A unidirectional variable bidirectional loading clamp type fixture for a universal testing machine

Abstract

This utility model discloses a unidirectional to bidirectional loading clamp-type fixture for a universal testing machine. The clamp-type plate includes a pin hole and a universal ball joint. The pin hole is located in the middle of the clamp-type plate, and a column bearing is inserted into the pin hole. The column bearing serves as the connecting fulcrum for the two clamp-type plates. The pin hole and the column bearing together constitute a pin hole-column bearing system for the clamp-type fixture. The clamp-type plate consists of an upper lever arm and a lower lever arm. A force transmission plate is fixedly connected to the cross brace end of the lower lever arm. A pressure plate is fixedly connected to one end of the force transmission plate, which is used to internally clamp the pressure plate. An innovative X-type hinged double-lever structure is adopted, connecting the two clamp-type plates through the column bearing to form a stable hinge fulcrum, achieving efficient conversion of axial force to horizontal force. This structure, through precise design of the lever arm ratio and angle optimization, combined with the torque balance equation, achieves a force transmission efficiency η ≥ 95%, overcoming the limitation of traditional universal testing machines that can only apply unidirectional loads, and realizing the simulation of a true two-dimensional stress state.

Description

Technical Field

[0001] This utility model relates to the field of universal testing machine fixture technology, specifically a unidirectional variable bidirectional loading clamp type fixture for a universal testing machine. Background Technology

[0002] Underground engineering is a crucial aspect of future human development. Drilling-while-drilling (DSD) technology and equipment for deep rock masses are essential technologies for future underground engineering exploration and construction drilling, enabling the acquisition and understanding of rock mass characteristics in advance during in-situ drilling. Digital drilling technology, by monitoring drilling parameters such as drilling speed (N), drilling pressure (F), torque (M), drilling rate (V), vibration, and sound intensity in real time, can efficiently infer and acquire the mechanical properties of rock masses, including rock type, state (e.g., degree of fracture development), compressive strength, and elastic modulus.

[0003] Effective analysis of field test data relies on establishing a sufficiently large database. This means determining in real-time what combinations of parameters such as torque, rotational speed, and drilling rate reflect about the rock formations and their physical and mechanical properties during drilling. This can only be achieved based on a large amount of measured data. For rapid, efficient, and accurate acquisition of this data, laboratory drilling-while-drilling tests are the most effective and economical method.

[0004] After the excavation of underground tunnels, the surrounding rock within a certain depth range of the tunnel wall can be considered to have no load (or be negligible) in the direction perpendicular to the tunnel wall. However, the surrounding rock at deeper depths away from the tunnel wall is under a certain stress state, namely a two-dimensional and three-dimensional stress state. Conducting laboratory research on rock properties under these two-dimensional and three-dimensional stress states (such as hydraulic fracturing, digital drilling, grouting, etc.) is of significant scientific importance. Therefore, there is an urgent need to provide equipment with multi-dimensional loading and drilling capabilities for samples. Following the convention of scientific research progressing from shallow to deep, the first step is to solve the problem of indoor drilling testing under two-dimensional loading conditions.

[0005] The main existing equipment with two-dimensional loading capabilities is the triaxial apparatus, which primarily uses water or hydraulic oil to provide confining pressure. However, its sample size is small, and drilling is not feasible. While universal testing machines (compression machines) are essential equipment in almost every engineering laboratory, they only provide uniaxial loading. By inventing a testing fixture, without adding other external power sources, the traditional uniaxial loading mode of the universal testing machine (compression machine) (which can only perform uniaxial compression tests on rock and concrete and tensile tests on steel bars) can be transformed into biaxial loading, more closely simulating the stress state of actual rock masses. This allows for the widespread adoption of biaxial loading on universal testing machines in numerous laboratories at extremely low cost, expanding the applications of uniaxial compression testing machines and demonstrating significant socio-economic and scientific value. Utility Model Content

[0006] The purpose of this invention is to provide a unidirectional to bidirectional loading clamp-type fixture for a universal testing machine, to solve the problem mentioned in the background art that the main equipment with two-dimensional loading function is a triaxial apparatus, which mainly uses water or hydraulic oil to provide confining pressure, and its sample size is small and drilling conditions are not available. However, universal testing machines are almost essential testing equipment in every engineering laboratory, but they can only provide unidirectional axial loading.

[0007] To achieve the above objectives, this utility model provides the following technical solution: a unidirectional variable bidirectional loading clamp-type fixture for a universal testing machine, a clamp-shaped plate, and also includes pin holes and universal balls. The universal ball array is embedded in the top and bottom of the clamp-shaped plate. The upper and lower pressure plates of the universal testing machine are in contact with the universal ball array at the top and bottom of the clamp-shaped plate. The pin hole is opened in the middle of the clamp-shaped plate, and a column bearing is inserted into the pin hole. The column bearing serves as the connection fulcrum between the two clamp-shaped plates. The pin hole and the column bearing together constitute a pin hole-column bearing system for the clamp-shaped fixture. The clamp-shaped plate is composed of an upper force arm and a lower force arm. A force transmission plate is fixedly connected to the cross brace end of the lower force arm. A pressure plate is fixedly connected to one end of the force transmission plate. The force transmission plate is used to internally clamp the pressure plate.

[0008] Based on the preferred embodiment of this technical solution, the upper lever arm is the power arm, and the vertical distance from the center of the column bearing 4 to the contact point of the top universal ball is 180-220mm; the lower lever arm is the resistance arm, and the vertical distance from the center of the column bearing 4 to the line of action of the force transmission plate 5 is 120-150mm.

[0009] Based on the preferred embodiment of this technical solution, the universal ball adopts a countersunk hole structure and is fixed with a retaining ring. The countersunk hole adopts a variable curvature ball-and-socket design, and the ball diameter is Φ2~5mm.

[0010] Based on the preferred embodiment of this technical solution, the clamp plate has a height of 400~500mm and a width of 300mm. A low-frequency MEMS tilt sensor is installed on the side of the clamp plate by means of magnetic adsorption base, and supports USB / Bluetooth dual output.

[0011] Based on the preferred embodiment of this technical solution, the cylindrical bearing has a solid cylindrical structure, and its outer diameter and the pin hole form a precision interference fit through the pin hole.

[0012] Based on the preferred embodiment of this technical solution, the force transmission plate, as the angle steel strip at the end of the lower lever arm cross brace, serves as the force conversion hub, decomposing and transmitting the horizontal force of the clamp plate. The end of the force transmission plate is provided with a dovetail-shaped pointed inner clamp, and the back of the pressure plate is provided with a dovetail groove guide rail groove. The dovetail-shaped pointed inner clamp of the force transmission plate is adapted to the dovetail groove guide rail groove of the pressure plate.

[0013] Based on the preferred embodiment of this technical solution, the pressure plate, as the execution terminal, is designed as a right-angle steel to clamp the sample to be loaded. The dovetail groove guide rail of the pressure plate has a groove depth of 15mm, and a 0.3mm thick polytetrafluoroethylene wear-resistant layer is laid at the bottom of the groove.

[0014] Compared with the prior art, the beneficial effects of this utility model are: 1. Force conversion structure design based on double lever-angle coupling This innovative design employs an X-shaped hinged double-lever structure, connecting two clamp-shaped plates via a column bearing to form a stable hinged fulcrum, achieving efficient conversion of axial force to horizontal force. Through precise design of the lever arm ratio and angle optimization, combined with the torque balance equation, this structure achieves a force transmission efficiency η ≥ 95%, overcoming the limitation of traditional universal testing machines that can only apply unidirectional loads, and enabling the simulation of realistic two-dimensional stress states.

[0015] 2. Multi-degree-of-freedom drag reduction and force transmission mechanism A high-precision omnidirectional ball array is embedded at the top and bottom of the clamp-shaped plate, employing a variable curvature ball-and-socket design and GCr15 bearing steel material. This transforms sliding friction into rolling friction, significantly reducing force transmission loss. The multi-degree-of-freedom adaptive characteristics of the omnidirectional balls can compensate for pressure plate deflection, ensuring unbiased axial load transmission and guaranteeing force conversion accuracy.

[0016] 3. Modular and scalable confining pressure application system The dovetail groove guide rail interface design between the force transmission plate and the pressure plate enables rapid replacement and adaptation of specimens of different sizes. A hydraulic bladder structure is installed inside the pressure plate to effectively eliminate stress concentration at corners and pressure attenuation at the specimen edges, achieving automatic and balanced distribution of confining pressure and improving loading uniformity and test consistency.

[0017] 4. Integrated angle monitoring and feedback control capabilities A MEMS tilt sensor is integrated on the side of the clamp plate via a magnetic base to monitor changes in the lever angle in real time, and outputs data to the control system via an SPI interface. Combined with the force conversion equation, closed-loop feedback control of the horizontal force F is achieved, supporting constant confining pressure loading mode and enhancing the accuracy and repeatability of the experimental process.

[0018] 5. Open sample testing interface design The pressure plate only surrounds the four sides of the sample, leaving the top and bottom surfaces freely exposed. This allows for in-situ operations such as drilling, sensor installation, and grouting, overcoming the limitations of closed equipment like triaxial apparatuses that cannot perform measurements while drilling and non-destructive testing. This design provides a physical interface for multi-field coupled testing, significantly expanding the possibilities for universal testing. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of one embodiment of the unidirectional variable bidirectional loading clamp type fixture of the universal testing machine of this utility model. Figure 2 This is a side view of the distribution structure of the universal ball and clamp plate of this utility model; Figure 3This is a right-side view of the distribution of the universal ball and clamp plate of this utility model; Figure 4 This is a schematic diagram of the connection structure between the force transmission plate and the pressure plate of this utility model; Figure 5 This is a schematic diagram of the force transmission plate structure of this utility model.

[0020] In the diagram: 1. Clamping plate; 2. Pin hole; 3. Universal ball; 4. Column bearing; 5. Force transmission plate; 6. Pressure plate; 7. Upper lever arm; 8. Lower lever arm. Detailed Implementation

[0021] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0022] Please see Figure 1-5 This utility model provides an embodiment: a unidirectional to bidirectional loading clamp-type fixture for a universal testing machine, a clamp plate 1, and also includes pin holes 2 and universal balls 3. The universal balls 3 are arrayed and embedded in the top and bottom of the clamp plate 1. The upper and lower pressure plates of the universal testing machine are in contact with the universal balls 3 array at the top and bottom of the clamp plate 1. The pin holes 2 are opened in the middle of the clamp plate 1, and a column bearing 4 is inserted into the pin holes 2. The column bearing 4 serves as the connection fulcrum of the two clamp plates 1. The pin holes 2 and the column bearing 4 together constitute the pin hole 2-column bearing 4 system for the clamp-type fixture. The clamp plate 1 is composed of an upper force arm 7 and a lower force arm 8. A force transmission plate 5 is fixedly connected to the cross brace end of the lower force arm 8. A pressure plate 6 is fixedly connected to one end of the force transmission plate 5. The force transmission plate 5 is used to internally clamp the pressure plate 6.

[0023] Please see Figure 1 A further scheme based on this embodiment is as follows: the upper lever arm 7 is the power arm, and the vertical distance from the center of the column bearing (4) to the contact point of the top universal ball 3 is 180-220mm; the lower lever arm 8 is the resistance arm, and the vertical distance from the center of the column bearing 4 to the line of action of the force transmission plate (5) is 120-150mm.

[0024] Please see Figure 2 and Figure 3 A further solution based on this embodiment is as follows: the universal ball 3 adopts a countersunk hole structure and is fixed with a retaining ring for the hole. The countersunk hole adopts a variable curvature ball-and-socket design with R ball / R socket = 1.005 and the ball diameter is Φ2~5mm with G100 grade precision.

[0025] Please see Figure 1A further solution based on this embodiment is as follows: the height of the clamp plate 1 is 400~500mm and the width is 300mm. A low-frequency MEMS tilt sensor is installed on the side of the clamp plate 1 by means of magnetic adsorption base, which supports USB / Bluetooth dual output.

[0026] Please see Figure 1 A further solution based on this embodiment is: the cylindrical bearing 4 is a solid cylindrical structure, and its outer diameter forms a precision interference fit with the pin hole 2 and passes through the pin hole 2.

[0027] Please see Figure 1 , Figure 4 and Figure 5 A further solution based on this embodiment is as follows: the force transmission plate 5 serves as the angle steel strip at the end of the horizontal support of the lower lever arm 8, and acts as the force conversion hub to decompose and transmit the horizontal force of the clamp plate 1. The end of the force transmission plate 5 is provided with a dovetail-shaped pointed corner inner clamp, and the back of the pressure plate 6 is provided with a dovetail groove guide rail groove. The dovetail-shaped pointed corner inner clamp of the force transmission plate 5 is adapted to the dovetail groove guide rail groove of the pressure plate 6.

[0028] Please see Figure 5 A further solution based on this embodiment is as follows: the pressure plate 6 is used as the execution terminal and is designed as a right angle steel to clamp the sample to be loaded. The dovetail groove guide rail of the pressure plate 6 has a groove depth of 15mm and a 0.3mm thick polytetrafluoroethylene wear-resistant layer is laid at the bottom of the groove.

[0029] Working principle: An X-type hinged clamp fixture with a cross-type double lever system is used. Two clamp plates 1 form an X-type hinge structure through column bearings 4, transforming the original axial loading of the press into horizontal loading. The upper lever arm 7 has a length of L1 from the fulcrum to the center of the universal ball 3, and the lower lever arm 8 has a length of L2 from the fulcrum to the center of the force transmission plate. The lever ratio K = L1 / L2, preferably in the range of 1.5-2.0. The synchronous angle deviation of the double levers is ≤0.5°. A conversion equation is established based on the torque balance principle: where: Fh - output horizontal force, Fv - input axial force; η - efficiency coefficient, generally ≥0.95, α - lever inclination angle, preferably 45°±5°. This solves the problem common in various laboratory universal testing machines that can only perform uniaxial loading and cannot perform biaxial loading.

[0030] The lower loading end of the clamp-type fixture is equipped with pressure plates 6 of different sizes, which can transform the single-direction loading into double-lateral loading. At the same time, in view of the drawbacks of rigid loading, such as stress concentration at the right angle of the angle steel of the pressure plate 6 and pressure attenuation zone at the edge of the sample, a 2mm thick hydraulic bladder is set inside the pressure plate 6. The hydraulic bladder is 0.5mm thick and filled with an incompressible fluid such as silicone oil to achieve automatic pressure equalization. This solves the problem of low stress at the right angle and edge when directly clamping a cube sample inside the conventional angle steel pressure plate 6.

[0031] The force transmission plate 5 is equipped with a dovetail groove guide rail to realize the standardized interface design between the force transmission plate 5 and the pressure plate 6, and to complete the replacement of pressure plates 6 of different sizes for samples of different sizes. This solves the problem of high friction between the fixture and the pressure plate contact surface. The friction coefficient is reduced to μ≤0.01 by the design of the universal ball 3, and the target conversion efficiency is ≥95% to ensure the force transmission accuracy, such as axial force error <5%.

[0032] The 3-axis universal ball array is embedded in the top and bottom of the clamp plate 1. It adopts a countersunk hole structure and is fixed with a retaining ring. The countersunk hole adopts a variable curvature ball-and-socket design with R ball / R socket = 1.005. The ball material is GCr15 bearing steel HRC60-62. It replaces surface contact sliding friction with point contact rolling friction. The multi-degree-of-freedom rotation of the 3-axis universal ball adapts to the slight deflection of the pressure plate during the axial loading process of the universal testing machine, reducing energy loss in the axial force transmission process.

[0033] With a clear and explicit quantitative relationship between vertical and horizontal loading conversion, and given that the lengths of each component are determined after the fixture is machined and finalized, the magnitude of the converted lateral load can be accurately calculated simply by measuring the angle and axial force during the loading process.

[0034] Low-frequency MEMS tilt sensors, such as the TDK InvenSense ICM-42605 or Bosch BMI323, are widely available on the market. They meet the following technical parameters: range ±90°, resolution 0.005°, sampling rate 1~50Hz, and support USB / Bluetooth dual output via SPI interface. They solve the problem of accurately calculating the horizontal force caused by the change in angle between the loading plates of the X-type hinged clamp during the loading process. An innovative X-type hinged clamp was designed and invented to adapt to a universal press, transforming the uniaxial force applied by the universal testing machine into a biaxial load on the sample. The clamp uses a high-strength alloy steel integral forged frame with a yield strength ≥800MPa. Universal balls 3 are used at the top and bottom of the clamp where it contacts the testing machine's pressure plate, with the top being the load-bearing end and the bottom the loading end. This effectively reduces contact resistance and ensures conversion efficiency while changing the original vertical load to a horizontal one.

[0035] The pressure plate 6 is equipped with a dovetail groove guide rail to realize the standardized interface design between the pressure plate 6 and the force transmission plate, and to complete the replacement of the pressure plate 6 of different sizes for different sized samples. It is suitable for force transmission plates for loading samples of different sizes and can be combined in a modular manner.

[0036] Through force analysis, a formula for calculating the lateral force conversion of the clamp clamp was established, the optimal clamp angle was determined, and the angle change of the X-type hinge clamp clamp during loading was considered. The initial clamp angle of the clamp clamp is given by the angle change and the small angle change that occurs during loading. Then, based on the angle change and the calculated horizontal stress value, the axial stress is servo-adjusted to maintain the constant horizontal force, that is, the constant loading of the confining pressure of the sample.

[0037] Considering the resistance issues during loading, a matrix-type omnidirectional ball array of 3 is set at the top and bottom: ① array arrangement inside the top and bottom ends of the clamp plate; ② ball diameter Φ2~5mm G100 grade precision, which can be customized according to local process level; ③ rolling friction coefficient μ≤0.003ASTM D1894 standard.

[0038] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A unidirectional variable bidirectional loading jaw type clamp of a universal testing machine, characterized by: The clamp plate (1) also includes a pin hole (2) and a universal ball (3). The universal ball (3) array is embedded in the top and bottom of the clamp plate (1). The upper and lower pressure plates of the universal testing machine are in contact with the universal ball (3) array at the top and bottom of the clamp plate (1). The pin hole (2) is opened in the middle of the clamp plate (1). A column bearing (4) is inserted at the pin hole (2). The column bearing (4) serves as the connection fulcrum of the two clamp plates (1). The pin hole (2) and the column bearing (4) together constitute the pin hole (2)-column bearing (4) system for the clamp clamp. The clamp plate (1) is composed of an upper force arm (7) and a lower force arm (8). The cross brace end of the lower force arm (8) is fixedly connected to a force transmission plate (5). One end of the force transmission plate (5) is fixedly connected to a pressure plate (6). The force transmission plate (5) is used to internally clamp the pressure plate (6).

2. The unidirectional variable bidirectional loading jaw type clamp of the universal testing machine according to claim 1, characterized in that: The upper lever arm (7) is the power arm, and the vertical distance from the center of the column bearing (4) to the contact point of the top universal ball (3) is 180-220mm. The lower lever arm (8) is the resistance arm, and the vertical distance from the center of the column bearing (4) to the line of action of the force transmission plate (5) is 120-150mm.

3. The unidirectional variable bidirectional loading clamp-type fixture for the universal testing machine according to claim 2, characterized in that: The universal ball (3) adopts a countersunk hole structure and is fixed with a hole retaining ring. The countersunk hole adopts a variable curvature ball socket design.

4. The unidirectional variable bidirectional loading clamp-type fixture for the universal testing machine according to claim 3, characterized in that: The clamp plate (1) has a height of 400~500mm and a width of 300mm. A low-frequency MEMS tilt sensor is installed on the side of the clamp plate (1) by means of magnetic adsorption base, and supports USB / Bluetooth dual output.

5. The unidirectional variable bidirectional loading clamp-type fixture for the universal testing machine according to claim 4, characterized in that: The cylindrical bearing (4) is a solid cylindrical structure, and its outer diameter and pin hole (2) form a precision interference fit through the pin hole (2).

6. The unidirectional variable bidirectional loading clamp-type fixture for the universal testing machine according to claim 5, characterized in that: The force transmission plate (5) serves as the angle steel strip at the end of the cross brace of the lower lever arm (8) and acts as the force conversion hub to decompose and transmit the horizontal force of the clamp plate (1). The end of the force transmission plate (5) is provided with a dovetail-shaped inner clamp, and the back of the pressure plate (6) is provided with a dovetail groove guide rail groove. The dovetail-shaped inner clamp of the force transmission plate (5) is compatible with the dovetail groove guide rail groove of the pressure plate (6).

7. The unidirectional variable bidirectional loading clamp-type fixture for the universal testing machine according to claim 6, characterized in that: The pressure plate (6) is designed as a right-angle steel as the execution terminal to hold the sample to be loaded. The dovetail groove guide rail of the pressure plate (6) has a groove depth of 15mm and a 0.3mm thick polytetrafluoroethylene wear-resistant layer at the bottom of the groove.

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