Low friction constant displacement loading mechanism for wedge open loading of specimens

Abstract

The application provides a low-friction constant displacement loading mechanism for wedge opening loading samples, which is used for wedge opening loading samples, and a prefabricated crack is arranged on the wedge opening loading sample; a loading hole and a threaded hole are respectively arranged on both sides of the loading arm on the upper part of the prefabricated crack; the loading hole penetrates through the thickness direction of the wedge opening loading sample; the axis of the threaded hole is perpendicular to the axis of the loading hole; the threaded hole is in communication with the loading hole; the loading mechanism comprises a bolt and a loading assembly; the loading assembly is arranged in the loading hole; the loading assembly comprises a bearing block, a thrust ball bearing and a pressure pad; the race of the thrust ball bearing is connected with the bearing block; the pressure pad is connected with the shaft ring of the thrust ball bearing; and the bolt is connected with the pressure pad after penetrating through the threaded hole. Through the cooperation of the thrust ball bearing and the pressure pad in the loading structure, the main friction form during loading is changed from sliding friction to rolling friction, the resistance during screwing is greatly reduced, and the problem that the traditional loading mechanism cannot be screwed is solved.

Description

Technical Field

[0001] This invention relates to the field of material mechanical property testing technology, and more specifically, to a low-friction constant displacement loading mechanism for wedge-shaped opening loading specimens. Background Technology

[0002] In the field of materials fracture mechanics and environmental failure research, wedge-shaped open-loaded specimens (WOL) are widely used to determine the stress corrosion critical stress intensity factor (KISCC) and crack propagation rate of materials due to their ability to achieve constant displacement loading through self-tightening.

[0003] The traditional loading method uses side bolts to be directly screwed on, and the semi-circular loading block is pushed by the bolt end face to cause the crack in the sample to open. This traditional method has significant defects: (1) There is a large rotational sliding friction between the bolt end face and the loading block plane, and the threaded pair also has the problem of sliding friction. As the loading process progresses, the frictional resistance increases sharply, which not only makes the operation extremely laborious, but also makes it difficult to achieve precise load control; (2) The bolt has to withstand excessively high torsional and shear stress during the loading process, which is very easy to cause brittle fracture, seriously reducing the success rate of the experiment and the safety of operation; (3) In a corrosive environment, the metal parts of the traditional loading mechanism are directly exposed to the corrosive medium, which is prone to rust and jamming. At the same time, the contact between the metal parts will form galvanic corrosion, which will interfere with the experimental results.

[0004] Chinese patent CN204789086U discloses a test specimen for stress corrosion cracking at the crack tip with a constant displacement load loading device. The specimen includes a specimen body, a crack opening displacement load loading device, and an insulating rubber pad. A trapezoidal notch is located at the top center of the specimen body. Two pre-fabricated fatigue crack preparation loading holes are located on either side of the trapezoidal notch on the upper part of the specimen body. A fatigue crack pre-fabricated notch and a pre-fabricated fatigue crack are located in the middle of the specimen body. The crack opening displacement load loading device includes an expansion sleeve and a bolt. The upper part of the expansion sleeve is a cuboid connecting block, and the lower part consists of a left connecting plate and a right connecting plate arranged in a V-shape. The bolt consists of an integrally formed trapezoidal bolt head, a smooth rod, and a threaded rod. The trapezoidal bolt head is engaged within the expansion sleeve. This patent has a simple structure, is easy to implement, and has a low cost, thus improving testing efficiency to a certain extent. However, significant rotational sliding friction also exists between the trapezoidal bolt head and the expansion sleeve. As the loading process progresses, the frictional resistance increases dramatically, making operation extremely laborious and difficult to achieve precise load control. Furthermore, the smooth rod and screw must withstand excessively high torsional and shear stresses during loading, making them highly susceptible to brittle fracture, severely reducing the success rate of experiments and operational safety. Currently, there is a lack of integrated loading solutions in existing technologies that can simultaneously achieve low-friction, precise loading, high structural reliability, and adaptability to harsh corrosive environments. Summary of the Invention

[0005] The problem solved by this invention is that the prior art lacks a loading structure for a wedge-shaped opening loading specimen that can simultaneously achieve low-friction precise loading, high structural reliability, and adaptability to harsh corrosive environments.

[0006] This invention discloses a low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen. The wedge-shaped opening loading specimen has a pre-formed crack. Loading holes and threaded holes are respectively provided on loading arms on both sides of the upper part of the pre-formed crack. The loading hole penetrates the thickness direction of the wedge-shaped opening loading specimen. The axis of the threaded hole is perpendicular to the axis of the loading hole and extends from the side of the wedge-shaped opening loading specimen towards the loading hole, communicating with the loading hole. The loading mechanism includes a bolt and a loading assembly. The loading assembly is disposed in the loading hole and includes a bearing block, a thrust ball bearing, and a pressure pad. The seat ring of the thrust ball bearing is connected to the bearing block, and the pressure pad is connected to the shaft ring of the thrust ball bearing. The bolt passes through the threaded hole and connects to the pressure pad, for applying axial thrust to the loading assembly.

[0007] Furthermore, the bearing block is a cylindrical body with a semi-circular cross-section, with a flat surface on the side facing the bolt and an arc surface on the side away from the bolt, and the shape of the loading hole is adapted to the bearing block.

[0008] Furthermore, a bearing seat is provided on the plane of the bearing block. The bearing seat has a groove structure, which is recessed towards the side away from the bolt. The thrust ball bearing and pressure pad are disposed in the bearing seat.

[0009] Furthermore, plug-in connection structures are respectively provided between the bolt and the pressure pad, between the seat ring of the thrust ball bearing and the bearing seat, and between the shaft ring of the thrust ball bearing and the pressure pad, and the plug-in connection structures are interference fit connections.

[0010] Furthermore, a crosshead is provided at the end of the bolt, and a cross groove is correspondingly provided on the pressure pad, with the crosshead and the cross groove being interference-fitted.

[0011] Furthermore, a plurality of race retaining strips are provided on the outer periphery of the race of the thrust ball bearing, and a plurality of race retaining grooves are correspondingly provided on the side wall of the bearing seat, wherein the race retaining strips and race retaining grooves are interference-fitted together.

[0012] Furthermore, a plurality of ring retaining strips are provided on the ring of the thrust ball bearing, and a plurality of ring retaining grooves are correspondingly provided on the pressure pad, wherein the ring retaining strips and the ring retaining grooves are interference-fitted together.

[0013] Furthermore, the bolt is provided with a trapezoidal thread, and the threaded hole is a trapezoidal threaded hole, which is used to mate with the trapezoidal threaded hole for connection.

[0014] Furthermore, the surface of the trapezoidal thread is coated with anti-seize grease.

[0015] Furthermore, the surfaces of the bearing block, thrust ball bearing, pressure pad, and bolts are all coated with an anti-corrosion and insulating coating, which is a polyether ether ketone coating.

[0016] Compared with the prior art, the low-friction constant displacement loading mechanism for wedge-shaped opening loading specimens described in this invention has the following advantages:

[0017] 1) By combining the thrust ball bearing and pressure pad in the loading structure, this invention changes the main friction mode during loading from sliding friction to rolling friction, reducing the turning resistance by more than 90%, and making the operation smooth and light, thus completely solving the problem of "cannot be turned" in the traditional loading method.

[0018] 2) The load application process is smooth and continuous, the relationship between torque and axial force is linear, and the initial stress (KI initial value) can be precisely controlled. The stress state of the bolt is optimized, the risk of fracture is greatly reduced, and the loading accuracy and safety are significantly improved.

[0019] 3) The PEEK coating effectively protects precision bearings and threaded pairs from corrosive media, eliminates the problem of jamming failure caused by component corrosion, and avoids interference from electrochemical sensitive tests caused by galvanic cells formed by metal contact, ensuring load stability and data reliability in long-term tests of thousands of hours, demonstrating excellent environmental adaptability.

[0020] 4) The modular design of the loading device allows the core bearing assembly to be replaced as a whole, making maintenance simple and convenient, and improving the standardization and maintainability of the loading mechanism;

[0021] The loading mechanism provided by this invention offers a high-performance, high-reliability standardized loading solution for WOL sample testing, significantly improving experimental efficiency and success rate. Attached Figure Description

[0022] Figure 1 This is an exploded structural diagram of the wedge-shaped opening loading specimen and the loading mechanism described in an embodiment of the present invention;

[0023] Figure 2 This is an exploded view of the loading component described in an embodiment of the present invention;

[0024] Figure 3 This is an exploded view of the loading component from another angle according to an embodiment of the present invention;

[0025] Figure 4 This is an exploded structural diagram of the thrust ball bearing described in an embodiment of the present invention;

[0026] Figure 5 This is an exploded structural diagram of the thrust ball bearing described in an embodiment of the present invention from another angle.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1. Wedge-shaped opening loading specimen; 2. Loading assembly; 3. Bolt; 4. Trapezoidal thread; 5. Crosshead; 6. Loading hole; 7. Threaded hole; 8. Bearing block; 9. Bearing seat; 10. Seat ring groove; 11. Thrust ball bearing; 12. Pressure pad; 13. Cross groove; 14. Shaft ring groove; 15. Seat ring; 16. Seat ring retainer; 17. Slide rail; 18. Rolling element; 19. Cage; 20. Steel ball; 21. Shaft ring; 22. Shaft ring retainer. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the described embodiments are only some, not all, of the embodiments of this invention. The specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0030] The following describes in detail, with reference to the accompanying drawings, a low-friction constant displacement loading mechanism for a wedge-shaped opening loading specimen according to an embodiment of the present invention.

[0031] This embodiment provides a low-friction constant-displacement loading mechanism for wedge-shaped opening loading specimens, such as... Figures 1-5 As shown, a wedge-shaped opening loading specimen 1 is used. A pre-fabricated crack is provided on the wedge-shaped opening loading specimen 1. Loading holes 6 and threaded holes 7 are respectively provided on the loading arms on both sides of the upper part of the pre-fabricated crack. The loading hole 6 penetrates the thickness direction of the wedge-shaped opening loading specimen 1. The axis of the threaded hole 7 is perpendicular to the axis of the loading hole 6. The threaded hole 7 extends from the side of the wedge-shaped opening loading specimen 1 towards the loading hole 6 and communicates with the loading hole 6. The loading mechanism includes a bolt 3 and a loading assembly 2. The loading assembly 2 is disposed in the loading hole 6. The loading assembly 2 includes a bearing block 8, a thrust ball bearing 11, and a pressure pad 12. The seat ring 15 of the thrust ball bearing 11 is connected to the bearing block 8. The pressure pad 12 is connected to the shaft ring 21 of the thrust ball bearing 11. The bolt 3 passes through the threaded hole 7 and is connected to the pressure pad 12 to apply axial thrust to the loading assembly 2.

[0032] Specifically, such as Figure 1 As shown, the loading hole 6 is located on one side of the pre-existing crack in the wedge-shaped opening loading specimen 1, and the loading hole 6 penetrates the thickness of the wedge-shaped opening loading specimen 1. The threaded hole 7 is located on the other side of the wedge-shaped opening loading specimen 1, and the axis of the threaded hole 7 is perpendicular to the axis of the loading hole 6. Specifically, the threaded hole 7 extends in the left-right direction (with...). Figure 1 (The left and right directions are consistent). Accordingly, the loading hole 6 extends in the front-to-back direction, and the threaded hole 7 extends from the right side wall of the wedge-shaped open loading sample 1 to the left and finally communicates with the loading hole 6. Preferably, the axis of the loading hole 6 and the axis of the threaded hole 7 are on the same horizontal plane, and the axis of the thrust ball bearing 11 coincides with the axis of the threaded hole 7. This arrangement facilitates the uniformity of loading of the bolt 3 and avoids the distortion of the stress field at the crack tip caused by eccentric loading, thereby ensuring the loading stability of the loading mechanism. Specifically, the shape of the loading hole 6 is adapted to the shape of the bearing block 8 so that the bearing block 8 can be stably placed in the loading hole 6.

[0033] In this example, the arrangement of the loading hole 6 and the threaded hole 7 provides a precise positioning basis and a compact spatial layout for the loading mechanism. The bearing block 8, as the force-bearing end, is located in the loading hole 6 and is used to apply the force it bears to the inner wall of the loading hole 6. The seat ring 15 of the thrust ball bearing 11 is connected to the bearing block 8, and the pressure pad 12 is connected to the shaft ring 21 of the thrust ball bearing 11. The arrangement of the bolt 3 passing through the threaded hole 7 and connecting to the pressure pad 12 ensures that when the bolt 3 is screwed toward the bearing block 8, the axial thrust of the bolt 3 directly acts on the pressure pad 12. The perpendicular arrangement of the threaded hole 7 and the loading hole 6 ensures that the axis of the bolt 3 is collinear with the force direction of the bearing block 8, avoiding stress field distortion at the crack tip due to off-center loading. The pressure pad 12 efficiently transmits the axial thrust to the thrust ball bearing 11 through the shaft ring 21, and the thrust ball bearing 11 transmits the axial thrust to the bearing block 8. Finally, the bearing block 8 pushes the inner wall of the loading hole 6 to open the pre-existing crack. During this process, the shaft ring 21 in the thrust ball bearing 11 rotates synchronously with the bolt 3 and the pressure pad 12, while the seat ring 15 and the bearing block 8 remain stationary. The rolling element 18 rolls in the slide, which transforms the rotational sliding friction between the end face of the bolt 3 and the loading block in the traditional loading method into rolling friction, reducing the frictional resistance by more than 90%. This fundamentally solves the technical problem that the loading mechanism of the traditional wedge-shaped opening loading sample 1 is difficult to operate and has difficulty in ensuring loading accuracy due to excessive sliding friction.

[0034] As one optional example, the bearing block 8 is a cylindrical body with a semi-circular cross-section. The side of the bearing block 8 facing the bolt 3 is a flat surface, while the side facing away from the bolt 3 is an arc surface. The shape of the loading hole 6 is adapted to the bearing block 8. The semi-circular cylindrical body refers to a cross-sectional arc angle greater than 180°. The specific arc angle is preferably such that a groove structure capable of accommodating the thrust ball bearing 11 and the pressure pad 12 can be provided on the flat surface of the bearing block 8; this is not further limited here. The flat surface of the bearing block 8 is used for bearing, and the arc surface fits into the inner wall of the loading hole 6, so that the bearing block 8 and the loading hole 6 form a large area of ​​surface contact. This facilitates a more even distribution of the axial thrust transmitted by the bolt 3 on the contact surface between the loading hole 6 and the bearing block 8, avoiding local stress concentration that could cause plastic deformation or damage to the loading hole 6, thereby protecting the integrity of the sample. In addition, the semi-circular cross-section design allows the bearing block 8 to have good positioning and guiding effects within the loading hole 6, ensuring that the thrust direction is always perpendicular to the crack surface of the pre-existing crack, avoiding distortion of the stress field at the crack tip due to eccentric loading, and ensuring the accuracy of the test.

[0035] Preferably, a bearing seat 9 is provided on the plane of the bearing block 8. The bearing seat 9 has a groove structure, which is recessed towards the side away from the bolt 3. The thrust ball bearing 11 and pressure pad 12 are disposed in the bearing seat 9. Optionally, the groove structure is a rectangular cavity structure. Preferably, when the thrust ball bearing 11 and pressure pad 12 are disposed in the bearing seat 9, the end face of the pressure pad 12 near the bolt 3 is flush with the plane of the bearing block 8, or recessed towards the side away from the bolt 3 relative to the plane. This arrangement facilitates the placement of the bearing block 8, thrust ball bearing 11, and pressure pad 12 in the loading hole 6 after initial assembly, without interference with the loading hole 6, ensuring smooth assembly of the loading mechanism. In this example, the bearing seat 9 provides a precise installation and positioning space for the thrust ball bearing 11 and pressure pad 12 on the bearing block 8, ensuring that the thrust ball bearing 11 is in a centered position when bearing axial loads, preventing wear of the thrust ball bearing 11 due to radial offset. Furthermore, placing the thrust ball bearing 11 and pressure pad 12 in the bearing seat 9 makes the structure of the loading assembly 2 more compact, facilitating the miniaturization design of the loading mechanism. In addition, the groove structure of the bearing seat 9 provides a certain degree of protection for the thrust ball bearing 11 and pressure pad 12, reducing the direct erosion of the component by corrosive media and improving the durability of the loading assembly 2.

[0036] Optionally, plug-in connection structures are provided between the bolt 3 and the pressure pad 12, between the seat ring 15 of the thrust ball bearing 11 and the bearing seat 9, and between the shaft ring 21 of the thrust ball bearing 11 and the pressure pad 12, respectively. These plug-in connection structures are interference fit connections. The interference fit connection method ensures that the components maintain a state of no relative movement when bearing loads, preventing loosening due to long-term use or vibration, thus guaranteeing the stability of the force transmission path and consistency during repeated loading.

[0037] Specifically, a crosshead 5 is provided at the end of the bolt 3, and a cross groove 13 is correspondingly provided on the pressure pad 12. The crosshead 5 and the cross groove 13 are connected by an interference fit. It should be noted that the crosshead 5 can also be provided on the pressure pad 12, and the corresponding cross groove 13 can be provided on the end face of the bolt 3. Considering that the pressure pad 12 needs to be completely set in the groove structure and not exceed the plane, it is better to set the crosshead 5 at the end of the bolt 3. In addition, the crosshead 5 can also be set as a slotted head, a star-shaped head, or other protruding structures, and the corresponding connection structure can be set as a slotted head or a star-shaped groove, which will not be elaborated here. Through the interference fit of the crosshead 5 and the cross groove 13, a firm connection structure is formed between the bolt 3 and the pressure pad 12. When the bolt 3 is tightened, there is no relative movement gap between the crosshead 5 and the cross groove 13. The rotation of the bolt 3 can be transmitted to the pressure pad 12 without delay and loss, thereby driving the shaft ring 21 to rotate synchronously. The above connection method effectively avoids frictional losses caused by relative sliding between the bolt 3 end face and the loading block plane in traditional structures, thus significantly improving the torque transmission efficiency during loading. Furthermore, because the mating surfaces of the crosshead 5 and the cross groove 13 are tightly fitted under interference, even in corrosive environments or after repeated loading and unloading operations, there will be no loosening or wear leading to fit failure, thereby ensuring the reliability of the entire loading mechanism during thousands of hours of testing. Specifically, the crosshead 5 is located on the end of the bolt 3 near the pressure pad 12, and the cross groove 13 is located on the end face of the pressure pad 12 near the bolt 3.

[0038] As one example, a plurality of race retaining strips 16 are provided on the outer periphery of the race 15 of the thrust ball bearing 11, and a plurality of race retaining grooves 10 are correspondingly provided on the side wall of the bearing seat 9. The race retaining strips 16 and the race retaining grooves 10 are connected by an interference fit. The race 15 is annularly arranged, and the race retaining strips 16 are evenly distributed on the outer periphery of the race 15 and extend away from the race 15. The race retaining strips 16 and the race retaining grooves 10 are arranged in a one-to-one correspondence. In this example, the interference fit forms a firm axial and circumferential positioning between the race 15 and the bearing seat 9. During assembly, the race retaining strips 16 are embedded into the race retaining grooves 10 under pressure, ensuring that the race 15 will not rotate or move axially relative to the bearing seat 9 when subjected to axial thrust, thus ensuring the stability of the axial thrust transmission path and further ensuring the accuracy of the test results. As one optional example, there are four seat ring retaining strips 16 and four seat ring retaining slots 10, with the four seat ring retaining strips 16 evenly distributed along the annular outer circumference of the seat ring 15. It should be noted that the number of seat ring retaining strips 16 can also be set as needed, and is not limited here.

[0039] Optionally, a plurality of ring retaining strips 22 are provided on the ring 21 of the thrust ball bearing 11, and a plurality of ring retaining grooves 14 are correspondingly provided on the pressure pad 12. The ring retaining strips 22 and the ring retaining grooves 14 are interference-fitted. Specifically, the ring 21 is annularly arranged, the ring retaining strips 22 are provided on the end face of the ring 21 facing the pressure pad 12, and the ring retaining grooves 14 are provided on the end face of the pressure pad 12 facing the ring 21. The ring retaining strips 22 and the ring retaining grooves 14 are arranged in a one-to-one correspondence. If there is a connection gap or looseness between the pressure pad 12 and the ring 21, the rotation of the ring 21 will become unstable, making the thrust ball bearing 11 prone to jamming, thereby compromising the low-friction characteristics of the thrust ball bearing 11. In this example, the pressure pad 12 and the shaft ring 21 are fixed together by an interference fit, so that there is no relative displacement between the pressure pad 12 and the shaft ring 21. When the bolt 3 drives the pressure pad 12 to rotate, the shaft ring 21 rotates synchronously. With the help of the intermediate rolling element 18, the axial thrust is efficiently transmitted. At the same time, the sliding friction between the shaft ring 21 and the seat ring 15 is converted into rolling friction, which pushes the pre-fabricated crack of the bearing block 8 and the wedge-shaped opening loading sample 1 to produce opening displacement. During this process, there is almost no relative sliding between the end face of the bolt 3 and the pressure pad 12. As one optional example, there are six shaft ring retaining strips 22 and six shaft ring retaining grooves 14. The six shaft ring retaining strips 22 are radially and evenly arranged on the annular end face of the shaft ring 21 with the center of the end face of the shaft ring 21 as the center. It should be noted that the number of shaft ring retaining strips 22 can also be set as needed, and is not limited here.

[0040] As a preferred example, the bolt 3 is provided with a trapezoidal thread 4, and the threaded hole 7 is a trapezoidal threaded hole, with the trapezoidal thread 4 used for mating connection with the trapezoidal threaded hole. During constant displacement loading, the threaded pair is the primary source of friction besides bearings. Due to its small tooth angle and optimized contact area, the trapezoidal thread 4 significantly reduces frictional resistance during tightening, allowing the operator to apply the required load more easily. Compared to ordinary triangular threads, it also has higher transmission efficiency and better centering. Furthermore, the trapezoidal thread 4 maintains good self-locking performance even under large axial loads. This performance is particularly important for stress corrosion tests that require long-term constant displacement, effectively preventing load attenuation caused by thread creep or external vibration, and ensuring the stability of crack opening displacement during long-term testing. Optionally, the trapezoidal thread 4 is a Tr10×2 specification thread.

[0041] Preferably, the surface of the trapezoidal thread 4 is coated with an anti-seize grease. Specifically, the anti-seize grease is a high-performance anti-seize grease, such as a MoS2-based anti-seize paste. This grease forms a stable and extremely thin oil film between the thread contact surfaces, transforming direct metal-to-metal contact friction into shear friction within the lubricating medium, thereby reducing the sliding friction coefficient to an extremely low level, making the tightening process smoother and less strenuous. Furthermore, the solid lubricant particles in the anti-seize grease effectively isolate the metal surface, preventing cold welding or adhesion between the bolt 3 and the wedge-shaped open-loaded specimen 1 during long-term testing, effectively avoiding the risk of loading failure or specimen scrap due to thread seizure. The high-performance anti-seize grease also possesses excellent anti-corrosion properties, forming a protective layer on the thread surface to block the intrusion of corrosive media, ensuring a flexible and adjustable state even in corrosive environment tests.

[0042] As a preferred example, the surfaces of the bearing block 8, thrust ball bearing 11, pressure pad 12, and bolt 3 are all coated with an anti-corrosion and insulating coating, which is a polyetheretherketone (PEEK) coating. PEEK exhibits excellent chemical corrosion resistance, enabling it to operate stably for extended periods in harsh corrosive environments such as strong acids, strong alkalis, and salt spray. This effectively protects the internal metal substrate from corrosive media, overcoming the problem of traditional loading mechanisms easily rusting and jamming in corrosive environments. Furthermore, the coating possesses good wear resistance, able to withstand contact stress generated during testing without damage, significantly extending the service life of the bearing block 8, thrust ball bearing 11, pressure pad 12, and bolt 3. In addition, the coating has excellent electrical insulation properties, forming reliable electrical isolation between the loading mechanism and the wedge-shaped opening loading sample 1. This cuts off potential galvanic corrosion circuits between different metal components, preventing interference from galvanic currents on the sample's electrochemical signal and ensuring the accuracy of electrochemical test data such as stress corrosion cracking.

[0043] Specifically, the thrust ball bearing 11 further includes rolling elements 18, each comprising a plurality of steel balls 20 and a cage 19. The steel balls 20 are evenly arranged in the circumferential direction of the cage 19. Slides 17 for accommodating the rolling elements 18 are respectively provided on the opposite end faces of the seat ring 15 and the shaft ring 21. The rolling elements 18 are disposed between the seat ring 15 and the shaft ring 21, allowing the shaft ring 21 to rotate relative to the seat ring 15. In this example, the plurality of steel balls 20, constrained by the cage 19, can roll freely within the annular slide 17 between the seat ring 15 and the shaft ring 21. When the shaft ring 21 rotates with the bolt 3, the steel balls 20 perform pure rolling motion within the slide 17, eliminating any possible sliding friction between the shaft ring 21 and the seat ring 15. This reduces frictional resistance to an extremely low level, effectively solving the technical problem of excessive sliding friction causing laborious operation and difficulty in precise control in traditional wedge-shaped opening loading sample 1 loading mechanisms.

[0044] In specific testing, the loading mechanism is assembled as follows:

[0045] Step S1, Pre-treatment: Before assembly, PEEK (polyether ether ketone) coating is evenly sprayed on the surfaces of the bearing block 8, thrust ball bearing 11, pressure pad 12 and bolt 3 to achieve the effects of corrosion resistance, wear resistance and insulation.

[0046] Step S2, Assembly of loading component 2: The bearing block 8, seat ring 15, rolling element 18, shaft ring 21 and pressure pad 12 are sequentially pressed into place coaxially to form a complete integrated loading component 2;

[0047] Step S3, Lubrication treatment: Apply high-performance anti-seize grease, such as MoS2-based anti-seize paste, evenly to the trapezoidal thread 4 of bolt 3;

[0048] Step S4, Installation and debugging: Pass the bolt 3 through the threaded hole 7 on the wedge-shaped opening loading sample 1, and manually screw it in several turns to press the cross head 5 at the end of the bolt 3 into the cross groove 13 on the outer end face of the pressure pad 12, and ensure that the arc surface of the bearing block 8 is in close contact with the loading hole 6.

[0049] Step S5, Loading operation: Use a torque wrench to load smoothly, and the bolt 3 pushes the pressure pad 12 and the shaft ring 21. The force is transmitted to the stationary seat ring 15 and the bearing block 8 through the rolling element 18, which causes the pre-crack to open until the pre-crack opening displacement reaches the desired value.

[0050] The test system is set up using the above loading mechanism and assembly method. The steps are simple and convenient, and the resistance during the entire twisting process is extremely small. The twisting resistance can be reduced by more than 90%, and the operation is smooth and light, which completely solves the problem of "cannot be twisted" in the traditional loading method.

[0051] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "tail end," "head end," and "center," are only used to explain the relative positional relationships and connection situations between components in a specific state. They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0052] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen, characterized in that, For a wedge-shaped opening loading specimen (1), a pre-fabricated crack is provided on the wedge-shaped opening loading specimen (1). Loading holes (6) and threaded holes (7) are respectively provided on the loading arms on both sides of the upper part of the pre-fabricated crack. The loading hole (6) penetrates the thickness direction of the wedge-shaped opening loading specimen (1). The axis of the threaded hole (7) is perpendicular to the axis of the loading hole (6), and the threaded hole (7) extends from the side of the wedge-shaped opening loading specimen (1) towards the loading hole (6) and communicates with the loading hole (6). The loading mechanism includes a bolt (3) and a loading assembly (2). The loading assembly (2) is disposed in a loading hole (6). The loading assembly (2) includes a bearing block (8), a thrust ball bearing (11), and a pressure pad (12). The seat ring (15) of the thrust ball bearing (11) is connected to the bearing block (8). The pressure pad (12) is connected to the shaft ring (21) of the thrust ball bearing (11). The bolt (3) passes through the threaded hole (7) and is connected to the pressure pad (12) to apply axial thrust to the loading assembly (2).

2. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 1, characterized in that, The bearing block (8) is a cylindrical body with a semi-circular cross section. The side of the bearing block (8) facing the bolt (3) is a plane, and the side of the bearing block (8) away from the bolt (3) is an arc surface. The shape of the loading hole (6) is adapted to the bearing block (8).

3. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 2, characterized in that, A bearing seat (9) is provided on the plane of the bearing block (8). The bearing seat (9) is a groove structure. The groove structure is recessed to the side away from the bolt (3). The thrust ball bearing (11) and pressure pad (12) are provided in the bearing seat (9).

4. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 1, characterized in that, An interlocking connection structure is provided between the bolt (3) and the pressure pad (12), between the seat ring (15) of the thrust ball bearing (11) and the bearing seat (9), and between the shaft ring (21) of the thrust ball bearing (11) and the pressure pad (12). The interlocking connection structure is an interference fit connection.

5. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 4, characterized in that, A crosshead (5) is provided at the end of the bolt (3), and a cross groove (13) is provided on the pressure pad (12) accordingly. The crosshead (5) and the cross groove (13) are connected by an interference fit.

6. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 4, characterized in that, A plurality of seat ring retaining strips (16) are provided on the outer periphery of the seat ring (15) of the thrust ball bearing (11), and a plurality of seat ring retaining grooves (10) are correspondingly provided on the side wall of the bearing seat (9). The seat ring retaining strips (16) and the seat ring retaining grooves (10) are connected by interference fit.

7. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 4, characterized in that, A plurality of ring retaining strips (22) are provided on the ring (21) of the thrust ball bearing (11), and a plurality of ring retaining grooves (14) are provided on the pressure pad (12) respectively. The ring retaining strips (22) and the ring retaining grooves (14) are interference fit connected.

8. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 1, characterized in that, A trapezoidal thread (4) is provided on the bolt (3), and the threaded hole (7) is a trapezoidal threaded hole. The trapezoidal thread (4) is used to connect with the trapezoidal threaded hole.

9. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 8, characterized in that, The surface of the trapezoidal thread (4) is coated with anti-seize grease.

10. The low-friction constant-displacement loading mechanism for a wedge-shaped opening loading specimen as described in claim 1, characterized in that, The surfaces of the bearing block (8), thrust ball bearing (11), pressure pad (12) and bolt (3) are all coated with an anti-corrosion and insulating coating, which is a polyether ether ketone coating.

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