Teaching testing device for bending normal stress of variable cross-section beam

Abstract

The invention relates to the field of mechanical experiment equipment, and discloses a variable cross-section beam bending normal stress teaching test device, which comprises a connecting base column, frame mechanisms are mounted on the left side and the right side of the connecting base column, limiting mechanisms are mounted at the bottoms of the frame mechanisms, and lubricating mechanisms are arranged in the limiting mechanisms. A movable loading mechanism is arranged outside the limiting mechanism, a transmission line is fixedly connected to the outside of the movable loading mechanism, a displayer is fixedly connected to the other end of the transmission line, a clamping mechanism is installed outside the connecting foundation pillar, and a variable cross-section fish belly sill is arranged inside the clamping mechanism; the frame mechanism comprises two supporting columns. Strain data of different sections and different positions are measured autonomously, the problems that the dangerous section of the variable-section beam can change along with the load position, and how the stress uniformity is influenced by section shape adjustment are analyzed, passive operation is converted into active exploration, and the exploration desire is effectively stimulated.

Description

Technical Field

[0001] This invention relates to the field of mechanical experimental equipment technology, specifically to a teaching and testing device for bending normal stress of a variable cross-section beam. Background Technology

[0002] Mechanical experimental equipment refers to specialized instruments, devices, or systems used to measure, verify, and study the motion state, deformation laws, and mechanical properties of objects under the action of force. Widely used in teaching, research, and engineering, it is a core tool connecting mechanical theory with practical applications. The variable cross-section beam bending normal stress teaching and testing device helps learners understand and verify the theoretical knowledge of "beam bending normal stress" in mechanics of materials through concrete experimental operations and data measurement, and helps them master related experimental skills. It is a core teaching tool connecting abstract theory with engineering practice.

[0003] In existing technologies, the stress characteristics of rectangular cross-section beams (such as linear stress distribution along the cross-section height and fixed critical sections) are analyzed and derived in detail in textbooks. Students have already formed clear expectations about the experimental results before the experiment, which leads to the experimental process becoming a mechanical process of "operating according to steps and verifying known conclusions". It is difficult to stimulate students' interest in exploration and their initiative in thinking, and it is difficult to meet the higher-level goal of "cultivating innovative thinking and scientific research exploration ability" in modern teaching. Moreover, when storing in the laboratory, non-disassembled devices require a complete three-dimensional space (for example, if they can be stacked after disassembly, storing them as a whole requires reserving a larger length, width and height dimension). Especially in teaching laboratories with limited space, this will squeeze the storage space of other equipment and reduce the space utilization rate. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a teaching and testing device for bending normal stress of variable cross-section beams, which solves the problems of rectangular cross-section beam experiments failing to stimulate students' interest in exploration, failing to meet higher-order teaching objectives, and the low utilization rate of laboratory storage space due to the difficulty in disassembling traditional devices.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a teaching and testing device for bending normal stress of a variable cross-section beam, comprising a connecting base column, frame mechanisms installed on the left and right sides of the connecting base column, a limiting mechanism installed at the bottom of the frame mechanisms, a lubrication mechanism inside the limiting mechanism, a movable loading mechanism outside the limiting mechanism, a transmission line fixedly connected to the outside of the movable loading mechanism, a display fixedly connected to the other end of the transmission line, a clamping mechanism installed outside the connecting base column, and a variable cross-section fish-belly beam installed inside the clamping mechanism; The frame structure includes two support columns, with their adjacent sides fixedly connected to the left and right sides. Connectors are detachably connected to both the front and rear sides of the support columns. Bottom columns are detachably connected to the bottom of the two connectors. Removal bolts are threaded inside the support columns, and crossbeams are detachably connected to the outside of the removal bolts.

[0006] Preferably, the limiting mechanism includes two limiting blocks, the tops of the two limiting blocks are fixedly connected to the bottom left and right sides of the crossbeam column, and two limiting guide columns are fixedly connected to the adjacent side of the two limiting blocks. Moving blocks are slidably connected to the outer left and right sides of the limiting guide columns.

[0007] Preferably, the lubrication mechanism includes multiple springs, the top of each spring is fixedly connected to the inside of the movable block, the bottom of each spring is fixedly connected to a movable column, the movable column has an oil outlet channel inside, the movable block has an oil reservoir inside, and multiple protrusions are fixedly connected to the outside of each limiting guide column.

[0008] Preferably, the clamping mechanism includes two sliding plates, the bottoms of which are slidably connected to the left and right sides of the connecting base column. A fixed box is fixedly connected to the top of the sliding plates. A rotating shaft is rotatably connected inside the fixed box. A rotating handle is fixedly connected to the outside of the rotating shaft. A circular plate is fixedly connected to the rear side of the rotating shaft. A spiral annular block is fixedly connected to the rear side of the circular plate. A square column is slidably connected inside the fixed box. Multiple limiting columns are fixedly connected to the front side of each square column. Limiting bolts are threadedly connected to the outside of the fixed box.

[0009] Preferably, a top plate is fixedly connected to the top of the square column, and mounting plates are fixedly connected to the front and rear sides of the top of the top plate. A sliding groove is opened inside the mounting plate, and a square plate is slidably connected inside the sliding groove. Limit nuts are threadedly connected to the front and rear sides of the square plate, and multiple positioning bolts are threadedly connected to the inside of the square plate. The top plate is threadedly connected to the outside of the multiple positioning bolts.

[0010] Preferably, the left and right sides of the crossbeam column are in contact with the adjacent side of the two supporting columns, and the adjacent side of the two connectors is detachably connected to the outside of the connecting base column.

[0011] Preferably, the outer side of the movable column is slidably connected to the inside of the movable block, and the outer side of the movable column is in contact with the outer side of the protrusion.

[0012] Preferably, the top of the movable block is slidably connected to the bottom of the crossbeam column, the bottom of the movable block is fixedly connected to the top of the movable loading mechanism, and the rear side of the display is fixedly connected to the front side of one of the support columns.

[0013] Preferably, one side of the limiting bolt is in contact with the outside of the square column, and the outside of the limiting column is in contact with the outside of the spiral annular block.

[0014] Preferably, the front side of the circular plate is rotatably connected to the front inner wall of the fixed box, the top of the variable cross-section fish belly beam is in contact with the bottom of the top plate II, and the bottom of the variable cross-section fish belly beam is in contact with the top of the square plate.

[0015] This invention provides a teaching and testing device for the bending normal stress of a variable cross-section beam. It has the following beneficial effects: 1. This invention uses two support columns installed on both sides of the base and fixed to the base column with connectors to form a stable frame structure. Subsequently, the crossbeam column is installed between the support columns using disassembly bolts. Since the stress distribution law of the variable cross-section beam is not deeply derived in the textbook, students find it difficult to predict the complete experimental results in advance. During the experiment, students need to independently measure strain data at different cross-sections and positions to analyze questions such as "why the dangerous section of the variable cross-section beam changes with the load position" and "how the adjustment of the cross-sectional shape affects stress uniformity." This transforms students from "passive operation" to "active exploration," effectively stimulating their desire to explore. Furthermore, after disassembly, the beam, support, and loading components can be stacked and stored separately, eliminating the need to reserve three-dimensional space for the entire device. Especially in teaching laboratories with limited space, this avoids compressing the storage space of other equipment and improves the overall space utilization of the laboratory.

[0016] 2. When the movable block slides, multiple protrusions fixed on the limiting guide column will repeatedly press the movable column. The movable column reciprocates under the action of the spring, and the lubricating oil in the oil tank flows out through the oil outlet channel to continuously lubricate the guide column. In the bending normal stress test of variable cross-section beam, accurate load application and strain measurement are crucial. Lubrication can ensure the stability and accuracy of the loading mechanism, so that the applied load can be accurately transmitted to the beam. At the same time, it can also reduce the interference of friction on the strain gauge measurement results, thereby improving the measurement accuracy.

[0017] 3. This invention rotates the handle, causing the rotating shaft to rotate. The rotating shaft then rotates the circular plate, which in turn rotates the spiral ring block. The spiral ring block pushes the square column with multiple limiting posts to move, thereby driving the upper clamp of the top plate to move. Finally, the variable cross-section fish-belly beam is placed between the square plate and the top plate, and the beam is firmly fixed by adjusting the positioning bolts and tightening the limiting bolts. The lifting mechanisms on both sides can adjust the position and posture of the beam to a certain extent, avoiding damage to the beam or failure of the experimental equipment due to improper installation or unreasonable load during the experiment, thus improving the safety of the experiment. Attached Figure Description

[0018] Figure 1 This is a perspective view of the present invention; Figure 2 This is a schematic diagram of the frame mechanism of the present invention; Figure 3 This is a schematic diagram of the limiting mechanism of the present invention; Figure 4 for Figure 3 Enlarged view of point A in the image; Figure 5 This is a schematic diagram of the clamping mechanism of the present invention; Figure 6 for Figure 5 Enlarged view of point B in the image.

[0019] Among them, 1. Connecting base column; 2. Frame mechanism; 21. Support column; 22. Connector; 23. Bottom column; 24. Disassembly bolt; 25. Crossbeam column; 3. Limiting mechanism; 31. Limiting block; 32. Limiting guide column; 33. Moving block; 4. Lubrication mechanism; 41. Spring; 42. Moving column; 43. Oil outlet channel; 44. Oil tank; 45. Protrusion; 5. Movable loading mechanism; 6. Transmission line; 7. Display; 8. Clamping mechanism; 81. Sliding plate; 82. Fixed box; 83. Rotating shaft; 84. Rotating handle; 85. Circular plate; 86. Spiral ring block; 87. Square column; 88. Limiting column; 89. Limiting bolt; 810. Top plate one; 811. Mounting plate; 812. Slide groove; 813. Limiting nut; 814. Square plate; 815. Positioning bolt; 816. Top plate two; 9. Variable cross-section fish belly beam. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see the appendix Figure 1 To be continued Figure 3 This invention provides a teaching and testing device for bending normal stress of a variable cross-section beam, including a connecting base column 1, a frame mechanism 2 installed on the left and right sides of the connecting base column 1, a limiting mechanism 3 installed at the bottom of the frame mechanism 2, a lubrication mechanism 4 inside the limiting mechanism 3, a movable loading mechanism 5 outside the limiting mechanism 3, a transmission line 6 fixedly connected to the outside of the movable loading mechanism 5, a display 7 fixedly connected to the other end of the transmission line 6, a clamping mechanism 8 installed outside the connecting base column 1, and a variable cross-section fish belly beam 9 inside the clamping mechanism 8. The frame mechanism 2 includes two support columns 21. The adjacent sides of the two support columns 21 are fixedly connected to the left and right sides of the connecting base column 1. The front and rear sides of the support columns 21 are detachably connected to the connectors 22, which are used to connect the support columns 21 to the base column 23, thereby enhancing the stability and integrity of the bottom of the frame mechanism 2 and allowing for quick assembly and disassembly. The bottom of the two connectors 22 is detachably connected to the base column 23, which cooperates with the connectors 22 to ensure that the entire device is stably placed on the connecting base column 1 and prevents it from tipping over due to an unstable center of gravity. The internal threads of the support columns 21 are connected to the disassembly bolts 24, which reliably fix the crossbeam column 25 between the two support columns 21 through the threaded connection, so as to withstand the shear force and bending moment generated during loading. Its detachable feature makes the installation and disassembly of the crossbeam column 25 convenient and quick. The external parts of the disassembly bolts 24 are detachably connected to the crossbeam column 25, which serves as a horizontal member connecting the two support columns 21 and enhances the overall rigidity of the frame. The limiting mechanism 3 includes two limiting blocks 31, fixed to the bottom of the crossbeam column 25, serving as the mounting base for the limiting guide column 32. This ensures the parallelism and accuracy of the guide rail, providing a foundation for the smooth movement of the loading mechanism. The tops of the two limiting blocks 31 are fixedly connected to the left and right sides of the bottom of the crossbeam column 25. Two limiting guide columns 32 are fixedly connected to the adjacent sides of the two limiting blocks 31. Moving blocks 33 are slidably connected to the left and right sides of the outer side of the limiting guide column 32, serving as sliding components connecting the loading mechanism and the limiting guide column 32. The internal structure integrates a lubrication mechanism 4, which can achieve automatic lubrication while sliding along the limiting guide column 32, ensuring the smoothness and precision of the loading process. The lubrication mechanism 4 includes multiple springs 41, providing restoring force. When the moving column 42 is pressed by the protrusion 45 on the limiting guide column 32, the spring 41 can quickly push it back to its original position. This forms a reciprocating motion. The top of the spring 41 is fixedly connected to the inside of the moving block 33, and the bottom of the spring 41 is fixedly connected to the moving column 42, which is the actuating component of the lubrication mechanism 4. Under the action of the spring 41, the outside of the moving column 42 contacts the protrusion 45 and reciprocates. Through the internal oil circuit design, automatic lubrication is achieved. The inside of the moving column 42 is provided with an oil outlet channel 43 to achieve effective lubrication of the guide column. The inside of the moving block 33 is provided with an oil tank 44 to store lubricating oil, ensuring that the guide column can be fully lubricated and maintain a low friction state during long-term repeated loading experiments. Multiple protrusions 45 are fixedly connected to the outside of the limiting guide column 32. The multiple protrusions 45 are regularly distributed on the surface of the limiting guide column 32. Their function is to act as a trigger. When the moving block 33 slides, it repeatedly presses the moving column 42 in the lubrication mechanism 4, thereby starting the oil pumping process and achieving fully automatic lubrication during the movement process. Please see the appendix Figure 4 To be continued Figure 6The clamping mechanism 8 includes two sliding plates 81, which serve as the movable base of the clamping mechanism 8 and can slide left and right on the connecting base column 1 to adjust the overall position of the clamping mechanism 8. A rotating shaft 83 is rotatably connected inside the fixed box 82. The rotational torque applied by the operator through the rotating handle 84 is transmitted to the circular plate 85 and the spiral ring block 86 at the rear end. The rotating handle 84 is fixedly connected to the outside of the rotating shaft 83, and a circular plate 85 is fixedly connected to the rear side of the rotating shaft 83, connected to the end of the rotating shaft 83, and rotates synchronously with the rotating shaft 83. Its main function is to transmit the rotational motion of the rotating shaft 83 to the spiral ring block 86, acting as a transmission disc. The spiral ring block 86 is fixedly connected to the rear side of the circular plate 85, and its helical surface contacts the limiting post 88. When it rotates… It can push the limiting column 88 and the square column 87 to produce precise linear displacement, thereby achieving the clamping or loosening of the beam. The square column 87 is slidably connected inside the fixed box 82. Under the push of the spiral ring block 86, it slides linearly inside the fixed box 82. Multiple limiting columns 88 are fixedly connected to the front side of the square column 87. As a driven member, its exterior contacts the curved surface of the spiral ring block 86, converting the rotational force of the spiral ring block 86 into a linear thrust on itself and the square column 87. The external thread of the fixed box 82 is connected to the limiting bolt 89. After the square column 87 completes the clamping action, tightening the bolt can prevent the square column 87 from accidentally loosening or displacing due to vibration or external force, providing additional safety and stability for long-term experiments. A top plate 810 is fixedly connected to the top of the square column 87. Mounting plates 811 are fixedly connected to the front and rear sides of the top of the top plate 810, providing guide rails with grooves 812 for the installation of the square plate 814. This allows it to better adapt to and clamp specimens of different shapes or sizes. The mounting plates 811 have grooves 812 inside, ensuring that the square plate 814 maintains a stable and correct posture during position adjustments. The square plate 814 is slidably connected inside the grooves 812, and together with the top plate 816, they form an upper and lower clamping structure for the beam. Its flat surface provides a stable support surface for the beam. The front and rear sides of the outer side of the plate 814 are threaded with limit nuts 813, which are used in conjunction with the threaded square plate 814 to lock the square plate 814 after its position is adjusted, preventing it from sliding accidentally in the slide groove 812. The inside of the square plate 814 is threaded with multiple positioning bolts 815, which pass through the square plate 814 and are threaded with the top plate 816. By adjusting the tightness of these bolts, the height and angle of the top plate 816 can be finely adjusted to achieve precise positioning and pre-tightening of the variable cross-section fish belly beam 9, ensuring firm and accurate clamping. The external threads of the multiple positioning bolts 815 are connected to the top plate 816. The movable column 42, acting as the core piston of the lubricating oil pump, slides up and down inside the movable block 33, which serves as the pump body, to achieve the pumping action. It is slidably connected to the interior of the movable block 33. The exterior of the movable column 42 is periodically pressed by multiple protrusions 45, which act as triggering mechanisms, to activate the lubrication function. The top of the movable block 33, serving as the sliding base of the entire loading mechanism, moves precisely along the bottom of the crossbeam column 25, which acts as the main track, to change the loading point position. It is slidably connected to the bottom of the crossbeam column 25. The bottom of the movable block 33 is fixedly connected to the top of the movable loading mechanism 5, which is responsible for applying specific loads, ensuring that the loading force can be reliably transmitted to the crossbeam column 25 through the movable block 33. The rear of the display 7 provides a stable and easily observable mounting position for data display, and is fixedly connected to one of the support columns 21, which serves as the main support frame. On the front side, one side of the limiting bolt 89 is screwed into and tightened against the outside of the square column 87, which serves as the clamping actuator, to reliably lock the clamping position and prevent it from loosening. It contacts the outside of the square column 87. The outside of the limiting column 88, as the driven member, contacts the outer spiral surface of the spiral annular block 86, which serves as the driving member, to accurately convert the rotational motion into linear thrust. It contacts the outside of the spiral annular block 86. The front side of the circular plate 85 serves as a rotating transmission disk and is rotatably connected to the inner wall of the front side of the fixed box 82, which serves as the supporting shell, to ensure that it can rotate stably and transmit torque. The top of the variable cross-section fish belly beam 9 is in close contact with the bottom of the top plate 816, which serves as the upper clamping body and directly applies pressure, to achieve a firm top fixation. It contacts the bottom of the top plate 816. The bottom of the variable cross-section fish belly beam 9 is in contact with the top of the square plate 814, which serves as the lower clamping body and provides a stable support plane, to jointly complete the clamping of the beam. It contacts the top of the square plate 814.

[0022] Working principle: The operation of this teaching and testing device begins with the preparation and setup of the experiment. First, two support columns 21 are installed on both sides of the base 1 and fixed to the base column 23 by the connector 22 to form a stable frame structure 2. Then, the crossbeam column 25 is installed between the support columns 21 using the disassembly bolts 24. The detachable design of the entire frame facilitates classified storage after the experiment and improves space utilization.

[0023] Next, the clamping mechanism 8 is operated. By rotating the rotating handle 84, the rotating shaft 83 is driven to rotate. The rotating shaft 83 drives the circular plate 85 to rotate. The circular plate 85 drives the spiral ring block 86 to rotate. The spiral ring block 86 pushes the square column 87 with multiple limit posts 88 to move, thereby driving the upper clamp of the top plate 1 810 to move. Finally, the variable cross-section fish belly beam 9 is placed between the square plate 814 and the top plate 2 816, and the beam is firmly fixed by adjusting the positioning bolt 815 and locking the limit bolt 89.

[0024] The mechanism is suspended from the limiting guide column 32 below the crossbeam column 25 by the movable block 33, which can slide freely along the beam length to apply loads at different positions. To ensure the accuracy of the loading process and the accuracy of the measurement, when the movable block 33 slides, multiple protrusions 45 fixed on the limiting guide column 32 will repeatedly press the movable column 42. The movable column 42 reciprocates under the action of the spring 41, and the lubricating oil in the oil tank 44 flows out through the oil outlet channel 43, continuously providing lubrication for the guide column, which greatly reduces friction and ensures the stability of the loading and the reliability of the strain measurement results.

[0025] Once the experiment officially begins, students apply bending force to designated locations on the variable cross-section fish-belly beam 9 by operating the movable loading mechanism 5. The deformation and stress data generated by the beam under load are collected and transmitted in real time to the display 7 fixed on the support column 21 via the transmission line 6. Students can intuitively read the normal stress data at different loading positions and cross sections. By moving the loading point and observing the changes in the data on the display 7, students can actively explore the changing law of the critical section of the variable cross-section beam and the influence of the cross-sectional shape on the stress distribution. This realizes the transformation from passive operation to active exploration, and deepens their understanding of the relevant principles in mechanics of materials. At the same time, the lifting and clamping mechanisms on both sides also provide a guarantee for experimental safety.

[0026] Although embodiments of the 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 invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A teaching and testing device for bending normal stress of a variable cross-section beam, comprising a connecting base column (1), characterized in that, A frame mechanism (2) is installed on the left and right sides of the connecting base column (1). A limiting mechanism (3) is installed at the bottom of the frame mechanism (2). A lubrication mechanism (4) is provided inside the limiting mechanism (3). A movable loading mechanism (5) is provided outside the limiting mechanism (3). A transmission line (6) is fixedly connected to the outside of the movable loading mechanism (5). A display (7) is fixedly connected to the other end of the transmission line (6). A clamping mechanism (8) is installed outside the connecting base column (1). A variable cross-section fish belly beam (9) is provided inside the clamping mechanism (8). The frame mechanism (2) includes two support columns (21), with the two support columns (21) fixedly connected to the left and right sides of (1) on their adjacent sides. The front and rear sides of the support columns (21) are detachably connected to connectors (22), and the bottom of the two connectors (22) is detachably connected to a bottom column (23). The internal threads of the support columns (21) are connected to a disassembly bolt (24), and the external parts of the disassembly bolts (24) are detachably connected to a crossbeam column (25).

2. The teaching and testing device for bending normal stress of a variable cross-section beam according to claim 1, characterized in that, The limiting mechanism (3) includes two limiting blocks (31). The tops of the two limiting blocks (31) are fixedly connected to the bottom left and right sides of the crossbeam column (25). Two limiting guide columns (32) are fixedly connected to the adjacent side of the two limiting blocks (31). Moving blocks (33) are slidably connected to the outer left and right sides of the limiting guide columns (32).

3. The teaching and testing device for bending normal stress of a variable cross-section beam according to claim 2, characterized in that, The lubrication mechanism (4) includes multiple springs (41). The top of the springs (41) is fixedly connected to the inside of the moving block (33). The bottom of the springs (41) is fixedly connected to a moving column (42). An oil outlet channel (43) is opened inside the moving column (42). An oil storage tank (44) is opened inside the moving block (33). Multiple protrusions (45) are fixedly connected to the outside of the limiting guide column (32).

4. The teaching and testing device for bending normal stress of a variable cross-section beam according to claim 1, characterized in that, The clamping mechanism (8) includes two sliding plates (81). The bottom of the two sliding plates (81) is slidably connected to the left and right sides of the outside of the connecting base column (1). A fixed box (82) is fixedly connected to the top of the sliding plates (81). A rotating shaft (83) is rotatably connected inside the fixed box (82). A rotating handle (84) is fixedly connected to the outside of the rotating shaft (83). A circular plate (85) is fixedly connected to the rear side of the rotating shaft (83). A spiral ring block (86) is fixedly connected to the rear side of the circular plate (85). A square column (87) is slidably connected inside the fixed box (82). Multiple limiting columns (88) are fixedly connected to the front side of the square column (87). Limiting bolts (89) are threadedly connected to the outside of the fixed box (82).

5. The teaching and testing device for bending normal stress of a variable cross-section beam according to claim 4, characterized in that, The top of the square column (87) is fixedly connected to a top plate (810). The top front and rear sides of the top plate (810) are fixedly connected to mounting plates (811). The mounting plate (811) has a sliding groove (812) inside. The sliding groove (812) is slidably connected to a square plate (814). The front and rear sides of the square plate (814) are threaded with limit nuts (813). The square plate (814) is threaded with multiple positioning bolts (815) inside. The multiple positioning bolts (815) are threaded with a top plate (816) outside.

6. The teaching and testing device for bending normal stress of a variable cross-section beam according to claim 1, characterized in that, The left and right sides of the crossbeam column (25) are in contact with the adjacent side of the two support columns (21), and the adjacent side of the two connectors (22) is detachably connected to the outside of the connecting base column (1).

7. The teaching and testing device for bending normal stress of a variable cross-section beam according to claim 3, characterized in that, The outside of the movable column (42) is slidably connected to the inside of the movable block (33), and the outside of the movable column (42) is in contact with the outside of the protrusion (45).

8. The teaching and testing device for bending normal stress of a variable cross-section beam according to claim 2, characterized in that, The top of the movable block (33) is slidably connected to the bottom of the crossbeam column (25), the bottom of the movable block (33) is fixedly connected to the top of the movable loading mechanism (5), and the rear side of the display (7) is fixedly connected to the front side of one of the support columns (21).

9. A teaching and testing device for bending normal stress of a variable cross-section beam according to claim 4, characterized in that, One side of the limiting bolt (89) is in contact with the outside of the square column (87), and the outside of the limiting column (88) is in contact with the outside of the spiral annular block (86).

10. A teaching and testing device for bending normal stress of a variable cross-section beam according to claim 5, characterized in that, The front side of the circular plate (85) is rotatably connected to the front inner wall of the fixed box (82), the top of the variable cross-section fish belly beam (9) is in contact with the bottom of the top plate (816), and the bottom of the variable cross-section fish belly beam (9) is in contact with the top of the square plate (814).

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