Device and method for testing high-temperature III-type fracture toughness of rock

Abstract

The invention discloses a device and a method for testing the high-temperature III-type fracture toughness of rocks, and the device comprises a cuboid sample with circumferential cracks, torsion clamps clamped at the two ends of the cuboid sample, a high-temperature furnace sleeved outside the circumferential cracks on the cuboid sample, and two synchronous rotating wheels sleeved on the cuboid sample, the two synchronous rotating wheels are symmetrically arranged on the two sides of the high-temperature furnace, angle sensors are arranged on the synchronous rotating wheels in a synchronous rotating mode, the torsion clamp is driven by a torsion testing machine, and the angle sensors and the torsion testing machine are connected to a computer through wires. The testing method comprises the following steps of: 1, acquiring data through the testing device; and 2, deducing a high-temperature III-type fracture toughness calculation formula by adopting a displacement method of a finite element method. The invention provides a new method for obtaining the III-type fracture toughness of the rock by using the pure torsional load and a suggested size of the sample, provides a new research method for a rock multi-field coupling fracture mechanical test, and fills the technical blank in the field.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical testing experiments, and particularly to a testing device and method for the high-temperature mode III fracture toughness of rocks. Background Art

[0002] The stress intensity factor is a physical quantity reflecting the strength of the elastic stress field at the crack tip, and has great application value and research value in the engineering field. At present, domestic and foreign research mainly focuses on the mode I and mode II stress intensity factors, and there is no testing equipment and testing method for the mode III stress intensity factor KIII and the mode III fracture toughness. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a testing device and method for the high-temperature mode III fracture toughness of rocks, and a new method for obtaining the mode III fracture toughness of rocks using pure torsional load and the recommended size of the specimen are proposed, providing a new research method for the multi-field coupling fracture mechanics testing of rocks and filling the technical gap in this field.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: a testing device for the high-temperature mode III fracture toughness of rocks, including a cuboid specimen with a circumferential crack, a torsional fixture clamped at both ends of the cuboid specimen, a high-temperature furnace sleeved outside the circumferential crack of the cuboid specimen, and two synchronous rotating wheels sleeved on the cuboid specimen. The two synchronous rotating wheels are symmetrically arranged on both sides of the high-temperature furnace, and angle sensors are synchronously rotated on the synchronous rotating wheels. The torsional fixture is driven by a torsional testing machine, and both the angle sensor and the torsional testing machine are connected to a computer through wires.

[0005] As a preferred technical solution of the present invention, a spacer is clamped between the torsional fixture and the cuboid specimen, and the torsional fixture and the cuboid specimen are fixed by bolts.

[0006] As a preferred technical solution of the present invention, the high-temperature furnace includes a base and a furnace body arranged on the base. The outer circle of the furnace body is square inside, the square hole in the center of the furnace body matches the size of the cuboid specimen, and an asbestos heat insulation layer is laid on the outer shell of the furnace body.

[0007] As a preferred technical solution of the present invention, the synchronous rotating wheel and the angle sensor are driven by static friction, and the synchronous rotating wheel is fixed on the cuboid specimen by 4 fastening bolts.

[0008] A testing method for the high-temperature mode III fracture toughness of rocks includes the following steps:

[0009] Step 1. Obtain data through the testing device: Pass the cuboid specimen through the square hole of the high-temperature furnace to heat the circumferential crack of the cuboid specimen by the high-temperature furnace. The synchronous rotating wheel rotates synchronously with the cuboid specimen. Adjust the two torsion clamps to be torsionally coaxial through the torsion testing machine. The angle sensor rotates synchronously with the synchronous rotating wheel through static friction and obtains the relative torsion angle through conversion, which is transmitted to the computer through the data line. After the high-temperature furnace reaches the specified temperature, keep it warm, apply torque at both ends of the clamp until the specimen fails, and record the torque-angle curve of the experimental process.

[0010] S2. Calculate the mode III fracture toughness through the maximum torque: Use the displacement method of the finite element method to deduce the calculation formula for the high-temperature mode III fracture toughness as follows:

[0011]

[0012] In the formula: T—the total torque on the original crack surface, a—the crack depth; F—the shape factor.

[0013] The beneficial effects produced by adopting the above technical solutions are as follows: The present invention proposes a new method for obtaining the rock mode III fracture toughness using pure torsional load and the recommended specimen size, providing a new research method for the multi-field coupling fracture mechanics testing of rocks and filling the technical gap in this field. Description of the Drawings

[0014] The following further describes the present invention in detail in conjunction with the drawings and specific embodiments.

[0015] Figure 1 is the structural diagram of the testing device for high-temperature mode III fracture toughness;

[0016] Figure 2 is the specimen size diagram;

[0017] Figure 3 is the structural schematic diagram of the high-temperature furnace;

[0018] Figure 4 is the schematic diagram of the synchronous rotating wheel collecting the torsion angle;

[0019] Figure 5 is the rectangular coordinate system and polar coordinate system established at the crack tip;

[0020] Figure 6 is the fitting diagram of the stress intensity factor and the shape factor;

[0021] Figure 7 is the pure mode III fracture trajectory diagram.

[0022] In the figure: 1. Cuboid specimen; 2. Torsion fixture; 3. High-temperature furnace; 4. Synchronous rotating wheel; 5. Angle sensor; 6. Angle sensor support; 7. Bolt; 8. Fixture clamping pad; 9. Data cable; 10. Angle sensor shaft; 11. Square hole; 12. Furnace body; 13. Asbestos heat insulation layer; 14. Rotatable asbestos sealing cover; 15. Base; 16. Fastening bolt. Specific implementation mode

[0023] The test device for the high-temperature mode III fracture toughness of rocks according to the present invention includes a cuboid specimen with a circumferential crack, a torsion fixture clamped at both ends of the cuboid specimen, a high-temperature furnace sleeved outside the circumferential crack of the cuboid specimen, and two synchronous rotating wheels sleeved on the cuboid specimen. The two synchronous rotating wheels are symmetrically arranged on both sides of the high-temperature furnace. An angle sensor is synchronously rotated on the synchronous rotating wheel. The torsion fixture is driven by a torsion testing machine, and both the angle sensor and the torsion testing machine are connected to a computer through wires.

[0024] A pad is clamped between the torsion fixture and the cuboid specimen, and the torsion fixture and the cuboid specimen are fixed by bolts.

[0025] The high-temperature furnace includes a base and a furnace body arranged on the base. The outer circle of the furnace body is square and the inner is round. The square hole in the center of the furnace body matches the size of the cuboid specimen, and an asbestos heat insulation layer is laid on the outer shell of the furnace body.

[0026] The synchronous rotating wheel and the angle sensor are driven by static friction, and the synchronous rotating wheel is fixed on the cuboid specimen by 4 fastening bolts.

[0027] The test method for the high-temperature mode III fracture toughness of rocks according to the present invention includes the following steps:

[0028] Step 1. Obtain data through the test device: Pass the cuboid specimen through the square hole of the high-temperature furnace, heat the circumferential crack of the cuboid specimen by the high-temperature furnace, the synchronous rotating wheel rotates synchronously with the cuboid specimen, adjust the two torsion fixtures to be torsionally coaxial through the torsion testing machine, the angle sensor rotates synchronously with the synchronous rotating wheel through static friction, and obtain the relative torsion angle through conversion, and transmit it to the computer through the data cable. After the high-temperature furnace reaches the specified temperature, keep it warm, apply torque at both ends of the fixture until the specimen is damaged, and record the torque-angle curve of the experimental process.

[0029] S2. Calculate the mode III fracture toughness through the maximum torque: Use the displacement method of the finite element method to deduce the calculation formula for the high-temperature mode III fracture toughness as:

[0030]

[0031] In the formula: T - the total torque on the original crack surface, a - the crack depth; F - the shape factor.

[0032] The derivation process of the high-temperature type III fracture toughness calculation formula is as follows: A rectangular coordinate system and a polar coordinate system as shown in Figure 5 are established at the crack tip. Select several nodes i(r,θ) on the original crack surface, and calculate the anti-plane shear displacement w of each node in the Z direction under the action of a unit load i . According to the fracture mechanics theory, the displacement component w of any point i(r,θ) near the crack tip in the Z direction i is:

[0033]

[0034] Where: —The type III stress intensity factor at node i;

[0035] G—Shear elastic modulus,

[0036] Take several nodes i with θ = ±180° on the original crack surface, and substitute the w i value obtained from the finite element calculation into equation (1) to get:

[0037]

[0038] Then the relative displacement W of node i in the Z direction i is:

[0039]

[0040] Substitute equation (3) into equation (1) to obtain:

[0041]

[0042] From equation (4), the relationship between the stress intensity factor near the crack tip of specimens with different crack lengths and the node position r can be obtained, as shown in Figure 2 . Fit the relationship between the obtained and r by linear regression using the least squares method. The intercept of the straight line (r = 0) is the stress intensity factor K III at the crack tip.

[0043] According to the fracture mechanics theory, K III generally has the following form:

[0044]

[0045] Where: T—The total torque on the original crack surface

[0046] a—Crack depth;

[0047] F—Shape factor.

[0048] It can be obtained from Equation (5):

[0049]

[0050] Substitute the finite element calculation results into Equation (6), and the calculation results of the shape factor F of specimens with different crack lengths (2a / W) can be obtained. Figure 3 That is the relationship between the shape factor F and 2a / h. By performing curve fitting on it using the least squares method, the relationship formula between F and 2a / h can be obtained as follows:

[0051]

[0052] The calculation formula for the mode III fracture toughness is:

[0053]

[0054] The above description is only proposed as a technical solution that can be implemented in the present invention, and does not serve as a single limiting condition for the technical solution itself.

Claims

1. A testing device for the high-temperature mode III fracture toughness of rocks, characterized in that: A cuboid specimen including a circumferential crack, torsion jigs clamped at both ends of the cuboid specimen, a high-temperature furnace sleeved outside the circumferential crack on the cuboid specimen, and two synchronous rotating wheels sleeved on the cuboid specimen. The two synchronous rotating wheels are symmetrically arranged on both sides of the high-temperature furnace. Angle sensors are synchronously rotated and arranged on the synchronous rotating wheels. The torsion jigs are driven by a torsion testing machine. Both the angle sensors and the torsion testing machine are connected to a computer through wires.

2. The testing device according to claim 1, wherein: A spacer block is clamped between the torsion jig and the cuboid specimen, and the torsion jig and the cuboid specimen are fixed by bolts.

3. The test device according to claim 1, wherein: The high-temperature furnace includes a base and a furnace body arranged on the base. The outer circle of the furnace body is round and the inner part is square. The square hole in the center of the furnace body matches the size of the cuboid specimen. An asbestos heat-insulating layer is laid on the outer shell of the furnace body.

4. The test device according to claim 1, wherein: The synchronous rotating wheel and the angle sensor are driven by static friction. The synchronous rotating wheel is fixed on the cuboid specimen by 4 fastening bolts.

5. A method for testing the high-temperature mode III fracture toughness of rocks using the testing device according to claim 1, characterized in that: Including the following steps Step 1: Obtain data through the testing device: Pass the cuboid specimen through the square hole of the high-temperature furnace to heat the circumferential crack of the cuboid specimen by the high-temperature furnace. The synchronous rotating wheel rotates synchronously with the cuboid specimen. Adjust the two torsion jigs to be torsionally coaxial through the torsion testing machine. The angle sensor rotates synchronously with the synchronous rotating wheel by static friction, and the relative torsional angle is obtained through conversion and transmitted to the computer through a data line. After the high-temperature furnace reaches the specified temperature, keep it warm, apply torque at both ends of the jig until the specimen is damaged, and record the torque-angle curve of the experimental process. S2. Calculate the mode III fracture toughness through the maximum torque: The calculation formula for the stress intensity factor KIII is deduced by the displacement method of the finite element method as: The calculation formula for the high-temperature fracture toughness of Type III is as follows: Where: T—the total torque on the original crack surface, a—the crack depth; F—the shape factor, T max —the maximum total torque on the original crack surface.

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