A high temperature pull-pull fatigue testing system and method

Abstract

The application discloses a high-temperature tensile-tensile fatigue test system and method, and designs a clamping device which can adapt to thickness change of a sample and ensure accurate centering of the sample based on a cold clamping mode; a movable thermocouple device is also designed, the thermocouple contacts the sample in the heating and heat preservation stage, and the thermocouple is slid to a position 3-6 mm away from the surface of the sample when the fatigue loading is formally started; and a silica aerogel composite material is selected to make a heat insulation felt which is arranged at the upper opening of a high-temperature furnace to block the hot air flow continuously rising from the high-temperature furnace, eliminate the risk of overheating of the chuck and the sensor system above the testing machine in a long-time fatigue test, and improve the stability and uniformity of the temperature field of the high-temperature furnace. The application makes technical innovations from three aspects of the clamping device, temperature measurement and control and heat insulation of the high-temperature furnace, effectively solves the technical problems of the high-temperature tensile-tensile fatigue test, and improves the technical level of the high-temperature tensile-tensile fatigue test of SiC-based composite materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material mechanical property testing, in particular to a SiC-based composite material high-temperature tensile-tensile fatigue testing system and method, which is specially designed for the tensile-tensile fatigue test of silicon-based composite materials under long-time and high-temperature conditions, and the high-temperature tensile-tensile fatigue test of other materials can be referred to. BACKGROUND

[0002] Ceramic matrix composite refers to a composite material formed by introducing a reinforcing material into a ceramic matrix. Ceramic matrix composite can have the advantages of high strength, high modulus, high temperature resistance, corrosion resistance, etc. of ceramic materials, while the reinforcing material can improve the material's ability to resist crack propagation and overcome the weakness of ceramic materials - brittleness. There are three types of commonly used ceramic matrices: (1) glass-ceramic matrix, typical representative calcium alumino-silicate glass; (2) oxide matrix, typical representative Al2O3; (3) non-oxide matrix, typical representative SiC. It is generally believed that the ceramic matrix composite that can be finally applied to the hottest parts of an aero-engine is a continuous fiber reinforced SiC matrix composite, especially SiC f / SiC.

[0003] Tensile-tensile fatigue performance is a mechanical property that must be investigated in the evaluation of almost all material applications, especially for SiC-based composite materials. SiC matrix is relatively brittle, and under tensile-tensile fatigue cyclic loading, the matrix will crack first, and with the gradual expansion of the crack in the matrix, micro-damage such as fiber-matrix interface debonding and fiber pull-out will be induced, eventually leading to fatigue fracture of the material. The real service environment of SiC-based composite materials is high temperature. In order to evaluate the long-term service performance of the material, it is necessary to carry out tensile-tensile fatigue test of SiC-based composite materials under high temperature environment. The tensile-tensile fatigue performance of SiC-based composite materials under high temperature is the main indicator for evaluating the performance of the material, and is also an important basis for design and life prediction.

[0004] However, under the existing technical conditions, there are three technical difficulties in the implementation of SiC-based composite material high-temperature tensile-tensile fatigue test:

[0005] (1)Clamping device. The existing clamping device is divided into three kinds of hydraulic clamping, Y type end sample hanging and pin connection. Among them, the hydraulic clamping needs to paste the sample with reinforcing sheet, and the sample is easy to be clamped broken directly with the clamp block of the testing machine. In the fatigue test, the stress concentration at the clamping root and the alternating load are superimposed on each other, so that the sample is often broken at the clamping position or the clamping root. The clamping device of Y type end sample hanging utilizes the principle that the slope of the sample side and the slope of the clamp groove side are the same, realizes the self-locking of stretching, but has the problems of difficult to ensure the accurate centering of the sample and unstable force transmission. The pin connection method needs to punch holes on the sample and wear pins to connect with the testing machine. SiC-based composite material is relatively brittle, and the bolt connection method often causes damage at the punching hole. By reducing the hole diameter, the use of multiple holes and pin connection method also leads to difficult sample processing and high cost.

[0006] (2) Temperature measurement technology. There is a certain temperature gradient and temperature deviation in high temperature furnace, and the above problems are more serious in small size high temperature furnace used with cold clamping method. The conventional method is to bind three precious metal thermocouples with asbestos rope in the sample gauge length range (one at each end of the gauge length and one in the middle of the gauge length), and make the temperature measurement terminal of the precious metal thermocouple closely contact with the sample surface. By accurately measuring and controlling the temperature of the two thermocouples, the sample gauge length is ensured to reach the required test temperature. Because SiC-based composite material will react chemically with Bt in precious metal thermocouple in long time high temperature environment, the precious metal thermocouple cannot be in direct contact with SiC-based composite material sample in fatigue test. However, if there is no direct contact, the accurate control of the sample temperature cannot be guaranteed.

[0007] (3) Heat insulation of high temperature furnace. The service condition of SiC-based composite material is harsh, the temperature is higher, and the life to be tested is longer. The double tests of long time and high temperature make the heat insulation problem of high temperature furnace prominent. A large number of practices show that during the fatigue test, the hot gas in the high temperature furnace continuously flows out through the gap between the high temperature furnace and the sample, continuously heating the upper parts and system of the testing machine. In long time high temperature fatigue test, the clamping block, chuck and sensor of the upper part of the testing machine continuously heat up, which may affect the accuracy of the sensor of the testing machine, and even cause damage to the testing machine system and its parts. Therefore, the high temperature furnace used in high temperature fatigue test must be insulated. In addition, effective insulation means can improve the heating efficiency and temperature uniformity of the high temperature furnace, and reduce the temperature fluctuation. SUMMARY

[0008] Therefore, the application aims at the three technical problems in the SiC-based composite material high-temperature tensile-tensile fatigue performance test, designs a high-temperature tensile-tensile fatigue test system and method, starts from the three aspects of clamping device, temperature measurement and control, and high-temperature furnace heat insulation, designs a high-temperature fatigue test clamping device which can adapt to any thickness sample and can be accurately centered, designs a temperature measurement device which can separate the thermocouple welding head from the sample without opening the furnace in the fatigue test, realizes the test temperature measurement and control method of contact temperature measurement in the heating and holding stage and indirect temperature measurement in the fatigue test stage, and proposes an effective high-temperature furnace heat insulation scheme.

[0009] To achieve the above object, the application provides the following technical scheme.

[0010] A high-temperature tensile-tensile fatigue test system, comprising: a clamping device;

[0011] The clamping device comprises a first assembly and a second assembly which are paired and identical in structure; the first assembly comprises a first inclined block;

[0012] The first inclined block is provided with a first groove for installing a sample on the clamping surface side, the first groove has an end side wall and two opposite inclined side walls, the two ends of the end side wall are respectively connected to the first ends of the two inclined side walls, and the second ends of the two inclined side walls form an end slot opposite to the end side wall;

[0013] The width of the end slot is smaller than the width of the end side wall.

[0014] Preferably, the first groove is an isosceles trapezoidal groove, the two inclined side walls are two waists respectively, and the end side wall and the end slot are two bottoms respectively.

[0015] Preferably, the depth of the first groove is smaller than half the thickness of the sample;

[0016] The second assembly comprises a second inclined block;

[0017] When the sample is installed in the first grooves of the first inclined block and the second inclined block, a gap is formed between the first inclined block and the second inclined block.

[0018] Preferably, the depth of the first groove is 0.05mm-0.25mm smaller than half the thickness of the sample.

[0019] Preferably, the first assembly further comprises a first clamping block;

[0020] The clamping surface side of the first clamping block is provided with a second groove matched with the shape of the first inclined block.

[0021] Preferably, the shape of the first inclined block is T-shaped, and the second groove is a T-shaped groove.

[0022] Preferably, the first clamp block is provided with a water hole;

[0023] And / or, the first clamp block is provided with a first clamp block fixing rod and a second clamp block fixing rod on both sides respectively.

[0024] Preferably, further comprising: a high-temperature furnace, a thermocouple, a bracket, a bracket base and a slide rail;

[0025] The outer wall of the high-temperature furnace is provided with a through hole for the thermocouple to pass through, the thermocouple is installed on the bracket, the bracket is slidably installed on the slide rail through the bracket base, and the slide rail is parallel to the axial direction of the through hole.

[0026] Preferably, further comprising: a high-temperature furnace and a heat insulation felt;

[0027] The heat insulation felt is arranged above the high-temperature furnace at the middle opening for the sample to pass through.

[0028] Preferably, the material of the heat insulation felt is aerogel composite material.

[0029] Preferably, the high-temperature furnace comprises: a high-temperature furnace left half and a high-temperature furnace right half;

[0030] The heat insulation felt comprises: a first heat insulation felt arranged on the top of the high-temperature furnace left half and a second heat insulation felt arranged on the top of the high-temperature furnace right half;

[0031] The first heat insulation felt and the second heat insulation felt are respectively provided with a rectangular opening at the center of the opposite side, and the rectangular openings form a rectangular passage for the sample to pass through.

[0032] A high-temperature tensile-tensile fatigue test method is adopted in the high-temperature tensile-tensile fatigue test system.

[0033] As can be seen from the above technical solutions, the beneficial effects of the present application are:

[0034] 1. The SiC-based composite material high-temperature tension-tension fatigue test system and method of the present application, a clamping device composed of a T-shaped groove clamping block and a T-shaped inclined block with trapezoidal grooves is designed, the Y-shaped end sample part is hung in the trapezoidal groove of the T-shaped inclined block during clamping, the sum of the depths of the trapezoidal grooves in a pair of T-shaped inclined blocks is less than the thickness of the sample, when assembled with the sample, a small gap exists between the two T-shaped inclined blocks, the existence of the small gap can ensure that the clamping block provides a transverse clamping force to the sample, the load can be transmitted to the sample by inducing friction force during tension loading, and the Y-shaped end of the sample and the T-shaped inclined block are pressed together to form a structural self-locking after the Y-shaped end of the sample is pressed against the T-shaped inclined block, the load is transmitted through contact pressure, the clamping device realizes the mixing of hydraulic clamping and Y-shaped end sample hanging clamping mode, and the load of the testing machine is transmitted through the front, rear, left and right four surfaces of the sample and the clamp, wherein the load transmission of the front and rear surfaces is based on the principle of hydraulic clamping, and the load transmission of the left and right sides is based on the principle of Y-shaped end sample hanging clamping, so that the stress concentration at the contact surface of the clamp and the sample in the case of using any of the above clamping modes alone can be reduced, the abnormal clamping damage of the sample can be prevented, and effective load transmission can be ensured.

[0035] 2. The SiC-based composite material high-temperature tension-tension fatigue test system and method of the present application, a clamping device composed of a T-shaped groove clamping block and a T-shaped inclined block with trapezoidal grooves is designed, several groups of T-shaped inclined blocks with different groove depths can be processed to adapt to any change in sample thickness, when the thickness of a group of samples changes little, T-shaped inclined blocks with appropriate depth trapezoidal grooves can be selected to ensure accurate centering of each sample. When the thickness of different groups of samples changes greatly, only a set of T-shaped inclined blocks meeting the groove depth requirement needs to be replaced, so that the clamping device has good universality and significant economy.

[0036] 3. The SiC-based composite material high-temperature tension-tension fatigue test system and method of the present application, a movable thermocouple test system is designed to realize contact temperature measurement during the heating and holding stages and indirect temperature measurement during the fatigue test stage, mainly including three armored thermocouples, a slidable thermocouple support, and a high-temperature furnace with a circular hole passage to ensure smooth passage of the thermocouple. During the heating and holding stages of the fatigue test, the thermocouple measurement welding head is in close contact with the sample surface, and when the fatigue load is started, the thermocouple measurement welding head can be separated from the sample by moving the support without manually removing the thermocouple, which can achieve the same temperature measurement accuracy and temperature control accuracy as the thermocouple being bound to the sample surface throughout the process, while effectively avoiding the problem of chemical reaction between the thermocouple welding head and the sample in the high-temperature environment.

[0037] 4. The SiC-based composite material high-temperature tension-tension fatigue test system and method provided by the application first proposes a technical solution of using aerogel to make a high-temperature furnace heat insulation anvil for high-temperature fatigue, which can effectively block the hot air flow rising from the high-temperature furnace, and the temperature of the system components above the testing machine does not obviously increase in long-time fatigue loading, thereby eliminating the risk of excessively high temperature rise of the system components of the testing machine in high-cycle and long-time fatigue tests. The use of the aerogel composite material heat insulation anvil also greatly improves the sealing performance of the high-temperature furnace, so that the temperature field in the high-temperature furnace is more stable and uniform. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0039] Figure 1 The first assembly of the embodiment of the application is provided with an explosive structure schematic diagram.

[0040] Figure 2 The three-dimensional structure schematic diagram of the two parts of the clamping device and the sample assembly provided by the embodiment of the application is provided.

[0041] Figure 3 The plan view structure schematic diagram of the clamping device and the sample assembly provided by the embodiment of the application is provided.

[0042] Figure 4 The top view structure schematic diagram of the sample and a pair of inclined blocks after assembly is provided by the embodiment of the application.

[0043] Figure 5 The structure schematic diagram of the heat insulation felt arranged above the heating furnace provided by the embodiment of the application is provided.

[0044] Figure 6 The shape detail view of the heat insulation felt provided by the embodiment of the application is provided.

[0045] Figure 7 The assembly structure schematic diagram of each part of the high-temperature tension-tension fatigue test system provided by the embodiment of the application is provided.

[0046] Figure 8 The assembly structure schematic diagram of the high-temperature tension-tension fatigue test system and the testing machine provided by the embodiment of the application is provided.

[0047] Wherein, 1 - first clamp block; 2 - first inclined block; 3 - sample; 4 - third clamp block; 5 - third inclined block; 6 - second clamp block; 7 - second inclined block; 8 - fourth clamp block; 9 - fourth inclined block; 11 - T-shaped groove, 111 - first inclined surface; 12 - water hole; 13 - first clamp block fixing rod, 14 - second clamp block fixing rod; 21 - trapezoidal groove, 211 - end side wall, 212 - inclined side wall, 213 - end slot, 22 - first part, 23 - second part, 231 - second inclined surface; 27 - gap; 31 - high temperature furnace left half; 32 - high temperature furnace right half; 33 - support; 34 - support base; 35 - slide rail; 36 - connecting arm; 37 - connecting beam; 41 - test machine left column, 42 - test machine right column; 43 - system support frame; 44 - test machine upper chuck, 45 - test machine lower chuck; 101 - first armored thermocouple, 102 - second armored thermocouple, 103 - third armored thermocouple; 104 - first circular hole passage, 105 - second circular hole passage, 106 - third circular hole passage; 310 - first heat insulation felt, 320 - second heat insulation felt; 330 - rectangular passage. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0049] The high-temperature tension-tension fatigue test system provided by the embodiments of the present application comprises a clamping device, which can refer to the structure shown in the drawings. Figures 1-3

[0050] The clamping device comprises a first assembly and a second assembly which are matched in pairs (respectively clamping the two sides of the upper end of the sample 3) and have the same structure, and a third assembly and a fourth assembly which are matched in pairs (respectively clamping the two sides of the lower end of the sample 3) and have the same structure.

[0051] The clamping surface of the first inclined block 2 is provided with a first recess for mounting the sample 3, and the first recess has an end side wall 211 and two opposite inclined side walls 212, the two ends of the end side wall 211 are respectively connected to the first ends of the two inclined side walls 212, and the second ends of the two inclined side walls 212 form an end slot 213 opposite to the end side wall 211.

[0052] The width of the end slot 213 is smaller than the width of the end side wall 211, that is, both of the two inclined side walls 212 are inwardly inclined towards the end slot 213, and outwardly inclined towards the end side wall 211.

[0053] ​From the above technical solutions can be seen, the high temperature tension-tension fatigue test system provided by the embodiment of the application, the first inclined block 2 is matched with the two inclined sides of the sample 3 through the first groove inclined side wall 212, as shown in Figure 1 and Figure 2 under the action of the tensile load, the shape of the sample 3 and the first groove which become narrower from top to bottom can realize the tensile self-locking through the inclined surface contact between them.

[0054] Specifically, the first groove is an isosceles trapezoidal groove 21, the two inclined side walls 212 are two waists respectively, and the end side wall 211 and the end groove opening 213 are two bottoms respectively, and the structure can refer to Figures 1-3 as shown. The end side wall 211 and the end groove opening 213 are perpendicular to the sample 3 and the tensile direction thereof.

[0055] In order to further optimize the above technical solutions, the depth of the first groove is less than half of the thickness of the sample 3;

[0056] The foregoing second assembly includes: a second inclined block 7, which is used to be matched with the first inclined block 2 to clamp the two sides of the sample 3 respectively;

[0057] As shown in Figure 4 when the sample 3 is installed in the first groove of the first inclined block 2 and the second inclined block 7, a gap 27 is formed between the first inclined block 2 and the second inclined block 7. That is, after the first inclined block 2 and the second inclined block 7 clamp the sample 3, the pair of inclined blocks do not fit but exist a small gap 27; and the existence of the small gap 27 can ensure that the clamping device can adapt to the thickness change of the sample 3 and ensure the accurate centering of the central axis of each sample 3 and the central axis loading line of the test piece.

[0058] As a preferred, the depth of the first groove is 0.05mm-0.25mm less than half of the thickness of the sample 3. That is, when a pair of inclined blocks are relatively folded from the slotted side, the depth of the trapezoidal groove formed by the two inclined blocks is 0.1mm-0.5mm less than the thickness of the sample, so that the sample can have sufficient side clamping and ensure that the sample is naturally centered after clamping. Correspondingly, the application can also process a series of T-shaped inclined blocks with different groove depths, in order to adapt to the samples with obvious thickness difference.

[0059] In the embodiment, the first assembly further includes: a first clamping block 1, and the structure thereof can refer to Figure 1 and Figure 2 as shown;

[0060] The clamping surface side of the first clamping block 1 is provided with a second groove which is completely same as the outer shape of the first inclined block 2. That is, the clamping device is a split structure, and the heat transfer of the sample 3 through the T-shaped inclined block to the T-shaped groove clamping block is limited, so that the T-shaped groove clamping block can be prepared by using ordinary steel which meets the requirements of rigidity and hardness, without considering the high temperature resistance problem.

[0061] Specifically, the first inclined block 2 has a T-shaped outer shape, and the second groove is a T-shaped groove 11. Figure 1 As shown in the drawings, the first inclined block 2 comprises a first part 22 and a second part 23; the first part 22 extends along a first direction, and the second part 23 extends along a second direction perpendicular to the first direction; a first end of the second part 23 is connected to the first part 22. Further, both sides of the second part 23 along the first direction are second inclined surfaces 231, and the second inclined surfaces 231 are towards a second end of the second part 23; a side wall of the T-shaped groove 11 has a first inclined surface 111 matched with the second inclined surface 231.

[0062] As preferred, the first clamping block 1 is provided with a water hole 12, and its structure can be referred to Figure 1 As shown in the drawings, the water hole 12 is used to connect with circulating water in the fatigue test, so as to realize cooling of the clamping block;

[0063] Further, the two sides of the first clamping block 1 are respectively provided with a first clamping block fixing rod 13 and a second clamping block fixing rod 14, which are used to be connected with a testing machine chuck; when the clamping block is installed to the testing chuck, the clamping block is connected with the testing machine chuck by using a spring, so as to realize fixation.

[0064] The high-temperature tension-tension fatigue test system provided by the embodiment of the present application further comprises a high-temperature furnace, a thermocouple, a bracket 33, a bracket base 34 and a sliding rail 35, and their structures can be referred to Figure 7 As shown in the drawings;

[0065] The high-temperature furnace is provided with a through hole for the thermocouple to pass through, the thermocouple is installed on the bracket 33, the bracket 33 is slidably installed on the sliding rail 35 through the bracket base 34, and the sliding rail 35 is parallel to the axial direction of the through hole. In the heating and heat preservation stage of the fatigue test, the thermocouple temperature measuring contact is in close contact with the surface of the sample, and when the fatigue load is started, the thermocouple temperature measuring contact is separated from the sample by moving the bracket without opening the high-temperature furnace to manually remove the thermocouple, so as to prevent the problem that the thermocouple contact and the SiC-based composite material sample will chemically react for a long time in the high-temperature environment, and at the same time, the same temperature measurement precision and temperature control accuracy as that of the thermocouple being bound on the surface of the sample throughout the process are achieved.

[0066] The high-temperature tension-tension fatigue test system provided by the embodiment of the present application further comprises a high-temperature furnace and a heat insulation felt, and their structures can be referred to Figure 5 and Figure 7 As shown in the drawings;

[0067] The heat insulation felt is arranged at the middle opening of the high-temperature furnace through which the sample 3 passes, so as to seal the high-temperature furnace and block the hot air flow rising from the high-temperature furnace.

[0068] Preferably, the material of the heat insulation felt is aerogel composite material (silica as matrix, mullite fiber as reinforcing phase), which can meet the requirements of high temperature test.

[0069] Further, the high temperature furnace comprises a high temperature furnace left half part 31 and a high temperature furnace right half part 32, the structure of which can refer to Figure 5 and Figure 7 ;

[0070] The heat insulation felt comprises a first heat insulation felt 310 arranged on the top of the high temperature furnace left half part 31 and a second heat insulation felt 320 arranged on the top of the high temperature furnace right half part 32.

[0071] The first heat insulation felt 310 and the second heat insulation felt 320 are respectively provided with a rectangular opening at the center of the opposite side, and the rectangular openings are combined to form a rectangular passage 330 to cooperate with the sample 3, the structure of which can refer to Figure 6 .

[0072] The embodiment of the present application also provides a high temperature tensile fatigue test method, which adopts the high temperature tensile fatigue test system as described above.

[0073] The present application will be further described in combination with specific schemes as follows:

[0074] The present application can be more clearly understood, but does not limit the protection scope of the present application.

[0075] The SiC-based composite material high temperature tensile fatigue test system of the present application is technically innovative from three aspects of clamping device, temperature measurement and control, and high temperature furnace heat insulation, effectively solves the technical problems of SiC-based composite material high temperature tensile fatigue test, and the technical schemes of the above three aspects will be described as follows.

[0076] 1. Clamping device - combination of open trapezoidal groove T-shaped inclined block and open T-shaped groove wedge-shaped clamping block.

[0077] A SiC-based composite material high temperature tensile fatigue test system and method, characterized by comprising a clamping device which can adapt to any change of sample thickness and ensure accurate centering of the sample, the clamping device is composed of four T-shaped groove wedge-shaped clamping blocks and four T-shaped inclined blocks, and each wedge-shaped clamping block and T-shaped inclined block is used in combination. Figure 1As shown, the first assembly is composed of a first T-shaped groove clamping block 1 and a first T-shaped inclined block 2. The first T-shaped groove clamping block 1 has a T-shaped groove 11 in the middle of its clamping surface. The shape and size of the T-shaped groove 11 are the same as those of the first T-shaped inclined block 2. During the test, the first T-shaped inclined block 2 is placed in the first T-shaped groove clamping block 1. In addition, a water hole 12 is punched on the side surface of the first T-shaped groove clamping block 1 for connecting with circulating water during the fatigue test to achieve the cooling of the clamping block. In addition, two clamping block fixing rods 13 and 14 are designed on both sides of the clamping block for connecting with the chuck of the testing machine. When the clamping block is installed in the chuck of the testing machine, the spring is used to connect the clamping block with the chuck of the testing machine to achieve fixation. The first T-shaped inclined block 2 has a trapezoidal groove 21 in the middle of its lower surface. The shape of the trapezoidal groove is the same as that of the Y-shaped end fatigue specimen 3. As an example, the assembly of the left pair of wedge-shaped clamping blocks and the T-shaped inclined block is used to install the specimen in the clamping device. The upper and lower ends of the Y-shaped end specimen 3 are hung and clamped in the first T-shaped inclined block 2 and the third T-shaped inclined block 5. The three-dimensional view and the plan view of the Y-shaped end specimen and the upper and lower T-shaped inclined blocks 2 and 5, and the T-shaped inclined block and the T-shaped groove clamping block 1 and 4 after assembly are shown in Figure 2 and Figure 3 .

[0078] In addition, in order to adapt to different specimen thicknesses and ensure the accurate centering of the central axis of the specimen and the loading line of the testing machine, the depth of the trapezoidal groove in the T-shaped inclined block is slightly smaller than half of the thickness of the specimen. When the pair of T-shaped inclined blocks are closed from the side of the groove surface, the depth of the trapezoidal groove formed by the two T-shaped inclined blocks is 0.1 mm to 0.5 mm smaller than the thickness of the specimen. Therefore, after the specimen is clamped between the pair of T-shaped inclined blocks, the pair of T-shaped inclined blocks do not fit together but have a small gap (0.1 mm to 0.5 mm) therebetween. As an example, the pair of T-shaped inclined blocks 2 and 7 used in the pair of wedge-shaped clamping blocks in the chuck of the testing machine are used to install the specimen in the clamping device. The specimen is clamped between the pair of T-shaped inclined blocks 2 and 7. The upper and lower ends of the specimen are hung and clamped in the first T-shaped inclined block 2 and the third T-shaped inclined block 5. The three-dimensional view and the plan view of the specimen and the upper and lower T-shaped inclined blocks 2 and 7 after assembly are shown in Figure 4As shown, when the upper end of the Y-shaped end sample 3 is clamped at the trapezoidal grooves of the pair of T-shaped wedges 2, 7, the sum of the depths of the two trapezoidal grooves of the T-shaped wedges 2, 7 is slightly smaller than the thickness of the Y-shaped end sample 3, and when the sample is clamped between the pair of T-shaped wedges 2, 7, the pair of T-shaped wedges 2, 7 does not fit but a small gap 27 exists. The existence of the small gap can realize accurate centering of each sample, can also generate transverse pressing force, increase the force transmission channel of the front and rear surfaces of the sample based on the principle of friction, reduce the contact pressure of the two side surfaces of the sample, prevent the sample from being crushed at this place in advance, and can also improve the stability of the force transmission of the clamping device. A series of T-shaped wedges with different slotting depths can be processed, and during the test, for any thickness of the sample, the T-shaped wedges can be replaced to meet the requirement that the depth of the trapezoidal groove formed by the two T-shaped wedges is 0.1mm-0.5mm smaller than the thickness of the sample. Since the T-shaped wedges are in direct contact with the sample, the T-shaped wedges can be overheated, in order to ensure that the T-shaped wedges can still effectively constrain the sample at high temperature and do not deform and damage, it is suggested to use high-temperature alloy with a temperature resistance of above 600℃ to prepare the T-shaped wedges. The T-shaped wedges and the T-shaped groove clamping block are separate, the heat transferred from the T-shaped wedges to the T-shaped groove clamping block is limited, and therefore the T-shaped groove clamping block can be made of ordinary steel material meeting the requirements of rigidity and hardness, without considering the high-temperature resistance problem.

[0079] The T-shaped wedges have the following advantages: only a plurality of T-shaped wedges with different slotting depths need to be processed, for any thickness of the sample, the T-shaped wedges with appropriate slotting depths can be selected to meet the requirement that the depth of the trapezoidal groove formed by the two T-shaped wedges is 0.1mm-0.5mm smaller than the thickness of the sample, and therefore the designed clamping device can be applied to the tensile-tensile fatigue test of the sample with a large change in thickness range. In addition, the T-shaped wedges and the wedge-shaped clamping block are separate, the sample is in direct contact with the T-shaped wedges for heat transfer, and therefore only the T-shaped wedges need to be made of high-temperature alloy, and the wedge-shaped clamping block can be made of ordinary steel material, so that the manufacturing difficulty and processing cost of the clamping device are low.

[0080] 2. Temperature measurement - contact temperature measurement during the heating and holding stages, and indirect temperature measurement during the fatigue test process.

[0081] High temperature furnace has certain temperature gradient and temperature deviation. The above problems are more serious in small size high temperature furnace with cold clamping mode. The conventional method is to bind the precious metal thermocouple with asbestos rope in the sample gauge length range (one at each end of the gauge length and one in the middle of the gauge length), and make the temperature measuring terminal of the precious metal thermocouple closely contact with the sample surface. The temperature of the two thermocouples is precisely measured and controlled to ensure that the sample gauge length reaches the required test temperature. Since the SiC-based composite material will react chemically with Bt in the precious metal thermocouple in a long time high temperature environment, the precious metal thermocouple cannot be in direct contact with the SiC-based composite material sample during fatigue test. However, if it is not in direct contact, the temperature of the sample cannot be accurately controlled. In order to solve the above technical difficulties, a fatigue test temperature measurement and control scheme is proposed, which is to contact the temperature during the heating and holding stage and indirectly measure the temperature during the fatigue test process. For this purpose, a movable thermocouple testing system is designed. Three armored thermocouples 101, 102 and 103 used for temperature measurement of the gauge length are installed on a bracket 33. The bracket base 34 below the bracket 33 is designed in T shape so as to slide on the T-shaped slot slide rail 35 below it. The slide rail 35 is connected to the connecting beam 37 through a connecting arm 36. The connecting beam 37 is used to connect the parts of the system and is connected to the testing machine. During the test process, the distance between the thermocouples and the sample surface can be adjusted by moving the position of the bracket base 34 on the slide rail 35. As a match, the high temperature furnace needs to be opened on one side to form three circular hole passages 104, 105 and 106. The diameter of the circular hole should be slightly larger than the diameter of the armored thermocouple, so that the three armored thermocouples can smoothly pass through the corresponding circular holes and extend into the high temperature furnace. During the fatigue test, the positions of the three thermocouples can be adjusted during the heating and holding stage to make the temperature measuring welding heads of the three thermocouples directly contact with the sample surface, so as to ensure the accuracy of temperature measurement and control. When the fatigue test is started, the high temperature furnace does not need to be opened. By pulling the thermocouple bracket above the slide rail, the temperature measuring welding heads of the thermocouples are separated from the sample surface by 3mm to 6mm.

[0082] 3. Heat insulation of heating system - aerogel composite material (silica as matrix and mullite fiber as reinforcing phase) insulation felt.

[0083] A large number of practices show that during the fatigue test, the hot air current rising in the high temperature furnace flows out through the gap between the high temperature furnace and the sample, continuously heating the components and system above the testing machine. In a long time high temperature fatigue test, the clamping block, chuck and sensor above the testing machine continuously heat up, causing overheating, which may affect the accuracy of the sensor of the testing machine. In severe cases, it may cause damage to the testing machine system and its components. Therefore, the high temperature furnace used in high temperature fatigue test must be insulated. In addition, effective insulation can improve the heating efficiency of the heating system, improve the temperature uniformity of the high temperature furnace and reduce the temperature fluctuation of the high temperature furnace.

[0084] Two pieces of aerogel composite are used to make two pieces of thermal insulation felt 310, 320, which are placed at the middle opening of the high-temperature furnace through which the sample passes, and a rectangular opening is cut at the center of each piece of thermal insulation felt 310, 320, and the two pieces of thermal insulation felt are combined to form a rectangular passage 330, which needs to be slightly smaller than the cross section of the sample at the contact with the thermal insulation felt. Before the high-temperature furnace is turned on and heated, the sample is inserted into the rectangular opening of the two pieces of silica aerogel composite thermal insulation felt, and then the silica aerogel composite thermal insulation felt is placed on the top of the high-temperature furnace, the contact between the thermal insulation felt and the sample and the furnace is adjusted to ensure good sealing, so that the thermal insulation felt does not generate additional force on the sample, and at the same time effectively blocks the upward channel of the hot gas flow.

[0085] A schematic diagram of a SiC-based composite high-temperature tensile-tensile fatigue test system including all components is shown in Figure 7 The entire system is connected to a guide rail-mounted support frame 43 through a connecting beam 37, and the support frame is connected to two columns 41, 42 of the testing machine, and the connection mode and assembly with the testing machine are shown in Figure 8 .

[0086] As a preferred mode, all components of the entire system are connected to a guide rail-mounted support frame through a connecting beam, and the support frame is connected to two columns of the testing machine, and the connecting structure has adjustable position to ensure that it can adapt to the mechanical test of samples of different sizes.

[0087] As a preferred mode, the T-shaped inclined block in the designed clamping device is suggested to be made of high-temperature alloy resistant to high temperature above 600℃, and the wedge-shaped clamping block with a T-shaped slot is suggested to be made of steel material meeting the requirements of rigidity and hardness.

[0088] The SiC-based composite high-temperature tensile-tensile fatigue test system and method can only be used in cooperation with a small-volume high-temperature furnace shorter than the sample length because it is based on a cold clamping mode.

[0089] The SiC-based composite high-temperature tensile-tensile fatigue test system and method can be applied to the tensile-tensile fatigue test of SiC-based composites in a high-temperature environment below 1600℃.

[0090] The SiC-based composite high-temperature tensile-tensile fatigue test system and method are suitable for the tensile-tensile fatigue test of SiC-based composite Y-shaped end samples.

[0091] The SiC-based composite high-temperature tensile-tensile fatigue test system and method are specifically designed for the high-temperature fatigue test of fiber-reinforced ceramic matrix composites with SiC as the matrix, and the high-temperature fatigue test of other materials that will chemically react with noble metal thermocouples in long-term contact can also be used for reference.

[0092] For a better understanding of the present application, the content of the present application is further described below in conjunction with specific examples, but the content of the present application is not limited only to the following examples:

[0093] Example: SiC with orthogonal lay-up f The high-temperature tensile-tensile fatigue test of the material at 1200℃ was carried out, the loading frequency was 30Hz, the maximum stress level was 140MPa, and the stress ratio was 0.01. The fatigue testing machine was an MTS hydraulic servo fatigue testing machine, the heating device was a high-temperature furnace with an outer shape height of 110mm, a uniform heating zone of 30mm long, and a silicon-carbon rod heating. The specific steps of the method implementation are as follows:

[0094] (1) The width and thickness of the Y-shaped end fatigue specimen gauge section were measured, which were 5.93mm and 2.93mm respectively, the cross-sectional area of the specimen gauge section was calculated, and the maximum load P of the fatigue loading was calculated according to the set stress level of 140MPa max 2085N, the fatigue test parameters such as load, loading frequency, stress ratio, data acquisition frequency, and sampling frequency were set on the testing machine.

[0095] (2) Four wedge-shaped water-cooled clamps with T-shaped slots were installed in the upper and lower clamps 44, 45 of the testing machine, a set of (including four) T-shaped inclined blocks with appropriate specifications was selected according to the thickness of the specimen, the four T-shaped inclined blocks were installed in the four wedge-shaped clamps respectively, the upper and lower ends of the specimen were installed in the two T-shaped inclined blocks on the left side of the testing system, the testing machine clamps were controlled to clamp the specimen, the trapezoidal groove bottoms in the two T-shaped inclined blocks on the right side were made to adhere to the specimen, the clamping force was set to about 1MPa, and a preload of about 50N was applied at the same time, so that the specimen was hung and clamped in the T-shaped inclined blocks in the wedge-shaped clamps.

[0096] (3) The position of the high-temperature furnace was adjusted to make the high-temperature furnace centered relative to the length direction of the specimen, the position of the thermocouple support on the slide rail was adjusted to make the welding heads of the three armored thermocouples contact the side surface of the specimen, the two parts of the high-temperature furnace were combined, and aerogel composite insulation felt was placed at the upper opening of the high-temperature furnace to ensure the sealing between the aerogel composite insulation felt, the specimen, and the high-temperature furnace. The heating temperature was set on the high-temperature furnace controller, the water pipe was connected to the water hole on the wedge-shaped clamp, the circulating water was turned on, the flowing water passed through the water-cooled clamp, and the heating function of the heating furnace was turned on.

[0097] (4) The temperature readings of the three armored thermocouples were monitored to reach the set target temperature, and after reaching the target temperature, the temperature was kept for 20 minutes. After the heat preservation was completed, the position of the thermocouple support on the slide rail was moved slightly away from the high-temperature furnace without turning on the high-temperature furnace, and the moving distance was about 3-6mm, so that the temperature measuring welding head of the thermocouple was separated from the surface of the specimen.

[0098] (5) Start the fatigue testing machine and load the specimen according to the pre-set parameters. During the test, the temperature of the three armored thermocouples which are detached from the surface of the specimen is monitored to ensure that the temperature of the high-temperature furnace is controlled within the required range. Since the system uses aerogel composite insulation blanket for sealing, the temperature field in the high-temperature furnace is more uniform and stable, which also ensures the effectiveness of accurate temperature control of the high-temperature furnace by monitoring the temperature values of the three armored thermocouples detached from the surface of the specimen.

[0099] (6) When the pre-set target cycle number is reached or the specimen is broken, stop the test.

[0100] In this embodiment, the SiC / SiC composite fatigue specimen did not break after 10 f cycles of the target life. 7 cycles of the target life.

[0101] Each of the embodiments in the specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0102] The above description of the disclosed embodiments enables those skilled in the art to carry out or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high temperature tension-tension fatigue testing system, characterized by, Comprise: Clamping device; The clamping device comprises: a first assembly and a second assembly which are matched and structurally identical; the first assembly comprises: a first inclined block (2); The clamping surface side of the first inclined block (2) is provided with a first groove for mounting a sample (3), the first groove has an end side wall (211) and two opposite inclined side walls (212), the two ends of the end side wall (211) are respectively connected to the first ends of the two inclined side walls (212), and the second ends of the two inclined side walls (212) form an end slot (213) opposite to the end side wall (211); The width of the end slot (213) is smaller than the width of the end side wall (211); The depth of the first groove is 0.05mm-0.25mm less than half the thickness of the sample (3), and a gap (27) is formed between the first inclined block (2) and the second assembly to accommodate samples of any thickness and accurately center.

2. The high-temperature push-pull fatigue testing system of claim 1, wherein, The first groove is an isosceles trapezoidal groove (21), the two inclined side walls (212) are two legs respectively, and the end side wall (211) and the end slot (213) are two bases respectively.

3. The high-temperature push-pull fatigue testing system of claim 1, wherein, The depth of the first groove is less than half the thickness of the sample (3); The second assembly comprises: a second inclined block (7); When the sample (3) is mounted in the first groove of the first inclined block (2) and the second inclined block (7), a gap (27) is formed between the first inclined block (2) and the second inclined block (7).

4. The high-temperature push-pull fatigue testing system of any of claims 1-3, wherein, The first assembly further comprises: a first clamping block (1); The clamping surface side of the first clamping block (1) is provided with a second groove matching the shape of the first inclined block (2).

5. The high-temperature push-pull fatigue testing system of claim 4, wherein, The shape of the first inclined block (2) is T-shaped, and the second groove is a T-shaped groove (11).

6. The high-temperature push-pull fatigue testing system of claim 4, wherein, The first clamping block (1) is provided with a water hole (12); And / or, the two sides of the first clamping block (1) are respectively provided with a first clamping block fixing rod (13) and a second clamping block fixing rod (14).

7. The high-temperature push-pull fatigue testing system of claim 1, wherein, Further comprising: High-temperature furnace, thermocouple, bracket (33), bracket base (34) and slide rail (35); The outer wall of the high-temperature furnace is provided with a through hole for the thermocouple to pass through, the thermocouple is mounted on the bracket (33), the bracket (33) is slidably mounted on the slide rail (35) through the bracket base (34), and the slide rail (35) is parallel to the axial direction of the through hole; In the heating and holding stage of the fatigue test, the positions of the brackets are adjusted to make the three thermocouple temperature measurement welding heads directly contact the surface of the sample, ensuring the accuracy of temperature measurement and control; when the fatigue test is started, the high-temperature furnace does not need to be opened, the thermocouple bracket above the slide rail is pulled to make the thermocouple temperature measurement welding head spaced apart from the surface of the sample by 3mm-6mm; the movable thermocouple test system realizes the test temperature measurement and control method of contact temperature measurement in the heating and holding stage and indirect temperature measurement in the fatigue test stage.

8. The high-temperature push-pull fatigue testing system of claim 1, wherein, Further comprising: High-temperature furnace and heat insulation felt; the heat insulation felt is made of silica-based aerogel and mullite fiber composite material; The heat insulation felt is arranged on the top of the left and right half parts of the high temperature furnace, and forms a rectangular passage (330) as the intermediate opening for the sample (3) to pass through after being folded.

9. The high-temperature push-pull fatigue testing system of claim 8, wherein, The material of the heat insulation felt is aerogel composite material.

10. The high-temperature push-pull fatigue testing system of claim 8, wherein, The high temperature furnace comprises a left half part (31) and a right half part (32). The heat insulation felt comprises a first heat insulation felt (310) arranged on the top of the left half part (31) and a second heat insulation felt (320) arranged on the top of the right half part (32). Rectangular openings are respectively arranged at the center of the opposite sides of the first heat insulation felt (310) and the second heat insulation felt (320), and the rectangular openings are combined to form a rectangular passage (330) for the sample (3) to pass through.

11. A high temperature pull-pull fatigue testing method, characterized by, The high temperature tension-tension fatigue test system comprises a clamping device combined by a T-shaped clamping block with a T-shaped inclined block with a trapezoidal groove, a test temperature measurement and control method based on a movable thermocouple test system to realize contact temperature measurement in the heating and holding stages and indirect temperature measurement in the fatigue test stage, and a high-division heat insulation felt made of silica-based aerogel and mullite fiber composite aerogel.

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