A thermal expansion triaxial loading method and device thereof

Abstract

The invention relates to a thermal expansion type triaxial loading method and a device thereof; the loading method utilizes the temperature stress generated by the temperature change of the surrounding medium to realize the loading and unloading process of the test object; the loading device is an application of the loading method involved in the invention, and the loading method of the invention converts the temperature change into deformation for the first time, and then converts it into a load to be applied to the test object, so as to realize the loading of a large-size model sample in a high stress state; the loading of true triaxial, conventional triaxial and other stress states can be realized by selecting the surrounding medium; the loading device of the invention has a simple structure, reduces the labor intensity of personnel, and significantly reduces the cost; it can be applied to various materials and objects such as metals and rocks that require high temperature and high pressure loading, has wide practicality, and is very suitable for promotion and application in rock mechanics experiments and other related disciplines.

Description

Technical Field

[0001] The invention belongs to the technical field of mechanical testing, and in particular relates to a thermal expansion type triaxial loading method and a device thereof. Background Art

[0002] Mechanical tests are extremely common in the field of engineering technology. In these experiments, it is necessary to load the test object with force, such as typical material mechanics tests of metals and rocks, and even mechanical tests of soil. Many materials with higher strength often require a larger load to achieve their purpose. For existing mechanical loading test technologies based on pump work, applying a larger load means a larger investment. In recent years, with the continuous development of engineering construction, for example, the development and utilization of deep energy resources and deep underground space has received increasing attention and has been continuously promoted. Many of them require high stress loading, which has also given rise to the demand for high stress large-scale model experiments. Therefore, how to control costs and achieve effective high stress loading to support large-scale experiments is an urgent need for many engineering mechanics studies.

[0003] Among various loading test methods, the sample size is one of the decisive factors. The widely used small cylindrical samples (φ50mm×100mm) are actually used to study the material properties of the tested object, and it is difficult to truly represent or imitate the "structural characteristics" of the research object (such as a large rock mass). For this reason, it is often necessary to carry out so-called "model" experiments. The sample size of the model experiment should be significantly increased. A reasonably designed model experiment is of great value. Due to the large sample size, the model test provides the possibility of revealing more experimental phenomena, and its test results often have a good similarity with the actual engineering situation, and the guidance for the actual engineering is more targeted.

[0004] However, the load output of the test system is proportional to the square of the specimen size. For example, to achieve the same stress of 60MPa, the load required for a 100mm×100mm cross section is 0.6MN. When the specimen size is 1m×1m×1m, the required load increases to 60MN, which is a huge tonnage. At present, hydraulic loading is widely used. Such tonnage not only makes the oil cylinder and loading frame extremely large, but also extremely expensive. It can be seen that it is difficult to apply high stress to large-sized model specimens under low cost conditions. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a thermal expansion type triaxial loading method and a device thereof, which is a method of generating temperature changes in the surrounding medium and generating temperature stress to be applied to the test object, so as to simulate the stress conditions of the test object in different states, and the test results thereof often have a good similarity with the actual engineering conditions; the loading method of the present invention can be used for a variety of materials such as metals and rocks to realize the loading of the test object in true triaxial, conventional triaxial, three-way isobaric and other stress states, and has a wide range of applications; more importantly, when the temperature of the surrounding medium is reduced, the force can also be unloaded; the device of the present invention has a simple structure, low labor intensity, and high stability, and is expected to significantly reduce construction costs and personnel costs.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A thermal expansion triaxial loading method utilizes the temperature stress generated by the temperature change of the surrounding medium to realize the loading and unloading process of the test object.

[0008] The thermal expansion triaxial loading method specifically includes the following contents: wrapping the test object 1 in a surrounding medium 2 and fitting it with the surrounding medium 2, then heating the surrounding medium 2, and limiting the deformation of the surrounding medium 2 except for the target loading direction to zero during the heating process, so that the surrounding medium 2 generates temperature stress due to temperature change and deformation constraint, which is applied to the test object 1 to achieve stress loading on the test object 1; after loading is completed, cooling the surrounding medium 2, so that the surrounding medium 2 shrinks due to temperature change and deformation, and the contact with the test object 1 is released, thereby achieving a stress unloading process for the test object 1.

[0009] The thermal expansion triaxial loading method is characterized in that, according to different loading purposes, by controlling the temperature stress generated by the surrounding medium 2 to be applied in one direction, two directions, not equal, three directions fully equal, three directions partially equal, and three directions completely not equal, the loading of the test object in uniaxial, two-way isobaric, two-way unequal, three-way isobaric, conventional triaxial, and true triaxial temperature stress states is achieved respectively.

[0010] A thermal expansion type triaxial loading device comprises: surrounding medium 2, an upper end cover 31, a lower bottom plate 32, a longitudinal loading pressure head 4, a heat source item 51, an intermediate heat hoop tube 52, a temperature control switch 6, a thermal insulation layer 7, a temperature sensor and a pressure sensor; wherein the intermediate heat hoop tube 52 with the heat source item 51 built into the tube wall is sleeved in the upper end cover 31, the bottom of the upper end cover 31 is fixedly connected to the lower bottom plate 32, four surrounding media 2 are evenly arranged on the inner wall of the intermediate heat hoop tube 52, the outer side wall of each surrounding medium 2 is in contact with the inner wall of the intermediate heat hoop tube 52, and a temperature sensor and a pressure sensor are placed inside each surrounding medium 2, and the thermal insulation layer 7 is wrapped around the outer side of the main body of the upper end cover 31.

[0011] The surrounding medium 2 has a thermal expansion coefficient greater than 10 -7 ℃ -1 The upper end cover 31, the lower base plate 32, the middle heat hoop 52, and the longitudinal loading pressure head 4 are all made of materials with a thermal expansion coefficient that is less than 0.001 times the thermal expansion coefficient of the surrounding medium 2.

[0012] The outer side wall of the surrounding medium 2 is a curved surface for fitting with the inner wall of the intermediate heat hoop 52, and the outer side wall of the surrounding medium 2 is provided with a positioning strip 26, and the surrounding medium 2 is connected with the positioning groove 521 of the inner wall of the intermediate heat hoop 52 through the positioning strip 26 on its outer side wall. The inner side wall of the surrounding medium 2 is a plane, and a groove 25 is provided on the inner side wall of the surrounding medium 2, and a temperature sensor and a pressure sensor are placed in the groove 25. The leads of the temperature sensor and the pressure sensor extend along the groove 25 to the upper end cover 31 and pass through the lead hole at the top of the upper end cover 31.

[0013] The upper end cover 31 has a square through hole at the top, and four lead holes for the temperature sensor and the pressure sensor lead wires are provided on the upper end cover 31 around the square through hole. The bottom skirt of the upper end cover 31 has multiple bolt holes for connecting with the lower base plate 32.

[0014] The inner circle of the lower base plate 32 is provided with a plurality of vertical through holes for the lead wires of the heat source item 51 to pass through, and a plurality of bolt holes are opened along the circumference of the lower base plate 32 for connection with the upper end cover 31 .

[0015] The longitudinal loading pressure head 4 contacts the longitudinal end surface of the test object 1 through the square through hole at the top end of the upper end cover 31 .

[0016] The heat source item 51 is an electromagnetic coil or a heating resistance wire.

[0017] Four positioning grooves 521 are evenly arranged inside the middle heat hoop 52, which cooperate with the positioning strips 26 on the outer wall of the surrounding medium 2. The middle heat hoop 52 is sleeved inside the upper end cover 31, and the outer wall of the middle heat hoop 52 is in contact with the inner wall of the upper end cover 31.

[0018] The method for performing thermal expansion triaxial loading using the thermal expansion triaxial loading device comprises the following steps:

[0019] Step 1: prepare a square test object 1, and level and polish the outer end surface of the test object 1;

[0020] Step 2: Connect the lead wire of the heat source item 51 to the temperature control switch 6 through the vertical through hole of the lower bottom plate 32;

[0021] Step 3: placing the test object 1 obtained in step 1 between the first surrounding medium 21 and the second surrounding medium 22, so that the inner side walls of the first surrounding medium 21 and the second surrounding medium 22 are respectively in contact with the outer end surfaces of the test object 1 on both sides in the X direction;

[0022] The inner side walls of the third surrounding medium 23 and the fourth surrounding medium 24 are respectively attached to the outer end surfaces of both sides of the test object 1 in the Y direction;

[0023] Step 4: Manually pre-tighten to make the inner side walls of the four surrounding media completely fit with the outer end surfaces of the four sides of the test object 1, and make the outer side walls of the four surrounding media completely fit with the inner wall surface of the middle heat hoop 52 respectively;

[0024] Step 5: Lead the temperature and pressure sensor leads through the four lead holes at the top of the upper end cover 31, and connect the leads to the external data acquisition card;

[0025] Step 6: Start the temperature control switch 6 to heat the heat source item 51 to a temperature of 80-300° C. During the heating process, the test object 1 is subjected to the temperature stress of the four surrounding media. The temperature and pressure of the test object 1 are obtained by reading the data of the temperature sensors and pressure sensors in each surrounding medium.

[0026] Step 7: When the temperature sensor and pressure sensor data in each surrounding medium reach the temperature and pressure values ​​required by the test design, it means that the temperature and pressure of the test object 1 meet the requirements of the test design, and the temperature control switch 6 is turned off to stop heating, and insulation is achieved through the insulation layer 7;

[0027] Step 8: Adjust the direction of the longitudinal loading pressure head 4 so that the longitudinal loading pressure head 4 contacts the upper end surface of the test object 1 inside the middle heat hoop cylinder 52 and the surrounding medium through the square through hole of the upper end cover 31, and then contact the cylinder rod of the vertical hydraulic jack with the longitudinal loading pressure head 4. The cylinder rod of the vertical hydraulic jack applies a gradually increasing load to the test object 1 through the longitudinal loading pressure head 4 until the longitudinal pressure of the test object 1 reaches the required test pressure, thereby completing the triaxial loading test of the test object 1;

[0028] Step nine: After the loading test is completed, the longitudinal loading pressure head 4 is ejected to separate it from the test object 1, and the thermal insulation layer 7 is removed;

[0029] Step 10: Start the temperature control switch 6, heat the heat source item 51, make its temperature reach room temperature, realize reverse heating of the four surrounding media, when the pressure sensor data in each surrounding medium is zero, it means that the pressure of the test object 1 is restored to zero, stop heating, that is, turn off the temperature control switch 6, and complete the stress unloading process of the test object 1.

[0030] If the four surrounding media in the middle heat hoop 52 are materials with the same thermal expansion coefficient, this method is a conventional triaxial test performed on the test object 1;

[0031] If the two surrounding media arranged opposite to each other laterally in the middle heat hoop 52 are made of materials with the same thermal expansion coefficient, and the two surrounding media 2 arranged opposite to each other longitudinally are made of materials with another thermal expansion coefficient, that is, the first surrounding medium 21 and the second surrounding medium 22 are made of materials with the same thermal expansion coefficient, and the third surrounding medium 23 and the fourth surrounding medium 24 are made of materials with another thermal expansion coefficient, this method is a true triaxial loading test performed on the test object 1.

[0032] Beneficial effects of the present invention:

[0033] (1) The present invention relates to a thermal expansion triaxial loading method, which for the first time realizes the conversion of ambient temperature changes into the deformation capacity of the surrounding medium, and then into temperature stress applied to the test object, and can realize the high stress loading and unloading process of large-scale model specimens;

[0034] (2) The thermal expansion triaxial loading method of the present invention can realize the loading and unloading of the stress states of the test object such as true triaxial, conventional triaxial, biaxial, and uniaxial by means of the selection of the surrounding medium and the material, so as to meet various loading requirements;

[0035] (3) The present invention relates to a thermal expansion type triaxial loading device, which is equipped with a new loading method and a pressure chamber of a new structure. Compared with the existing loading methods and devices, it can save some loading links, and the structure of the present invention is simpler. In actual operation, it can greatly reduce the labor intensity of personnel, and is expected to significantly reduce the construction cost and personnel cost;

[0036] (4) The device of the present invention can replace the surrounding medium with metal or alloy materials with the same or different thermal expansion coefficients according to the required temperature and stress conditions, thereby meeting the requirements of conventional triaxial or true triaxial tests of large-sized model specimens under different temperature and stress conditions;

[0037] (5) The loading method and device of the present invention can be applied to various materials and objects such as metals and rocks that require high temperature and high pressure loading. It has low cost, wide practicability and strong promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of a thermal expansion type triaxial loading device of the present invention;

[0039] Figure 2 It is a schematic diagram of the overall structure of a thermal expansion type triaxial loading device of the present invention;

[0040] Figure 3It is a partial structural schematic diagram of a thermal expansion type triaxial loading device of the present invention;

[0041] Figure 4 It is a top view of a part of the structure of a thermal expansion type triaxial loading device of the present invention;

[0042] Figure 5 It is a transverse cross-sectional view of a part of the structure of a thermal expansion type triaxial loading device of the present invention;

[0043] Figure 6 It is a schematic diagram of the surrounding medium structure in a thermal expansion type triaxial loading device of the present invention;

[0044] In the figure: 1 test object, 21 first surrounding medium, 22 second surrounding medium, 23 third surrounding medium, 24 fourth surrounding medium, 25 groove, 26 positioning bar, 31 upper end cover, 32 lower bottom plate, 4 longitudinal loading pressure head, 51 heat source item, 52 middle heat hoop, 521 positioning groove, 6 temperature control switch, 7 insulation layer. DETAILED DESCRIPTION

[0045] Example 1

[0046] A thermal expansion triaxial loading method utilizes the temperature stress generated by the temperature change of the surrounding medium to realize the loading and unloading process of the test object.

[0047] The thermal expansion triaxial loading method specifically includes the following contents: wrapping the test object 1 in the surrounding medium 2 and making it fit tightly with the surrounding medium 2, then heating the surrounding medium 2, and limiting the deformation of the surrounding medium 2 except for the target loading direction to zero during the heating process, so that the surrounding medium 2 generates temperature stress due to temperature change and deformation constraint, which is applied to the test object 1 to achieve stress loading on the test object 1; after loading is completed, cooling the surrounding medium 2, so that the surrounding medium 2 shrinks due to temperature change and deformation, and the contact with the test object 1 is released, thereby achieving the stress unloading process of the test object 1.

[0048] The thermal expansion triaxial loading method is characterized in that, according to different loading purposes, by controlling the temperature stress generated by the surrounding medium 2 to be applied in one direction, two directions, not equal, three directions fully equal, three directions partially equal, and three directions completely not equal, the loading of the test object in uniaxial, two-way isobaric, two-way unequal, three-way isobaric, conventional triaxial, and true triaxial temperature stress states is achieved respectively.

[0049] The thermal expansion triaxial loading method is characterized in that it has no restrictions on the type of the test object 1, which can be metal, rock or concrete material.

[0050] A thermal expansion type triaxial loading device comprises: surrounding medium 2, an upper end cover 31, a lower bottom plate 32, a longitudinal loading pressure head 4, a heat source item 51, an intermediate heat hoop tube 52, a temperature control switch 6, a thermal insulation layer 7, a temperature sensor and a pressure sensor; wherein the intermediate heat hoop tube 52 with the heat source item 51 built in the tube wall is sleeved in the upper end cover 31, the bottom of the upper end cover 31 is fixedly connected to the lower bottom plate 32, four surrounding media 2 are evenly arranged on the inner wall of the intermediate heat hoop tube 52, the outer wall of each surrounding medium 2 is in contact with the inner wall of the intermediate heat hoop tube 52, and a temperature sensor and a pressure sensor are placed inside each surrounding medium 2, and the thermal insulation layer 7 is wrapped around the outer side of the main body of the upper end cover 31 for heat preservation and reducing heat loss.

[0051] The surrounding medium 2 has a thermal expansion coefficient greater than 10 -7 ℃ -1 The upper end cover 31, the lower base plate 32, the middle heat hoop 52, and the longitudinal loading pressure head 4 are all made of materials with a thermal expansion coefficient that is less than 0.001 times the thermal expansion coefficient of the surrounding medium 2.

[0052] The outer side wall of the surrounding medium 2 is a curved surface for fitting with the inner wall of the intermediate heat hoop 52, and the outer side wall of the surrounding medium 2 is provided with a positioning strip 26, and the surrounding medium 2 is connected with the positioning groove 521 of the inner wall of the intermediate heat hoop 52 through the positioning strip 26 on its outer side wall. The inner side wall of the surrounding medium 2 is a plane, and a groove 25 is provided on the inner side wall of the surrounding medium 2, and a temperature sensor and a pressure sensor are placed in the groove 25. The leads of the temperature sensor and the pressure sensor extend along the groove 25 to the upper end cover 31 and pass through the lead hole at the top of the upper end cover 31.

[0053] The upper end cover 31 has a square through hole at the top, and four lead holes for the temperature sensor and the pressure sensor lead wires are provided on the upper end cover 31 around the square through hole. The bottom skirt of the upper end cover 31 has multiple bolt holes for connecting with the lower base plate 32.

[0054] The inner circle of the lower base plate 32 is provided with a plurality of vertical through holes for the lead wires of the heat source item 51 to pass through, and a plurality of bolt holes are opened along the circumference of the lower base plate 32 for connection with the upper end cover 31 .

[0055] The longitudinal loading pressure head 4 contacts the longitudinal end surface of the test object 1 through the square through hole at the top end of the upper end cover 31 and applies a longitudinal load.

[0056] The heat source item 51 is an electromagnetic coil or a heating resistor wire, which directly provides heat, and the lead wire of the heat source item 51 is connected to the temperature control switch 6.

[0057] Four positioning grooves 521 are evenly arranged inside the middle heat hoop 52, which cooperate with the positioning strips 26 on the outer wall of the surrounding medium 2. The middle heat hoop 52 is sleeved inside the upper end cover 31, and the outer wall of the middle heat hoop 52 fits with the inner wall of the upper end cover 31.

[0058] The method for performing thermal expansion triaxial loading using the thermal expansion triaxial loading device comprises the following steps:

[0059] Step 1: prepare a square test object 1, and level and polish the outer end surface of the test object 1;

[0060] Step 2: Connect the lead wire of the heat source item 51 to the temperature control switch 6 through the vertical through hole of the lower bottom plate 32;

[0061] Step 3: placing the test object 1 obtained in step 1 between the first surrounding medium 21 and the second surrounding medium 22, so that the inner side walls of the first surrounding medium 21 and the second surrounding medium 22 are respectively in contact with the outer end surfaces of the test object 1 on both sides in the X direction;

[0062] The inner side walls of the third surrounding medium 23 and the fourth surrounding medium 24 are respectively attached to the outer end surfaces of both sides of the test object 1 in the Y direction;

[0063] Step 4: Manually pre-tighten to make the inner side walls of the four surrounding media completely fit with the outer end surfaces of the four sides of the test object 1, and make the outer side walls of the four surrounding media completely fit with the inner wall surface of the middle heat hoop 52 respectively;

[0064] Step 5: Lead the temperature and pressure sensor leads through the four lead holes at the top of the upper end cover 31, and connect the leads to the external data acquisition card;

[0065] Step 6: Start the temperature control switch 6 to heat the heat source item 51 to a temperature of 80-300° C. During the heating process, the test object 1 is subjected to the temperature stress of the four surrounding media. The temperature and pressure of the test object 1 are obtained by reading the data of the temperature sensors and pressure sensors in each surrounding medium.

[0066] Step 7: When the temperature sensor and pressure sensor data in each surrounding medium reach the temperature and pressure values ​​required by the test design, it means that the temperature and pressure of the test object 1 meet the requirements of the test design, and the temperature control switch 6 is turned off to stop heating, and insulation is achieved through the insulation layer 7;

[0067] Step 8: Adjust the direction of the longitudinal loading pressure head 4 so that the longitudinal loading pressure head 4 contacts the upper end surface of the test object 1 inside the middle heat hoop cylinder 52 and the surrounding medium through the square through hole of the upper end cover 31, and then contact the cylinder rod of the vertical hydraulic jack with the longitudinal loading pressure head 4. The cylinder rod of the vertical hydraulic jack applies a gradually increasing load to the test object 1 through the longitudinal loading pressure head 4 until the longitudinal pressure of the test object 1 reaches the required test pressure, thereby completing the triaxial loading test of the test object 1;

[0068] Step nine: After the loading test is completed, the longitudinal loading pressure head 4 is ejected to separate it from the test object 1, and the thermal insulation layer 7 is removed;

[0069] Step 10: Start the temperature control switch 6, heat the heat source item 51, make its temperature reach room temperature, realize reverse heating of the four surrounding media, when the pressure sensor data in each surrounding medium is zero, it means that the pressure of the test object 1 is restored to zero, stop heating, that is, turn off the temperature control switch 6, and complete the stress unloading process of the test object 1.

[0070] If the four surrounding media in the middle heat hoop 52 are materials with the same thermal expansion coefficient, this method is a conventional triaxial test performed on the test object 1;

[0071] If the two surrounding media arranged opposite to each other laterally in the middle heat hoop 52 are made of materials with the same thermal expansion coefficient, and the two surrounding media 2 arranged opposite to each other longitudinally are made of materials with another thermal expansion coefficient, that is, the first surrounding medium 21 and the second surrounding medium 22 are made of materials with the same thermal expansion coefficient, and the third surrounding medium 23 and the fourth surrounding medium 24 are made of materials with another thermal expansion coefficient, this method is a true triaxial loading test performed on the test object 1.

[0072] Example 2

[0073] The core idea of ​​the present invention is to utilize the temperature stress generated by the temperature change of the surrounding medium to realize the loading and unloading process of the test object.

[0074] The present invention discloses a thermal expansion triaxial loading method, which specifically comprises: wrapping a test object 1 in a surrounding medium 2 and fitting the surrounding medium 2 tightly, and then heating the surrounding medium 2, and limiting the deformation of the surrounding medium 2 except for the target loading direction to zero during the heating process, so that the surrounding medium 2 generates temperature stress due to temperature change and deformation constraint, and applies the temperature stress to the test object 1 to achieve stress loading on the test object 1; further, cooling the surrounding medium 2, so that the surrounding medium 2 shrinks due to temperature change and deformation, and the contact with the test object 1 is released, thereby achieving a stress unloading process for the test object 1; the thermal expansion triaxial loading method can realize the loading of the test object in true triaxial, conventional triaxial, biaxial and other stress states by means of whether the surrounding medium is selected and its material model, so as to meet different loading schemes and test requirements.

[0075] The thermal expansion type triaxial loading device of the present invention is a specific implementation of the thermal expansion type triaxial loading method of the present invention. Figures 1 to 6 For further detailed description, it should be noted that the following description is only for explaining the device of the present invention and does not limit its content.

[0076] As attached Figures 1 to 6As shown, a thermal expansion type triaxial loading device comprises: a first surrounding medium 21, a second surrounding medium 22, a third surrounding medium 23, a fourth surrounding medium 24, an upper end cover 31, a lower bottom plate 32, a longitudinal loading pressure head 4, a heat source item 51, an intermediate heat hoop 52, a temperature control switch 6, and a thermal insulation layer 7; the inner side walls of the first surrounding medium 21 and the second surrounding medium 22 are in contact with the outer end surface of the test object 1 in the X direction; the inner side walls of the third surrounding medium 23 and the fourth surrounding medium 24 are in contact with the outer end surface of the test object 1 in the Y direction; the inner side walls of the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24 are all provided with vertical grooves 25 for placing temperature and pressure sensors; the upper end cover 31 is connected to the lower bottom plate 32 by bolts; the upper end cover 31 is provided with a groove having a size similar to that of the test object 1 The square through holes of the same shape are convenient for adding the longitudinal loading pressure head 4; the upper end cover 31 is provided with 4 lead holes, and the leads of the temperature and pressure sensors are led out from the lead holes and connected to the data acquisition card; the lower base plate 32 is provided with a number of circular lead holes, and the leads of the heat source item 5 are led out from the lead holes and connected to the temperature control switch 6; the intermediate heat hoop 52 is fixedly connected to the lower base plate 32; the longitudinal loading pressure head 4 contacts the upper end surface of the test object 1 and applies an axial load; the inner wall positioning groove 521 of the intermediate heat hoop 52 is installed to overlap with the outer wall positioning strip 26 of the surrounding medium; the outer wall surface of the intermediate heat hoop 52 is tightly fitted with the inner wall surface of the main cylinder of the upper end cover 31; the cylinder wall of the intermediate heat hoop 52 is provided with a non-through pipe for placing the heat source item 51; the thermal insulation layer 7 is tightly fitted with the outer wall surface of the main cylinder of the upper end cover 31 to reduce heat loss.

[0077] The first surrounding medium 21 and the second surrounding medium 22 of the device of the present invention are made of materials with the same and larger thermal expansion coefficient; the third surrounding medium 23 and the fourth surrounding medium 24 are made of materials with the same and larger thermal expansion coefficient; according to different loading purposes, the first surrounding medium 21, the second surrounding medium 22 and the third surrounding medium 23, the fourth surrounding medium 24 can choose materials with the same or different thermal expansion coefficients to achieve conventional triaxial or true triaxial loading of the test material 1; the upper end cover 31, the lower base plate 32, and the middle heat hoop 52 are all made of materials with high rigidity, small deformation, and a thermal expansion coefficient much smaller than that of the four surrounding media 2.

[0078] The temperature control switch 6 of the device of the present invention controls the temperature increase or decrease of the heat source item 51, and the heat is evenly transferred to the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24 through the intermediate heat hoop 52. The temperature change causes the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24 to deform. At the same time: the upper end cover 31 of the device of the present invention limits the axial upward deformation of the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24, and the lower bottom plate 32 limits the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 2 4 axially downward deformation, the middle heat hoop 52 limits the circumferential outward deformation of the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24. The above constraints are all achieved through surface contact. So far, the deformation of the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24 can only be circumferentially inward, thereby "squeezing" the test object 1 to achieve a loading test on the test object 1; or, under the condition of cooling, the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24 are deformed and contracted, and their inner side walls are separated from the outer end surface of the test object 1, thereby achieving an unloading test on the test object 1.

[0079] To better explain the feasibility of the present invention, the following example is given:

[0080] (1) Example: True triaxial loading

[0081] The first surrounding medium 21 and the first surrounding medium 22 are made of hot working die steel with the label 4Cr5MoSiV, and the linear expansion coefficient at 20℃~300℃ is 11.4×10 -6 ℃ -1 , the elastic modulus is 216000MPa; the third surrounding medium 23 and the fourth surrounding medium 24 are made of 4Cr5W2VSi hot working die steel, and its linear expansion coefficient is 8.7×10 -6 ℃ -1 ,, the elastic modulus is 210000MPa; the upper end cover 31, the lower base plate 32, and the middle hot hoop tube 52 are all made of cold working die steel, and their thermal expansion is negligible.

[0082]

[0083] Where ε is the strain caused by thermal expansion of the surrounding medium, l is the thickness of the surrounding medium, and α is the linear expansion coefficient of the surrounding medium (℃ -1 ), E is the elastic modulus of the surrounding medium (MPa), σ is the stress generated by the surrounding medium (MPa), and T is the heating temperature (℃).

[0084] According to formula (1), the following calculation is performed: Considering that the thickness of the first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24 are all 85 mm;

[0085] When heated to 300°C, the stresses of the first surrounding medium 21 and the second surrounding medium 22 generated by heat are calculated by formula (2):

[0086]

[0087] When heated to 300°C, the stress of the third surrounding medium 23 and the fourth surrounding medium 24 due to heat is calculated by formula (3):

[0088]

[0089] Since σ2=738.72MPa≠σ3=548.1MPa, it can be considered that the present invention can achieve true triaxial loading with the support of existing technology.

[0090] (2) Example: Conventional triaxial loading

[0091] The first surrounding medium 21, the second surrounding medium 22, the third surrounding medium 23, and the fourth surrounding medium 24 are all made of hot working die steel with a label of 4Cr5MoSiV, and its linear expansion coefficient is 11.4×10 -6 ℃ -1 , the elastic modulus is 216000MPa; the upper end cover 31, the lower base plate 32, and the middle hot hoop tube 52 are all made of cold-working die steel, and their thermal expansion is negligible.

[0092] According to formula (1), the following calculation is performed: Considering that the thickness of the first surrounding medium 21, the second surrounding medium 22, the upper end cover 31, and the lower bottom plate 32 are all 85 mm;

[0093] When heated to 300°C, the stress of the first surrounding medium 21 and the second surrounding medium 22 generated by heat is calculated by formula (4):

[0094]

[0095] When heated to 300°C, the stress of the third surrounding medium 23 and the fourth surrounding medium 24 due to heat is calculated by formula (5):

[0096]

[0097] Since σ2=738.72 MPa=σ3=738.72 MPa, it can be considered that the present invention can achieve conventional triaxial loading with the support of existing technology.

[0098] The specific method of using the above device to carry out triaxial loading and unloading tests on the model is as follows:

[0099] Step 1: prepare a square test object 1, and level and polish the outer end surface of the test object 1;

[0100] Step 2: Place the heat source item 51 inside the wall of the middle heat hoop 52, the middle heat hoop 52 is placed on the lower bottom plate 32, and the lead wire of the heat source item 51 is connected to the temperature control switch 6 through the lead wire hole at the bottom of the lower bottom plate 32;

[0101] Step 3: Install the positioning strips 26 on the outer walls of the first surrounding medium 21 and the second surrounding medium 22 in cooperation with the positioning grooves 521 on the inner wall of the middle heat hoop 52;

[0102] Step 4: Place the temperature and pressure sensors in the inner wall grooves 22 of the first surrounding medium 21 and the second surrounding medium 22, and lead the sensor wires out from the grooves 25;

[0103] Step 5: placing the test object 1 obtained in step 1 between the first surrounding medium 21 and the second surrounding medium 22, so that the inner side walls of the first surrounding medium 21 and the second surrounding medium 22 are in contact with the outer end surface of the test object 1 in the X direction;

[0104] Step 6: Place the temperature and pressure sensors in the inner wall grooves 25 of the third surrounding medium 23 and the fourth surrounding medium 24, and lead the sensor wires out of the grooves 25;

[0105] Step 7: Install the outer wall positioning strips 26 of the third surrounding medium 23 and the fourth surrounding medium 24 in cooperation with the inner wall positioning grooves 521 of the middle heat hoop 52, and make the inner wall of the inner wall fit with the outer end surface of the test object 1 in the Y direction;

[0106] Step 8: Manually pre-tighten to make the inner side walls of the four surrounding media completely fit with the outer end surface of the test object 1, and make the outer side walls of the four surrounding media completely fit with the inner wall surface of the middle heat hoop 52;

[0107] Step 9: Lead the temperature and pressure sensor leads through the four lead holes on the top of the upper end cover 31, and connect the leads to the external data acquisition card;

[0108] Step 10: Assemble the upper end cover 31 and the lower base plate 32 with bolts to form a complete rigid system;

[0109] Step 11: Cover the thermal insulation layer 7 on the outer wall of the main cylinder of the upper end cover 31;

[0110] Step 12: Start the temperature control switch 6 to heat the heat source item 51 (target: high temperature). During the heating process, the test object 1 is subjected to the temperature stress of the surrounding medium 2. The temperature and pressure of the test object 1 are obtained by reading the temperature and pressure sensor data of each surrounding medium 2.

[0111] Step 13: When the temperature and pressure sensor data of the test object 1 reach the test design temperature and pressure values, it means that the temperature and pressure of the test object 1 meet the test design requirements, and the temperature control switch 6 is turned off to stop heating, and the insulation layer 7 is used to achieve insulation;

[0112] Step 14: Adjust the direction of the longitudinal loading pressure head 4 so that the pressure head 4 contacts the upper end surface of the test object 1 inside the middle heat hoop 52 and the surrounding medium 2 through the square through hole of the upper end cover 31, and then contact the cylinder rod of the vertical hydraulic jack with the pressure head 4. The cylinder rod of the vertical hydraulic jack applies a gradually increasing load to the test object 1 through the pressure head 4 until the longitudinal pressure of the test object 1 reaches the test requirement, thereby completing the triaxial loading test of the test object 1;

[0113] Step 15: After the loading test is completed, the longitudinal loading pressure head 4 is ejected to separate it from the test object 1;

[0114] Step 16: Remove the insulation layer 7, and be careful to prevent high temperature burns;

[0115] Step seventeen: Start the temperature control switch 6, heat the heat source item 51 (target: low temperature), and reversely heat the surrounding medium. When the pressure sensor data in each surrounding medium are all zero, it means that the pressure of the test object 1 has returned to zero, and stop heating, that is, turn off the temperature control switch 6, and complete the stress unloading process of the test object 1.

Claims

1. A thermal expansion triaxial loading device, characterized in that include: Surrounding medium (2), an upper end cover (31), a lower bottom plate (32), a longitudinal loading pressure head (4), a heat source item (51), an intermediate heat hoop tube (52), a temperature control switch (6), a thermal insulation layer (7), a temperature sensor and a pressure sensor; wherein the intermediate heat hoop tube (52) having a heat source item (51) built into the tube wall is sleeved inside the upper end cover (31), the bottom of the upper end cover (31) is fixedly connected to the lower bottom plate (32), four surrounding media (2) are evenly arranged on the inner wall of the intermediate heat hoop tube (52), the outer wall of each surrounding medium (2) is in contact with the inner wall of the intermediate heat hoop tube (52), and a temperature sensor and a pressure sensor are placed inside each surrounding medium (2), and the thermal insulation layer (7) is wrapped around the outer side of the main body of the upper end cover (31); The top of the upper end cover (31) is provided with a square through hole, and the upper end cover (31) around the square through hole is provided with four lead holes for passing the lead wires of the temperature sensor and the pressure sensor, and the bottom skirt of the upper end cover (31) is provided with a plurality of bolt holes for connecting with the lower base plate (32); The inner circle of the lower base plate (32) is provided with a plurality of vertical through holes for the lead wires of the heat source item (51) to pass through, and the upper edge of the lower base plate (32) is provided with a plurality of bolt holes in the circumferential direction for connection with the upper end cover (31); The longitudinal loading pressure head (4) contacts the longitudinal end surface of the test object (1) through the square through hole at the top end of the upper end cover (31); Four positioning grooves (521) are evenly arranged inside the middle heat hoop tube (52) and cooperate with the positioning strips (26) on the outer wall of the surrounding medium (2). The middle heat hoop tube (52) is sleeved inside the upper end cover (31), and the outer wall of the middle heat hoop tube (52) fits with the inner wall of the upper end cover (31).

2. A thermal expansion triaxial loading device according to claim 1, characterized in that The surrounding medium (2) has a thermal expansion coefficient greater than 10 -7 ℃ -1 and the upper end cover (31), the lower base plate (32), the middle heat hoop cylinder (52), and the longitudinal loading pressure head (4) are all made of materials with a thermal expansion coefficient that is less than 0.001 times the thermal expansion coefficient of the surrounding medium (2).

3. A thermal expansion triaxial loading device according to claim 2, characterized in that The outer wall of the surrounding medium (2) is a curved surface for fitting with the inner wall of the middle heat hoop tube (52), and the outer wall of the surrounding medium (2) is provided with a positioning strip (26), and the surrounding medium (2) is connected with the positioning groove of the inner wall of the middle heat hoop tube (52) through the positioning strip (26) on the outer wall thereof, and the inner wall of the surrounding medium (2) is a plane, and the inner wall of the surrounding medium (2) is provided with a groove (25), and a temperature sensor and a pressure sensor are placed in the groove (25), and the leads of the temperature sensor and the pressure sensor extend along the groove (25) to the upper end cover (31) and pass through the lead hole at the top of the upper end cover (31).

4. A method for performing thermal expansion triaxial loading using the thermal expansion triaxial loading device according to claim 1, characterized in that The steps include: Step 1: preparing a square test object (1), and leveling and polishing the outer end surface of the test object (1); Step 2: Connect the lead wire of the heat source item (51) to the temperature control switch (6) through the vertical through hole of the lower base plate (32); Step 3: placing the test object (1) obtained in step 1 between the first surrounding medium (21) and the second surrounding medium (22), so that the inner side walls of the first surrounding medium (21) and the second surrounding medium (22) are respectively in contact with the outer end surfaces of the test object (1) on both sides in the X direction; The inner side walls of the third surrounding medium (23) and the fourth surrounding medium (24) are respectively attached to the outer end surfaces of both sides of the test object (1) in the Y direction; Step 4: Manually pre-tighten so that the inner side walls of the four surrounding media are completely in contact with the outer end surfaces of the four sides of the test object (1), and the outer side walls of the four surrounding media are completely in contact with the inner wall surface of the middle heat hoop (52); Step 5: Lead the temperature and pressure sensor leads through the four lead holes at the top of the upper end cover (31), and connect the leads to an external data acquisition card; Step 6: Start the temperature control switch (6) to heat the heat source item (51) to a temperature of 80-300° C. During the heating process, the test object (1) is subjected to temperature stresses from four surrounding media. The temperature and pressure of the test object (1) are obtained by reading data from temperature sensors and pressure sensors in each surrounding medium. Step 7: When the temperature sensor and pressure sensor data in each surrounding medium reach the temperature and pressure values ​​required by the test design, it means that the temperature and pressure of the test object (1) have reached the requirements of the test design, and the temperature control switch (6) is turned off to stop heating, and heat preservation is achieved through the heat preservation layer (7); Step 8: Adjust the direction of the longitudinal loading pressure head (4) so ​​that the longitudinal loading pressure head (4) contacts the upper end surface of the test object (1) inside the middle heat hoop cylinder (52) and the surrounding medium through the square through hole of the upper end cover (31), and then contact the cylinder rod of the vertical hydraulic jack with the longitudinal loading pressure head (4). The cylinder rod of the vertical hydraulic jack applies a gradually increasing load to the test object (1) through the longitudinal loading pressure head (4) until the longitudinal pressure of the test object (1) reaches the required test pressure, thereby completing the triaxial loading test on the test object (1); Step nine: After the loading test is completed, the longitudinal loading pressure head (4) is ejected to separate it from the test object (1), and the thermal insulation layer (7) is removed; Step 10: Start the temperature control switch (6) to heat the heat source item (51) to make its temperature reach room temperature, so as to realize reverse heating of the four surrounding media. When the pressure sensor data in each surrounding medium is zero, it means that the pressure of the test object (1) has returned to zero, and the heating is stopped, that is, the temperature control switch (6) is turned off, and the stress unloading process of the test object (1) is completed.

5. The method of thermal expansion triaxial loading according to claim 4, characterized in that: If the four surrounding media in the middle heat hoop (52) are materials with the same thermal expansion coefficient, this method is a conventional triaxial test performed on the test object (1); If the two surrounding media disposed opposite to each other laterally in the middle heat hoop (52) are made of materials with the same thermal expansion coefficient, and the two surrounding media (2) disposed opposite to each other longitudinally are made of materials with another thermal expansion coefficient, that is, the first surrounding medium (21) and the second surrounding medium (22) are made of materials with the same thermal expansion coefficient, and the third surrounding medium (23) and the fourth surrounding medium (24) are made of materials with another thermal expansion coefficient, this method is a true triaxial loading test performed on the test object (1).

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