Tension-torsion multi-axis fatigue experiment device and method based on synchrotron radiation and neutrons

Abstract

The invention discloses a tension-torsion multi-axial fatigue experiment device and method based on synchrotron radiation and neutrons. The experimental device comprises a base, a lower cavity, an acrylic / aluminum alloy projection window, an upper cavity, a supporting rod, a supporting plate, a hydraulic actuator, an upper connecting rod, a load sensor, an upper clamp, a multi-axial fatigue sample, a lower clamp, an angle sensor, a lower connecting rod, a torsion servo motor, a motor controller, an advanced light source receiver, an advanced light source entrance slit and the like. And performing macroscopic three-dimensional damage distribution characterization and microstructure evolution and damage evolution process experiments in the sample by penetrating the metal sample through X-rays and neutron beams. The method provides direct and reliable experimental data support for establishing a multi-axial fatigue theoretical model, revealing a material failure mechanism and engineering structure anti-fatigue design.

Description

Technical Field

[0001] This invention relates to multiaxial fatigue testing devices, and more particularly to a tensile-torsional multiaxial fatigue testing device and method based on synchrotron radiation and neutrons. Background Technology

[0002] In critical engineering fields such as aerospace, rail transportation, and energy, many key service components (such as turbine disks and blades of aero-engines, wheel axles and bogies of high-speed trains, and drill pipes and drill collars in oil drilling tools) experience typical multiaxial stress loading and non-proportional cyclic loading characteristics during their service life, especially tensile and torsional loads. During long-term service, these load-bearing components continuously experience a complex multiaxial stress field composed of alternating axial stress and alternating torsional shear stress. The synergistic and coupling effects of this multiaxial cyclic stress field have become the core mechanism for inducing multiaxial fatigue failure of components, seriously threatening the service safety and structural integrity of high-end equipment. It is the primary factor causing sudden equipment failure, structural lifespan significantly shorter than design expectations, and a substantial decline in service safety and reliability.

[0003] The fundamental difference between multiaxial fatigue and uniaxial fatigue lies in the high complexity of its microscopic damage evolution mechanism. This complexity manifests as a deep dependence of microscopic crack initiation and propagation behavior on load parameters and loading paths (linear, circular, or rhomboid loading paths, etc.), making it a core challenge in current basic research and engineering applications. Unlike uniaxial fatigue cracks that propagate in a single direction, multiaxial fatigue crack propagation exhibits significant multi-path characteristics: under multiaxial proportional loading (phase difference φ = 0°), tensile and torsional stress components change synchronously, with cracks preferentially initiating in the 45° maximum shear amplitude region; however, under multiaxial non-proportional loading (phase difference φ ≠ 0°), tensile and torsional stress components change asynchronously, and the principal stress or principal strain plane undergoes continuous dynamic shift over time. The crack initiation location migrates with the spatiotemporal evolution of cyclically accumulated plastic damage (such as the non-proportional additional hardening zone), completely deviating from the fixed-angle constraint framework. Crack propagation paths, driven by tensile and torsional stresses, generally exhibit helical deflection or branching, further increasing the complexity of the damage mechanism.

[0004] Existing technologies for characterizing the microscopic damage mechanisms of materials under tensile-torsional multiaxial fatigue loading have limitations. On the one hand, they lack compatibility with synchrotron radiation sources; on the other hand, there is a gap in their synergistic application with neutron characterization techniques. The core requirement for achieving synchrotron X-ray scanning imaging is unobstructed propagation of the X-ray beam across the entire 0° to 360° angular range, ensuring the detector acquires complete projection data to support the accurate implementation of tomographic reconstruction algorithms such as filtered back-projection. While conventional electro-hydraulic servo multiaxial fatigue testing machines can achieve tensile-torsional loading, during the 360° rotational scanning of synchrotron radiation three-dimensional imaging, the symmetrically distributed columns on both sides of the sample stage periodically block the light path as the sample rotates around the axis. Within the blocked area, X-rays are largely absorbed, causing a sharp decrease in the photon flux received by the detector, or even preventing the acquisition of effective data. This data tomography directly leads to artifacts such as blurred edges and structural distortion in the reconstructed image, severely reducing spatial resolution and quantitative analysis accuracy. Neutron beams possess unique advantages such as deep penetration, sensitivity to light elements, and the ability to distinguish isotopes. They can be used to analyze the internal stress distribution, texture evolution, and microscopic defect evolution of materials, making them an important technique to supplement synchrotron X-ray characterization and reveal multiaxial fatigue damage mechanisms. However, existing experimental setups are either designed only for uniaxial loads and cannot achieve tensile-torsional multiaxial loading, or although they can achieve multiaxial loading, their structural design does not consider the propagation characteristics of neutron beams. The loading mechanism or support structure may block the neutron beam path, failing to meet the requirements of in-situ neutron transmission or diffraction experiments. This greatly limits the application of neutron characterization techniques in multiaxial fatigue research.

[0005] In summary, revealing the microscopic damage mechanism of multiaxial tensile-torsional fatigue faces a dual bottleneck: insufficient adaptation of synchrotron radiation and neutron characterization techniques. This limits the accurate characterization of the macroscopic three-dimensional damage distribution within materials and restricts in-depth analysis of microscopic stress-strain, texture, and defect evolution. Therefore, developing an experimental method and apparatus that is compatible with both synchrotron radiation and neutron characterization, stably and accurately controls multiaxial tensile-torsional fatigue loads, and meets the requirements of high spatiotemporal resolution characterization techniques has become an urgent scientific and engineering need to overcome characterization bottlenecks and support the long-life service design of high-end equipment. Summary of the Invention

[0006] To address the above problems, this invention provides a tensile-torsional multiaxial fatigue testing apparatus and method based on synchrotron radiation and neutrons.

[0007] The present invention provides a multiaxial fatigue testing device based on synchrotron radiation and neutrons, comprising a base, a lower cavity, an acrylic / aluminum alloy projection window, an upper cavity, a support rod, a support plate, a hydraulic actuator, an upper connecting rod, a load sensor, an upper clamp, a multiaxial fatigue specimen, a lower clamp, an angle sensor, a lower connecting rod, a torsion servo motor, a motor controller, an advanced light source receiver, and an advanced light source entrance slit.

[0008] The lower cavity is bolted to the base. A torsion servo motor is installed inside the lower cavity and connected to the base. The torsion servo motor is connected to the lower clamp via a lower connecting rod. An angle sensor is installed on the top of the lower connecting rod. The upper cavity is connected to the support plate via support rods. Four support rods are arranged in a circular array. Both the upper cavity and the support plate have circular mounting holes. A hydraulic actuator is installed on the support plate. The hydraulic actuator is connected to the upper clamp via an upper connecting rod. A load sensor is installed at the bottom of the upper connecting rod. An acrylic / aluminum alloy viewing window is connected to the upper cavity and the lower cavity respectively. All three are installed coaxially in a cylindrical manner. An advanced light source entrance slit and an advanced light source receiver are located outside the platform. The acrylic / aluminum alloy viewing window is located on the light path of the advanced light source. The torsion servo motor is connected to the motor controller.

[0009] Furthermore, the upper clamp has the following specific structure: the V-shaped clamping block is connected to the right-hand threaded wedge block and the left-hand threaded wedge block respectively. The left-hand and right-hand threaded wedge blocks are respectively installed at both ends of the threaded round bars with different directions of rotation. The multiaxial fatigue specimen is clamped by rotating the threaded round bars with different directions of rotation at both ends. The threaded round bars with different directions of rotation at both ends are installed in the through hole inside the wedge groove. The wedge groove is embedded in the inner cavity of the clamp body. The two are assembled without clearance by the interference fit of the pin.

[0010] The lower clamp has the same structure as the upper clamp.

[0011] The present invention provides an in-situ three-dimensional imaging experimental method based on X-rays, specifically comprising the following steps:

[0012] Step 1: First, assemble and connect all parts of the aforementioned experimental setup. Then, place the experimental setup on the X-ray source sample stage. Adjust the installation position according to the X-ray height. Use the laser positioning system to accurately locate the sample test position, ensuring that the X-rays pass through the sample gauge length range. Calibrate the sample stage and the central axis of the experimental setup. Determine the imaging field of view and X-ray energy experimental parameters according to the material, size, and experimental purpose of the sample to be tested.

[0013] Step 2: Based on the experimental objective, determine the experimental load parameters, including vertical stress, torque, and phase difference; the radial load range is 0~5kN, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; the torsional servo motor output torque range is 0~5Nm, the torsion angle range is 0~90°, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; control the hydraulic actuator and the torsional servo motor respectively to convert the electrical signals into reciprocating vertical displacement and torsional angle output by the upper and lower connecting rods, and measure and read the actual loading stress by the load sensor and angle sensor, which is then transmitted to the sample to be loaded through the flanges of the upper and lower clamps.

[0014] Step 3: After several cycles of loading, damage to the gauge length of the sample is observed on the external controller screen in the laboratory. The hydraulic actuator and torsional servo motor are then controlled to stop loading and remain static so that the sample remains in a damaged state while ensuring that the damage features are clearly visible.

[0015] Step 4: At this time, the X-ray generator is turned on. The X-rays pass through the entrance slit. The base is controlled to rotate, which drives the experimental device to rotate 180° at a constant speed. During the rotation, the X-rays emitted by the X-ray generator and passing through the acrylic / aluminum viewing window and the gauge length of the sample are received by the X-ray receiver, thereby acquiring image data.

[0016] Step 5: After completing the 180° imaging of the current damage state, restart the hydraulic actuator and torsion servo motor for cyclic loading, repeat the operation of Step 4 until the expected damage state is achieved, and then turn off the X-ray generator.

[0017] Step 6: Perform three-dimensional reconstruction on the obtained image data to complete the three-dimensional morphological characterization of the internal damage of the sample.

[0018] The present invention provides an in-situ transmission or diffraction experimental method based on neutrons, specifically comprising the following steps:

[0019] S1: First, assemble and connect all parts of the aforementioned experimental setup. Then, place the experimental setup on the neutron spectrometer sample stage. Adjust the installation position according to the neutron beam height. Use the laser positioning system to accurately locate the sample test position to ensure that the incident and diffracted neutron beams pass through the sample gauge length range. Calibrate the sample stage and the central axis of the experimental setup. Determine the test neutron wavelength range and neutron spectrometer operation mode experimental scheme according to the material, size, and experimental purpose of the sample to be tested. Due to the different experimental principles, the main body of the experimental setup needs to be placed horizontally and the experimental stage does not need to be rotated.

[0020] S2: Based on the experimental objective, determine the experimental load parameters, including vertical stress, torque, and phase difference; the radial load range is 0~5kN, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; the torsional servo motor output torque range is 0~5Nm, the torsional angle range is 0~90°, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; control the hydraulic actuator and the torsional servo motor respectively to convert the electrical signals into reciprocating vertical displacement and torsional angle output by the upper and lower connecting rods, and the actual loading stress measured and read by the load sensor and the angle sensor is transmitted to the sample to be loaded through the flanges of the upper and lower clamps respectively.

[0021] S3: After several cycles of loading, damage to the gauge length of the sample is observed on the external controller screen in the laboratory. The hydraulic actuator and torsional servo motor are controlled to stop loading and remain static so that the sample remains in a damaged state while ensuring that the damage features are clearly visible.

[0022] S4: Change the neutron diffraction or imaging mode according to the change of the angle between the incident slit and the signal receiver; when the angle between the incident slit and the signal receiver is 180 degrees, it is the transmission imaging mode, and when it is ±90 degrees, it is the diffraction mode. The angle difference applied to the reactor neutron source needs to be specifically calculated and analyzed based on the actual experimental wavelength and the selection of the diffraction crystal plane.

[0023] S5: Analyze neutron diffraction or transmission data to construct microstructure changes in the sample material, including stress-strain, texture, phase transition, or internal defects, in order to understand the relationship between microstructure changes and fatigue processes and reveal the damage mechanism.

[0024] The beneficial technical effects of this invention compared to the prior art are as follows:

[0025] 1. This invention discloses a multi-axis fatigue testing device for tension and torsion. The device has the advantages of being lightweight, compact in structure, having precise and controllable load, and being easy to disassemble. It meets the requirements of advanced light source experimental platforms for device weight, spatial dimensions, and installation location, and the experimental platform system has good compatibility.

[0026] 2. The structure of the device of the present invention is divided into three parts: upper, middle and lower. The upper and lower parts are supported by aluminum alloy plates to achieve stable mechanical load-bearing. The middle part is made of high yield strength acrylic material and aluminum alloy material to meet the requirements of high energy X-ray and neutron beam imaging, which effectively reduces the absorption loss of the material to X-rays and ensures the imaging quality.

[0027] 3. This invention uses V-shaped clamping blocks as clamping elements for cylindrical bar specimens. The specimen is clamped by the surface contact between the symmetrical plane of the V-groove and the cylindrical surface of the specimen. Two V-shaped clamping blocks are connected to wedge-shaped sliders by bolts, and the screw holes of the two wedge-shaped sliders have opposite rotational directions. Combined with the rotational movement of the threaded cylindrical bars with different rotational directions at both ends, clamping forces can be applied / unloaded simultaneously onto the specimen. For specimen positioning, the specimen is coaxially installed in a pre-set circular hole inside the wedge-shaped groove. The high-precision fit between the circular hole and the outer diameter of the specimen achieves dual precise constraint of the specimen in both the radial and axial directions. A pin-type connection scheme is used to achieve precise assembly between the fixture body and the wedge-shaped groove. The pin is made of hardened alloy steel, and its outer diameter is interference-fitted with the mating holes of the fixture body and the wedge-shaped groove, achieving gapless positioning of the connecting parts and ensuring the relative positional accuracy of the wedge-shaped groove and the fixture body.

[0028] 4. The vertical mechanical loading module of the device described in this invention uses a hydraulic actuator as the load driving element, and the torsional angle loading module uses a servo motor as the torque driving element. Both can simultaneously provide both static and dynamic loading modes, and can achieve synchronous / asynchronous operation. Real-time acquisition of vertical load and torsional angle is achieved through load sensors and angle sensors, and the acquired data is fed back to the control system terminal, realizing high-precision closed-loop control of vertical load and torsional angle.

[0029] 5. This invention features a dual-path control system, both inside and outside the experimental lead chamber. This dual control system allows for real-time monitoring of the initiation, propagation, and fracture of complex failure behaviors, such as fatigue crack initiation, propagation, and fracture, of the specimen's gauge length outside the experimental lead chamber. Remote control enables rapid pausing of mechanical loading, thereby ensuring the accuracy and reliability of the in-situ experimental results. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the tensile-torsional multiaxial fatigue experimental device based on synchrotron radiation and neutrons according to the present invention.

[0031] In the diagram: 1. Base; 2. Lower cavity; 3. Acrylic / aluminum alloy projection window; 4. Upper cavity; 5. Support rod; 6. Support plate; 7. Hydraulic actuator; 8. Upper connecting rod; 9. Load sensor; 10. Upper clamp; 11. Multiaxial fatigue specimen; 12. Lower clamp; 13. Angle sensor; 14. Lower connecting rod; 15. Torsional servo motor; 16. Motor controller; 17. Advanced light source receiver; 18. Advanced light source entrance slit.

[0032] Figure 2 This is a schematic diagram of the clamp structure of the present invention.

[0033] In the figure: 10a, V-shaped clamping block; 10b, right-hand threaded wedge block; 10c, round bar with threads at both ends in different directions; 10d, clamping body; 10e, wedge groove; 10f, pin; 10g, left-hand threaded wedge block.

[0034] Figure 3 This is a cross-sectional view of the sample and fixture structure.

[0035] Figure 4 This is a schematic diagram of a structure based on X-ray imaging.

[0036] Figure 5 This is a schematic diagram based on the principle of neutron transmission and diffraction structure. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0038] The present invention provides a tensile-torsional multiaxial fatigue testing device based on synchrotron radiation and neutrons, such as... Figure 1 As shown, it includes a base 1, a lower cavity 2, an acrylic / aluminum alloy projection window 3, an upper cavity 4, a support rod 5, a support plate 6, a hydraulic actuator 7, an upper connecting rod 8, a load sensor 9, an upper clamp 10, a multi-axis fatigue specimen 11, a lower clamp 12, an angle sensor 13, a lower connecting rod 14, a torsion servo motor 15, a motor controller 16, an advanced light source receiver 17, and an advanced light source entrance slit 18.

[0039] like Figure 1 As shown, the lower cavity 2 is bolted to the base 1. The torsional servo motor 15 is installed inside the lower cavity 2 and connected to the base 1. The torsional servo motor 15 is connected to the lower clamp 12 via the lower connecting rod 14. The angle sensor 13 is installed on the top of the lower connecting rod 14. The upper cavity 4 is connected to the support plate 6 via the support rod 5. The four support rods 5 are arranged in a circular array. Both the upper cavity 4 and the support plate 6 have circular mounting holes. The hydraulic actuator 7 is installed on the support plate 6. The hydraulic actuator 7 is connected to the upper clamp 10 via the upper connecting rod 8. The load sensor 9 is installed at the bottom of the upper connecting rod 8. The acrylic / aluminum alloy viewing window 3 is connected to the upper cavity 4 and the lower cavity 2 respectively. The three are installed coaxially in a cylindrical manner. An advanced light source entrance slit 18 and an advanced light source receiver 17 are located outside the platform. The acrylic / aluminum alloy viewing window is located on the light path of the advanced light source. The torsional servo motor 15 is connected to the motor controller 16.

[0040] Furthermore, such as Figure 2 As shown, the upper clamp 10 has the following specific structure: V-shaped clamping block 10a is connected to right-hand threaded wedge block 10b and left-hand threaded wedge block 10g respectively. The left-hand and right-hand threaded wedge blocks are respectively installed at both ends of threaded round bars 10c with different helix directions. The multiaxial fatigue specimen 11 is clamped by rotating the threaded round bars 10c with different helix directions. The threaded round bars 10c with different helix directions are installed in the through hole inside the wedge groove 10e. The wedge groove 10e is embedded in the inner cavity of the clamp body 10d. The two are assembled without clearance by interference fit of pin 10f.

[0041] The lower clamp 12 has the same structure as the upper clamp 10, and will not be described again. The multiaxial fatigue specimen 11 is held by the cooperation of the lower clamp 12 and the upper clamp 10, with the following effect: Figure 3 As shown.

[0042] The construction process of a tension-torsion multiaxial fatigue test apparatus based on synchrotron radiation and neutrons according to the present invention:

[0043] The lower cavity 2 is placed on the base 1, the acrylic / aluminum alloy projection window 3 is placed on the lower cavity 2, and the upper cavity 4 is placed on the acrylic / aluminum alloy projection window 3, and they are fixedly connected with screws. The torsional servo motor 15 is placed on the base 1 and fixedly connected with screws, and connected to the motor controller 16 with a flexible cable. The angle sensor 13 is connected to the torsional servo motor 15, and the lower connecting rod 14 passes through the angle sensor 13 and connects to the bottom surface of its top flange. The top of the angle sensor 13 is fixedly connected to the bottom of the lower clamp 12 with bolts. The top and bottom of the multiaxial fatigue specimen 11 are coaxially connected to the inner circular holes of the lower clamp 12 and the upper clamp 10 in sequence. The top of the upper clamp 10 is fixedly connected to the bottom of the upper connecting rod 8 with bolts. The load sensor 9 passes through the upper connecting rod 8 and connects to the top surface of its bottom flange. The upper connecting rod 8 is connected to the hydraulic actuator 7. The support plate 6 has a central hole and is connected to the upper cavity 4 through four circular array support rods 5 to support the hydraulic actuator 7. By adjusting the height of the base 1, the center height of the multiaxial fatigue specimen 11 is determined to be at the same height as the optical path between the entrance slit 18 and the advanced light source receiver 17. At this point, the experimental setup is complete.

[0044] The principle of the in-situ three-dimensional imaging experimental method based on X-rays of the present invention is as follows: Figure 4 As shown, the specific steps include:

[0045] Step 1: First, assemble and connect all parts of the aforementioned experimental setup. Then, place the experimental setup on the X-ray source sample stage. Adjust the installation position according to the X-ray height. Use the laser positioning system to accurately locate the sample test position, ensuring that the X-rays pass through the sample gauge length range. Calibrate the sample stage and the central axis of the experimental setup. Determine the imaging field of view and X-ray energy experimental parameters according to the material, size, and experimental purpose of the sample to be tested.

[0046] Step 2: Based on the experimental objective, determine the experimental load parameters, including vertical stress, torque, and phase difference; the radial load range is 0~5kN, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; the torque output range of the torsion servo motor is 0~5Nm, the torsion angle range is 0~90°, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; control the hydraulic actuator 7 and the torsion servo motor 15 respectively to convert the electrical signals into the reciprocating vertical displacement and torsion angle output by the upper and lower connecting rods, and measure and read the actual loading stress by the load sensor 9 and the angle sensor 13, and transfer it to the sample to be loaded through the flanges of the upper clamp 10 and the lower clamp 12.

[0047] Step 3: After several cycles of loading, damage to the gauge length of the sample is observed on the external controller screen in the laboratory. The hydraulic actuator 7 and the torsional servo motor 15 are then controlled to stop loading and remain static so that the sample remains in a damaged state while ensuring that the damage features are clearly visible.

[0048] Step 4: At this time, the X-ray generator is started. The X-ray passes through the entrance slit 18. The base 1 is controlled to rotate, which drives the experimental device to rotate 180° at a constant speed. During the rotation, the X-rays emitted by the X-ray generator and passing through the acrylic / aluminum viewing window 3 and the gauge length of the sample are received by the X-ray receiver 17, thereby acquiring image data.

[0049] Step 5: After completing the 180° imaging of the current damage state, restart the hydraulic actuator 7 and the torsion servo motor 15 to perform cyclic loading, repeat the operation of step 4 until the expected damage state is achieved, and then turn off the X-ray generator.

[0050] Step 6: Perform three-dimensional reconstruction on the obtained image data to complete the three-dimensional morphological characterization of the internal damage of the sample.

[0051] The principle of the in-situ transmission or diffraction experimental method based on neutrons of the present invention is as follows: Figure 5 As shown, the specific steps include:

[0052] S1: First, assemble and connect all parts of the aforementioned experimental setup. Then, place the experimental setup on the neutron spectrometer sample stage. Adjust the installation position according to the neutron beam height. Use the laser positioning system to accurately locate the sample test position to ensure that the incident and diffracted neutron beams pass through the sample gauge length range. Calibrate the sample stage and the central axis of the experimental setup. Determine the test neutron wavelength range and neutron spectrometer operation mode experimental scheme according to the material, size, and experimental purpose of the sample to be tested. Due to the different experimental principles, the main body of the experimental setup needs to be placed horizontally and the experimental stage does not need to be rotated.

[0053] S2: Based on the experimental objective, determine the experimental load parameters, including vertical stress, torque, and phase difference; the radial load range is 0~5kN, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; the torque output range of the torsion servo motor is 0~5Nm, the torsion angle range is 0~90°, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; control the hydraulic actuator 7 and the torsion servo motor 15 respectively to convert the electrical signals into the reciprocating vertical displacement and torsion angle output by the upper and lower connecting rods, and the actual loading stress measured and read by the load sensor 9 and the angle sensor 13 is transmitted to the sample to be loaded through the flanges of the upper clamp 10 and the lower clamp 12 respectively.

[0054] S3: After several cycles of loading, damage to the gauge length of the sample is observed on the external controller screen in the laboratory. The hydraulic actuator 7 and the torsional servo motor 15 are controlled to stop loading and remain static so that the sample remains in a damaged state while ensuring that the damage characteristics are clearly visible.

[0055] S4: Change the neutron diffraction or imaging mode according to the change of the angle between the incident slit 18 and the signal receiver 17; when the angle between the incident slit 18 and the signal receiver 17 is 180 degrees, it is the transmission imaging mode, and when it is ±90 degrees, it is the diffraction mode. The angle difference applied to the reactor neutron source needs to be specifically calculated and analyzed based on the actual experimental wavelength and the selection of the diffraction crystal plane.

[0056] S5: Analyze neutron diffraction or transmission data to construct microstructure changes in the sample material, including stress-strain, texture, phase transition, or internal defects, in order to understand the relationship between microstructure changes and fatigue processes and reveal the damage mechanism.

[0057] In summary, the experimental apparatus of this invention utilizes a mechanical loading mechanism composed of a hydraulic actuator and a torsional servo motor to achieve reciprocating lifting and cyclic torsional motion of the clamp, respectively. This apparatus possesses technical advantages such as lightweight design, compact structure, precise and controllable load, and convenient disassembly, meeting the requirements of advanced light source experimental platforms such as synchrotron radiation and neutron spectrometers regarding weight, spatial dimensions, and installation location. Synchrotron radiation X-rays and neutron beams can penetrate metal samples to characterize the macroscopic three-dimensional damage distribution and study the microstructure evolution and damage evolution process within the sample. The obtained material damage evolution information can quantitatively reveal the coupling effect of tensile and torsional load parameters (stress amplitude, phase difference, loading frequency, etc.) on the material's service performance, providing direct and reliable experimental data support for establishing multiaxial fatigue theoretical models, revealing material failure mechanisms, and fatigue-resistant design of engineering structures. This invention provides indispensable experimental methods and apparatus support for characterizing the damage evolution process and studying the failure mechanism of test samples under tensile and torsional multiaxial fatigue loading by combining synchrotron radiation and neutron characterization techniques.

Claims

1. A multiaxial tensile-torsional fatigue testing apparatus based on synchrotron radiation and neutrons, characterized in that, Includes a base (1), a lower cavity (2), an acrylic / aluminum alloy projection window (3), an upper cavity (4), a support rod (5), a support plate (6), a hydraulic actuator (7), an upper connecting rod (8), a load sensor (9), an upper clamp (10), a multi-axis fatigue specimen (11), a lower clamp (12), an angle sensor (13), a lower connecting rod (14), a torsion servo motor (15), a motor controller (16), an advanced light source receiver (17), and an advanced light source entrance slit (18); The lower cavity (2) is bolted to the base (1). The torsion servo motor (15) is installed inside the lower cavity (2) and connected to the base (1). The torsion servo motor (15) is connected to the lower clamp (12) via the lower connecting rod (14). The angle sensor (13) is installed on the top of the lower connecting rod (14). The upper cavity (4) is connected to the support plate (6) via support rods (5). The four support rods (5) are arranged in a circular array. Both the upper cavity (4) and the support plate (6) have circular mounting holes. The hydraulic actuator (7) is installed. On the support plate (6), the hydraulic actuator (7) is connected to the upper clamp (10) via the upper connecting rod (8), and the load sensor (9) is installed at the bottom of the upper connecting rod (8); the acrylic / aluminum alloy viewing window (3) is connected to the upper cavity (4) and the lower cavity (2) respectively, and the three are installed coaxially in a cylindrical manner. An advanced light source entrance slit (18) and an advanced light source receiver (17) are provided outside the platform, and the acrylic / aluminum alloy projection window is located on the light path of the advanced light source; the torsion servo motor (15) is connected to the motor controller (16).

2. The multiaxial fatigue testing apparatus based on synchrotron radiation and neutrons according to claim 1, characterized in that, The upper clamp (10) has the following specific structure: V-shaped clamping block (10a) is connected to right-hand threaded wedge block (10b) and left-hand threaded wedge block (10g) respectively. The left-hand and right-hand threaded wedge blocks are respectively installed at both ends of threaded round bars (10c) with different helix directions. The multiaxial fatigue specimen (11) is clamped by rotating the threaded round bars (10c) with different helix directions. The threaded round bars (10c) with different helix directions are installed in the through hole inside the wedge groove (10e). The wedge groove (10e) is embedded in the inner cavity of the clamp body (10d). The two are assembled without clearance by interference fit of pin (10f). The lower clamp (12) has the same structure as the upper clamp (10).

3. An in-situ three-dimensional imaging experimental method based on X-rays, characterized in that, The tensile-torsional multiaxial fatigue testing apparatus described in claim 1 specifically includes the following steps: Step 1: First, assemble and connect all parts of the experimental setup. Then, place the experimental setup on the X-ray source sample stage. Adjust the installation position according to the X-ray height. Use the laser positioning system to accurately position the sample test position to ensure that the X-ray passes through the sample gauge length range. Calibrate the sample stage and the central axis of the experimental setup. Determine the imaging field of view and X-ray energy experimental parameters according to the material, size and experimental purpose of the sample to be tested. Step 2: Based on the experimental objective, determine the experimental load loading parameters, including vertical stress, torque and phase difference; the radial load range is 0~5kN, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; the torque output range of the torsion servo motor is 0~5Nm, the torsion angle range is 0~90°, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; control the hydraulic actuator (7) and the torsion servo motor (15) respectively to convert the electrical signals into the reciprocating vertical displacement and torsion angle output by the upper and lower connecting rods, and measure and read the actual loading stress by the load sensor (9) and the angle sensor (13), and transfer it to the sample to be loaded through the flanges of the upper clamp (10) and the lower clamp (12); Step 3: After several cycles of loading, damage to the gauge length of the sample is observed on the external controller screen in the laboratory. The hydraulic actuator (7) and the torsional servo motor (15) are controlled to stop loading and remain static so that the sample remains in a damaged state while ensuring that the damage features are clearly visible. Step 4: At this time, the X-ray generator is started. The X-ray passes through the entrance slit (18). The control base (1) rotates to drive the experimental device to rotate at a constant speed of 180°. During the rotation, the X-ray receiver (17) receives the X-ray emitted by the X-ray generator and passes through the acrylic / aluminum viewing window (3) and the gauge length of the sample, thereby collecting image data. Step 5: After completing the 180° imaging of the current damage state, restart the hydraulic actuator (7) and the torsion servo motor (15) to perform cyclic loading, repeat the operation of step 4 until the expected damage state is achieved, and then turn off the X-ray generator; Step 6: Perform three-dimensional reconstruction on the obtained image data to complete the three-dimensional morphological characterization of the internal damage of the sample.

4. A neutron-based in-situ transmission or diffraction experimental method, characterized in that, The tensile-torsional multiaxial fatigue testing apparatus described in claim 1 specifically includes the following steps: S1: First, assemble and connect all parts of the experimental setup. Then, place the experimental setup on the neutron spectrometer sample stage. Adjust the installation position according to the neutron beam height. Use the laser positioning system to accurately locate the sample test position, ensuring that the incident and diffracted neutron beams pass through the sample gauge length range. Calibrate the sample stage and the central axis of the experimental setup. Determine the test neutron wavelength range and neutron spectrometer operation mode experimental scheme according to the material, size, and experimental purpose of the sample to be tested. Due to the different experimental principles, the main body of the experimental setup needs to be placed horizontally and the experimental stage does not need to be rotated. S2: Based on the experimental purpose, determine the experimental load loading parameters, including vertical stress, torque and phase difference; the radial load range is 0~5kN, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; the torque output range of the torsion servo motor is 0~5Nm, the torsion angle range is 0~90°, the loading frequency is 1~50Hz, and the stress ratio range is -1~0.99; control the hydraulic actuator (7) and the torsion servo motor (15) respectively to convert the electrical signals into the reciprocating vertical displacement and torsion angle output by the upper and lower connecting rods, and the actual loading stress measured and read by the load sensor (9) and the angle sensor (13) is transmitted to the sample to be loaded through the flanges of the upper clamp (10) and the lower clamp (12); S3: After several cycles of loading, damage to the gauge length of the sample is observed on the external controller screen of the laboratory. The hydraulic actuator (7) and the torsional servo motor (15) are controlled to stop loading and remain static so that the sample remains in a damaged state while ensuring that the damage features are clearly visible. S4: Change the neutron diffraction or imaging mode according to the angle between the incident slit (18) and the signal receiver (17); when the angle between the incident slit (18) and the signal receiver (17) is 180 degrees, it is the transmission imaging mode, and when it is ±90 degrees, it is the diffraction mode. The angle difference applied to the reactor neutron source needs to be specifically calculated and analyzed according to the actual experimental wavelength and the selection of the diffraction crystal plane. S5: Analyze neutron diffraction or transmission data to construct microstructure changes in the sample material, including stress-strain, texture, phase transition, or internal defects, in order to understand the relationship between microstructure changes and fatigue processes and reveal the damage mechanism.

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