Sandwich structure multidirectional stretching and in-situ nondestructive monitoring device and method

Abstract

The application discloses a kind of interlayer structure multidirectional stretching and in situ nondestructive monitoring device and method, adaptive edge restraint top platform forms full open detection window, and the edge of sample is clamped;Multi-directional load applying assembly can slide horizontally, realize coaxial or eccentric stretching;Monitoring link uses flexible hinged and high-frequency force sensor;Nondestructive testing system probe is located just above window.The application realizes the fusion of mechanics loading and nondestructive testing hardware;It can simulate eccentric tearing working condition flexibly, fills in the blank of asymmetric tensile in situ detection;With smooth loading and closed-loop load preservation function, it also realizes the synchronous coordination of in situ loading, in situ detection and damage evolution whole process characterization: in the process of stretching, nondestructive testing system captures the change of sample inside bonding interface in real time, load data and damage atlas are aligned on the same time axis, can complete record bonding interface from damage initiation, expansion to the evolution process of final failure under the condition of not interrupting loading, not transferring sample.

Description

Technical Field

[0001] This invention relates to the field of mechanical testing and non-destructive testing of sandwich structures, specifically to a multi-directional tensile and in-situ non-destructive monitoring device and method for sandwich structures, applicable to multi-directional tensile and in-situ non-destructive monitoring of the pull-out mechanical properties of sandwich structures (such as lightweight heat-insulating structures) and the adhesive layer of sandwich structures. Background Technology

[0002] In sandwich structures, functional layers (such as thermal insulation layers) are typically bonded to the substrate via adhesive layers, forming a multi-layered composite structure. To verify the bond strength at the adhesive interface and its mechanical properties under load, tensile strength testing is necessary. However, existing testing methods and apparatus have significant limitations for sandwich structures with adhesive layers and porous, low-density, and brittle interfaces in the bulk material.

[0003] (1) Traditional clamping methods lead to failure of internal non-destructive testing: For the detection of internal defects and interface quality of non-metallic porous sandwich structures, the industry usually uses non-destructive testing technologies such as terahertz penetration and ultrasonic phased array. However, the traditional universal tensile testing machine clamps cannot directly clamp the fragile porous body material. In order to conduct tensile tests, a metal pull-out block must be bonded to the top of the body material with high-strength structural adhesive to withstand the pull-out force. Since electromagnetic waves or sound waves will be totally reflected on the metal surface and cannot penetrate at all, this traditional mechanical testing method that must rely on the metal pull-out block directly and physically covers the detection window, causing the non-destructive testing method to completely fail under this test condition and lose the most critical dynamic process data of critical failure.

[0004] (2) Lack of simulation capability for eccentric / asymmetric stress conditions: When conducting tests, traditional tensile testing machines can only apply an absolutely perpendicular coaxial pull-out force along the geometric center axis of the sample. However, in actual service environments, due to airflow disturbances or local surface morphology, the aerodynamic forces on the surface of the sandwich structure are often uneven, which can easily generate asymmetric pull-out forces (eccentric loads) that deviate from the center. Such eccentric loads can easily cause stress concentration at the local edges of the bonding interface, leading to tearing and peeling failure of the main material. The load axis of existing conventional testing machines is fixed, and the position of the tensile force application point cannot be adjusted at will, thus failing to truly simulate the physical process of interface anti-peeling of heat-resistant tiles under eccentric stress conditions.

[0005] (3) Disturbances during loading: The brittle interface of porous materials requires extremely high loading stability. Traditional counterweight loading has a large step size and is prone to introducing impact loads; while ordinary motor-driven tensile machines are prone to high-frequency vibrations when maintaining load at extremely low speeds, which will seriously affect the imaging quality of high-precision non-destructive optical scanning or high-frequency acoustic sampling. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a multi-directional tensile and in-situ non-destructive monitoring device and method for sandwich structures. It is firmly clamped, has a fully open non-destructive detection window, and can realize stable micro-loading, eccentric multi-directional tensile and in-situ non-destructive monitoring of sandwich structures.

[0007] The objective of this invention is achieved through the following technical solution, as shown in the accompanying drawings:

[0008] This invention provides a multi-directional tensile and in-situ non-destructive testing device for sandwich structures, including a supporting main frame 1, an adaptive edge constraint top platform 2, a multi-directional load application assembly 4, a high-precision vector force monitoring link 5, and an in-situ non-destructive testing system 6. The adaptive edge constraint top platform 2 is disposed on the top of the supporting main frame 1 and forms a detection window, which is used to hold the sandwich structure sample 3 under test. The in-situ non-destructive testing system 6 is mounted on the top of the supporting main frame 1, and its probe 62 is located directly above the detection window of the adaptive edge constraint top platform 2. The load application assembly 4 is installed in the middle of the supporting main frame 1. It includes a servo drive loading unit 41, which is slidably installed in the middle of the supporting main frame 1. A vertically arranged precision linear transmission screw 42 is fixed at the power output end of the servo drive loading unit 41. The high-precision vector force monitoring link 5 includes a high-frequency digital force sensor 51. The top of the high-frequency digital force sensor 51 is hung on the bottom of the sandwich structure sample 3 to be tested, and the bottom of the high-frequency digital force sensor 51 is hung on the top of the precision linear transmission screw 42 of the multi-directional load application assembly 4.

[0009] Furthermore, the in-situ non-destructive testing system 6 includes a two-dimensional scanning moving module 61, which is fixed on the top of the supporting main frame 1 and is used to provide displacement in the horizontal XY plane. The probe 62 is mounted on the two-dimensional scanning moving module 61, and the position of the probe 62 is adjusted by the two-dimensional scanning moving module 61 so that the probe 62 is located directly above the detection window of the adaptive edge constraint top platform 2. The detection beam passes through the lower detection window and directly penetrates the sandwich structure sample 3 under test vertically downward.

[0010] Furthermore, the adaptive edge constraint top platform 2 includes a grid rigid constraint beam and a slide groove. The slide groove is installed on the top of the supporting main frame 1. The grid rigid constraint beam is composed of 4 rigid beams distributed in a grid shape. The 4 rigid beams can synchronously contract and slide along the slide groove and be locked by fastening bolts to form the detection window, which holds the outermost edge of the sandwich structure sample 3 of different sizes to be tested.

[0011] Furthermore, a rigid connecting member is fixed to the bottom of the sandwich structure sample 3 to be tested. The bottom rigid connecting member is bonded to the center of the bottom of the load-bearing substrate layer of the sample by high-strength structural adhesive. The bottom rigid connecting member is used to hang the high-precision vector force monitoring link 5.

[0012] Furthermore, the high-precision vector force monitoring link 5 includes a high-frequency digital force sensor 51, a bottom quick-release buckle 52, and a top quick-release buckle 53; the high-frequency digital force sensor 51 is located in the middle section of the link; one end of the top quick-release buckle 53 is connected to the top of the high-frequency digital force sensor 51, and the other end is hung on the rigid connecting member at the bottom of the sandwich structure sample 3 to be tested; one end of the bottom quick-release buckle 52 is connected to the bottom of the high-frequency digital force sensor 51, and the other end is hung on the precision linear transmission screw 42 of the multi-directional load application assembly 4.

[0013] Furthermore, the multi-directional load application assembly 4 includes a servo drive loading unit 41, a precision linear transmission screw 42, a transverse guide rail 43, and a slide rail positioning and locking seat 44; the transverse guide rail 43 is laid parallel to the crossbeam in the middle of the supporting main frame 1, and the slide rail positioning and locking seat 44 is slidably connected to the transverse guide rail 43; the servo drive loading unit 41 is fixed to the slide rail positioning and locking seat 44; the precision linear transmission screw 42 is connected to the power output end of the servo drive loading unit 41; a flange is fixed at the top of the precision linear transmission screw 42, and a mounting hole is opened on the flange for connecting the high-precision vector force monitoring link 5.

[0014] This invention also provides a method for multi-directional tensile and in-situ non-destructive testing of sandwich structures, which is achieved through the aforementioned synchronous testing device. The synchronous testing method includes the following two test conditions:

[0015] Condition 1: Coaxial tensile testing and synchronous in-situ inspection, including:

[0016] Step S11, Centering and clamping: Clamp the sandwich structure sample 3 to be tested onto the detection window of the adaptive edge constraint top platform 2; adjust the multi-directional load application assembly 4 to ensure that the force transmission link composed of the rigid connecting component at the bottom of the sandwich structure sample 3 to be tested, the high-precision vector force monitoring link 5, and the precision linear transmission screw 42 of the multi-directional load application assembly 4 is in an absolutely vertical coaxial state.

[0017] Step S12, Benchmark Construction: Start the in-situ non-destructive testing system 6 and perform the first benchmark scan of all bonding interfaces inside the sandwich structure sample 3 under stress-free conditions, as the digital background for subsequent damage comparison.

[0018] Step S13, Smooth Loading: The servo drive loading unit 41 of the multi-directional load application assembly pulls the precision linear transmission screw 42 downward at a preset constant rate. Through the guiding effect of the high-precision vector force monitoring link 5, the upward pulling reaction force is evenly distributed to the edge of the sandwich structure sample 3 under test, thus avoiding local crushing of the sandwich structure sample 3 under test due to the concentration of clamping stress.

[0019] Step S14, Closed-loop synchronization and load-bearing detection: During the tensile process, the high-frequency digital force sensor collects tensile force data in real time and observes internal minute deformations and crack initiation in real time; the probe performs fine scanning of the newly formed defect area;

[0020] Step S15, Limit Assessment: After the probe scan is completed, continue loading until the sample completely fractures and fails. Read the macroscopic tensile peak value and output the spatiotemporal mapping spectrum of the entire debonding evolution process under pure vertical tension.

[0021] Working Condition 2: Eccentric Composite Load Condition Test and Synchronous In-situ Inspection

[0022] Step S21, Offset Adjustment: The sandwich structure sample 3 to be tested is clipped onto the detection window of the adaptive edge constraint top platform 2; the multi-directional load application assembly 4 is slid horizontally along the transverse guide rail by a specific offset distance, and then locked and limited;

[0023] Step S22, Construction of the inclined link: The rigid connecting component at the bottom of the sandwich structure sample 3 to be tested, the high-precision vector force monitoring link 5, and the precision linear transmission screw 42 of the multi-directional load application assembly 4 are connected so that the high-precision vector force monitoring link 5 presents a certain tilt angle as a whole.

[0024] Step S23, Application of composite load: After loading begins, the servo drive loading unit 41 continues to pull the precision linear transmission screw 42 vertically downward; at this time, the force transmitted to the bottom of the sample is a tensile force vector with a certain angle to the normal. This tensile force vector is decomposed at the interface into a composite effect of vertically downward tensile stress and transversely parallel shear stress.

[0025] Step S24, In-situ capture of tear damage: The in-situ non-destructive testing system 6 performs high-frequency key monitoring on the eccentrically stressed edge. When the tear initiation point caused by eccentric tearing is captured, the eccentric load mechanical data at this time is synchronized and the self-locking load protection mechanism is triggered.

[0026] Step S25, Evolution Evaluation: After acquiring a high-resolution image of the tear initiation point under load, the eccentric composite tensile force is continuously increased, and the non-destructive testing system fully records the dynamic peeling process of the crack gradually expanding from the edge of the stressed side to the geometric center of the sample.

[0027] Furthermore, the load-holding detection adopts a damage signal trigger-load-holding fine scanning mechanism: the macroscopic tensile curve is bound to the microscopic imaging image through a unified timestamp; once abnormal debonding characteristics are detected inside, the system will issue an interrupt command, and the servo drive loading unit will brake and switch to constant force load-holding mode after receiving the command.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) Strong applicability: It abandons the traditional testing method that requires bonding a metal pull-out block to the top of the sample and innovatively designs a fully open adaptive edge constraint top platform. This structure not only achieves rigid and coordinated clamping of the large stress area of ​​the heat-resistant tile to avoid local crushing, but also reserves an unobstructed detection window at the top. This design is not only suitable for terahertz wave penetration, but also applicable to in-situ non-destructive testing methods such as ultrasonic waves and acoustic emission, realizing a perfect hardware integration of mechanical loading and non-destructive testing.

[0030] (2) Innovatively, it realizes flexible simulation of eccentric tension and asymmetric tearing conditions, breaking through the barrier that traditional equipment can only perform coaxial tension. This invention enables the servo loading assembly to be flexibly translated and positioned in the horizontal direction by setting a transverse guide rail and a sliding rail positioning locking seat at the bottom. Combined with the bidirectional universal adaptive adjustment joint in the mechanical monitoring link, it can accurately apply eccentric tensile (tension-shear composite) loads with specific offset angles and offset distances to the sandwich structure sample, thereby truly examining the tear resistance and peel resistance performance of the internal adhesive layer under uneven stress conditions, filling a gap in the field.

[0031] (3) A high-precision closed-loop damage triggering-load holding detection mechanism was proposed: a precision servo drive component was used in conjunction with a lead screw drive to overcome the shortcomings of vibration and provide a stable physical imaging environment. More importantly, the method integrates the time axis synchronization technology of macroscopic load data and microscopic flaw detection signals. When the critical microcrack debonding signal is detected, the servo motor can brake and maintain a constant load (load holding), thereby enabling high-precision dynamic evolution observation. Attached Figure Description

[0032] Figure 1 This is an isometric side view of the overall structure of the multi-directional tensile and in-situ non-destructive monitoring device for a sandwich structure as described in Embodiment 1 of the present invention;

[0033] Figure 2 This is a side view of a multi-directional tensile and in-situ non-destructive monitoring device for a sandwich structure as described in Embodiment 1 of the present invention;

[0034] Figure 3 This is a schematic diagram of the internal structure of the load transfer and monitoring link in Embodiment 1 of the present invention;

[0035] Figure 4This is a top view of the supporting main frame and adaptive edge constraint top platform in Embodiment 1 of the present invention (showing the location of the detection window).

[0036] Figure 5 This is a schematic diagram of the layer structure of the sandwich structure sample to be tested in Embodiment 1 of the present invention (including three-layer and multi-layer structures).

[0037] Figure 6 This is a schematic diagram of the test status of the multi-directional tensile and in-situ non-destructive testing device for a sandwich structure as described in Embodiment 1 of the present invention under simulated eccentric composite load (asymmetric diagonal tearing) conditions.

[0038] In the picture:

[0039] 1-Supporting main frame; 2-Adaptive edge constraint top platform; 3-Sample of sandwich structure to be tested; 4-Multi-directional load application assembly; 5-High-precision vector force monitoring link; 6-In-situ non-destructive testing system; 41-Servo drive loading unit; 42-Precision linear transmission screw; 43-Transverse guide rail; 44-Slide rail positioning and locking seat; 51-High-frequency digital force sensor; 52-Bottom quick-release buckle; 53-Top quick-release buckle; 61-Two-dimensional scanning moving module; 62-Probe. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it.

[0041] Example 1

[0042] like Figures 1 to 5As shown, this embodiment is a multi-directional tensile and in-situ non-destructive testing device for a sandwich structure, including a supporting main frame 1, an adaptive edge constraint top platform 2, a multi-directional load application assembly 4, a high-precision vector force monitoring link 5, and an in-situ non-destructive testing system 6. The top of the supporting main frame 1 is the detection constraint area. The adaptive edge constraint top platform 2 is set on the top of the supporting main frame 1 and forms a detection window. The detection window is used to hold the sandwich structure sample 3 under test. The in-situ non-destructive testing system 6 is mounted on the top of the supporting main frame 1, and its probe 62 is located directly above the detection window of the adaptive edge constraint top platform 2. The upper part of the supporting main frame 1 is the force transmission area. The high-precision vector force monitoring link 5 is located in the force transmission area and is responsible for flexible force transmission. The high-precision vector force monitoring link 5 includes a high-frequency digital force sensor 51. The top of the high-frequency digital force sensor 51 is attached to the bottom of the sandwich structure sample 3 to be tested, and the bottom of the high-frequency digital force sensor 51 is attached to the multi-directional load application assembly 4. The lower part of the supporting main frame 1 is the power drive area. The multi-directional load application assembly 4 is installed in the middle of the supporting main frame 1 and is responsible for providing displacement and off-center load power. The multi-directional load application assembly 4 includes a servo drive loading unit 41. The servo drive loading unit 41 is slidably installed in the middle of the supporting main frame 1. A vertically set precision linear transmission screw 42 is fixed at the power output end of the servo drive loading unit 41. The top of the precision linear transmission screw 42 is connected to the high-precision vector force monitoring link 5.

[0043] Furthermore, the supporting main frame 1 is made of industrial-grade high tensile stiffness aluminum profile spliced ​​with high-strength corner pieces and bolts, which ensures that the system does not deform during composite destructive tensile stress.

[0044] Furthermore, such as Figure 1 , Figure 2 As shown, the in-situ non-destructive testing system 6 includes a two-dimensional scanning moving module 61, which is fixed to the top of the supporting main frame 1 to provide high-precision displacement in the horizontal XY plane. A probe 62 is mounted on the two-dimensional scanning moving module 61. The position of the probe 62 is adjusted by the two-dimensional scanning moving module 61 so that the probe 62 is directly above the detection window of the adaptive edge constraint top platform 2. The detection beam passes through the lower detection window and directly penetrates the sandwich structure sample 3 under test vertically downwards. The two-dimensional scanning moving module 61 drives the probe 62 to move in a plane, and the emitted detection beam is not obstructed by any mechanical clamps, directly penetrating the sample surface vertically downwards. Depending on the testing requirements, the probe 62 can be flexibly configured as a terahertz time-domain spectroscopy scanning probe, an ultrasonic phased array probe, or a high-resolution X-ray emitter.

[0045] Furthermore, such as Figure 1 , Figure 4As shown, the adaptive edge constraint top platform 2 includes a grid-like rigid constraint beam and a sliding groove. The sliding groove is installed on the top of the supporting main frame 1. The grid-like rigid constraint beam consists of four rigid beams arranged in a grid pattern. The four rigid beams can slide synchronously along the sliding groove and are locked by fastening bolts to form the detection window, thereby adaptively holding the outermost edge of the sandwich structure sample 3 of different sizes. The detection window is a hollow area, specifically reserved for the detection beam above, avoiding any physical obstruction. Traditional tensile testing machines usually use upper and lower clamps. However, in this embodiment, in order to protect the porous heat-resistant material and not obstruct the detection beam above, four rigid constraint beams that can slide and adjust along the profile sliding groove are designed. These four constraint beams are arranged in a grid pattern. The operator can loosen the fastening bolts according to the specific length and width dimensions of the sample 3 and synchronously retract the four rigid constraint beams inward until they tightly and evenly hold the outer edge of the sandwich structure body material of the sandwich structure sample 3 under test (the overlap width is usually set to 5mm-15mm). Once locked, the geometric center of the four rigid constraint beams naturally forms an open, completely unobstructed detection window. The unobstructed design of the detection window allows electromagnetic waves or sound waves to penetrate all the aforementioned non-metallic layers in sequence, enabling cross-layer in-situ three-dimensional reconstruction imaging of manufacturing defects or load-bearing damage such as debonding, pores, and microcracks at multiple internal interfaces.

[0046] Furthermore, such as Figure 1 , Figure 5 As shown, the bottom of the sandwich structure sample 3 to be tested is fixed with a rigid connecting member. The bottom rigid connecting member is bonded to the center of the bottom of the load-bearing substrate layer of the sample by high-strength structural adhesive. It has a hanging hole or pin for hanging the top quick-release buckle 53 of the high-precision vector force monitoring link 5 as the guide point for transmitting the pull-out force downward.

[0047] Furthermore, such as Figure 1 , Figure 2As shown, the high-precision vector force monitoring link 5 includes a high-frequency digital force sensor 51, a bottom quick-release buckle 52, and a top quick-release buckle 53. The high-frequency digital force sensor 51 is located in the middle of the link and is used to collect macroscopic tensile force or composite eccentric load data in real time. One end of the top quick-release buckle 53 is connected to the top of the sensor 51, and the other end is hung on the rigid connecting member at the bottom of the sandwich structure sample 3 to be tested. One end of the bottom quick-release buckle 52 is connected to the bottom of the sensor 51, and the other end is hung on the top flange of the multi-directional load application assembly 4 below. This flexible hinged link formed by the series connection of double shackles ensures adaptive centering of the force direction. The core of the high-precision vector force monitoring link 5 is a high-frequency digital force sensor 51, which is connected to high-strength quick-release buckles at its upper and lower ends. This flexible serial link design gives the force transmission system multi-directional adaptive centering characteristics in three-dimensional space. Even if the bottom power mechanism is laterally offset, the force transmission vector can still be automatically kept on the line connecting the two suspension points through the free sliding and deflection of the hanging ring, completely avoiding the lateral bending moment error caused by mechanical rigid jamming.

[0048] Furthermore, such as Figure 1 , Figure 2 , Figure 3 , Figure 6 As shown, the multi-directional load application assembly 4 includes a servo-driven loading unit 41, a precision linear transmission screw 42, a transverse guide rail 43, and a slide rail positioning and locking seat 44. The transverse guide rail 43 is laid parallel to the crossbeam in the middle of the supporting main frame 1. The slide rail positioning and locking seat 44 is slidably connected to the transverse guide rail 43. The slide rail positioning and locking seat can be arbitrarily translated to the left or right along the transverse guide rail 43 and locked, thereby realizing coaxial stretching or eccentric stretching at a set distance. The servo-driven loading unit 41 is fixed on the slide rail positioning and locking seat 44 and integrates a high-resolution AC servo motor and a harmonic reducer to eliminate low-speed vibration. The precision linear transmission screw 42 is connected to the power output end of the servo-driven loading unit 41 and is used to convert the rotational motion of the servo-driven loading unit 41 into a downward linear displacement force. A flange is fixed at the top of the precision linear transmission screw 42. The flange has a hanging hole for suspending and receiving the bottom quick-release buckle 52 of the high-precision vector force monitoring link 5 above. In this embodiment, the servo drive loading unit 41 integrates a high-resolution AC servo motor and a low backlash harmonic reducer to eliminate torque pulsation and high-frequency vibration when the motor is running at extremely low speeds.

[0049] The testable sandwich structure sample 3 of this invention covers a variety of composite hierarchical structures, not limited to a single form, including:

[0050] Classic three-layer structure: includes a top heat protection / insulation layer (such as PMI porous foam, aerogel composite material, etc.), a middle structural adhesive layer (such as silicone rubber-based adhesive), and a bottom load-bearing matrix layer (such as aluminum alloy or carbon fiber resin-based composite material); complex five-layer or multi-layer structure: in order to realistically simulate thermal protection systems or high-performance composite structures under high-temperature environments, sample 3 can also be a complex five-layer structure from top to bottom: anti-oxidation and anti-erosion coating + porous ceramic heat insulation tile + strain isolation pad (SIP) + bottom adhesive layer + structural matrix (such as skin or load-bearing component).

[0051] Example 2

[0052] This embodiment is a method for multi-directional tensile and in-situ non-destructive testing of sandwich structures, which is implemented using the device described in Embodiment 1. Depending on the complex load environments that the sandwich structure may endure, it supports the following two typical test conditions and operating procedures:

[0053] Condition 1: Pure Vertical Tension (Coaxial Tensile) Test and Synchronous In-situ Detection: This embodiment is mainly used to evaluate the macroscopic ultimate tensile strength and microscopic damage initiation mechanism of the internal interface of the heat-resistant material under uniform aerodynamic lift; including:

[0054] Step S11, Centering and Clamping: The prepared sandwich structure sample 3 to be tested is clamped onto the detection window of the adaptive edge constraint top platform 2; the slide rail positioning locking seat 44 of the multi-directional load application assembly 4 is adjusted to slide along the transverse guide rail 43 to the geometric center position and locked; by adjustment, it is ensured that the entire force transmission link composed of the rigid connecting component at the bottom of the sandwich structure sample 3 to be tested, the top quick-release buckle 53 of the high-precision vector force monitoring link 5, the high-frequency digital force sensor 51, the bottom quick-release buckle 52, and the precision linear transmission screw 42 of the multi-directional load application assembly 4 is in an absolutely vertical coaxial state.

[0055] Step S12, Benchmark Construction: Start the in-situ non-destructive testing system 6 and perform the first benchmark scan of all bonding interfaces inside the sandwich structure sample 3 under stress-free conditions, as the digital background for subsequent damage comparison.

[0056] Step S13, Smooth Loading: The control system instructs the servo-driven loading unit 41 of the multi-directional load application assembly to pull the precision linear transmission screw 42 downward at an extremely low constant rate (e.g., displacement control mode of 0.5 mm / min). Due to the guiding effect of the high-precision vector force monitoring link 5, the upward pulling reaction force is absolutely and evenly distributed to the edge of the wide area of ​​the sandwich structure sample 3 under test, avoiding local crushing of the sandwich structure sample 3 under test due to the concentration of clamping stress.

[0057] Step S14, Closed-Loop Synchronization and Load Holding Detection: During the tensile process, a high-frequency digital force sensor collects tensile force data in real time, and the non-destructive testing screen observes internal minute deformations and crack initiation in real time. This invention proposes a damage signal triggering-load holding fine scanning mechanism: the main control computer binds the macroscopic tensile curve with the microscopic imaging screen through a unified timestamp; once the algorithm of the main control computer identifies abnormal debonding characteristics inside, the system will issue an interrupt command, and the servo motor will brake and switch to constant force holding mode (maintaining the current tensile load unchanged) after receiving the command. Under stable physical conditions, the probe performs slow, high-resolution fine scanning of the newly formed defect area.

[0058] Step S15, Limit Assessment: After the probe scan is completed, continue loading until the sample completely fractures and fails. Read the macroscopic tensile peak value and output the spatiotemporal mapping spectrum of the entire debonding evolution process under pure vertical tension.

[0059] Working Condition 2: Eccentric Composite Load (Asymmetric Diagonal Tear) Working Condition Test and Synchronous In-situ Inspection:

[0060] Combination Figure 6 This working condition is the core breakthrough of this invention, used to realistically simulate the failure process of heat-resistant tiles during actual service, caused by localized stress concentration and boundary tearing (Type I / II composite fracture) resulting from strong airflow. Traditional fixed-axis tensile testing machines are completely incapable of performing this type of test. This includes:

[0061] Step S21, Offset Adjustment: First, perform centering and clamping, and clamp the prepared sandwich structure sample 3 to be tested onto the detection window of the adaptive edge constraint top platform 2; according to the requirements of the real aerodynamic off-center load simulation calculation, loosen the slide rail positioning locking seat 44 of the multi-directional load application assembly 4, and slide the bottom multi-directional load application assembly 4 horizontally to the left or right along the transverse guide rail by a specific offset distance (for example, 40mm or 60mm away from the central axis), and then re-lock it.

[0062] Step S22, Construction of the inclined cable link: This involves connecting the rigid connecting component at the bottom of the sandwich structure sample 3 under test, the top quick-release buckle 53 of the high-precision vector force monitoring link 5, the high-frequency digital force sensor 51, the bottom quick-release buckle 52, and the precision linear transmission screw 42 of the multi-directional load application assembly 4, as shown below. Figure 6 As shown, due to the significant lateral shift of the force-receiving point at the bottom of the sandwich structure sample 3 under test, the high-precision vector force monitoring link 5 exhibits a certain tilt angle (the direction of the tension is no longer perpendicular to the bottom surface of the sample) through the free rotation compensation of the upper and lower quick-release buckles.

[0063] Step S23, Application of Composite Load: After loading begins, the servo-driven loading unit 41 continues to pull the precision linear transmission screw 42 vertically downwards. However, at this time, the force transmitted to the bottom of the sample is actually a tensile force vector at a certain angle to the normal. This vector decomposes at the interface into a composite effect of vertically downward tensile stress (normal peeling force) and transversely parallel shear stress.

[0064] Step S24, In-situ capture of tear damage: This highly asymmetrical composite load will cause a large stress concentration to occur first on one side of the heat-resistant sample edge (showing a prying-like trend). The in-situ non-destructive testing system 6 performs high-frequency key monitoring on this eccentrically stressed edge. When the first interfacial micro-crack (tear initiation point) is captured due to eccentric tearing at the edge, the main control program immediately synchronizes the eccentric load mechanical data at this time and triggers the self-locking load protection mechanism.

[0065] Step S25, Evolution Assessment: After acquiring a high-resolution image of the crack initiation point under load, the eccentric composite tensile force is continuously increased. The non-destructive testing system will fully record the dynamic peeling process as the crack gradually propagates from the stressed edge towards the geometric center of the sample. Ultimately, the ultimate tear resistance data of the sandwich structure under a real asymmetric load environment is obtained. This innovative method fills the technical gap in the industry where in-situ microscopic flaw detection is impossible during eccentric tensile testing.

Claims

1. A multi-directional tensile and in-situ non-destructive monitoring device for a sandwich structure, characterized in that, The system includes a supporting main frame (1), an adaptive edge constraint top platform (2), a multi-directional load application assembly (4), a high-precision vector force monitoring link (5), and an in-situ non-destructive testing system (6). The adaptive edge constraint top platform (2) is set on top of the supporting main frame (1) and forms a detection window, which is used to hold the sample of the sandwich structure (3) under test. The in-situ non-destructive testing system (6) is mounted on top of the supporting main frame (1), and its probe (62) is located directly above the detection window of the adaptive edge constraint top platform (2). The multi-directional load application assembly (4) is installed on the supporting main frame. The body frame (1) includes a servo drive loading unit (41) in the middle. The servo drive loading unit (41) is slidably installed in the middle of the supporting body frame (1). The power output end of the servo drive loading unit (41) is fixed with a vertically arranged precision linear transmission screw (42). The high-precision vector force monitoring link (5) includes a high-frequency digital force sensor (51). The top of the high-frequency digital force sensor (51) is connected to the bottom of the sandwich structure sample (3) to be tested. The bottom of the high-frequency digital force sensor (51) is connected to the top of the precision linear transmission screw (42) of the multi-directional load application assembly (4).

2. The multi-directional tensile and in-situ non-destructive testing device for a sandwich structure as described in claim 1, characterized in that, The in-situ non-destructive testing system (6) includes a two-dimensional scanning moving module (61), which is fixed on the top of the supporting main frame (1) to provide displacement in the horizontal XY plane; the probe (62) is installed on the two-dimensional scanning moving module (61), and the position of the probe (62) is adjusted by the two-dimensional scanning moving module (61) so that the probe (62) is located directly above the detection window of the adaptive edge constraint top platform (2), and the detection beam passes through the detection window below and directly penetrates the sandwich structure sample (3) under test vertically downward.

3. The multi-directional tensile and in-situ non-destructive testing device for a sandwich structure as described in claim 1, characterized in that, The adaptive edge constraint top platform (2) includes a grid rigid constraint beam and a chute. The chute is installed on the top of the supporting main frame (1). The grid rigid constraint beam is composed of 4 rigid beams distributed in a grid shape. The 4 rigid beams can slide synchronously along the chute and be locked by fastening bolts to form the detection window, which holds the outermost edge of the sandwich structure sample (3) of different sizes to be tested.

4. The multi-directional tensile and in-situ non-destructive testing device for a sandwich structure as described in claim 1, characterized in that, The bottom of the sandwich structure sample (3) to be tested is fixed with a rigid connecting member. The bottom rigid connecting member is bonded to the center of the bottom of the load-bearing matrix layer of the sample by high-strength structural adhesive. The bottom rigid connecting member is used to hang the high-precision vector force monitoring link (5).

5. The composite tensile and in-situ non-destructive testing device for sandwich structures as described in claim 1, characterized in that, The high-precision vector force monitoring link (5) includes a high-frequency digital force sensor (51), a bottom quick-release buckle (52), and a top quick-release buckle (53); the high-frequency digital force sensor (51) is located in the middle of the link; one end of the top quick-release buckle (53) is connected to the top of the high-frequency digital force sensor (51), and the other end is hung on the rigid connecting member at the bottom of the sandwich structure component (3) to be tested; one end of the bottom quick-release buckle (52) is connected to the bottom of the high-frequency digital force sensor (51), and the other end is hung on the precision linear transmission screw (42) of the multi-directional load application assembly (4).

6. The multi-directional tensile and in-situ non-destructive testing device for sandwich structures as described in claim 1, characterized in that, The multi-directional load application assembly (4) includes a servo drive loading unit (41), a precision linear transmission screw (42), a transverse guide rail (43), and a slide rail positioning locking seat (44). The transverse guide rail (43) is laid parallel to the crossbeam in the middle of the supporting main frame (1), and the slide rail positioning locking seat (44) is slidably connected to the transverse guide rail (43). The servo drive loading unit (41) is fixed to the slide rail positioning locking seat (44). The precision linear transmission screw (42) is connected to the power output end of the servo drive loading unit (41). A flange is fixed at the top of the precision linear transmission screw (42), and a mounting hole is opened on the flange for connecting the high-precision vector force monitoring link (5).

7. A method for multi-directional tensile and in-situ non-destructive monitoring of a sandwich structure, implemented by the device described in any one of claims 1 to 6, characterized in that, The method includes the following two test conditions: Condition 1: Coaxial tensile testing and synchronous in-situ inspection, including: Step S11, centering and clamping: clamp the sandwich structure sample (3) to be tested onto the detection window of the adaptive edge constraint top platform (2); adjust the multi-directional load application assembly (4) to ensure that the force transmission link composed of the rigid connecting component at the bottom of the sandwich structure sample (3), the high-precision vector force monitoring link (5), and the precision linear transmission screw (42) of the multi-directional load application assembly (4) is in an absolutely vertical coaxial state; Step S12, Benchmark Construction: Start the in-situ non-destructive testing system (6) and perform the first benchmark scan of all bonding interfaces inside the sandwich structure sample (3) under stress-free conditions, as the digital background for subsequent damage comparison; Step S13, Smooth loading: The servo drive loading unit (41) of the multi-directional load application assembly pulls down the precision linear transmission screw (42) at a preset constant rate. Through the guiding effect of the high-precision vector force monitoring link (5), the upward pulling reaction force is evenly distributed to the edge of the sandwich structure sample (3) under test, thus avoiding the local crushing of the sandwich structure sample (3) under test due to the concentration of clamping stress. Step S14, Closed-loop synchronization and load-bearing detection: During the tensile process, the high-frequency digital force sensor collects tensile force data in real time and observes internal minute deformations and crack initiation in real time; the probe performs fine scanning of the newly formed defect area; Step S15, Limit Assessment: After the probe scan is completed, continue loading until the sample completely fractures and fails. Read the macroscopic tensile peak value and output the spatiotemporal mapping spectrum of the entire debonding evolution process under pure vertical tension. Working Condition 2: Eccentric Composite Load Condition Test and Synchronous In-situ Inspection Step S21, Offset Adjustment: The sandwich structure sample (3) to be tested is snapped into the detection window of the adaptive edge constraint top platform (2); the multi-directional load application assembly (4) is slid horizontally along the transverse guide rail by a specific offset distance, and then locked and limited; Step S22, Construction of the inclined link: The rigid connecting component, the high-precision vector force monitoring link (5) and the precision linear transmission screw (42) of the multi-directional load application assembly (4) at the bottom of the sandwich structure sample (3) to be tested are connected to make the high-precision vector force monitoring link (5) present a certain tilt angle as a whole. Step S23, Application of composite load: After the loading starts, the servo drive loading unit (41) continues to pull the precision linear transmission screw (42) vertically downward; at this time, the force transmitted to the bottom of the sample is a tensile force vector with a certain angle to the normal. This tensile force vector is decomposed at the interface into a composite effect of vertically downward tensile stress and transversely parallel shear stress. Step S24, in-situ capture of tear damage: The in-situ non-destructive testing system (6) performs high-frequency key monitoring on the eccentrically stressed edge. When the tear initiation point caused by eccentric tearing is captured, the eccentric load mechanical data at this time is synchronized and the self-locking load protection mechanism is triggered. Step S25, Evolution Evaluation: After acquiring a high-resolution image of the tear initiation point under load, the eccentric composite tensile force is continuously increased, and the non-destructive testing system fully records the dynamic peeling process of the crack gradually expanding from the edge of the stressed side to the geometric center of the sample.

8. The method for multi-directional tensile and in-situ non-destructive monitoring of a sandwich structure as described in claim 7, characterized in that, The load-holding detection adopts a damage signal trigger-load-holding fine scanning mechanism: the macroscopic tensile curve is bound to the microscopic imaging image through a unified timestamp; once an abnormal debonding feature is detected inside, the system will issue an interrupt command, and the servo drive loading unit will brake and switch to constant force load-holding mode after receiving the command.

9. The method for multi-directional tensile and in-situ non-destructive monitoring of a sandwich structure as described in claim 7, characterized in that, In the synchronous testing method, in-situ loading, in-situ detection, synchronous monitoring, and evolution characterization are achieved collaboratively as follows: throughout the entire process of applying tensile load to the sandwich structure sample under test by the multi-directional load application assembly, the in-situ non-destructive testing system is always aligned with the detection window to acquire microstructure images or signals of the bonding interface inside the sample in real time; through a unified time axis synchronization method, the continuous load curve output by the high-precision vector force monitoring link is aligned frame by frame with the spatial distribution damage map output by the in-situ non-destructive testing system; under the conditions of no sample transfer, no interruption of loading, and no disassembly of the fixture, the evolution process of the bonding interface from damage initiation and expansion to final failure is fully recorded, realizing the in-situ correlation characterization of mechanical properties and internal structural evolution.

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