Apparatus and method for measuring residual stress in rock masses under non-uniform temperatures

Abstract

This invention discloses an apparatus and method for measuring the residual stress of rock mass under non-uniform temperature, including a sample cell, a heating and temperature control system, and an X-ray diffractometer system. The sample cell includes an upper base and a lower base, and the rock mass sample to be tested is placed in the upper base. The heating and temperature control system includes a thermocouple, a heating element, and a PID temperature controller. By changing the non-uniform temperature evolution process during X-ray diffraction testing through the heating and temperature control system, the non-uniform temperature environment of the rock mass under real working conditions is simulated. In-situ testing of the rock mass under non-uniform temperature conditions is performed using the X-ray diffractometer, and diffraction peak data of the rock mass at each dipping angle ψ is collected using the dipping method, thereby determining the residual stress evolution process of the rock mass at different temperatures. Simultaneously, the rock mass sample can be subjected to stress-relief annealing treatment through the heating and temperature control system to study the changes in residual stress after stress-relief annealing treatment under different non-uniform temperature fields.

Description

Technical Field

[0001] This invention relates to the field of residual stress characterization technology for rock mass materials, and in particular to an apparatus and method for measuring the residual stress of rock mass under non-uniform temperature. Background Technology

[0002] Residual stress refers to the internal stress that maintains self-equilibrium within a material even under conditions such as the absence of external loads or varying temperature environments. For rock materials, residual stress can lead to crack propagation, reduce the material's resistance to hydraulic fracturing, and consequently affect the stability of geological engineering projects. Therefore, measuring the residual stress in rock materials is of great significance for the safety of geological engineering projects.

[0003] Among the methods for characterizing residual stress in rock materials, X-ray diffraction (XRD) is widely used for measuring residual stress due to its advantages of being non-destructive, rapid, and accurate. The sin(θ) method is one such method. 2 The ψ-method is suitable for samples with large and flat test surfaces and can be used to characterize residual stress in rock materials. The isoclipt method performs XRD characterization at different isoclipt angles ψ (the angle between the sample surface and the X-ray beam), recording the diffraction angle θ (the angle between the X-ray and the diffraction crystal plane) at each isoclipt angle ψ. Then, based on Bragg's equation, elasticity theory, and combined with the Poisson's ratio and elastic modulus of the rock mass, the magnitude and distribution of residual stress in the material can be analyzed. Currently, the isoclipt method is typically used for characterization tests at room temperature. However, in actual working conditions, rock materials are usually under unevenly distributed temperature fields. On the other hand, studying stress-relief annealing of rock materials under different temperature conditions can effectively remove residual stress in the rock material, enhancing its stability and reliability. Therefore, characterizing residual stress in rock materials under non-uniform temperature fields has significant scientific value and practical application significance for fields such as geology and engineering. Summary of the Invention

[0004] The main objective of this invention is to provide a device for measuring the residual stress of rock masses under non-uniform temperatures. This device achieves a non-uniform temperature field condition for the sample cell by using heating elements composed of materials with different resistivities. Thermocouples are used to monitor the non-uniform temperature field distribution on the sample's test surface in real time. In-situ XRD with the same inclination method is used to measure the diffraction angle θ of the sample at each inclination angle. The magnitude and distribution law of the residual stress are calculated through theoretical derivation. Based on this device, this invention realizes the measurement of residual stress in rock materials under non-uniform temperature field conditions. Furthermore, through stress-relief annealing processes and related theoretical methods, it reveals the relationship between stress-relief annealing of rock materials under different non-uniform temperature field conditions and the magnitude and distribution law of their residual stress.

[0005] The technical solution adopted in this invention is:

[0006] An apparatus for measuring residual stress in rock mass under non-uniform temperature includes a sample cell, a heating and temperature control system, and an X-ray diffractometer system. The sample cell includes an upper base and a lower base, and the rock mass sample to be tested is placed inside the upper base. The heating and temperature control system includes thermocouples, heating elements, and a PID temperature controller. Several thermocouples are arranged radially on the upper base to measure the temperature at different locations within the sample cell. Each thermocouple is electrically connected to the PID temperature controller to transmit the measured temperature signal. Several heating elements with different resistivities are arranged between the upper and lower bases, and each heating element is electrically connected to the PID temperature controller. The PID temperature controller transmits the measured temperature signal to the heating element. The actual temperature measured by the thermocouple is compared with the preset temperature. By controlling the energizing time of the heating element, the actual temperature is made closer to the preset temperature, thereby achieving control of non-uniform temperature. The X-ray diffractometer system includes an X-ray emitter, an X-ray detector, an X-ray diffraction sample stage, and an X-ray diffractometer control system. The sample cell is placed on the X-ray diffraction sample stage. The X-ray emitter and X-ray detector are located above the sample cell and are respectively connected to the X-ray diffractometer control system. The X-ray detector receives the intensity of the diffracted rays and the diffraction angle θ after the X-ray emitter enters the sample and transmits the signal to the X-ray diffractometer control system. The X-ray diffractometer control system can change the angle ψ between the sample surface being tested and the X-ray emitted by the X-ray emitter.

[0007] In the above scheme, the sample cell also includes a transparent beryllium window, which is made of beryllium metal and is placed on the upper surface of the base of the sample cell, above the sample.

[0008] In the above scheme, the sample cell also includes a sample cell shell, which is detachably fixed to the upper base of the sample cell; the upper base of the sample cell is detachably fixed to the lower base of the sample cell.

[0009] In the above scheme, the connection between the upper base and the lower base of the sample cell is provided with heating holes in the horizontal direction for inserting each heating element, and each heating element is pre-embedded in the heating hole in a straight line.

[0010] In the above scheme, three thermocouples are arranged in a pre-embedded manner along a certain radial direction of the sample cell base, namely thermocouple I, thermocouple II and thermocouple III. Thermocouple I and thermocouple III are located at the two ends, and thermocouple II is located at the midpoint between thermocouple I and thermocouple III.

[0011] In the above scheme, two heating elements are arranged in parallel, namely heating element I and heating element II. Heating element I is arranged between thermocouple I and thermocouple II, and heating element II is arranged between thermocouple II and thermocouple III.

[0012] In the above scheme, let the position of thermocouple I be x = 0, the position of thermocouple III be x = D, then the position of thermocouple II be x = D / 2. The temperature distribution in the sample cell with respect to position x is calculated by formula (2), which is as follows:

[0013]

[0014] In equation (2), T x Let T be the temperature at point x in the sample cell, T0 be the temperature at thermocouple I, and T... D The temperature at thermocouple III;

[0015] By pre-setting multiple temperature distribution scenarios, the variation of residual stress in the same rock sample under different non-uniform temperature fields can be compared.

[0016] This invention also proposes a method for measuring the residual stress of rock mass under non-uniform temperature, using the aforementioned apparatus, comprising the following steps:

[0017] Step 1: Place the cut and polished rock sample in the base of the sample cell, place the transparent beryllium window above the sample, and place the sample cell on the X-ray diffraction sample stage.

[0018] Step 2: Turn on the heating and temperature control system to preheat. Set the temperature to the preset temperature and wait until the temperature difference between thermocouple I and thermocouple III stabilizes at 5-10℃.

[0019] Step 3: After the temperature stabilizes, start the XRD test. Set the X-ray diffractometer system to the preset conditions, with the inclination angle ψ being 0° and the measurement range being 10 to 80°. Perform the first characterization to obtain the highest diffraction intensity of the sample and its corresponding diffraction angle θ.

[0020] Step 4: Use the X-ray diffractometer control system to change the inclination angle ψ between the transparent beryllium window and the X-ray emitter, perform XRD tests at multiple inclination angles, and record the highest diffraction intensity and its corresponding diffraction angle θ at each inclination angle.

[0021] Step 5: Calculate the stress value σ of the sample at each tilt angle ψ, and plot the stress value σ at each tilt angle as the vertical axis, and the square of the sine of the tilt angle sin ψ. 2 Plot the image with ψ as the horizontal axis, perform linear fitting on the data, and obtain the residual stress at the test point of the sample;

[0022] Step 6: Adjust the heating and temperature control system to change the temperature in the sample cell, and repeat steps 3-5 to record the variation curve of residual stress of the same sample under different non-uniform temperature field conditions.

[0023] In the above method, in step 5, the interplanar spacing d of the sample at each tilt angle ψ is calculated using formula (3). ψ Formula (3) is:

[0024] nλ=2d ψ ·sinθ (3)

[0025] In equation (3), n is the diffraction order, usually taken as 1, representing the first-order diffraction; λ represents the wavelength of the X-ray source; d ψ θ is the interplanar spacing of the sample under test at the same tilt angle ψ; θ is the diffraction angle.

[0026] Then, the stress value σ at each tilt angle ψ is calculated using the elasticity theory formula (4). Formula (4) is:

[0027]

[0028] In equation (4), σ is the stress value at each inclination angle; E is the Young's modulus of the sample; ν is the Poisson's ratio of the sample; Δd ​​is the change in interplanar spacing of the sample at each inclination angle, Δd = d ψ -d0; d0 is the interplanar spacing of the sample when the tilt angle is 0.

[0029] In the above method, when it is necessary to study the effect of stress-relief annealing, step 6 is adjusted to: adjust the heating and temperature control system to perform stress-relief annealing on the rock sample, specifically by setting the temperature at thermocouple I to 200-300℃, holding it at that temperature for 1-3 hours, and then cooling it to room temperature. After cooling, steps 3-5 are repeated, and the changes in residual stress of the same sample after stress-relief annealing under non-uniform temperature fields are recorded. The method also includes step 7: adjust the heating and temperature control system to change the temperature in the sample cell, and repeat steps 3-6, recording the changes in residual stress of the same sample after stress-relief annealing under different non-uniform temperature fields, thereby optimizing the stress-relief annealing conditions.

[0030] The beneficial effects of this invention are:

[0031] The device proposed in this invention for measuring the residual stress of rock mass under non-uniform temperature achieves non-uniform temperature control of the sample cell through two electric heating elements with different resistivities. Combined with thermocouple temperature monitoring and PID temperature control, it simulates the non-uniform temperature environment of the rock mass under real-world conditions. In-situ testing of the rock mass under non-uniform temperature conditions is conducted using the X-ray dichroism method, collecting diffraction peak data of the rock mass at each dichroism angle ψ to determine the evolution of residual stress under different non-uniform temperatures. Simultaneously, stress-relief annealing can be performed on the rock mass through a heating and temperature control system to reduce the residual stress. The changes in residual stress of the same sample after stress-relief annealing under different non-uniform temperature fields are recorded, thereby optimizing the stress-relief annealing conditions. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the device of the present invention for measuring the residual stress of rock mass under non-uniform temperature;

[0034] Figure 2 yes Figure 1 Exploded view of the sample cell in the device;

[0035] Figure 3 yes Figure 1 A schematic diagram showing the distribution of thermocouples and heating elements in the device;

[0036] Figure 4 This is a flowchart of the method of the present invention for measuring the residual stress of rock mass under non-uniform temperature.

[0037] In the figure: 11. Transparent beryllium window; 12. Upper base of sample cell; 13. Lower base of sample cell; 14. Sample cell outer shell;

[0038] 21. Thermocouple; 211. Type I Thermocouple; 212. Type II Thermocouple; 213. Type III Thermocouple; 22. Type I Heating Element; 23. Type II Heating Element; 24. PID Temperature Controller;

[0039] 31. X-ray emitter; 32. X-ray detector; 33. X-ray diffraction sample stage; 34. X-ray diffractometer control system. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0042] In this invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0043] like Figure 1-2As shown, this invention proposes a device for measuring the residual stress of rock mass under non-uniform temperature, including a sample cell, a heating and temperature control system, and an X-ray diffractometer system. The sample cell includes an upper base 12 and a lower base 13, with the rock mass sample to be tested placed inside the upper base 12. The heating and temperature control system includes thermocouples 21, heating elements, and a PID temperature controller 24. Several thermocouples are arranged radially along the upper base 12 to measure the temperature at different locations within the sample cell. Each thermocouple is electrically connected to the PID temperature controller 24 to transmit the measured temperature signal. Several heating elements with different resistivities are arranged between the upper base 12 and the lower base 13, and each heating element is electrically connected to the PID temperature controller 24. The PID temperature controller 24 compares the actual temperature measured by each thermocouple with a preset temperature, and controls the energizing time of the heating elements to bring the actual temperature closer to the preset temperature, thereby achieving temperature control. The X-ray diffractometer system includes an X-ray emitter 31, an X-ray detector 32, an X-ray diffraction sample stage 33, and an X-ray diffractometer control system 34. The sample cell is placed on the X-ray diffraction sample stage 33, and the X-ray emitter 31 and the X-ray detector 32 are located above the sample cell. The X-ray detector 32 receives the intensity of the diffracted rays and the diffraction angle θ after the X-ray emitter 31 enters the sample. The X-ray diffractometer control system 34 can change the inclination angle ψ between the sample surface and the X-ray emitter 31. The inclination angle ψ is adjustable from 0 to 45°.

[0044] In one embodiment of the present invention, the sample cell further includes a transparent beryllium window 11, which is made of beryllium metal. The transparent beryllium window 11 is placed on the upper surface of the base 12 of the sample cell, above the sample, and can effectively reduce the attenuation of X-rays.

[0045] In one embodiment of the present invention, the sample cell further includes a sample cell housing 14, which is fixedly connected to the sample cell upper base 12 by a detachable means (such as a threaded connection).

[0046] In one embodiment of the present invention, the upper base 12 of the sample cell and the lower base 13 of the sample cell are fixedly connected by a detachable means (such as bolt connection).

[0047] In one embodiment of the present invention, heating holes for inserting heating elements are provided at the connection between the upper sample cell base 12 and the lower sample cell base 13 in the horizontal direction, and each heating element is pre-embedded in the heating hole in a straight line.

[0048] In one embodiment of the present invention, the sample cell base 12 can accommodate a maximum of The cylindrical sample has a transparent beryllium window 11 with dimensions of [missing information]. The diameter of the heating hole is

[0049] In one embodiment of the present invention, such as Figure 3 As shown, three thermocouples are pre-embedded along a radial direction of the base 12 on the sample cell. These are thermocouple I 211, thermocouple II 212, and thermocouple III 213. Thermocouple I 211 and thermocouple III 213 are located at opposite ends, while thermocouple II 212 is located at the midpoint between thermocouple I 211 and thermocouple III 213. All three thermocouples can monitor temperatures from 25 to 300°C with a temperature control accuracy of 0.1°C, and the temperature can be displayed on the panel of the PID temperature controller 24.

[0050] By selecting heating elements with different resistivities, a non-uniform temperature field can be applied to the sample cell simultaneously. The heat generated by heating elements with different resistivities can be expressed by Joule's law (1), and formula (1) is:

[0051] Q = I 2 Rt (1)

[0052] In equation (1), Q is the heat generated by the heating element, I is the current passing through the heating element, R is the resistance of the heating element, and t is the time it takes for the current to pass through the heating element.

[0053] In one embodiment of the present invention, such as Figure 3 As shown, two heating elements are arranged in parallel, namely heating element I 22 and heating element II 23. Heating element I 22 is arranged between thermocouple I 211 and thermocouple II 212, and heating element II 23 is arranged between thermocouple II 212 and thermocouple III 213, which can heat the sample cell at different temperature gradients.

[0054] Let the position of thermocouple I 211 be x = 0, and the position of thermocouple III 213 be x = D. Then the position of thermocouple II 212 is x = D / 2. The temperature distribution in the sample cell with respect to position x is calculated using formula (2), which is as follows:

[0055]

[0056] In equation (2), T x Tx is the temperature at point x in the sample cell, T0 is the temperature at thermocouple I 211, and T... D This is the temperature at thermocouple 213 of III.

[0057] According to equation (2), various temperature distribution scenarios can be preset to discuss the variation of residual stress of the same rock sample under different non-uniform temperature fields.

[0058] It has been verified that the actual measured temperature at thermocouple 212 of II is consistent with the T calculated by formula (2).D / 2 The difference is no more than 1℃, indicating that the temperature distribution of the non-uniform temperature field is as expected.

[0059] Before the experiment, thermocouples I 211, II 212, and III 213 are pre-embedded in the upper base 12 of the sample cell according to the design requirements and connected to the PID temperature controller 24. Heating element I 22 and heating element II 23 are inserted into the heating holes and connected to the PID temperature controller 24. Then, the upper base 12 and the lower base 13 of the sample cell are fixedly connected by bolts or screws. The rock sample is placed in the upper base 12 of the sample cell, and the transparent beryllium window 11 is placed on the upper base 12 of the sample cell. Then, the outer shell 14 of the sample cell is tightened. The sample cell is placed and fixed on the X-ray diffraction sample stage 33. The X-ray emitter 31 and the X-ray detector 32 are installed above the sample cell and connected to the X-ray diffractometer control system 34, thus forming the device of the present invention for measuring the residual stress of rock mass under non-uniform temperature.

[0060] Based on the above-mentioned device, the present invention also proposes a method for measuring the residual stress of rock mass under non-uniform temperature, such as... Figure 4 As shown, the method includes the following steps:

[0061] Step 1: Cut and grind the rock sample into... The cylindrical sample is placed in the upper base 12 of the sample cell to ensure that the sample test surface is flat and without defects. The transparent beryllium window 11 is placed above the sample. The outer shell 14 of the sample cell is tightened to the upper base 12 of the sample cell by screw rotation. The sample cell is then placed on the X-ray diffraction sample stage 33.

[0062] Step 2: Turn on the heating and temperature control system to preheat. Set the temperature to the preset temperature and wait for the temperature difference between thermocouple I 211 and thermocouple III 213 to stabilize at 5-10℃.

[0063] Step 3: After the temperature in Step 2 has stabilized, start the XRD test. Set the X-ray diffractometer system to the preset conditions: tilt angle ψ is 0°, measurement range is 10-80°, and scanning time is 10 min. Perform the first characterization and obtain the sample diffraction peak data.

[0064] Step 4: Use the X-ray diffractometer control system 34 to change the same tilt angle ψ between the transparent beryllium window 11 and the X-ray emitter 31, increasing by 15° each time to 45°, and perform XRD tests at multiple same tilt angles, recording the highest diffraction intensity and its corresponding diffraction angle θ at each tilt angle.

[0065] Step 5: Calculate the stress value σ of the sample at each tilt angle ψ. Specifically, calculate the interplanar spacing d of the sample at each tilt angle ψ using formula (3). ψ Formula (3) is:

[0066] nλ=2d ψ ·sinθ (3)

[0067] In equation (3), n is the diffraction order, usually taken as 1, representing the first-order diffraction; λ represents the wavelength of the X-ray source; d ψ ψ represents the interplanar spacing of the sample under test; θ is the diffraction angle.

[0068] Then, the stress value σ at each tilt angle ψ is calculated using the elasticity theory formula (4). Formula (4) is:

[0069]

[0070] In equation (4), σ is the stress value at each inclination angle; E is the Young's modulus of the sample; ν is the Poisson's ratio of the sample; Δd ​​is the change in interplanar spacing of the sample at each inclination angle, Δd = d ψ -d0; d0 is the interplanar spacing of the sample when the tilt angle is 0.

[0071] Then, with the stress value σ at each inclination angle as the vertical axis, the square of the sine value at the inclination angle is sin... 2 By plotting an image with ψ on the horizontal axis and performing linear fitting on the data, the residual stress at the test points of the sample can be obtained.

[0072] Step 6: Adjust the heating and temperature control system to change the temperature in the sample cell. Heate the sample according to thermocouple I 211 with a temperature gradient increasing by 25°C each time, and repeat steps 3-5. Record the variation curve of residual stress of the same sample under different non-uniform temperature field conditions.

[0073] Based on the above-mentioned device, this invention also proposes a method for measuring the change of residual stress in rock mass after stress-relief annealing under a non-uniform temperature field. Steps 1-5 of this method are the same as steps 1-5 of the method for measuring residual stress in rock mass under non-uniform temperature. The difference is that step 6 involves adjusting the heating and temperature control system to perform stress-relief annealing on the rock mass sample. Specifically, the temperature at thermocouple I is set to 250°C, held for one hour, and then cooled to room temperature. After cooling, steps 3-5 are repeated, and the change of residual stress in the same sample after stress-relief annealing under a non-uniform temperature field is recorded. The invention also includes step 7, adjusting the heating and temperature control system to change the temperature in the sample cell, and repeating steps 3-6 to record the change of residual stress in the same sample after stress-relief annealing under different non-uniform temperature fields. This optimizes the stress-relief annealing conditions, such as time, temperature, and heating rate.

[0074] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0075] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0076] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A device for measuring the residual stress of rock mass under non-uniform temperature, characterized in that, This includes a sample cell, a heating and temperature control system, and an X-ray diffraction system; The sample cell includes an upper base and a lower base, and the rock sample to be tested is placed inside the upper base. The heating and temperature control system includes thermocouples, heating elements, and a PID temperature controller. Three thermocouples, designated Thermocouple I, Thermocouple II, and Thermocouple III, are arranged radially along the upper base. Thermocouples I and III are located at opposite ends, and Thermocouple II is located at the midpoint between Thermocouples I and III. These thermocouples are used to measure the temperature at different locations within the sample cell. Each thermocouple is electrically connected to the PID temperature controller to transmit the measured temperature signal. The signal is fed to the PID temperature controller. Two heating elements with different resistivities, namely heating element I and heating element II, are arranged between the upper base and the lower base of the sample cell. Heating element I is arranged between thermocouples I and II, and heating element II is arranged between thermocouples II and III. Each heating element is electrically connected to the PID temperature controller. The PID temperature controller compares the actual temperature measured by the thermocouples with the preset temperature, and controls the energizing time of the heating elements to make the actual temperature approach the preset temperature, thereby achieving non-uniform temperature control. The X-ray diffractometer system includes an X-ray emitter, an X-ray detector, an X-ray diffraction sample stage, and an X-ray diffractometer control system. The sample cell is placed on the X-ray diffraction sample stage. The X-ray emitter and the X-ray detector are located above the sample cell and are respectively connected to the X-ray diffractometer control system. The X-ray detector receives the intensity of the diffracted rays and the diffraction angle θ signal after the X-ray emitter enters the sample and transmits it to the X-ray diffractometer control system. The X-ray diffractometer control system can change the angle ψ between the sample surface being tested and the X-ray emitted by the X-ray emitter.

2. The device for measuring residual stress in rock mass under non-uniform temperature according to claim 1, characterized in that, The sample cell also includes a transparent beryllium window, which is made of beryllium metal and is placed on the upper surface of the base of the sample cell, above the sample.

3. The device for measuring residual stress in rock mass under non-uniform temperature according to claim 1, characterized in that, The sample cell also includes a sample cell shell, which is detachably fixed to the upper base of the sample cell; the upper base of the sample cell is detachably fixed to the lower base of the sample cell.

4. The device for measuring residual stress in rock mass under non-uniform temperature according to claim 1, characterized in that, The connection between the upper and lower bases of the sample cell is provided with heating holes along the horizontal direction for inserting each heating element, and each heating element is pre-embedded in the heating hole in a straight line.

5. The apparatus for measuring residual stress in rock mass under non-uniform temperature according to claim 1, characterized in that, Three thermocouples are pre-embedded on the base of the sample cell.

6. The apparatus for measuring residual stress in rock mass under non-uniform temperature according to claim 4, characterized in that, The two heating elements are arranged in parallel.

7. The apparatus for measuring residual stress in rock mass under non-uniform temperature according to claim 1, characterized in that, Let the position of thermocouple I be x=0 and the position of thermocouple III be x=D. Then the position of thermocouple II is x=D / 2. The temperature distribution in the sample cell with respect to position x is calculated using formula (2), which is as follows: （2） In equation (2), T x Let T be the temperature at point x in the sample cell, T0 be the temperature at thermocouple I, and T... D The temperature at thermocouple III; By pre-setting multiple temperature distribution scenarios, the variation of residual stress in the same rock sample under different non-uniform temperature fields can be compared.

8. A method for measuring residual stress in rock mass under non-uniform temperature, characterized in that, The apparatus according to any one of claims 1-7 comprises the following steps: Step 1: Place the cut and polished rock sample in the base of the sample cell, place the transparent beryllium window above the sample, and place the sample cell on the X-ray diffraction sample stage. Step 2: Turn on the heating and temperature control system to preheat. Set the temperature to the preset temperature and wait until the temperature difference between thermocouple I and thermocouple III stabilizes at 5~10℃. Step 3: After the temperature stabilizes, start the XRD test. Set the X-ray diffractometer system to the preset conditions, with the inclination angle ψ being 0° and the measurement range being 10~80°. Perform the first characterization to obtain the highest diffraction intensity of the sample and its corresponding diffraction angle θ. Step 4: Use the X-ray diffractometer control system to change the inclination angle ψ between the transparent beryllium window and the X-ray emitter, perform XRD tests at multiple inclination angles, and record the highest diffraction intensity and its corresponding diffraction angle θ at each inclination angle. Step 5: Calculate the stress value σ of the sample at each tilt angle ψ, and plot the stress value σ at each tilt angle as the vertical axis, and the square of the sine of the tilt angle sin ψ. 2 Plot the image with ψ as the horizontal axis, perform linear fitting on the data, and obtain the residual stress at the test point of the sample; Step 6: Adjust the heating and temperature control system to change the temperature in the sample cell, and repeat steps 3-5 to record the variation curve of residual stress of the same sample under different non-uniform temperature field conditions.

9. The method for measuring residual stress in rock mass under non-uniform temperature according to claim 8, characterized in that, In step 5, the interplanar spacing d of the sample at each tilt angle ψ is calculated using formula (3). ψ Formula (3) is: （3） In equation (3), n is the diffraction order; λ represents the wavelength of the X-ray source; d ψ θ is the interplanar spacing of the sample under test at the same tilt angle ψ; θ is the diffraction angle. Then, the stress value σ at each tilt angle ψ is calculated using the elasticity theory formula (4). Formula (4) is: （4） In equation (4), σ is the stress value at each angle of inclination; E is the Young's modulus of the sample. The Poisson's ratio corresponding to the sample; Δd is the change in interplanar spacing of the sample at each tilt angle, Δd = d ψ -d0; d0 is the interplanar spacing of the sample when the tilt angle is 0.

10. The method for measuring residual stress in rock mass under non-uniform temperature according to claim 8, characterized in that, When it is necessary to study the effect of stress-relief annealing, step 6 is adjusted to: adjust the heating and temperature control system, perform stress-relief annealing on the rock sample, specifically set the temperature at thermocouple I to 200~300℃, keep it at that temperature for 1~3 hours, and then cool it down to room temperature. After cooling down, repeat steps 3-5 respectively, and record the changes in residual stress of the same sample after stress-relief annealing under a non-uniform temperature field. It also includes step 7, adjusting the heating and temperature control system to change the temperature in the sample cell, and repeating steps 3-6 to record the changes in residual stress of the same sample after stress-relief annealing under different non-uniform temperature fields, thereby optimizing the stress-relief annealing conditions.

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