An experimental device for measuring the axial pressure and displacement relationship of a pressure bar and an experimental method thereof

Abstract

The application discloses an experimental device for measuring the axial pressure and displacement relationship of a compression rod, and the experimental device is provided with a frame, the upper part and the lower part of the frame are fixed with loading parts, the opposite surfaces of the loading parts are provided with upper movable workbenches and lower movable workbenches, the loading parts drive the upper movable workbenches and the lower movable workbenches to move towards each other or in the opposite direction, and the opposite surfaces of the upper movable workbenches and the lower movable workbenches are fixed with stiffness-adjustable supporting constraints for clamping test compression rods. The experimental device and the experimental method thereof can measure the critical pressure and the post-instability mechanical behavior of an axially compressed rod under different constraint conditions, namely the relationship between the axial pressure and the rod end displacement. The experimental device can be used for special scientific research, namely measuring the relationship between the axial pressure and the rod end displacement of an axially compressed rod under different constraint conditions, and can also be used for teaching experiments related to material mechanics and structural mechanics, so that the understanding of students on the related knowledge points of compression rod instability can be deepened.

Description

Technical Field

[0001] This invention relates to the technical field of experimental instruments, particularly experimental teaching aids for teaching engineering mechanics and methods of using such teaching aids. Background Technology

[0002] Currently, buckling tests on axially compressed members are mainly used for experimental teaching in courses such as mechanics of materials and structural mechanics. The main experimental content is to measure the critical pressure of axially compressed members with hinged ends and observe the buckling phenomenon. However, there are few experiments on verifying the mechanical behavior of the buckling member or measuring the relationship between the axial pressure and the displacement at the ends of the member under different constraint conditions. There is a lack of teaching tools for this type of experiment. Therefore, it is necessary to design an experimental setup and provide experimental methods to address this issue. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to realize an experimental device and experimental method for measuring the relationship between axial pressure and displacement of a pressure bar.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: an experimental device for measuring the relationship between axial pressure and displacement of a pressure bar. The experimental device is provided with a frame, and loading parts are fixed at the upper and lower parts of the frame. An upper movable worktable and a lower movable worktable are provided on the facing surfaces of the loading parts. The loading parts drive the upper movable worktable and the lower movable worktable to move in opposite directions. The facing surfaces of the upper movable worktable and the lower movable worktable are fixed with stiffness-adjustable support constraints for clamping the test pressure bar.

[0005] The frame is provided with an upper fixing plate and a lower fixing plate. The upper fixing plate and the lower fixing plate are connected by columns on both sides. The columns on both sides are provided with reinforcing connecting rods between the upper fixing plate and the lower fixing plate. The upper fixing plate and the lower fixing plate are provided with through threaded holes at their relative positions. The threaded holes are used to fix the loading screw.

[0006] The loading part is provided with two vertically arranged guide rods. The movable worktable has through holes on both sides for the guide rods to pass through. The movable worktable is fixed on the guide rods and slides along the guide rods. One end of the loading screw is fixed on the movable worktable through a rotating shaft, and the other end extends out of a threaded hole and is fixed with a loading handwheel.

[0007] Both the upper and lower fixed plates are provided with support frames extending along the guide rod. The guide rod is fixed on the support frame. A displacement sensor is provided between the upper movable worktable and the upper fixed plate. A force sensor is provided between the rotating shaft and the movable worktable. Both the displacement sensor and the force sensor are connected to the data display device via data cables.

[0008] The adjustable stiffness support constraint is provided with a bracket structure. The bracket structure has connecting lugs for fixing to the movable worktable. The bracket structure has two bearing seats, which fix the two ends of the roller. The bearing seats have locking screw holes, and roller fixing screws for locking or loosening the roller are installed in the locking screw holes. The roller has a specimen clamp, which is installed on the roller through a hoop. The hoop also has locking screw holes, and specimen clamp fixing screws for locking or loosening the specimen clamp are installed in the locking screw holes. The specimen clamp has specimen fixing screws for fixing the test pressure bar.

[0009] One end of the roller extends out of the bearing seat and is fixedly connected to a support stiffness adjustment rod. The support stiffness adjustment rod and the roller are L-shaped as a whole. The bracket structure is provided with a sliding groove along the support stiffness adjustment rod. A support stiffness adjustment block that slides along the sliding groove is embedded in the sliding groove. The support stiffness adjustment block is provided with a limiting hole. The support stiffness adjustment rod passes through the limiting hole and is clearance-fitted with the limiting hole. A scale is provided along the sliding groove.

[0010] The test pressure bar is in the form of a strip, a rod, or a rod with initial deflection. Both ends of the test pressure bar are provided with fixing holes, which are engaged with the specimen fixing screws.

[0011] An experimental method for measuring the relationship between axial pressure and displacement of a compression rod, the method using an experimental apparatus for measuring the relationship between axial pressure and displacement of a compression rod, includes the following steps:

[0012] Step 1: Adjust the spacing of the adjustable stiffness support constraints according to the length of the test compression bar, and then fix both ends of the test compression bar to the adjustable stiffness support constraints.

[0013] Step 2: Adjust the support stiffness adjustment block according to the constraint stiffness of the specimen corresponding to the test bar;

[0014] Step 3: Loosen the fixing screws of the specimen clamp so that the clamp ring of the specimen clamp can rotate relative to the roller. Test content: The test pressure bar is constrained by the hinges at both ends.

[0015] Step 4: Simultaneously tighten the locking screws of the specimen clamp and the roller clamp to fix the specimen clamp, roller and bearing seat into one unit. Test content: The test pressure bar is subject to fixed constraints at both ends.

[0016] Step 5: Keep the specimen clamp fixing screws in the tightened and locked state, loosen the roller fixing screws, so that the specimen clamp and roller are fixed together and can rotate in the bearing seat. Test content: The test pressure bar is subject to a certain amount of support stiffness constraint.

[0017] In steps 1-5, the support constraint stiffness of the test pressure bar is changed by adjusting the support stiffness adjustment block, and the value of the current support stiffness is read on the scale.

[0018] In steps 3-5, under different test conditions, the loading handwheel on the upper worktable is rotated to apply load, and the equal-volume stepwise loading method is used. The readings of the force sensor and displacement sensor are recorded to obtain the relationship between the axial pressure and axial displacement of the test rod and the critical pressure when the rod becomes unstable. Finally, the test results are compared with the theoretical solution to calculate the error.

[0019] The experimental apparatus and method of this invention can measure the critical pressure and post-instability mechanical behavior of axially compressed members under different constraint conditions, i.e., the relationship between axial pressure and end displacement. It can be used for specialized scientific research, i.e., measuring the relationship between axial pressure and end displacement of axially compressed members under different constraint conditions, and also for teaching experiments in materials mechanics and structural mechanics, deepening students' understanding of knowledge points related to member instability. Attached Figure Description

[0020] The following is a brief explanation of the content and markings in each of the accompanying drawings in this specification:

[0021] Figure 1 A schematic diagram of the experimental setup for measuring the relationship between axial pressure and displacement in a compression bar;

[0022] Figure 2 for Figure 1 Schematic diagram of a medium-stiffness adjustable support constraint structure;

[0023] Figure 3 for Figure 1 Schematic diagram of the loading and measuring components;

[0024] Figure 4 A mechanical model for calculating theoretical solutions when using the experimental setup;

[0025] The markings in the above figures are as follows: 1. Test pressure bar; 2. Adjustable stiffness support constraint; 3. Upper movable worktable; 4. Lower movable worktable; 5. Loading component; 6. Measuring component; 7. Frame; 2-1. Specimen clamp; 2-2. Roller fixing screw; 2-3. Roller; 2-4. Specimen fixing screw; 2-5. Bearing seat; 2-6. Specimen clamp fixing screw; 2-7. Connecting lug; 2-8. Support stiffness adjusting rod; 2-9. Support stiffness adjusting block; 2-10. Scale;

[0026] 5-1 Loading handwheel; 5-2 Loading screw; 5-3 Force sensor; 6-1 Guide rod; 6-2 Displacement sensor; 7-1 Support frame. Detailed Implementation

[0027] The following description, with reference to the accompanying drawings, details the specific implementation of the present invention, including the shape and structure of each component, the relative positions and connections between the parts, the function and working principle of each part, the manufacturing process, and the operation and use methods, to help those skilled in the art to have a more complete, accurate, and in-depth understanding of the inventive concept and technical solution of the present invention.

[0028] The experimental setup is used to measure the relationship between axial pressure and end displacement in axially compressed members with different constraints. It can easily realize the critical pressure and the relationship between axial pressure and end displacement in axially compressed members with different support stiffnesses on a single device, in order to verify the correctness of the theoretical solution. The structure of the experimental setup is as follows: Figure 1 As shown, it consists of a test pressure bar 1, a stiffness adjustable support constraint 2, an upper movable worktable 3, a lower movable worktable 4, a loading component 5, a displacement measuring component 6, and a frame 7.

[0029] The test specimen compression rod is the component to be tested and is part of the experimental apparatus. Multiple different types can be pre-selected for student operation. The test specimen compression rod can have a rectangular cross-section or other cross-sectional shapes such as circles. Depending on the experimental requirements, a rod with initial deflection can also be used. Both ends of the test compression rod 1 are provided with fixing holes, which mate with the test specimen fixing screws 2-4. This allows for easy fixing of the test specimen compression rod to the adjustable stiffness support constraint 2 component using the test specimen fixing screws 2-4.

[0030] Frame 7 is the supporting structure of the entire experimental setup. It consists of an upper fixed plate and a lower fixed plate, which are two parallel plate-like structures connected by columns on both sides. Because frame 7 needs to withstand significant supporting forces, it is primarily a rigid structure to prevent deformation from affecting the test results. Reinforcing rods are installed between the columns and the upper and lower fixed plates, forming a triangular structure with the fixed plates and columns, making frame 7 more stable and reliable. Both the upper and lower fixed plates have through-holes at their relative positions. Preferably, the two threaded holes are coaxial. These holes are used to fix the loading screws 5-2, which are either coaxial or parallel to each other.

[0031] like Figure 3As shown, at least two support frames 7-1 extend vertically from the lower surface of the upper fixed plate and the upper surface of the lower fixed plate. The guide rods 6-1 of the loading part are all fixed on the support frames 7-1. The guide rods 6-1 are parallel to each other to form a slide structure. The upper movable worktable 3 has through holes on both sides for the guide rods 6-1 to pass through. The upper movable worktable 3 is fixed on the guide rods 6-1 of the upper fixed plate and can slide along the guide rods 6-1. The lower movable worktable 4 has through holes on both sides for the guide rods 6-1 to pass through. The lower movable worktable 4 is fixed on the guide rods 6-1 of the lower fixed plate and can slide along the guide rods 6-1. One end of the loading screw 5-2 is fixed to the movable worktable through a rotating shaft, and the other end extends out of a threaded hole and is fixed with a loading handwheel 5-1. In this way, the upper movable worktable 3 and the lower movable worktable 4 can move up and down within the slide rail of the frame 7. The loading component 5 consists of a loading handwheel 5-1, a transmission screw, and a force sensor 5-3. Rotating the loading handwheel 5-1 drives the loading screw 5-2 to rotate, thereby pushing the movable worktable to move up and down under the guidance of the guide rod 6-1.

[0032] A displacement sensor 6-2 is installed between the upper movable worktable 3 and the upper fixed plate, and a force sensor 5-3 is installed between the rotating shaft and the movable worktable. Both the displacement sensor 6-2 and the force sensor 5-3 are connected to a data display device via data cables. The axial force acting on the test pressure rod 1 is measured by the force sensor 5-3. The displacement of the upper movable worktable 3 is also the axial displacement of the test pressure rod 1, which is measured by the displacement sensor 6-2 of the displacement measuring component 6. Thus, the pressure parameters and displacement parameters can be obtained.

[0033] The adjustable stiffness support constraint 2 component is used to adjust the support stiffness of the test pressure bar 1, such as... Figure 2 As shown, it mainly consists of a specimen clamp 2-1, roller fixing screws 2-2, roller 2-3, specimen fixing screws 2-4, bearing seat 2-5, specimen clamp fixing screws 2-6, connecting lugs 2-7, support stiffness adjusting rod 2-8, support stiffness adjusting block 2-9, and scale 2-10. The stiffness adjustable support constraint 2 is equipped with a bracket structure. One side of the bracket structure is used to fix it to the upper movable worktable 3 or the lower movable worktable 4 and to contact the movable worktable. The other side fixes other components of the stiffness adjustable support constraint 2. It is estimated that there are at least two connecting lugs 2-7 on the side of the bracket structure. The connecting lugs 2-7 can be bolted to fix the components of the stiffness adjustable support constraint 2 to the upper movable worktable 3 and the lower movable worktable 4 respectively.

[0034] The support structure has two bearing seats 2-5, and the roller 2-3 is set in the two bearing seats 2-5 and can rotate within the bearing seats 2-5. The bearing seats 2-5 are provided with locking screw holes, and the locking screw holes are provided with roller fixing screws 2-2. When the roller fixing screws 2-2 are tightened, the roller fixing screws 2-2 will move into the bearing seats 2-5 and contact the roller 2-3, then the roller 2-3 will be locked and cannot rotate. Conversely, when the roller fixing screws 2-2 are loosened, the roller fixing screws 2-2 will move out of the bearing seats 2-5 and disengage from the roller 2-3, then the roller 2-3 will be unlocked and can rotate relative to the bearing seats 2-5.

[0035] A specimen clamp 2-1 is mounted on the roller 2-3. The specimen clamp 2-1 consists of four parts: a hoop, a fixing seat, a specimen clamp fixing screw 2-6, and a specimen fixing screw 2-4. The hoop is fitted onto the roller 2-3 with a clearance fit, allowing it to rotate on the roller 2-3. The hoop also has a locking screw hole, in which the specimen clamp fixing screw 2-6 is installed for locking or loosening the specimen clamp 2-1. Tightening the specimen clamp fixing screw 2-6 will cause the specimen clamp to... When the fixing screw 2-6 of the specimen clamp moves inward into the hoop and contacts the roller 2-3, the hoop and the roller 2-3 are locked and cannot rotate. Conversely, when the fixing screw 2-6 of the specimen clamp is loosened, the fixing screw 2-6 of the specimen clamp will move outward from the hoop and disengage from the roller 2-3, thus the hoop and the roller 2-3 are unlocked and can rotate relative to each other. The fixing seat is fixed on the outer surface of the hoop. The fixing seat is provided with specimen fixing screw 2-4 for fixing the test rod 1. The end of the test rod 1 is fixed by the specimen fixing screw 2-4.

[0036] One end of the roller 2-3 extends out of the bearing seat 2-5 and is fixedly connected to a support stiffness adjusting rod 2-8. The support stiffness adjusting rod 2-8 and the roller 2-3 are L-shaped as a whole. The support structure is provided with a slide groove along the support stiffness adjusting rod 2-8. A support stiffness adjusting block 2-9 that slides along the slide groove is embedded in the slide groove. The support stiffness adjusting block 2-9 is provided with a limiting hole. The support stiffness adjusting rod 2-8 passes through the limiting hole and is clearance-fitted with the limiting hole. By adjusting the position of the support stiffness adjusting block 2-9 on the slide groove, the support stiffness can be controlled. A scale 2-10 is provided along the slide groove, which can be used to read the adjusted parameter information.

[0037] The test pressure bar 1 is fixed in the test specimen clamp 2-1 by the test specimen fixing screw 2-4. When the test specimen clamp fixing screw 2-6 is loosened, the test specimen clamp 2-1 is loosely fitted on the roller 2-3, and at this time, the test pressure bar 1 is a compression member constrained by hinges at both ends. When the test specimen clamp fixing screw 2-6 and the roller fixing screw 2-2 are tightened simultaneously, the test specimen clamp 2-1, the roller 2-3, and the bearing seat 2-5 are fixed together, and the test pressure bar 1 becomes a compression member constrained by fixed ends. When the test specimen clamp fixing screw 2-6 is tightened and the roller fixing screw 2-2 is loosened, the test specimen clamp 2-1 and the roller 2-3 are fixed together, but can rotate in the bearing seat 2-5, and the test pressure bar 1 becomes a compression member constrained by a certain support stiffness. Since the roller 2-3 and the support stiffness adjustment rod 2-8 form an L-shaped component, the support constraint stiffness of the test pressure rod 1 can be adjusted by adjusting the support stiffness adjustment block 2-9, and the value of its support stiffness can be read on the scale 2-10.

[0038] Based on the experimental setup described above for measuring the relationship between axial pressure and displacement of a compression rod, the experimental method and steps are as follows:

[0039] 1) Based on the length of the test specimen, rotate the loading handwheel 5-1 on the lower workbench to adjust the relative position of the upper and lower workbench, and install the test specimen in the specimen clamp 2-1 of the stiffness adjustable support constraint 2 component, and tighten the specimen fixing screws 2-4 to fix the specimen.

[0040] 2) Select the appropriate specimen constraint stiffness according to the constraint requirements of the test;

[0041] When the specimen clamp fixing screw 2-6 is loosened, the specimen clamp 2-1 is loosely fitted on the roller 2-3. At this time, the test pressure bar 1 is the pressure bar constrained by the hinges at both ends.

[0042] When the specimen clamp fixing screw 2-6 and the roller fixing screw 2-2 are tightened at the same time, the specimen clamp 2-1, the roller 2-3 and the bearing seat 2-5 are fixed together. At this time, the test pressure rod 1 becomes a pressure rod constrained by both ends.

[0043] When the specimen clamp fixing screw 2-6 is tightened and the roller fixing screw 2-2 is loosened, the specimen clamp 2-1 and the roller 2-3 are fixed together, but can rotate in the bearing seat 2-5. At this time, the test pressure bar 1 becomes a pressure bar constrained by a certain support stiffness.

[0044] The support constraint stiffness of the test pressure bar 1 can be adjusted by adjusting the support stiffness adjustment block 2-9, and the value of its support stiffness can be read on the scale 2-10.

[0045] 3) Rotate the loading handwheel 5-1 on the upper worktable to load the material. Use the equal-amount step-by-step loading method to load the material. Record the readings of the force sensor 5-3 and the displacement sensor 6-2 to obtain the relationship between the axial pressure and axial displacement of the test pressure bar 1 and the critical pressure when the pressure bar becomes unstable.

[0046] 4) Compare the experimental results with the theoretical solution and calculate the error.

[0047] A mechanical model for calculating the axial compressive force versus displacement relationship of test compression bar 1 with different support stiffness constraints is as follows: Figure 3 As shown, k1 and k2 are the stiffness coefficients of the elastic constraints at both ends, and y is the lateral deflection of the column. Taking the origin of the coordinate system as the starting point, the arc length of the column after buckling is chosen as the independent variable. According to the large deflection theory, the governing equation for its deformation is:

[0048]

[0049] Introducing variable P makes Substituting into the above equation and using its boundary conditions, we obtain the following mathematical model:

[0050]

[0051] The theoretical solution (numerical solution) to this problem can be obtained by solving the above equation using computer programming.

[0052] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. An experimental apparatus for measuring the relationship between axial pressure and displacement of a compression rod, characterized in that: The experimental apparatus is provided with a frame, and loading parts are fixed at the upper and lower parts of the frame. The opposing surfaces of the loading parts are provided with an upper movable worktable and a lower movable worktable. The loading parts drive the upper movable worktable and the lower movable worktable to move in opposite directions. The opposing surfaces of the upper movable worktable and the lower movable worktable are fixed with stiffness-adjustable support constraints for clamping the test pressure bar. The adjustable stiffness support constraint is provided with a bracket structure. The bracket structure has connecting lugs for fixing to the movable worktable. The bracket structure has two bearing seats, which fix the two ends of the roller. The bearing seats have locking screw holes, and roller fixing screws for locking or loosening the roller are installed in the locking screw holes. The roller is provided with a specimen clamp, which is installed on the roller through a hoop. The hoop also has locking screw holes, and specimen clamp fixing screws for locking or loosening the specimen clamp are installed in the locking screw holes. The specimen clamp is provided with specimen fixing screws for fixing the test pressure bar. One end of the roller extends out of the bearing seat and is fixedly connected to a support stiffness adjustment rod. The support stiffness adjustment rod and the roller are L-shaped as a whole. The bracket structure is provided with a sliding groove along the support stiffness adjustment rod. A support stiffness adjustment block that slides along the sliding groove is embedded in the sliding groove. The support stiffness adjustment block is provided with a limiting hole. The support stiffness adjustment rod passes through the limiting hole and is clearance-fitted with the limiting hole. A scale is provided along the sliding groove.

2. The experimental apparatus for measuring the relationship between axial pressure and displacement of a compression rod according to claim 1, characterized in that: The frame is provided with an upper fixing plate and a lower fixing plate. The upper fixing plate and the lower fixing plate are connected by columns on both sides. The columns on both sides are provided with reinforcing connecting rods between the upper fixing plate and the lower fixing plate. The upper fixing plate and the lower fixing plate are provided with through threaded holes at their relative positions. The threaded holes are used to fix the loading screw.

3. The experimental apparatus for measuring the relationship between axial pressure and displacement of a compression rod according to claim 2, characterized in that: The loading part is provided with two vertically arranged guide rods. The movable worktable has through holes on both sides for the guide rods to pass through. The movable worktable is fixed on the guide rods and slides along the guide rods. One end of the loading screw is fixed on the movable worktable through a rotating shaft, and the other end extends out of a threaded hole and is fixed with a loading handwheel.

4. The experimental apparatus for measuring the relationship between axial pressure and displacement of a compression rod according to claim 3, characterized in that: Both the upper and lower fixed plates are provided with support frames extending along the guide rod. The guide rod is fixed on the support frame. A displacement sensor is provided between the upper movable worktable and the upper fixed plate. A force sensor is provided between the rotating shaft and the movable worktable. Both the displacement sensor and the force sensor are connected to the data display device via data cables.

5. The experimental apparatus for measuring the relationship between axial pressure and displacement of a compression rod according to claim 4, characterized in that: The test pressure bar is in the form of a strip, a rod, or a rod with initial deflection. Both ends of the test pressure bar are provided with fixing holes, which are engaged with the specimen fixing screws.

6. An experimental method for measuring the relationship between axial pressure and displacement of a compression rod based on any one of the experimental apparatuses described in claims 1-5, characterized in that: The experimental method uses an experimental apparatus to measure the relationship between axial pressure and displacement of a compression rod, and includes the following steps: Step 1: Adjust the spacing of the adjustable stiffness support constraints according to the length of the test compression bar, and then fix both ends of the test compression bar to the adjustable stiffness support constraints. Step 2: Adjust the support stiffness adjustment block according to the constraint stiffness of the specimen corresponding to the test bar; Step 3: Loosen the fixing screws of the specimen clamp so that the clamp ring of the specimen clamp can rotate relative to the roller. Test content: The test pressure bar is constrained by hinges at both ends. Step 4: Simultaneously tighten the locking screws of the specimen clamp and the roller clamp to fix the specimen clamp, roller and bearing seat into one unit. Test content: The test pressure bar is subject to fixed constraints at both ends. Step 5: Keep the specimen clamp fixing screws in the tightened and locked state, loosen the roller fixing screws, so that the specimen clamp and roller are fixed together and rotate in the bearing seat. Test content: The test pressure bar is constrained by the support stiffness.

7. The experimental method according to claim 6, characterized in that: In steps 1-5, the support constraint stiffness of the test pressure bar is changed by adjusting the support stiffness adjustment block, and the value of the current support stiffness is read on the scale.

8. The experimental method according to claim 6 or 7, characterized in that: In steps 3-5, under different test conditions, the loading handwheel on the upper worktable is rotated to apply load, and the equal-volume stepwise loading method is used. The readings of the force sensor and displacement sensor are recorded to obtain the relationship between the axial pressure and axial displacement of the test rod and the critical pressure when the rod becomes unstable. Finally, the test results are compared with the theoretical solution to calculate the error.

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