A stress corrosion cracking fixture and method for applying complex stress conditions

Abstract

This invention discloses a stress corrosion cracking fixture for applying complex stress conditions, comprising a frame body, an adjustment knob assembly, a mechanical transmission mechanism, a pressing drive component, a fixture lowering component, a transmission link, and a positioning buckle. The adjustment knob assembly is located on one side of the frame body and is connected to the pressing drive component via the mechanical transmission mechanism. The lower part of the pressing drive component is connected to the fixture lowering component. One lowering side rod of the fixture lowering component is hinged to one end of the transmission link, and the other end of the transmission link is also hinged to the positioning buckle. This invention provides a loading mechanism that can independently and synchronously apply precise and controllable axial tensile and torsional loads to the sample, realistically simulating the combined stress state of a downhole tubing string.

Description

Technical Field

[0001] This invention relates to the field of metal corrosion simulation technology, and in particular to a stress corrosion cracking fixture and a stress corrosion cracking method for applying complex stress conditions. Background Technology

[0002] With the in-depth development of ultra-deep, high-temperature, and high-pressure oil and gas fields (well depths often exceeding 7000m), the downhole environment is becoming increasingly extreme and complex. As a key pressure-bearing and structural component, the well tubing is constantly subjected to a multi-axial composite stress field consisting of "axial tensile stress from the tubing string's own weight + torsional stress from drilling torque + bending stress from wellbore bending + pressure difference stress inside and outside the wellbore." Simultaneously, it is coupled with a highly corrosive environment of acidic gases such as CO2 and H2S, facing severe risks of stress corrosion cracking (SCC) and hydrogen-induced cracking (HIC). The synergistic effect of stress and corrosion has become a core challenge restricting the safe lifespan and reliability of ultra-deep wells.

[0003] Four-point bending stress corrosion testing is a common method for evaluating the performance degradation of materials under the combined action of stress and corrosive media. Its results directly affect the selection of oil well tubing materials—it is necessary to prevent downhole brittle fracture accidents due to underestimating sensitivity, and also to avoid huge cost waste due to overly conservative material selection. However, the traditional four-point bending test method has the following core limitations, failing to match the actual service conditions of oil well tubing: Distortion of stress state and load spectrum: This test can only generate pure bending stress in the middle of the sample. Although it can simulate the bending stress of wellbore bending, it cannot achieve the synergistic loading of tensile, torsional, and differential pressure stresses, which is fundamentally different from the distribution and interaction effects of the multiaxial composite stress field actually borne by the oil well tubing; moreover, it can only achieve uniaxial bending loads under static or slow strain rates, and cannot simulate the dynamic or static multiaxial loading conditions of "tension-torsion" composite downhole conditions. Limited evaluation system: Fracture criteria based on a single stress parameter (such as bending stress or strain) are insufficient to characterize the true failure threshold and crack propagation behavior of materials under multiaxial stress synergistic corrosion.

[0004] Therefore, existing technologies lack a suitable stress corrosion testing device and method for oil well tubing structures that can realistically simulate the multi-field coupling effects of tension-torsion-pressure difference in ultra-deep, high-temperature, and high-pressure oil and gas well environments. In particular, it is crucial to solve the key technical challenges of independent / synchronous precise loading of axial tension (or bending) and torsion in highly corrosive media environments, and the control of internal and external pressure differences in tubular samples. Developing such a device and establishing a matching multiaxial stress corrosion evaluation method is of urgent and significant engineering value for improving the scientific basis of oil well tubing material selection, ensuring the safety of ultra-deep wells throughout their entire lifecycle, and optimizing development costs.

[0005] Therefore, there is an urgent need for a stress corrosion cracking fixture that can be subjected to complex stress conditions. Summary of the Invention

[0006] This invention provides, on one hand, a stress corrosion cracking fixture for applying complex stress conditions, solving the technical problem that existing four-point bending stress corrosion testing devices can only simulate a single bending stress state and cannot realistically reproduce the coupling effect of multiaxial mechanical loads (tension-torsion-internal and external pressure difference) and strong corrosive environment on well tubing in ultra-deep, high-temperature, and high-pressure oil and gas wells. On the other hand, this invention provides a stress corrosion cracking method.

[0007] A first aspect of the present invention provides a stress corrosion cracking fixture for applying complex stress conditions, comprising a frame body, an adjustment knob assembly, a mechanical transmission mechanism, a pressing drive, a fixture lowering member, a transmission link, and a positioning buckle. The adjustment knob assembly is provided on one side of the frame body. The adjustment knob assembly is connected to the pressing drive through the mechanical transmission mechanism. The lower part of the pressing drive is connected to the fixture lowering member. One lowering side rod of the fixture lowering member is hinged to one end of the transmission link. The other end of the transmission link is also hinged to the positioning buckle. A fixing member is provided on the bottom surface of the frame body for fixing the end of the test piece. When the adjustment knob assembly is turned, the mechanical transmission mechanism drives the pressing drive to move, thereby pushing the clamping lower pressure member to move downward, so as to apply axial pressure to the workpiece. When the clamping lower pressure member generates axial displacement, the transmission link can rotate relative to the clamping lower pressure member, and the positioning buckle can generate rotational movement under the drive of the transmission link.

[0008] A stress corrosion cracking fixture subjected to complex stress conditions, preferably, the pressing drive component includes a housing and an input shaft, the housing is fixed to the frame body, the input shaft is provided inside the housing, and the input shaft is connected to the adjusting knob assembly through the mechanical transmission mechanism.

[0009] A stress corrosion cracking fixture subjected to complex stress conditions, preferably, includes an adjusting knob assembly comprising an external knob portion and a central rotating shaft. One end of the central rotating shaft is provided with the external knob portion. The central rotating shaft is coaxially rigidly connected to a driving gear, which meshes with a driven gear. The mechanical transmission mechanism is a bevel gear pair. The other end of the central rotating shaft is rigidly connected to the driving gear of the bevel gear pair. The driven gear of the bevel gear pair is rotatably disposed inside the housing. The outer surface of the input shaft and the inner surface of the driven gear of the bevel gear pair are both provided with threaded structures. The input shaft passes through the driven gear of the bevel gear pair, and the two are connected by the threaded structures.

[0010] A stress corrosion cracking fixture subjected to complex stress conditions, preferably, includes an adjusting knob assembly comprising an external knob portion and a central rotating shaft. The central rotating shaft is connected to the input end of a mechanical transmission mechanism, which is a worm gear and a worm. The central rotating shaft is rigidly connected coaxially to the worm, and the worm meshes with the worm gear. The worm gear is rotatably disposed inside the housing. Both the inner surface of the worm gear and the outer surface of the input shaft are provided with threaded structures. The input shaft passes through the interior of the worm gear, and the two are connected by the threaded structures.

[0011] A stress corrosion cracking fixture subjected to complex stress conditions, preferably, the fixture's pressing component includes a connecting platform, pressing side rods, pressing main rods, and a pressing head. The connecting platform is rigidly connected to the bottom of the input shaft of the pressing drive component. The pressing side rods are respectively provided on both sides of the bottom of the connecting platform, and the pressing main rod is provided at the center of the bottom of the connecting platform. The pressing head or an elastic buffer pad is provided at the bottom of both the pressing side rods and the pressing main rod.

[0012] A stress corrosion cracking fixture subjected to complex stress conditions, preferably, has a hinge structure comprising a first pin, a second pin, and a hinge lug. The first pin passes through one end of the transmission link and is connected to a pressing side rod of the fixture's pressing member. The second pin passes through the other end of the transmission link and is connected to the positioning buckle. The hinge lug is provided at both ends of the first pin and the second pin, and the two ends of the first pin and the second pin are rotatably disposed within the hinge lug.

[0013] A stress corrosion cracking fixture subjected to complex stress conditions, preferably, has a hinge structure comprising a first rotating pin, a second rotating pin, and a bearing seat. The first rotating pin passes through one end of the transmission link and is connected to a pressing side rod of the fixture's pressing member. The second rotating pin's pin shaft passes through the other end of the transmission link and is connected to the positioning buckle. The bearing seats are respectively provided at both ends of the first rotating pin and the second rotating pin, and the two ends of the first rotating pin and the second rotating pin are rotatably disposed within the bearing seats.

[0014] A stress corrosion cracking fixture subjected to complex stress conditions, preferably, has a positioning buckle with a clamping groove, a locking slot, and a clamping device. The clamping groove has a U-shaped / arc-shaped groove for accommodating the end of the workpiece under test. The locking slot is located at the opening end and edge of the clamping groove. The clamping device is located at the top of the clamping groove and passes through the clamping groove to limit and fix the end of the workpiece under test in the clamping groove.

[0015] A second aspect of the present invention provides a method for stress corrosion cracking, comprising a stress corrosion cracking fixture for applying complex stress conditions, specifically including the following steps: Before the test, the test piece is installed in the working position below the clamping part, and one end of the test piece is locked in place with the positioning buckle. After installation, the outer knob part of the adjustment knob assembly is rotated, and the central shaft of the adjustment knob assembly rotates accordingly. The rotational motion is transmitted to the input shaft of the pressing drive through the mechanical transmission mechanism. After receiving the rotary input from the adjustment knob, the pressing drive converts the rotary motion into vertical linear motion through the screw and nut mechanism. The pressing drive can drive the clamping lower pressing part to move along the main body of the frame. When the clamping component moves downward, the pressure head or elastic buffer pad at its bottom directly presses against the upper end of the workpiece, thereby applying axial pressure to the workpiece. At the same time, the vertical displacement of the clamping component will drive one end of the transmission link to move synchronously. Under the action of this vertical displacement, the transmission link will deflect around its hinge point, forming an angular displacement. The deflection of the transmission link will further drive the positioning buckle to generate a rotational motion. The positioning buckle clamps the end of the workpiece, and the rotational motion of the positioning buckle is transmitted to the workpiece, thereby applying a torsional torque to the workpiece.

[0016] The beneficial effects are: This invention uses a rotating adjustment knob to drive the pressing drive component, which pushes the clamping lower component downwards. Simultaneously, this causes the transmission linkage to deflect, applying a torsional torque to the workpiece through the positioning latch. At the same time, the clamping lower component applies an axial tensile force to the workpiece. Because the tensile and torque forces are controlled collaboratively by the same drive source, synchronous loading of tensile-torsional composite stress is achieved. This invention features a compact structure, simple operation, and controllable load, making it particularly suitable for testing the mechanical properties of metallic materials, fasteners, and other components under complex stress conditions. It possesses excellent practicality and potential for widespread application.

[0017] This invention has a loading mechanism that can independently and synchronously apply precise and controllable axial tensile and torsional loads to tubular samples to realistically simulate the combined stress state of downhole tubing. It obtains stress corrosion cracking (SCC) and hydrogen-induced cracking (HIC) sensitivity data that can directly guide engineering material selection, fundamentally improving the accuracy of ultra-deep well tubing material evaluation while taking into account both safety and economy. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention.

[0019] In the picture: 1. Main frame; 2. Adjustment knob assembly; 3. Pressing drive component; 3-1. Housing; 3-2. Input shaft; 4. Clamping lowering component; 4-1. Connecting platform; 4-2. Lowering side rod; 4-3. Lowering main rod; 5. Transmission connecting rod; 6. Positioning buckle; 6-1. Clamping groove. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the system or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the use of terms such as "first," "second," etc., to define components is merely for the convenience of distinguishing the aforementioned components; unless otherwise stated, these terms have no special meaning and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "setting," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] This invention provides a stress corrosion cracking fixture for applying complex stress conditions, comprising a frame body, an adjusting knob assembly, a mechanical transmission mechanism, a pressing drive component, a fixture lowering component, a transmission link, and a positioning buckle. The adjusting knob assembly is located on one side of the frame body and is connected to the pressing drive component via the mechanical transmission mechanism. The pressing drive component is connected to the fixture lowering component at its lower end. One lowering side rod of the fixture lowering component is hinged to one end of the transmission link, and the other end of the transmission link is also hinged to the positioning buckle. A fixing component is provided on the bottom surface of the frame body for fixing the end of the workpiece under test. When the adjusting knob assembly rotates, the mechanical transmission mechanism drives the pressing drive component, which in turn pushes the fixture lowering component downwards to apply axial pressure to the workpiece. When the fixture lowering component undergoes axial displacement, the transmission link rotates relative to the fixture lowering component, and the positioning buckle rotates under the drive of the transmission link. This invention has a loading mechanism that can independently and synchronously apply precise and controllable axial tensile loads and torsional loads to tubular samples to realistically simulate the combined stress state of downhole tubing. It obtains stress corrosion cracking and hydrogen-induced cracking sensitivity data that can directly guide the selection of materials for engineering projects, fundamentally improving the accuracy of evaluation of ultra-deep well tubing materials while taking into account both safety and economy.

[0024] The following section uses a stress corrosion cracking fixture subjected to complex stress conditions as an example to illustrate the entire technical process in detail.

[0025] Example 1 like Figure 1 As shown, a stress corrosion cracking fixture for applying complex stress conditions includes a frame body 1, an adjustment knob assembly, a mechanical transmission mechanism, a pressing drive 3, a fixture lower pressing component 4, a transmission link 5, and a positioning buckle 6. An adjustment knob assembly is provided on one side of the frame body 1. The adjustment knob assembly is connected to the pressing drive 3 through the mechanical transmission mechanism. The lower part of the pressing drive 3 is connected to the fixture lower pressing component 4. One lower pressing side rod of the fixture lower pressing component 4 is connected to one end of the transmission link 5 by a hinge structure. The other end of the transmission link 5 is also connected to the positioning buckle 6 by a hinge structure. A fixing component is provided on the bottom surface of the frame body 1 for fixing the end of the test piece. When the adjustment knob assembly turns, the mechanical transmission mechanism drives the pressing drive 3 to move, which in turn pushes the clamping lower pressure member 4 to move downward, so as to apply axial pressure to the workpiece. When the clamping lower pressure member 4 produces axial displacement, the transmission link 5 can rotate relative to the clamping lower pressure member 4, and the positioning buckle 6 can rotate under the drive of the transmission link 5.

[0026] The pressing drive component 3 includes a housing 3-1 and an input shaft 3-2. The housing 3-1 is fixed on the frame body 1. The input shaft 3-2 is located inside the housing 3-1. The input shaft 3-2 is connected to the adjustment knob assembly through a mechanical transmission mechanism.

[0027] The adjustment knob assembly includes an external knob part 2 and a central rotating shaft. One end of the central rotating shaft is provided with the external knob part 2. The central rotating shaft is rigidly connected to the driving gear on the same axis. The driving gear meshes with the driven gear. The mechanical transmission mechanism is a bevel gear pair. The other end of the central rotating shaft is rigidly connected to the driving gear of the bevel gear pair. The driven gear of the bevel gear pair is rotatably set inside the housing 3-1. The outer surface of the input shaft 3-2 and the inner surface of the driven gear of the bevel gear pair are both provided with threaded structures. The input shaft 3-2 passes through the driven gear of the bevel gear pair and the two are connected by the threaded structure.

[0028] The adjustment knob assembly includes an external knob part 2 and a central rotating shaft. The central rotating shaft is connected to the input end of a mechanical transmission mechanism, which consists of a worm gear and a worm. The central rotating shaft of the adjustment knob 2 is rigidly connected to the worm gear on the same axis. The worm gear meshes with the worm wheel. The worm wheel is rotatably disposed inside the housing 3-1. Both the inner surface of the worm wheel and the outer surface of the input shaft 3-2 are provided with threaded structures. The input shaft 3-2 passes through the interior of the worm wheel, and the two are connected by the threaded structure.

[0029] The external knob 2 is a knurled disc structure, which allows the operator to manually apply force to rotate it.

[0030] The clamping lowering component 4 includes a connecting platform 4-1, a lowering side rod 4-2, a lowering main rod 4-3, and a pressure head 4-4. The connecting platform 4-1 is rigidly connected to the bottom of the input shaft of the pressing drive component 3. Lowering side rods 4-2 are respectively provided on both sides of the bottom of the connecting platform 4-1, and the lowering main rod 4-3 is located at the center of the bottom of the connecting platform 4-1. Both the lowering side rods 4-2 and the lowering main rod 4-3 have pressure heads or elastic buffer pads at their bottoms. The pressure heads or elastic buffer pads are used to directly press against the upper end face of the workpiece under test, thereby applying axial pressure to the workpiece. The elastic buffer pads can improve the contact uniformity between the clamping lowering component 4 and the workpiece under test, reduce local stress concentration, and prevent non-experimental damage to the surface of the workpiece under test during loading.

[0031] The hinge structure includes a first pin, a second pin, and a hinge lug. The first pin passes through one end of the transmission link 5 and is connected to a pressing side rod of the clamp pressing member 4. The second pin passes through the other end of the transmission link 5 and is connected to the positioning buckle 6. The two ends of the first pin and the second pin are respectively provided with hinge lugs. The two ends of the first pin and the second pin are rotatably set in the hinge lugs.

[0032] The hinge structure includes a first rotating pin, a second rotating pin, and a bearing seat. The first rotating pin passes through one end of the transmission link 5 and is connected to a pressing side rod of the clamp pressing member 4. The pin shaft of the second rotating pin passes through the other end of the transmission link 5 and is connected to the positioning buckle 6. Bearing seats are provided at both ends of the first rotating pin and the second rotating pin. The two ends of the first rotating pin and the second rotating pin are rotatably set in the bearing seats.

[0033] The positioning buckle 6 is provided with a clamping groove 6-1, a bayonet, and a clamping device. The clamping groove 6-1 has a U-shaped / arc-shaped groove to accommodate the end of the workpiece being measured. The bayonet is located at the opening end and edge of the clamping groove 6-1. The clamping device is located at the top of the clamping groove 6-1 and passes through the clamping groove 6-1 to limit and fix the end of the workpiece being measured within the clamping groove 6-1. The clamping device is a clamping screw or a clamping block structure.

[0034] The tested components are metal rods, tubular components, or fasteners.

[0035] The working process of the device of the present invention is as follows: Before the test, the test piece is installed on the fixing piece below the clamping part 4, and one end of the test piece is locked in place with the positioning buckle 6. After installation, the operator rotates the adjustment knob 2. The central shaft of the adjustment knob 2 rotates accordingly, and the rotational motion is transmitted to the input end of the pressing drive 3 through a gear transmission pair or worm gear mechanism.

[0036] After receiving the rotary input from the adjustment knob 2, the pressing drive 3 converts the rotary motion into vertical linear motion through the lead screw and nut mechanism. Since the output end of the pressing drive 3 is rigidly connected to the clamping lower pressure member 4, the pressing drive 3 can drive the clamping lower pressure member 4 to move along the frame body 1 when it is in motion.

[0037] When the clamping lower member 4 moves downward, the pressure head or elastic buffer pad at its bottom directly presses against the upper end of the workpiece, thereby applying axial pressure to the workpiece. Simultaneously, since one end of the transmission link 5 is hinged to the clamping lower member 4, the vertical displacement of the clamping lower member 4 will cause one end of the transmission link 5 to move synchronously. Under the action of this vertical displacement, the transmission link 5 deflects around its hinge point, forming an angular displacement.

[0038] The other end of the transmission link 5 is hinged to the positioning buckle 6, so the deflection of the transmission link 5 will further drive the positioning buckle 6 to rotate. Since the positioning buckle 6 clamps the end of the workpiece, the rotational motion of the positioning buckle 6 is transmitted to the workpiece, thereby applying a torsional torque to the workpiece.

[0039] Therefore, the rotation of the adjusting knob 2-1 determines, on the one hand, the output stroke of the pressing drive 3, which in turn determines the axial pressure applied to the test piece by the clamping lowering component 4; on the other hand, the pressing stroke of the clamping lowering component 4 determines the deflection angle of the transmission link 5, which in turn drives the positioning latch 6 to rotate, thus determining the torsional torque on the test piece. Therefore, axial pressure and torsional torque can be applied synchronously through the same adjusting knob 2-1, allowing the test piece to bear both axial and torsional loads simultaneously, thereby enabling stress corrosion cracking testing under complex stress conditions.

[0040] Example 2 A stress corrosion cracking method, specifically including a stress corrosion cracking fixture subjected to complex stress conditions as described in Example 1, specifically includes the following steps: S1: Before the test, the test piece is installed in the working position below the clamping part 4, and one end of the test piece is locked with the positioning buckle 6. After installation, the outer knob part 2 of the adjustment knob assembly is rotated, and the central shaft of the adjustment knob assembly rotates accordingly. The rotational motion is transmitted to the input shaft 3-2 of the pressing drive part 3 through the mechanical transmission mechanism. S2: After receiving the rotational input from the adjustment knob 2, the pressing drive 3 converts the rotational motion into a vertical linear motion through the screw and nut mechanism. The pressing drive 3 can drive the clamping lower pressing part 4 to move downward along the guide hole, guide column or slide rail on the frame body 1. S3: When the clamping lower pressure member 4 moves downward, the pressure head or elastic buffer pad at its bottom directly presses against the upper end of the workpiece, thereby applying axial pressure to the workpiece. At the same time, the vertical displacement of the clamping lower pressure member 4 will drive one end of the transmission link 5 to move synchronously. Under the action of this vertical displacement, the transmission link 5 deflects around its hinge point, forming an angular displacement. The deflection of the transmission link 5 will further drive the positioning buckle 6 to generate a rotational motion. The positioning buckle 6 clamps the end of the workpiece, and the rotational motion of the positioning buckle 6 is transmitted to the workpiece, thereby applying a torsional torque to the workpiece.

[0041] 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A stress corrosion cracking fixture subjected to complex stress conditions, characterized in that, The device includes a frame body (1), an adjustment knob assembly, a mechanical transmission mechanism, a pressing drive (3), a clamping lower pressure member (4), a transmission link (5), and a positioning buckle (6). The adjustment knob assembly is provided on one side of the frame body (1). The adjustment knob assembly is connected to the pressing drive (3) through the mechanical transmission mechanism. The lower part of the pressing drive (3) is connected to the clamping lower pressure member (4). One pressing side rod of the clamping lower pressure member (4) is connected to one end of the transmission link (5) by a hinge structure. The other end of the transmission link (5) is also connected to the positioning buckle (6) by a hinge structure. A fixing member is provided on the bottom surface of the frame body (1) for fixing the end of the test piece. When the adjustment knob assembly turns, the mechanical transmission mechanism drives the pressing drive (3) to move, thereby pushing the clamping lower pressure member (4) to move downward, so as to apply axial pressure to the test piece. When the clamping lower pressure member (4) generates axial displacement, the transmission link (5) can rotate relative to the clamping lower pressure member (4), and the positioning buckle (6) can generate rotational movement under the drive of the transmission link (5).

2. The stress corrosion cracking fixture under complex stress conditions according to claim 1, characterized in that, The pressing drive (3) includes a housing (3-1) and an input shaft (3-2). The housing (3-1) is fixed on the frame body (1). The input shaft (3-2) is provided inside the housing (3-1). The input shaft (3-2) is connected to the adjustment knob assembly through the mechanical transmission mechanism.

3. The stress corrosion cracking fixture under complex stress conditions according to claim 2, characterized in that, The adjustment knob assembly includes an external knob part (2) and a central rotating shaft. One end of the central rotating shaft is provided with the external knob part (2). The central rotating shaft is coaxially rigidly connected to the driving gear. The driving gear meshes with the driven gear. The mechanical transmission mechanism is a bevel gear pair. The other end of the central rotating shaft is rigidly connected to the driving gear of the bevel gear pair. The driven gear of the bevel gear pair is rotatably disposed inside the housing (3-1). The outer surface of the input shaft (3-2) and the inner surface of the driven gear of the bevel gear pair are both provided with threaded structures. The input shaft (3-2) passes through the driven gear of the bevel gear pair and the two are connected by the threaded structure.

4. The stress corrosion cracking fixture under complex stress conditions according to claim 2, characterized in that, The adjustment knob assembly includes an external knob part (2) and a central rotating shaft. The central rotating shaft is connected to the input end of the mechanical transmission mechanism. The mechanical transmission mechanism is a worm gear and a worm. The central rotating shaft is rigidly connected to the worm coaxially. The worm meshes with the worm gear. The worm gear is rotatably disposed inside the housing (3-1). The inner surface of the worm gear and the outer surface of the input shaft (3-2) are both provided with threaded structures. The input shaft (3-2) passes through the interior of the worm gear and the two are connected by the threaded structure.

5. The stress corrosion cracking fixture under complex stress conditions according to claim 3 or 4, characterized in that, The clamp pressing component (4) includes a connecting platform (4-1), a pressing side rod (4-2), a pressing main rod (4-3), and a pressing head (4-4). The connecting platform (4-1) is rigidly connected to the bottom of the input shaft of the pressing drive component (3). The pressing side rod (4-2) is provided on both sides of the bottom of the connecting platform (4-1). The pressing main rod (4-3) is provided at the center of the bottom of the connecting platform (4-1). The pressing head or elastic buffer pad is provided at the bottom of both the pressing side rod (4-2) and the pressing main rod (4-3).

6. The stress corrosion cracking fixture under complex stress conditions according to claim 5, characterized in that, The hinge structure includes a first pin, a second pin, and a hinge lug. The first pin passes through one end of the transmission link (5) and is connected to a pressing side rod of the clamp pressing member (4). The second pin passes through the other end of the transmission link (5) and is connected to the positioning buckle (6). The hinge lug is provided at both ends of the first pin and the second pin. The two ends of the first pin and the second pin are rotatably disposed in the hinge lug.

7. The stress corrosion cracking fixture under complex stress conditions according to claim 5, characterized in that, The hinge structure includes a first rotating pin, a second rotating pin, and a bearing seat. The first rotating pin passes through one end of the transmission link (5) and is connected to a pressing side rod of the clamp pressing member (4). The pin shaft of the second rotating pin passes through the other end of the transmission link (5) and is connected to the positioning buckle (6). The bearing seats are respectively provided at both ends of the first rotating pin and the second rotating pin. The two ends of the first rotating pin and the second rotating pin are rotatably disposed in the bearing seats.

8. The stress corrosion cracking fixture under complex stress conditions according to claim 5, characterized in that, The positioning buckle (6) is provided with a clamping groove (6-1), a bayonet, and a pressing device. The clamping groove (6-1) is provided with a U-shaped / arc groove to accommodate the end of the workpiece to be measured. The bayonet is located at the opening end and edge of the clamping groove (6-1). The pressing device is located at the top of the clamping groove (6-1) and passes through the clamping groove (6-1) to limit and fix the end of the workpiece to be measured in the clamping groove (6-1).

9. A method for stress corrosion cracking, characterized in that, The stress corrosion cracking fixture according to any one of claims 1 to 8, subjected to complex stress conditions, specifically includes the following steps: Before the test, the test piece is installed in the working position below the clamping part (4) and one end of the test piece is locked with the positioning buckle (6). After installation, the outer knob part (2-1) of the adjustment knob assembly is rotated, and the central shaft of the adjustment knob assembly rotates accordingly. The rotational motion is transmitted to the input shaft (3-2) of the pressing drive part (3) through the mechanical transmission mechanism. After receiving the rotational input from the adjustment knob (2), the pressing drive (3) converts the rotational motion into a linear motion in the vertical direction through the screw and nut mechanism. The pressing drive (3) can drive the clamping lower pressing part (4) to move along the frame body (1). When the clamping lower part (4) moves downward, the pressure head or elastic buffer pad at its bottom directly presses the upper end of the workpiece to be measured, thereby applying axial pressure to the workpiece. At the same time, the vertical displacement of the clamping lower part (4) will drive one end of the transmission link (5) to move synchronously. Under the action of this vertical displacement, the transmission link (5) deflects around its hinge point, forming an angular displacement. The deflection of the transmission link (5) will further drive the positioning buckle (6) to generate a rotational motion. The positioning buckle (6) clamps the end of the workpiece to be measured. The rotational motion of the positioning buckle (6) is transmitted to the workpiece to be measured, thereby applying a torsional torque to the workpiece to be measured.

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