A test device and method for accurately obtaining the ultimate tensile strain of rock-like materials

Abstract

The present invention provides a test device and method for accurately obtaining the ultimate tensile strain of rock-like materials. The entire device includes a fixing system and a mold system. The fixing system is used to ensure that during the test, the tensile force is always in the axial direction, and the generatrix of the rock-like material specimen is parabolic, so as to facilitate the subsequent conversion of the ultimate tensile strain. The method for measuring the ultimate tensile strain of the rock-like material specimen includes preparing the specimen through the test device of the invention, placing a strain gauge in the middle of the specimen along the axial direction, performing a pulling test, obtaining the ultimate tensile strain value obtained by the strain gauge, and finally obtaining the accurate ultimate tensile strain through transformation.

Description

Technical Field

[0001] The invention belongs to the technical field of rock mechanics, and in particular relates to a test device and method for accurately obtaining the ultimate tensile strain of rock-like materials. Background Art

[0002] The tensile strength of rock materials is much lower than their compressive strength, so the failure of rock structures is usually caused by tension. Therefore, the tensile strength of rock materials and the ultimate tensile strain of rock materials are important design parameters in structural design. At present, the tensile strength of rock materials in laboratories is usually determined by non-direct tensile test methods such as the Brazilian splitting method and the bending test method. The ultimate tensile strain of rock-like material specimens is usually measured by tensile tests on specimens with strain gauges. However, due to the uncertainty of the fracture position of the specimen during the stretching process, the ultimate tensile strain data of the rock-like material specimens finally measured is not accurate. Therefore, the test methods for the tensile strength and ultimate tensile strain of rock-like materials still need further research. Summary of the invention

[0003] Based on the above problems, the present invention provides a test device and method for accurately obtaining the ultimate tensile strain of rock-like materials. The test piece prepared by the device can be directly subjected to a pull-out test by a universal testing machine to obtain the tensile strength of the rock-like material without any theoretical assumptions. The test result is close to the actual tensile strength of the rock-like material. At the same time, the ultimate tensile strain of the rock-like material can also be obtained by conversion by attaching a strain gauge.

[0004] In order to achieve the above purpose, the invention adopts the following technical solutions:

[0005] In the first aspect, a test device capable of accurately obtaining the ultimate tensile strain of rock-like materials is characterized in that it comprises a fixing mechanism and a mold; the fixing mechanism comprises a fixed support, a fixed bracket, an upper clamp and a lower clamp; the fixed support is welded to the fixed bracket, the upper clamp is fixed to the upper part of the fixed bracket, the lower clamp is fixed to the lower part of the fixed bracket, and the lower clamp is located below the fixed support; the mold is installed on the fixed support, an upper connecting member is provided on the top of the mold, the upper connecting member is fixed by the upper clamp, and a lower connecting member is provided on the bottom of the mold, and the lower connecting member is fixed to the lower clamp.

[0006] As a further technical solution, the mold is a columnar cavity structure, the diameters of the upper and lower parts of which are larger than the diameter of the middle part; the generatrix of the upper and lower parts is a straight line, and the generatrix of the middle part is a parabola.

[0007] As a further technical solution, the mold includes two parts, which are connected by hinges and bolts.

[0008] As a further technical solution, the upper connecting member and the lower connecting member have the same structure, each consisting of a main claw and a secondary claw. The main claw is a large steel column with threads, and the secondary claw includes four small steel columns, which are connected to the bottom of the main claw at a certain angle.

[0009] As a further technical solution, the auxiliary claw of the upper connecting member is fixed in the mold, and the main claw passes through the top of the mold and is clamped by the upper clamp.

[0010] As a further technical solution, the auxiliary claw of the lower connecting member is fixed in the mold, and the main claw passes through the bottom of the mold and the fixed support in sequence and is clamped by the lower clamp.

[0011] As a further technical solution, the upper clamp includes two parts, which are connected by bolts.

[0012] As a further technical solution, the lower clamp includes two parts, which are connected by bolts.

[0013] In a second aspect, the present invention is based on a test method for the test device capable of accurately obtaining the ultimate tensile strain of rock-like materials, comprising the following steps:

[0014] (1) The lower connecting member is placed at the bottom of the mold, with the main claw of the lower connecting member extending outside the mold and the secondary claw remaining inside the mold, and the mold is tightened by bolts;

[0015] (2) Place the assembled mold on a fixed support, adjust the position of the lower connecting member so that it is vertically located in the center of the mold, and the main claw of the lower connecting member passes through the fixed support and is then fixed by the lower clamp;

[0016] (3) pouring the rock-like material into the mold, then inserting the auxiliary claw of the upper connecting member into the rock-like material from the top of the mold, and constantly adjusting its position so that after the pouring is completed, the auxiliary claw is located in the specimen, the main claw is vertically located at the center of the specimen, and the main claw of the upper connecting member is fixed by the upper clamp;

[0017] Vibrate and cure until initial setting;

[0018] (5) After initial setting, loosen the upper and lower clamps, remove the mold, loosen the mold, take out the initially set rock-like material specimen, and continue to cure to the set age;

[0019] (6) A strain gauge with a length of s cm is attached axially in the middle of the specimen, and then a direct tensile test is performed using a universal testing machine to obtain the ultimate tensile strain data ε0 measured by the strain gauge. The ultimate tensile strain ε of the rock-like material is obtained by calculation.

[0020] As a further technical solution, the calculation method of the ultimate tensile strain ε of rock-like materials is as follows:

[0021] Assume that the axial direction of the specimen is the X axis and the radial direction is the Y axis; take the midpoint of a generatrix as the origin, and the generatrix function equation in the middle of the specimen is known to be y1=ax 2 , suppose the generatrix function equation after stretching is y2=bx 2 , the end position of the strain gauge only moves along the x-axis direction; let the change be Δx, the projection length of the strain gauge on the x-axis be L, and solve it by combining the following equations:

[0022]

[0023]

[0024]

[0025]

[0026] in:

[0027] y1——Generator function equation in the middle of the specimen, y1=ax 2 ;

[0028] s——strain gauge length;

[0029] L——projection length of s on the x-axis;

[0030] y2——The central generatrix function equation of the specimen after being stretched, y2=bx 2 ;

[0031] Δx is the change in the projected length of the strain gauge in the x-axis direction;

[0032] ε0——strain data obtained by strain gauge;

[0033] a——constant in the generatrix function equation in the middle of the specimen;

[0034] b——The constant in the central generatrix function equation of the specimen after it is stretched;

[0035] ε——ultimate tensile strain of rock-like materials;

[0036] Finally, the accurate ultimate tensile strain ε of rock-like materials is obtained through the strain formula.

[0037] The beneficial effects of the present invention are as follows:

[0038] 1. The test piece made by the device proposed by the present invention is easy to make, low in cost, and the test piece and the test machine are easy to install, and can be used with the common universal testing machine in the laboratory, and the threshold for use is low. The upper clamp and the lower clamp on the fixing system are used to align the connecting member with the test piece, thereby ensuring that the load increases in the axial direction, so that uniform stress is generated on the cross section of the test piece, and at the same time, the probability of the test piece breaking in the uniform stress section is increased.

[0039] 2. The present invention clamps the upper connecting member and the testing machine, and the inverted eight-claw shape increases the contact area between the connecting member and the test piece, which not only prevents the member from being pulled out during the pulling process, but also makes the force inside the test piece more uniform, thereby obtaining more accurate results.

[0040] 3. The test piece made by the present invention can be subjected to a pull-out test by a testing machine to directly measure the tensile strength of rock-like materials. No theoretical assumptions or data conversion are required during the calculation, which facilitates the implementation and improves the measurement accuracy.

[0041] 4. The central generatrix of the specimen of the present invention is parabolic, thick at both ends and narrow in the middle, and is more likely to be damaged at the shortest diameter in the middle during tension. When the strain of the specimen is detected by attaching strain gauges, the ultimate tensile strain of the rock-like material specimen can be accurately obtained after a certain conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0043] Figure 1 It is a schematic diagram of the overall structure of the fixing system and the molding device of the present invention;

[0044] Figure 2 It is a schematic diagram of the fixing system of the present invention;

[0045] Figure 3 It is a schematic diagram of the mold after assembly of the present invention;

[0046] Figure 4 is a cross-sectional view of the mold of the present invention;

[0047] Figure 5 It is a schematic diagram of a test piece of the present invention;

[0048] Figure 6 It is a schematic diagram of the clamp of the present invention;

[0049] Figure 7 It is a schematic diagram of the connecting member of the present invention.

[0050] In the figure: 1. connecting column; 2. clamp; 3. lower connecting member; 4. fixed support; 5. lower bolt of mold; 6. lower hinge of mold; 7. mold body; 8. fixed support; 9. upper bolt of mold; 10. upper hinge of mold; 11. clamp fixing bolt; 12. main claw channel; 13. through hole; 14. clamp bolt hole; 15. specimen body; 16. main claw; 17. auxiliary claw; 18. upper connecting member; 19. ear plate; 20. connecting column bolt hole; 21. upper bolt hole; 22. lower bolt hole. DETAILED DESCRIPTION

[0051] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0052] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless otherwise explicitly stated in the present invention, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "include" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof;

[0053] For the convenience of description, if the words "up", "down", "left" and "right" appear in the present invention, they only indicate that they are consistent with the up, down, left and right directions of the drawings themselves, and do not limit the structure. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0054] Combine the following Figures 1 to 7 The technical solution of the present invention is further illustrated by specific embodiments.

[0055] like Figure 1 , Figure 2 , Figure 3 As shown, this embodiment discloses a test device that can accurately obtain the ultimate tensile strain of rock-like materials. The entire device includes a fixing mechanism and a mold; wherein, Figure 2 As shown, the fixing system includes a fixing support 4, a fixing bracket 8 and a clamp 2; the fixing system as a whole is a steel structure, the fixing support 4 is horizontally arranged, the fixing bracket 8 is vertically arranged, the fixing support 4 and the fixing bracket 8 are welded together to form a whole, and the fixing support 4 is fixed to the lower part of the fixing bracket 8, as shown in FIG. Figure 1 The bottom of the fixed support 4 is also supported by a pillar to improve the rigidity of the entire device.

[0056] Further, such as Figure 1 As shown, two ear plates 19 are welded to the upper and lower parts of the fixed bracket 8 respectively, and two holes are reserved on each ear plate 19 for passing the connecting column 1, wherein the connecting column 1 is a steel column which is smooth in the middle and has threads at both ends, and passes through the ear plate horizontally to connect the clamp and the ear plate to achieve the fixation of the clamp; the connecting column 1 passes through the ear plate and the clamp 2 to achieve the connection between the ear plate and the clamp 2, that is, a clamp 2 is fixed on the two upper ear plates 19, and a clamp 2 is fixed on the two lower ear plates, and the lower ear plate and clamp are located below the fixed support 4; the clamp 2 can rotate freely around the corresponding connecting column 1.

[0057] Furthermore, the fixed support 4 in this embodiment is a disc structure, and a through hole 13 is provided at the center of the fixed support 4, and the through hole cooperates with the lower connecting member 3 on the mold.

[0058] Furthermore, the fixture 2 in this embodiment is as follows Figure 6 As shown, the structures of the upper and lower clamps are exactly the same. One of them is taken as an example for explanation. In this embodiment, the clamp 2 is composed of two symmetrical parts. Two connecting column bolt holes 20 are reserved at the left end of the clamp 2. The connecting column bolt holes 20 cooperate with the connecting column 1 to realize the connection between the clamp and the ear plate. Two bolt holes 14 are reserved at the right end of the clamp 2. The bolt holes 14 cooperate with the fixing bolts 11. The two parts of the clamp are connected together by tightening the fixing bolts 11 of the clamp, and a mounting hole is formed between the two clamps after the connection. The connecting member 18 on the mold passes through the mounting hole on the upper clamp and is clamped by the upper clamp. The connecting member 3 on the mold passes through the mounting hole on the lower clamp and is clamped by the lower clamp.

[0059] Further, such as Figure 3 As shown, the mold system in this embodiment includes three parts: a mold body 7, an upper connecting member 3, and a lower connecting member 18; wherein, the mold body 7 is made of steel, and is a columnar cavity structure, the shape of the cavity is thick at the top and bottom and thin in the middle (that is, the upper diameter and the lower diameter are both larger than the diameter of the middle part), and the generatrix of the middle part is a parabola, and the generatrix of the upper and lower parts is a straight line; the middle part of the entire mold is set to a parabolic shape in order to more accurately obtain the ultimate tensile strain of the rock material and facilitate subsequent conversion work.

[0060] Furthermore, in order to facilitate demoulding, the mold body 7 is a cavity structure with an open top and a closed bottom. The mold body 7 is divided into two symmetrical parts. One side of the two symmetrical parts is connected by an upper hinge 10 and a lower hinge 6, and the other side is connected by two bolts 9 at the upper part and two bolts 5 at the lower part passing through corresponding upper bolt holes 21 and lower bolt holes 22; the upper hinge 10 is located at the upper part of the mold body 7, avoiding the thin part in the middle; the lower hinge 6 is located at the lower part of the mold body 7, avoiding the thin part in the middle; the upper bolt hole 21 is located on the ear plate extending from the upper part of the mold body 7, and the lower bolt hole 22 is located on the ear plate extending from the lower part of the mold body 7, and the upper and lower ear plates also avoid the thin part in the middle;

[0061] Furthermore, there is a main claw channel 12 (ie, a through hole) at the bottom center of the mold body 7; the main claw channel 12 is used to fix the main claw of the lower connecting member 3; and the upper connecting member 18 is inserted into the test piece.

[0062] Furthermore, when the mold is in use, bolts 9 and bolts 5 must be tightened symmetrically to ensure uniform force and a tight fit of the mold, so that the test block is smooth and symmetrical.

[0063] Furthermore, the upper connecting member 18 and the lower connecting member 3 have the same structure. Specifically, the upper connecting member 18 and the lower connecting member 3 are in the shape of an inverted octagon, and are composed of a main claw 16 and a secondary claw 17. The main claw 16 is a steel column with a thread, and the secondary claw 17 is composed of four small steel columns distributed at a certain angle at the end of the main claw 16, and the material is steel; the main claw 16 extends outside the mold through the main claw channel 12 of the mold, and the secondary claw 17 remains inside the mold. The upper main claw 16 passes through the mounting hole of the upper clamp 2, and the lower main claw 16 passes through the mounting hole of the lower clamp 2 to fix the mold body.

[0064] The method for accurately measuring the ultimate tensile strain of a rock-like material specimen using the above device comprises the following steps:

[0065] (1) According to the test requirements, the corresponding rock-like material is configured. Then, to facilitate demolding, a layer of oil is applied inside the mold. The lower connecting member 3 is placed at the bottom of the mold, and its main claw 16 extends out of the mold through the main claw channel 12 of the mold, and the auxiliary claw 17 remains inside the mold. The mold is then tightened by the upper and lower bolts 9 and bolt 5;

[0066] (2) Place the assembled mold on the fixed support 4, and adjust the position of the lower connecting member 3 by passing the main claw 16 of the lower connecting member 3 through the through hole 13 on the fixed support so that it is vertically located in the center of the mold, and then fix the lower connecting member 3 by adjusting the fixing bolt 11 on the clamp 2;

[0067] (3) pouring the rock-like material into the mold, then inserting the auxiliary claw of the upper connecting member 18 into the rock-like material from the top of the mold, and constantly adjusting its position so that after the pouring is completed, the auxiliary claw is located in the specimen, the main claw is vertically located at the center of the specimen, and the main claw of the upper connecting member 18 is fixed by the upper clamp;

[0068] (4) Vibrate and cure until initial setting;

[0069] (5) After initial setting, loosen the clamp 2, remove the mold, open the mold by loosening the upper and lower bolts 9 and bolt 5 of the mold, take out the initially set rock-like material specimen, and continue to cure it to the set age.

[0070] (6) A strain gauge with a length of s = 5 cm is attached to the middle of the specimen along the axial direction, and then a direct tensile test is performed using a universal testing machine to obtain the ultimate tensile strain data ε0 = 152 × 100 -6 .

[0071] 7) Assume that the axial direction of the specimen is the X-axis and the radial direction is the Y-axis. Figure 3 Take the orientation of the specimen as an example, the horizontal direction is the Y axis, and the vertical direction is the X axis) take the midpoint of a generatrix as the origin, and the generatrix function equation in the middle of the specimen is known to be y1=0.08x 2 , suppose the generatrix function equation after stretching is y2=bx 2 , the end position of the strain gauge only moves along the x-axis. Assume that the change is Δx, the projection of the strain gauge on the x-axis is L, and substitute the data into the following equation:

[0072]

[0073]

[0074]

[0075]

[0076] The solution is: the exact value of the ultimate tensile strain of rock-like materials ε = 159.6 × 10 -6

[0077] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A test device capable of accurately obtaining the ultimate tensile strain of rock-like materials, characterized in that: Including fixing mechanism and mold; The fixing mechanism comprises a fixing support, a fixing bracket, an upper clamp and a lower clamp; the fixing support is welded to the fixing bracket, the upper clamp is fixed to the upper part of the fixing bracket, the lower clamp is fixed to the lower part of the fixing bracket, and the lower clamp is located below the fixing support; the mold is installed on the fixing support, an upper connecting member is provided on the top of the mold, the upper connecting member is fixed by the upper clamp, and a lower connecting member is provided at the bottom of the mold, and the lower connecting member is fixed to the lower clamp; The upper connecting member and the lower connecting member have the same structure, each consisting of a main claw and a secondary claw. The main claw is a large steel column with threads, and the secondary claw includes four small steel columns, which are connected to the bottom of the main claw at a certain angle.

2. The test device for accurately obtaining the ultimate tensile strain of rock-like materials according to claim 1, characterized in that: The mold is a columnar cavity structure, the diameters of the upper and lower parts of which are larger than the diameter of the middle part; the generatrix of the upper and lower parts is a straight line, and the generatrix of the middle part is a parabola.

3. The test device for accurately obtaining the ultimate tensile strain of rock-like materials according to claim 1, characterized in that: The mold comprises two parts, which are connected by hinges and bolts.

4. The test device for accurately obtaining the ultimate tensile strain of rock-like materials according to claim 1, characterized in that: The auxiliary claw of the upper connecting member is fixed in the mold, and the main claw passes through the top of the mold and is clamped by the upper clamp.

5. The test device for accurately obtaining the ultimate tensile strain of rock-like materials according to claim 1, characterized in that: The auxiliary claw of the lower connecting member is fixed in the mold, and the main claw passes through the bottom of the mold and the fixed support in sequence and is clamped by the lower clamp.

6. The test device for accurately obtaining the ultimate tensile strain of rock-like materials according to claim 1, characterized in that: The upper clamp comprises two parts, which are connected by bolts.

7. The test device for accurately obtaining the ultimate tensile strain of rock-like materials according to claim 1, characterized in that: The lower clamp comprises two parts, which are connected by bolts.

8. The test method of the test device capable of accurately obtaining the ultimate tensile strain of rock-like materials according to any one of claims 1 to 7, characterized in that: The steps include: (1) The lower connecting member is placed at the bottom of the mold, with the main claw of the lower connecting member extending outside the mold and the secondary claw remaining inside the mold, and the mold is tightened by bolts; (2) Place the assembled mold on a fixed support, adjust the position of the lower connecting member so that it is vertically located in the center of the mold, and the main claw of the lower connecting member passes through the fixed support and is then fixed by the lower clamp; (3) pouring the rock-like material into the mold, then inserting the auxiliary claw of the upper connecting member into the rock-like material from the top of the mold, and constantly adjusting its position so that after the pouring is completed, the auxiliary claw is located in the specimen, the main claw is vertically located at the center of the specimen, and the main claw of the upper connecting member is fixed by the upper clamp; (4) Vibrate and cure until initial setting; (5) After initial setting, loosen the upper and lower clamps, remove the mold, loosen the mold, take out the initially set rock-like material specimen, and continue to cure to the set age; (6) A strain gauge with a length of s cm is attached axially in the middle of the specimen, and then a direct tension test is carried out to obtain the ultimate tensile strain data ε0 measured by the strain gauge. The ultimate tensile strain ε of the rock-like material is obtained by calculation.

9. The test method according to claim 8, characterized in that The calculation method of the ultimate tensile strain ε of rock-like materials is as follows: Assume that the axial direction of the specimen is the X axis and the radial direction is the Y axis; take the midpoint of a generatrix as the origin, and the generatrix function equation in the middle of the specimen is known to be y1=ax 2 , suppose the generatrix function equation after stretching is y2=bx 2 , the end position of the strain gauge only moves along the x-axis direction; let the change be Δx, the projection length of the strain gauge on the x-axis be L, and solve it by combining the following equations: in: y1——Generator function equation in the middle of the specimen, y1=ax 2 ; s——strain gauge length; L——projection length of s on the x-axis; y2——The central generatrix function equation of the specimen after being stretched, y2=bx 2 ; Δx is the change in the projected length of the strain gauge in the x-axis direction; ε0——strain data obtained by strain gauge; a——constant in the generatrix function equation in the middle of the specimen; b——The constant in the central generatrix function equation of the specimen after it is stretched; ε——ultimate tensile strain of rock-like materials; Finally, the accurate ultimate tensile strain ε of rock-like materials is obtained through the strain formula.

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