11). Material fixing components (5) are provided at the ends of both the first mounting mechanism (2) and the second mounting mechanism (3). The first heat insulation cavity (11) and the second heat insulation cavity (12) are connected by a combination of... Page (16) is hinged, and an observation window (14) is provided on the outside of the second heat insulation cavity (12). A camera (15) for monitoring the deformation of the adhesive joint is provided at the observation window (14). The first installation mechanism (2) includes an upper loading rod (24) that slides through the top of the split heat insulation cavity (1), and the second installation mechanism (3) includes a lower loading rod (34) that slides through the bottom of the split heat insulation cavity (1). The upper loading rod (24) and the lower loading rod (34) are coaxially arranged.

2. The in-situ testing device for adhesive joints of carbon fiber reinforced composite materials according to claim 1, characterized in that: The contact surfaces of the first heat insulation cavity (11) and the second heat insulation cavity (12) are provided with annularly distributed sealing strip grooves (18), and the sealing strip grooves (18) are embedded with high-temperature resistant fluororubber sealing strips (17). The outer sides of the first heat insulation cavity (11) and the second heat insulation cavity (12) are provided with buckle locking members (13) for locking the cavities. The top and bottom of the second heat insulation cavity (12) are provided with through holes (19), and the through holes (19) are used for the upper loading rod (24) and the lower loading rod (34) to pass through. A sealing member is provided between the through holes (19) and the upper loading rod (24) and the lower loading rod (34).

3. The in-situ testing device for adhesive joints of carbon fiber reinforced composite materials according to claim 1, characterized in that: The first installation mechanism (2) further includes a first movable sleeve (21), the top of the upper loading rod (24) passes through the top of the first movable sleeve (21), a first sealing gasket (210) is provided between the upper loading rod (24) and the first movable sleeve (21), a first dynamic compensation spring (27) is provided at one end of the upper loading rod (24) outside the first movable sleeve (21), an upper mechanical connecting rod (26) is provided at one end of the first dynamic compensation spring (27) away from the upper loading rod (24), the upper mechanical connecting rod (26) and the first dynamic compensation spring (27) both pass through the top of the first heat insulation cavity (11) and extend to the outside of the first heat insulation cavity (11), and the other end of the upper mechanical connecting rod (26) is connected to the clamp adapter on the testing machine.

4. The in-situ testing device for adhesive joints of carbon fiber reinforced composite materials according to claim 3, characterized in that: The first installation mechanism (2) further includes a first tension spring (25), which is located at the top of the first movable sleeve (21). The other end of the first tension spring (25) is fixedly connected to the top of the inside of the first heat insulation cavity (11). A first connecting sealing strip (22) is provided at the bottom of the first movable sleeve (21). A first side connector (23) is provided on the bottom side of the first movable sleeve (21). A first heating chamber (28) is sleeved on the outer periphery of the first movable sleeve (21). An intelligent heating element is provided inside the first heating chamber (28). A first temperature sensor (29) is provided inside the first movable sleeve (21).

5. The in-situ testing device for adhesive joints of carbon fiber reinforced composite materials according to claim 1, characterized in that: The second mounting mechanism (3) also includes a second movable sleeve (31). The top of the lower loading rod (34) passes through the top of the second movable sleeve (31). A second sealing gasket (310) is provided between the lower loading rod (34) and the second movable sleeve (31). A second dynamic compensation spring (37) is provided at one end of the lower loading rod (34) outside the second movable sleeve (31). A lower mechanical connecting rod (36) is provided at one end of the second dynamic compensation spring (37) away from the lower loading rod (34). The lower mechanical connecting rod (36) and the second dynamic compensation spring (37) both pass through the bottom of the first heat insulation cavity (11) and extend to the outside of the first heat insulation cavity (11). The other end of the lower mechanical connecting rod (36) is connected to the lower clamp adapter of the testing machine.

6. The in-situ testing device for a carbon fiber reinforced composite adhesive joint according to claim 5, characterized in that: The second mounting mechanism (3) further includes a second tension spring (35), which is located at the top of the second movable sleeve (31). The other end of the second tension spring (35) is fixedly connected to the top of the inside of the first heat insulation cavity (11). A second connecting sealing strip (32) is provided at the bottom of the second movable sleeve (31). A second side connector (33) is provided on the bottom side of the second movable sleeve (31). A second heating chamber (38) is sleeved on the outer periphery of the second movable sleeve (31). (38) An intelligent heating element is provided inside. The second connecting sealing strip (32) is matched and connected with the first connecting sealing strip (22). The second side connecting piece (33) is matched and connected with the first side connecting piece (23). A fixing bolt (4) is provided between the second side connecting piece (33) and the first side connecting piece (23). The second side connecting piece (33) and the first side connecting piece (23) are fixedly connected by the fixing bolt (4). A second temperature sensor (39) is provided inside the second movable sleeve (31).

7. The in-situ testing device for adhesive joints of carbon fiber reinforced composite materials according to claim 5, characterized in that: The second installation mechanism (3) further includes a sealing baffle (311), which is located inside the lower part of the second movable sleeve (31). The sealing baffle (311) has a hole in the middle for the lower loading rod (34) to pass through. A waterproof sealing strip is provided between the hole and the lower loading rod (34). A drain outlet (312) is provided on the side of the second movable sleeve (31), which is located above the sealing baffle (311). The second movable sleeve (31) has an inlet on the side away from the drain outlet (312). The inlet is equipped with an inlet pipe (315). The drain outlet (312) is equipped with a connecting pipe (314). The other end of the connecting pipe (314) is equipped with a drain pipe (313). The drain pipe (313) passes through the first heat insulation cavity (11) and extends to the outside of the first heat insulation cavity (11). Both the drain outlet (312) and the inlet are equipped with one-way valves.

8. The in-situ testing device for adhesive joints of carbon fiber reinforced composite materials according to claim 1, characterized in that: The material fixing assembly (5) includes a mounting block (51) fixed to the end of the upper loading rod (24) or the lower loading rod (34). The mounting block (51) has a groove (52) on its lower surface. A sliding rod (53) is fixedly connected in the groove (52). Two sliders (55) are slidably connected to the surface of the sliding rod (53). A clamping plate (54) is provided at the bottom of each of the two sliders (55). Anti-slip pads (58) are provided on the opposite side of each of the two clamping plates (54). A threaded rod (56) is provided between the two clamping plates (54). The threaded rod (56) has two threads with opposite directions and is threadedly connected to the clamping plates (54). A rotating disk (57) is provided at the end of the threaded rod (56).

9. A method of using an in-situ testing device for adhesive joints of carbon fiber reinforced composite materials, referring to the in-situ testing device for adhesive joints of carbon fiber reinforced composite materials according to any one of claims 1-8, characterized in that: Includes the following steps: S1. First, open the split-type heat insulation cavity (1), drive the upper mechanical connecting rod (26) and the lower mechanical connecting rod (36) to move through the control end of the testing machine, and adjust the distance between the upper loading rod (24) and the lower loading rod (34); install the split-type heat insulation cavity (1) between the columns of the testing machine through the bottom fixed bracket, and adjust the position of the cavity so that the axis of the loading rod coincides with the force center of the sensor of the testing machine; S2. Insert both ends of the carbon fiber reinforced composite adhesive joint sample into the clamps (54) of the upper and lower material fixing components (5); manually rotate the rotating disk (57), and drive the two clamps (54) to press towards the center synchronously through the bidirectional screw principle of the threaded rod (56), so that the axis of the sample is completely aligned with the center line of the loading rod, and the serrated structure of the anti-slip pad (58) is embedded into the sample surface to complete the mechanical pre-fixation of the sample. S3. Lock the first heat insulation chamber (11) and the second heat insulation chamber (12) with the hinge (16) and the snap-locking part (13) so that the high temperature resistant fluororubber sealing strip (17) forms a continuous sealed barrier on the contact surface; start the intelligent heating element in the first heating chamber (28) and the second heating chamber (38) and feed back the internal temperature field data in real time through the first temperature sensor (29) and the second temperature sensor (39); if it is necessary to simulate the humid heat condition, inject deionized water into the second movable sleeve (31) through the water inlet pipe (315). The liquid level should be at least 20 mm higher than the sample. The sample is completely immersed in the water. Use the saturated vapor pressure of water to form a stable humidity environment of 100% RH inside the chamber, avoid the interference of condensate water from traditional spraying, and maintain the humidity pressure inside the chamber through the one-way valve. S4. After the internal environment of the cavity reaches the preset equilibrium point, start the testing machine to perform tensile loading; the external load is transmitted to the dynamic compensation spring through the upper and lower mechanical connecting rods (36), and then introduced into the material fixing component (5) by the loading rod, and acts on the adhesive joint sample; during the entire loading process, the camera (15) collects the image of the adhesive area of ​​the sample in real time through the observation window (14), and monitors the micro-strain distribution of the interface between the adhesive layer and the composite material through digital image correlation technology; the first dynamic compensation spring (27) and the second dynamic compensation spring (37) automatically adjust the compression amount according to the thermal expansion in the cavity to eliminate the interference of thermal induced stress on the reading of the mechanical sensor.

10. The method of using the in-situ testing device for carbon fiber reinforced composite adhesive joints according to claim 9, characterized in that: Also includes: S5. When the adhesive joint breaks and fails, stop loading and turn off the heating element; drain excess humid heat medium through the drain outlet (312); The video stream of the entire process recorded by the camera (15) is retrieved and combined with the load-displacement curve exported by the testing machine to analyze the strength degradation law, failure mode and interface crack propagation rate of the adhesive joint under specific service environment, so as to complete a comprehensive assessment of the safety of the composite material structure.

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