CN111175151A

CN111175151A - Direct shear apparatus for layered experiment

Info

Publication number: CN111175151A
Application number: CN202010118469.0A
Authority: CN
Inventors: 刘钰; 赵国堂; 许乾奇; 付娜; 禹雷
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2020-02-26
Filing date: 2020-02-26
Publication date: 2020-05-19

Abstract

The invention relates to a shear strength measurement technology. The invention discloses a direct shear apparatus for a layering experiment, which comprises a shear box, a fixing device, a vertical loading device, a horizontal loading device and a measuring device, wherein the shear box is provided with a plurality of shear holes; the shearing box comprises an upper box, a middle box and a lower box; the middle box is divided into n layers, and each layer is respectively butted with an adjacent layer; the upper surface of the upper box is a box cover, the box cover is connected with a vertical loading device, and the lower surface of the upper box is butted with the middle box on the uppermost layer; the upper surface of the lower box is in butt joint with the middle box at the lowest layer, the lower surface of the lower box is a box bottom, and the box bottom is connected with the sliding device; the horizontal loading device and the fixing device are respectively arranged at two sides of the shearing box, and the horizontal loading device and the fixing device are provided with lifting mechanisms; n is an integer, n is not less than 1. The direct shear apparatus for the layering experiment can perform direct shear test of the interlayer interface of a multilayer heterostructure, and is particularly suitable for mechanical characteristic test of interlayer shear deformation of a slab ballastless track structure.

Description

Direct shear apparatus for layered experiment

Technical Field

The invention relates to a shear strength measurement technology of civil engineering materials, in particular to a shear strength measurement technology of a track structure with multiple layers of materials, and specifically relates to a layering experiment direct shear apparatus.

Background

In recent years, the high-speed railway of China is rapidly developed, and an eight-vertical eight-horizontal trunk high-speed railway network is formed preliminarily. The slab ballastless track structure is widely applied to high-speed rails in China due to the advantages of high stability, high smoothness, less maintainability and the like.

At present, plate type track structures mainly comprise three types, namely CRTS I, CRTS II and CRTS III plate type tracks. The CRTS I and the CRTS III adopt a unit structure, and the CRTS II adopts an integral longitudinal structure. No matter the unit structure or the longitudinal connection structure, the slab ballastless track belongs to a multilayer thin slab structure and mainly comprises a base plate, a CA mortar layer/self-compacting concrete layer and a track slab.

In the actual operation process, if diseases such as interlayer gap, interlayer void, mortar damage, track slab crack and the like occur in the ballastless track structure, great adverse effects are generated on the safety and comfort of high-speed train running.

On-site investigation shows that under the action of train load and temperature load, a mortar layer is easy to produce crack separation to cause void. The mortar layer is positioned between the track plate and the base plate, the upper part of the mortar layer is bonded with the track plate, and the lower part of the mortar layer is bonded with the base plate. Once the bonding between the track slab and the mortar layer and between the mortar layer and the base plate is damaged, the load transmission path is influenced, and further the overall structure of the slab ballastless track is damaged.

The results of investigations on the operated high-speed railway lines show that the top surface of the mortar layer has a large number of open joints with the track slab and the bottom surface has a small number of open joints with the bed slab. This is closely related to the interfacial bonding characteristics of the upper and lower surfaces of the mortar layer and the shear relationship between the heterogeneous materials. At present, systematic test research on the interlayer bonding characteristics of a multi-layer heterostructure consisting of a track slab, a mortar layer and a base plate is not carried out, and the mechanical properties of the interfaces of the upper surface and the lower surface of the mortar layer are in urgent need of research.

The shearing mechanical parameters of the interlaminar interface are measured, and a direct shear apparatus is usually adopted in the simplest mode.

A typical direct shear apparatus is shown in fig. 1, and mainly comprises a shear box 1, a vertical loading device 2, a horizontal loading device 3 and a measuring device 4.

The shear box 1 is usually made of a material with certain strength, such as steel, an aluminum alloy material, etc., the shear box 1 is composed of an upper box 11 and a lower box 13, the upper surface of the upper box 11 is a box cover 110, which is a structural component of the shear box and also serves as a force transmission plate to transmit pressure. The lower surface of the upper case 11 is butted against the upper surface of the lower case 13 to form a hollow column having a height h1+ h2 and a bottom area q × q for storing the test specimen 10. The lower surface of the lower box 13, which is the bottom of the shear box, is normally placed on the slide 5 so that the lower box 13 can be moved in the horizontal thrust direction by the horizontal loading device 3, as shown in fig. 1 and 2.

During measurement, a test sample is placed in the shear box 1, the vertical loading device 2 applies a certain vertical pressure to the test sample 10 through the pressure transmission plate 110 (which is also a box cover of the upper box), then the horizontal loading device 3 applies a horizontal thrust to the lower box 13, so that the lower box 13 moves for a distance s above the roller 5, the upper box and the lower box generate relative displacement, and the horizontal contact surface of the test sample at the joint of the upper box 11 and the lower box 13 in the shear box generates shear displacement until the horizontal contact surface is damaged, as shown in fig. 3.

In the test, the deformation and stress parameters of the test sample, such as the horizontal acting force, the vertical pressure, the transverse shearing displacement distance and the like, are measured, and then the shearing stress parameter of the test sample can be obtained according to the size of the shearing surface of the test sample (namely the size q multiplied by q of the butt joint area of the test sample in the shearing box).

However, conventional staight scissors tend to shear only against a single stationary plane of a single specimen. Aiming at the interlaminar interface shear mechanical parameter test of a multilayer heterostructure under the same condition, the traditional test device is obviously difficult to meet the requirement.

Disclosure of Invention

The invention mainly aims to provide a layered experiment direct shear apparatus to solve the problem that the direct shear apparatus in the prior art cannot be used for a multilayer structure interface.

In order to achieve the above object, according to an aspect of an embodiment of the present invention, there is provided a direct shear apparatus for a layered experiment, including a shear box, a fixing device, a vertical loading device, a horizontal loading device, and a measuring device; the shearing box is used for loading experimental articles, the fixing device is used for fixing the shearing box, the horizontal loading device is used for applying horizontal acting force to the shearing box, the vertical loading device is used for applying vertical acting force to a test sample, and the measuring system is used for measuring stress parameters of the test sample; the shearing box is characterized by comprising an upper box, a middle box and a lower box; the middle box is divided into n layers, and each layer is respectively butted with an adjacent layer; the upper surface of the upper box is a box cover, the box cover is connected with a vertical loading device, and the lower surface of the upper box is butted with the middle box on the uppermost layer; the upper surface of the lower box is in butt joint with the middle box at the lowest layer, the lower surface of the lower box is a box bottom, and the box bottom is connected with the sliding device; the horizontal loading device and the fixing device are respectively arranged at two sides of the shearing box, and the horizontal loading device and the fixing device are provided with lifting mechanisms; n is an integer, n is not less than 1.

In certain embodiments, the projection of the shear box in the horizontal plane is square.

In some embodiments, the vertical loading means is mounted on the door frame structure.

In some embodiments, the door frame structure includes two parallel posts and a beam perpendicular to the posts, the beam and posts being connected by nuts.

In some embodiments, the sliding means is constituted by a roller.

In certain embodiments, n ═ 1.

In some embodiments, the upper box, the middle box and the lower box are provided with connecting devices, and the upper box or the lower box can be fixedly connected with the middle box respectively.

In some embodiments, the connecting means are disposed on both sides of the upper case, the middle case, and the lower case.

In some embodiments, the connecting means are formed by bolt holes welded to both sides of the upper, middle and lower cases and their mating bolts.

In some embodiments, the bolt holes are arranged in two rows.

According to the technical scheme and the technical scheme further improved in some embodiments, the direct shear apparatus for the layering experiment can perform direct shear test on the interface between layers of the multilayer heterostructure under the same condition, has the advantages of simple structure and low manufacturing cost, and is particularly suitable for mechanical characteristic test of interlaminar shear deformation of a slab ballastless track structure.

The invention is further described with reference to the following figures and detailed description. Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic view of a prior art direct shear apparatus;

FIG. 2 is a top plan view of the shear box of FIG. 1;

FIG. 3 is a schematic view of a shear box undergoing a shear displacement;

FIG. 4 is a schematic structural diagram of a direct shear apparatus for a delamination experiment in example 1;

FIG. 5 is a left side view of the shear box and doorframe structure of FIG. 4;

FIG. 6 is a top view of the lid of FIG. 4;

FIG. 7 is a top view of the cassette of FIG. 4;

FIG. 8 is a schematic structural view of a direct shear apparatus for a delamination experiment in example 2;

FIG. 9 is a schematic structural diagram of a direct shear apparatus for a layering experiment in example 3.

In the figure:

1 is a cutting box;

2 is a vertical loading device;

3 is a horizontal loading device;

4 is a measuring device;

5 is a sliding device;

6 is a fixing device;

7 is a base;

8 is a column;

9 is a cross beam;

10 is a test sample;

11 is an upper box;

12 is a middle box;

13 is a lower box;

20 is a vertical loading mandril;

30 is a horizontal loading ejector rod;

31 is a horizontal loading adjusting upright post;

61 is a fixing device adjusting upright post;

80 is a connecting nut;

101 is a bolt hole;

102 is a bolt;

110 is a force transmission plate (box cover);

111 is a stiffener

121 is a first layer middle box;

122 is a second layer middle box.

Detailed Description

It should be noted that the specific embodiments, examples and features thereof may be combined with each other in the present application without conflict. The present invention will now be described in detail with reference to the attached figures in conjunction with the following.

In order to make the technical solutions of the present invention better understood, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, but not all embodiments. All other embodiments and examples obtained by a person skilled in the art without any inventive step should fall within the protection scope of the present invention.

Example 1

The invention discloses a direct shear apparatus for a layering experiment, which comprises a shear box 1, a fixing device 6, a vertical loading device 2, a horizontal loading device 3 and a measuring device 4. As shown in fig. 4.

The shear box of this example comprises an upper box 11, a middle box 12 and a lower box 13. The upper box 11 is used for loading a first layer of test articles, the middle box 12 is a single-layer mechanism and is used for loading a second layer of test samples, and the lower box 13 is used for loading a third layer of test samples, as shown in fig. 4 and 5.

In the shear box 1 of this embodiment, the upper surface of the upper box 11 is a box cover 110, the box cover 110 is connected to the vertical loading device, the lower surface of the upper box 11 is butted with the upper surface of the middle box 12, the upper surface of the lower box 13 is butted with the lower surface of the middle box 12, the lower surface of the lower box 13 is a box bottom, and the lower surface of the box bottom is connected to the sliding device 5.

As can be seen from fig. 4 and 5, the shearing box 1 of the direct shear apparatus for the layer test of the embodiment has a three-layer structure, and can be used for the shearing test of each layer of the slab ballastless track.

In order to fix the shear box during the experiment, the layered experiment direct shear apparatus of the present example is added with a fixing device 6, as shown in fig. 4. The fixing device 6 is arranged on both sides of the shear box 1 opposite to the horizontal loading device 3, as shown in fig. 4.

The horizontal loading device 3 in this example is composed of a hand-operated screw propulsion device, and applies horizontal force to the shear box through a horizontal loading mandril 30, see fig. 4.

The horizontal loading device 3 and the fixing device 6 in this example have a lifting mechanism. The horizontal loading device 3 can be adjusted up and down along the horizontal loading adjustment column 31 to align the shear box to be loaded. The fixing device 6 can be adjusted up and down along the fixing device adjusting upright post 61, so as to conveniently fix the shear box to be fixed, as shown in fig. 4.

The vertical loading device 2 of this embodiment is also a hand-operated screw propulsion device, and applies a vertical force to the test sample through the vertical loading ram 20 and the force transfer plate 110, see fig. 5.

The measuring device 4 comprises a displacement measuring instrument and a pressure sensor, and can measure the vertical pressure applied by the vertical loading device 2 to the test sample, the horizontal acting force applied by the horizontal loading device 3 to the shear box and the displacement distance of the shear box. The shear stress parameter of the test sample can be calculated through the stress parameters.

As can be seen from fig. 4, 5 and 6, the projection of the shear box 1 in the horizontal plane is square, and the profile of the shear box 1 is a regular quadrangular prism with a square bottom surface.

The box cover of the present embodiment, which is used as the cover of the shear box 1 and the force transmission plate 110 of the vertical loading device 2, is a square steel plate with a surface disposed with a stiffening rib 111, as shown in fig. 4, 5 and 6, and can bear the vertical pressure applied by the vertical loading device 2 and transmit the pressure to the test sample.

The vertical loading unit 2 of this example is mounted on a door frame tie as shown in figure 5.

The door frame structure comprises two parallel upright posts 8 and a cross beam 9 perpendicular to the upright posts 8, wherein the cross beam 9 is connected with the upright posts 8 through nuts 80, so that the height of the cross beam 9 can be conveniently adjusted according to the height of a shearing box, and the door frame structure is suitable for testing interlayer interface shearing mechanical parameters of multilayer structures with different thicknesses and layers.

In order to reduce the friction force, the bottom surface of the lower case 13 is placed on the roller-constituting slide 5, as shown in fig. 4.

The shear box 1 of the invention is a shear box with a multilayer structure, and in order to connect and fix the shear boxes of each layer conveniently, the two sides of the upper box 11, the middle box 12 and the lower box 13 are provided with bolt holes and connecting devices formed by matched bolts, so that the upper box or the lower box and the middle box can be conveniently connected and fixed together, and shear experiments can be carried out on interfaces between different layers. The connecting device formed by arranging two rows of bolt holes 101 can improve the fixing strength and ensure the smooth progress of the experiment, as shown in fig. 7.

As can be seen from fig. 4 and 5, the shear box of this example is loaded with three different test samples for simulating a slab ballastless track structure.

The experimental procedure was as follows:

firstly, filling a base plate material in a lower box 13, filling a CA mortar material in an intermediate box 12, filling a track plate material in an upper box 11, and installing the actual ballastless track to perform operation according to construction requirements;

2. after the materials of each layer are solidified, the upper box 11 and the middle box 12 are fixed together by bolts, and the shear box 1 is arranged right below the vertical loading device, so that the vertical loading mandril 20 is aligned with the central position of the force transfer plate 110, as shown in fig. 5;

3. adjusting the height of the fixing device 6 to fix the fixing device in alignment with the upper box and the middle box, as shown in fig. 4;

4. adjusting the horizontal loading means 3 to align the horizontal loading ram with the lower cassette 13, as shown in figure 4;

5. rotating the handle of the vertical loading device 2, and applying a certain vertical pressure to the test sample 10 through the vertical loading mandril 20;

6. rotating the handle of the horizontal loading device 3, and applying a certain horizontal acting force to the lower box 13 through the horizontal loading mandril 30;

7. the measuring system 4 reads the displacement distance of the lower box 13 and the size of the vertical pressure and the horizontal acting force, and the shearing mechanical parameters of the interface of the ballastless track base plate and the CA mortar layer are obtained through calculation.

Example 2

Fig. 8 shows a layering experiment direct shear apparatus for measuring interface shearing mechanical parameters of a ballastless track CA mortar layer track slab, and the structure of a shearing box 1 of the layering experiment direct shear apparatus of this embodiment is completely the same as that of the shearing box of embodiment 1.

The difference between this example and example 1 is that the connecting device connects and fixes the middle box 12 and the lower box 13 together, the fixing device is aligned and fixed with the upper box 11, the horizontal loading device 3 simultaneously pushes the middle box and the lower box, and the shearing stress occurs at the interface where the upper box 11 and the middle box are butted, as shown in fig. 8.

For the layering experiment direct shear apparatus, other mechanisms are described in example 1.

Example 3

Referring to fig. 9, this is a direct shear apparatus for layer test with a shear box of four-layer structure.

The middle box of the cutting box 1 of this example has 2 layers, and is divided into a first layer middle box 121 and a second layer middle box 122. The lower surface of the upper box 11 is butted with the upper surface of the box 121 in the first layer; the lower surface of the box 121 in the first layer is butted with the upper surface of the box 122 in the second layer; the lower surface of the box 122 in the second layer is butted with the upper surface of the lower box 13; the lower surface of the lower box 13 is a box bottom and is connected with the sliding device 5. As shown in fig. 9.

The shear box 1 of the present example can measure the shear stress at the interface between the layers of the roadbed having the 4-layer structure, and fig. 9 shows the state where the shear stress at the interface between the lower box 13 and the box 122 in the second layer is measured. In this state, the connecting device bolts 102 connect and fix the upper case 11 with the first layer middle case 121 and the second layer middle case 122 through the bolt holes 101, and fix them by the fixing device 6. The horizontal loading device 3 loads only the lower cassette 13.

It can be seen that by the configuration of the connecting means, in combination with the position adjustment of the fixing means 6 and the horizontal loading means 3, the measurement of the shear stress of each interface can be achieved.

If the upper box 11 and the first layer middle box 121 are connected and fixed by the connecting device and the fixing device 6, and then the lower box 12 and the second layer middle box 122 are connected by the connecting device, the horizontal loading device horizontally loads the connected lower box 13 and the second layer middle box 122, and the shear stress of the interface between the first layer middle box 121 and the second layer middle box 122 can be measured.

The lower box 13 is connected and fixed with the first layer middle box 121 and the second layer middle box 122 through the connecting device, the horizontal loading device 3 is used for loading simultaneously, the fixing device 6 is used for fixing the upper box 11, and then the shearing stress of the interface between the upper box 11 and the first layer middle box 121 can be measured.

For other structures of this example, refer to the description of example 1.

The shearing box of the direct shear apparatus for the layering experiment is generally formed by cutting and welding steel plates. The standardized structure is adopted, and the upper box, the lower box and the boxes in all layers have the same structure and size. And filling different materials in each layer according to different roadbed structures to make a test model. During testing, the models of the layers can be interchanged so as to adapt to the shear stress measurement of interfaces between different layers, thereby further simplifying the measurement process and being beneficial to reducing the manufacturing cost and the testing cost.

The height of the fixing device and the horizontal loading device of the direct shear apparatus for the layering experiment can be adjusted, the distance between the vertical loading device and the upper box can also be adjusted, the stress measurement of roadbed interfaces of various layering structures can be conveniently carried out, the direct shear apparatus is particularly suitable for the research and the test of the mechanical property of the slab ballastless track interfaces, and the direct shear apparatus for the layering experiment has very strong time sense and practical significance.

Claims

1. The direct shear apparatus for the layering experiment comprises a shear box, a fixing device, a vertical loading device, a horizontal loading device and a measuring device; the shearing box is used for loading experimental articles, the fixing device is used for fixing the shearing box, the horizontal loading device is used for applying horizontal acting force to the shearing box, the vertical loading device is used for applying vertical acting force to a test sample, and the measuring system is used for measuring stress parameters of the test sample; the shearing box is characterized by comprising an upper box, a middle box and a lower box; the middle box is divided into n layers, and each layer is respectively butted with an adjacent layer; the upper surface of the upper box is a box cover, the box cover is connected with a vertical loading device, and the lower surface of the upper box is butted with the middle box on the uppermost layer; the upper surface of the lower box is in butt joint with the middle box at the lowest layer, the lower surface of the lower box is a box bottom, and the box bottom is connected with the sliding device; the horizontal loading device and the fixing device are respectively arranged at two sides of the shearing box, and the horizontal loading device and the fixing device are provided with lifting mechanisms; n is an integer, n is not less than 1.

2. The direct shear apparatus for layered experiments according to claim 1, wherein the projection of the shear box in the horizontal plane is a square.

3. The direct shear apparatus for layered experiments according to claim 1, wherein the vertical loading device is mounted on a door frame structure.

4. The direct shear apparatus for layered experiments according to claim 1, wherein the door frame structure comprises two parallel columns and a beam perpendicular to the columns, and the beam and the columns are connected by nuts.

5. The direct shear apparatus for layered experiments according to claim 1, wherein said sliding means is constituted by a roller.

6. The direct shear apparatus for layered experiments according to any one of claims 1 to 5, wherein n is 1.

7. The direct shear apparatus for layered experiments according to claim 6, wherein the upper box, the middle box and the lower box are provided with connecting devices, and the upper box or the lower box can be fixedly connected with the middle box respectively.

8. The direct shear apparatus for layered experiments according to claim 7, wherein the connecting means are disposed at both sides of the upper, middle and lower cases.

9. The direct shear apparatus for layered experiments according to claim 7, wherein the connecting means is composed of bolt holes welded at both sides of the upper, middle and lower cases and their matching bolts.

10. The layered experimental direct shear apparatus of claim 7, wherein the bolt holes are arranged in two rows.