CN108806422B - Statics comprehensive experiment platform and experiment method - Google Patents

Abstract

The static comprehensive experiment platform comprises a rack with sliding grooves, a planar frame structure and a planar three-hinged arch structure which are arranged at the front end and the rear end of the rack, a loading upright post which is arranged at the middle part of the rack and is adjustable in position, a horizontal rod which is arranged above the loading upright post and can move up and down, and pulleys which are arranged at the end parts of the horizontal rod; the connection between the plane frame structure and the rack can adopt a mode that two ends are fixedly hinged or a mode that one end is fixedly hinged and the other end is movably hinged, the plane frame structure and the plane three-hinged arch structure rod piece material can adopt materials with different elastic moduli, the plane frame structure and the plane three-hinged arch structure adopt different loading positions in the experimental process, the transmissibility of contrast force influences constraint force and internal force on different structures, and the loading device with adjustable position height and azimuth can load the plane frame and the three-hinged arch independently, so that the measurement experiment of the friction coefficient can be independently completed.

Description

A statics comprehensive experimental platform and experimental method

Technical field

The invention relates to the field of mechanical experiments, and in particular to a statics comprehensive experimental platform and experimental methods.

Background technique

Most of the existing basic mechanics experimental platforms are aimed at knowledge points in materials mechanics courses. Experimental platforms for relevant knowledge points in theoretical mechanics courses are limited and the experimental projects are outdated. There is a lack of comprehensive experimental platform to support students to combine the knowledge points in theoretical mechanics and materials mechanics courses, conduct comprehensive experiments, and further understand the applicability of mechanical models and related principles.

Contents of the invention

In order to overcome the above problems, the purpose of the present invention is to propose a static comprehensive experimental platform and experimental method to realize plane static indeterminacy, super statically indeterminate structural restraint force, internal force measurement and friction coefficient measurement. The experiment includes statically determinate and superstatically indeterminate mechanical models composed of rods with different elastic modulus, which are loaded at different points. The effect of the transferability of the contrast force on the binding force and internal force of statically indeterminate and superstatically indeterminate structures provides an in-depth understanding. The application conditions and influence rules of force transmissibility, the loading device can independently measure the friction coefficient and verify the Euler friction formula. This comprehensive experiment has positive and important significance in strengthening the cultivation of students' comprehensive practical ability and stimulating students' in-depth understanding of the transferability properties, statically determined and superstatically determined model differences, static sliding friction, etc.

In order to achieve the above objects, the technical solution of the present invention is implemented as follows:

A static comprehensive experimental platform, including a platform 1 with a chute. The front and rear ends of the platform 1 are respectively equipped with a plane three-hinge arch structure 2 and a plane frame structure 3. The middle part of the platform 1 is equipped with a position-adjustable loader. The loading column 4 is provided with a horizontal rod 5 whose orientation is adjustable and can move up and down on the loading column 4. The end of the horizontal rod 5 is provided with a pulley 6; the plane three-hinge arch structure 2 and the plane frame structure 3 are both There are two loading points, preferably both loading points are on the vertical rods of the planar three-hinge arch structure 2 and the planar frame structure 3, and must be located on the same horizontal line; the planar three-hinge arch structure 2 and the planar frame structure 3 are also provided There are strain gauges connected to the strain tester that measure the strain of the member when loaded at two loading points.

The rods of the planar frame structure 3 and the planar three-hinge arch structure 2 can be replaced by rods with the same cross-sectional shape and size and different elastic modulus of materials.

The pulley 6 uses a movable pulley in the plane frame and three-hinge arch loading experiments, and a static pulley in the friction experiment.

The planar frame structure 3 and the platform 1 are connected by fixed hinges at both ends to form a statically indeterminate structure, or by fixed hinges at one end and movable hinges at the other end to form a statically indeterminate structure. The structural shape and size are exactly the same in the two connection modes.

The planar three-hinge arch structure 2 is a statically determined three-hinge arch formed by two right-angle rods hinged through hinges 11 .

The experimental method of the statics comprehensive experimental platform,

Connect both ends of the planar frame structure 3 to the platform 1 through fixed hinge supports to form a statically indeterminate structure. Adjust the orientation of the pulley 6 so that the plane where the radius of the pulley is located is coplanar with the planar frame structure 3. One end of the flexible cable is tied to the planar frame. At the loading point of structure 3, the other end crosses the pulley 6 to hang the weight. The two loading points on the vertical rod of the planar frame structure 3 are loaded in the horizontal direction. The strains of the rod at different loading positions are measured through strain gauges. , the signal of the strain gauge is connected to the strain tester placed next to the experimental device, wired according to the output characteristics of the Wheatstone bridge and the internal force testing principle, and the axial force and bending moment of the rod are tested. The test results reflect the force in the superstatically indeterminate structure. The effect of translation along its line of action on the binding force and internal force; the fixed hinge support at one end of the planar frame structure 3 is replaced with a movable hinge support, and the planar frame structure 3 becomes a statically determinate structure, with two loading points at the level of Load, measure strain, and calculate binding force and internal force; the measurement results reflect the impact of force translation along the line of action on the statically determined structure on the binding force and internal force.

For the planar three-hinge arch structure 2, a fixed hinge support is installed on the platform 1 to form a planar statically indeterminate structure. Two right-angle rods are hinged together, and the orientation of the horizontal rod 5 is changed so that the plane where the pulley radius is located is in line with the plane three-hinge The planes of the arch structure 2 are coplanar, and a flexible cable is used to cross the pulley to suspend the weight. Loads of the same size are sequentially loaded in the horizontal direction on the two loading points on the vertical rods of the plane three-hinge arch structure 2, and the different loads are measured through strain gauges. The strain at the loading position, the signal of the strain gauge is connected to the strain gauge placed next to the experimental device, the wiring is based on the Wheatstone bridge output characteristics and the internal force testing principle, and the axial force and bending moment of the rod are tested. The measurement results reflect the force along the The impact of the action line slip on the binding force at hinge 11 and the internal force at the location where the strain gauge is installed; replace the materials of the two right-angle rods, measure the binding force and internal force under the same loading conditions, and compare the statically determined three-hinge arches of different materials The restraining force and internal force under the same external load;

In the flat frame and three-hinge arch loading experiments, pulley 6 uses a movable pulley, and the weight of the weight suspended by the flexible cable is the size of the horizontal load. In addition to horizontal loading, the pulley is replaced with a static pulley, and a flexible cable is crossed over the pulley. A weight is suspended from one end of the flexible cable, and the other end is pulled by a force-measuring spring. Compare the weight of the weight with the tension measured by the force-measuring spring, and calculate the friction coefficient between the flexible cable and the static pulley according to Euler's friction formula.

The statics comprehensive experimental platform of the present invention can carry out restraining force measurement and internal force measurement experiments on planar statically indeterminate structures and superstatically indeterminate structures with different constraints and different materials. The static pulley on the loading device can be used to conduct friction coefficient measurement experiments. During the experiment, the students design the experiment completely according to the experimental task book. They can measure the change of the restraint force before and after the force slips along the line of action and the change of the internal force of the rod, observe the effect of the force before and after the force slips, and can also change the constraint type and compare The effect of the same magnitude of force on a statically indeterminate structure and a superstatically indeterminate structure is to replace the static pulley with different roughness, measure the static sliding friction coefficient, and verify the Euler friction formula. The invention has the advantages of replaceable rod materials, replaceable constraint types, replaceable loading positions, simple and compact structure, and convenient operation. The experimental projects that can be set up are of positive importance in strengthening the cultivation of students' comprehensive practical ability, stimulating students' in-depth understanding of transferable inference, understanding the impact of loads on statically determined and superstatically determined structures, and static sliding friction and friction coefficient measurement methods. meaning.

Description of the drawings

Figure 1 is a front view of the present invention.

Figure 2 is a front view of the frame structure.

Figure 3 is the front view of the three-hinge arch.

Detailed ways

The structural principle and working principle of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in Figures 1, 2 and 3, a static comprehensive experimental platform includes a platform 1 with a chute. A flat three-hinge arch structure 2 is installed in the front of the platform 1, and a flat frame structure 3 is installed in the back. A loading column 4 is installed in the middle of the frame 1. A horizontal rod 5 that can move up and down on the loading column 4 is installed on the loading column 4. A pulley 6 is installed at the end of the horizontal rod 5. The orientation of the horizontal rod 5 is adjustable. The orientation of the pulley 6 is adjusted. The plane where the radius of the pulley is located is coplanar with the planar frame structure 3. One end of the flexible cable is tied to the loading point of the planar frame structure 3, and the other end spans the pulley 6 to hang the weight. The 3D point of the planar frame structure is pasted with a planar frame strain gauge 14. There are two loading points on the frame structure 3. The sliding loading column 4 is loaded sequentially on the two loading points 7 and 8 on the vertical rods of the plane frame structure 3. The loading points 7 and 8 are on the same horizontal line, changing the level. The orientation of the rod 5 is such that the plane where the radius of the pulley is located is coplanar with the plane where the planar three-hinge arch structure 2 is. Use a flexible cable to hang the weight across the pulley. There are two loading points 9 and 9 on the vertical rod of the planar three-hinge arch structure 2. Loading points 10 are loaded sequentially, and loading points 9 and 10 are on the same horizontal line. A plane three-hinge arch strain gauge 15 is pasted on the E point of the right member of the plane three-hinge arch structure 2. The pulley 6 in the loading device can be a moving pulley or a static pulley. The movable pulley was used in the three-hinge arch and plane frame loading experiments, and the static pulley was used in the friction coefficient measurement experiment.

The planar frame structure 3 and the platform 1 can be connected by a fixed hinge support and a movable hinge support, or they can be connected by two fixed hinge supports to achieve two structures: statically indeterminate and superstatically indeterminate. The materials of the planar three-hinge arch structure 2 can be replaced, and materials with different elastic moduli are used to compare the impact of the elastic modulus of the materials on the experimental results. The pulley 6 can use static pulleys with different surface roughness, and measure different materials by suspending weights. static sliding friction coefficient.

The experimental method of the statics comprehensive experimental platform of the present invention is:

According to the self-designed and confirmed plan, the two ends of the plane frame structure 3 are connected to the platform 1 through fixed hinge supports to form a statically indeterminate structure. The orientation of the pulley 6 is adjusted so that the plane where the pulley radius is located is the same as the plane frame structure 3. Surface, one end of the flexible cable is tied to the loading point of the planar frame structure 3, and the other end crosses the pulley 6 to suspend the weight. It is loaded in the horizontal direction on the two loading points 7 and 8 respectively, and the different loads are measured through the planar frame strain gauge 14. The position is the strain of the rod at point D. The signal of the plane frame strain gauge 14 at point D is connected to the strain tester placed next to the experimental device. It is wired according to the Wheatstone bridge output characteristics and the internal force testing principle to test the axis of the rod. Force and bending moment, the test results reflect the impact of force translation along its line of action on the binding force and internal force in a statically indeterminate structure; the fixed hinge support at one end of the planar frame structure 3 is replaced with a movable hinge support, and the plane The frame structure 3 becomes a statically determinate structure, and is loaded horizontally at two loading points 7 and 8 respectively. The strain at point D is measured, and the restraining force and internal force are calculated. The measurement results reflect the effect of the force on the statically determinate structure on the restraining force due to translation along the line of action. and the influence of internal forces.

For the planar three-hinge arch structure 2, a fixed hinge support is installed on the platform 1 to form a planar statically indeterminate structure. Two right-angle rods are hinged together, and the orientation of the horizontal rod 5 is changed so that the plane where the pulley radius is located is in line with the plane three-hinge The planes of the arch structure 2 are coplanar, and a flexible cable is used to cross the pulley to suspend the weight. Loads of the same size are sequentially loaded in the horizontal direction on the two loading points 9 and 10 on the vertical rods of the plane three-hinge arch structure 2. Through the plane The three-hinge arch strain gauge 15 measures the strain at point E at different loading positions. The signal of the plane three-hinge arch strain gauge 15 at point E is connected to the strain gauge placed next to the experimental device, and is wired according to the Wheatstone bridge output characteristics and internal force testing principles. , test the axial force and bending moment of the rod, and the measurement results reflect the influence on the binding force at hinge 11 before and after the force slides along the line of action and the influence of the internal force at E. Replace the materials of the two right-angle rods, measure the restraining force and internal force under the same loading conditions, and compare the restraining force and internal force of the statically determinate three-hinge arch of different materials under the same external load.

The loading device used in this test bench is used in the flat frame and three-hinge arch loading experiments. Pulley 6 uses a movable pulley. The weight of the weight suspended by the flexible cable is the size of the horizontal load. In addition to horizontal loading, the pulley is replaced with a static pulley. A flexible cable is straddled over the static pulley. A weight is suspended at one end of the flexible cable. The weight is G. The other end is pulled by a force measuring spring. The weight is slowly raised. The lifting process ensures that the reading of the force measuring spring remains unchanged. The force measuring spring measures The magnitude of the tension obtained is F, and the wrapping angle of the cord on the pulley is β. Put the weight G, the reading of the force measuring spring F, and the wrapping angle β of the cord on the pulley into the Euler friction formula F=Ge ^uβ , the static sliding friction coefficient u of the flexible rope and the static pulley is calculated.

Claims (2)

1. The experimental method of the static comprehensive experimental platform comprises a rack (1) with sliding grooves, wherein a plane three-hinged arch structure (2) and a plane frame structure (3) are respectively arranged at the front end and the rear end of the rack (1), a loading upright post (4) with an adjustable position is arranged in the middle of the rack (1), a horizontal rod (5) which is adjustable in azimuth and can move up and down on the loading upright post (4) is arranged on the loading upright post (4), and a pulley (6) is arranged at the end part of the horizontal rod (5); the plane three-hinged arch structure (2) and the plane frame structure (3) are provided with two loading points, and when the two loading points are both positioned on the vertical rod of the plane three-hinged arch structure (2) and the plane frame structure (3), the two loading points are necessarily positioned on the same horizontal line; the plane three-hinged arch structure (2) and the plane frame structure (3) are also provided with strain gauges which are connected with the strain gauges and used for measuring the strain of the rod piece when the rod piece is loaded at two loading points;

the pulley (6) adopts a movable pulley in a plane frame and three-hinged arch loading experiment and adopts a static pulley in a friction experiment;

the planar frame structure (3) and the bench (1) are fixedly hinged at two ends to form a statically indeterminate structure, or one end is fixedly hinged and the other end is movably hinged to form a statically indeterminate structure, and the structural shape and the size are identical in the two connecting modes;

the plane three-hinged arch structure (2) is a statically determinate three-hinged arch formed by hinging two right-angle rods through a hinge (11);

the method is characterized in that: the experimental method is as follows:

connecting two ends of a planar frame structure (3) on a rack (1) through a fixed hinge support to form a hyperstatic structure, adjusting the orientation of a pulley (6) to enable a plane where the radius of the pulley is located to be coplanar with the planar frame structure (3), tying one end of a flexible rope on a loading point of the planar frame structure (3), hanging weights at the other end of the flexible rope across the pulley (6), respectively loading weights on two loading points on a vertical rod of the planar frame structure (3) along the horizontal direction, measuring the strain of a rod piece at different loading positions through a strain gauge, connecting the signal of the strain gauge with a strain tester placed beside an experimental device, wiring according to the output characteristic of a Wheatstone bridge and the internal force testing principle, and testing the axial force and bending moment of the rod piece, wherein the test result reflects the influence of the translation of the force along an action line of the force in the hyperstatic structure on the constraint force and the internal force; changing a fixed hinge support at one end of a planar frame structure (3) into a movable hinge support, enabling the planar frame structure (3) to be a statically determinate structure, horizontally loading at two loading points respectively, measuring strain, calculating constraint force and internal force, and enabling a measurement result to reflect the influence of translation of the force on the statically determinate structure along an action line on the constraint force and the internal force;

for a plane three-hinged arch structure (2), a fixed hinged support is arranged on a bench (1) to form a plane static-fixed structure, two right-angle rods are hinged together, the direction of a horizontal rod (5) is changed, so that the plane where the radius of a pulley is located is coplanar with the plane where the plane three-hinged arch structure (2) is located, a flexible rope is adopted to cross a pulley to hang weights, loads with the same size are sequentially loaded on two loading points on a vertical rod of the plane three-hinged arch structure (2) along the horizontal direction, strains at different loading positions are measured through strain gauges, signals of the strain gauges are connected to strain gauges placed beside an experimental device, the axial force and bending moment of a rod are tested according to the output characteristics of a Wheatstone bridge and the internal force testing principle, and the measuring result reflects the influence of the force on the constraint force at the hinge (11) before and after the sliding of the force along an action line and the influence of the internal force at the position of the strain gauges; changing the materials of the two right-angle rods, measuring the constraint force and the internal force under the same loading condition, and comparing the constraint force and the internal force of the statically determinate three-hinged arch of different materials under the same external load;

in a plane frame and three-hinged arch loading experiment, a movable pulley is adopted as a pulley (6), the weight of a weight hung by a flexible rope is the size of a horizontal load, except for the horizontal load, the pulley is replaced by a static pulley, a flexible rope is spanned on the pulley, the weight is hung at one end of the flexible rope, the other end of the flexible rope is pulled by a force measuring spring, and the friction coefficient between the flexible rope and the static pulley is calculated by comparing the weight of the weight and the tension measured by the force measuring spring.

2. The experimental method of the statics comprehensive experimental platform according to claim 1, wherein the experimental method comprises the following steps: the rod pieces of the planar frame structure (3) and the planar three-hinged arch structure (2) can be replaced by rod pieces with the same cross-sectional shape and size and different elastic modulus of the material.