High-temperature bending fatigue test device and test method

Abstract

The invention belongs to the technical field of high-temperature fatigue testing, and particularly relates to a high-temperature bending fatigue testing device and method.The main body structure of the testing device comprises a fatigue testing machine and a heating furnace which are connected into a whole, and a movable clamp and a static clamp which are arranged in the heating furnace; the fatigue performance and the fatigue life of the metal material are measured through a bending test; the specific technological process of the test method comprises the following steps: (1) determining the actual service working condition of a sample; (2) determining bending fatigue test key parameters; and (3) determining test time, carrying out a high-temperature fatigue bending test, reasonably determining high-temperature bending fatigue test parameters based on corrosion fatigue equivalent conversion, and rapidly reproducing fatigue damage of equipment under a long-term high-temperature service condition through a short-time test in a laboratory under the condition of not changing a high-temperature fatigue mechanism and a crack development process. And rapid screening and examination verification of the novel structure / material of the equipment are realized.

Description

Technical field:

[0001] The present invention belongs to the technical field of high temperature fatigue testing, and in particular relates to a high temperature bending fatigue testing device and a testing method, which can greatly shorten the testing time and reduce the testing cost. Background technology:

[0002] During the operation of aircraft, vehicles and other equipment, fatigue is inevitable under the action of alternating loads. As fatigue damage to the structure continues to accumulate, the residual strength decreases, cracks appear in the structure and continue to expand. What is more serious is that the interaction between high temperature and fatigue greatly shortens the crack initiation time and accelerates the crack expansion, causing the equipment to enter aging prematurely and produce more cracks, especially sensitive structures such as engine blades, casings, and brackets. Once a cracking accident occurs, it seriously threatens the safety and function of the equipment. Based on this, it is necessary to carry out high-temperature fatigue performance tests on related structures / materials to verify the fatigue performance of the alternating stress at a temperature higher than 0.5Tm (Tm is the melting point expressed in thermodynamic temperature) or above the recrystallization temperature, so as to provide a basis for the material selection and structural design of key parts such as equipment engines.

[0003] A high-temperature fatigue testing device disclosed in Chinese Patent 202011172180.3 includes a heating furnace, a power module, a control cabinet, a bracket that can be moved up and down, a transducer, an upper amplitude transformer, a lower amplitude transformer, a fatigue stretching machine and an ultrasonic fatigue power supply. The fatigue stretching machine is placed horizontally, and the transducer is connected to the upper chuck of the stretching machine; the upper amplitude transformer and the transducer are fixedly connected by pins; the lower chuck of the stretching machine is fixedly connected to the lower amplitude transformer by pins; the specimen is installed between the upper amplitude transformer and the lower amplitude transformer, and is fixed by the upper amplitude transformer and the lower amplitude transformer; two movable joints are respectively installed on both sides of the fatigue stretching machine, and the bracket is connected to it and placed horizontally; the heating furnace is hung on the bracket; the heating furnace is composed of two left and right parts hinged together, the middle part of the heating furnace is a furnace, the upper and lower sides of the furnace are furnace mouths, the furnace is equipped with a heating element, and the furnace is surrounded by a mullite refractory layer and a fiber insulation layer. It can simulate the high temperature conditions in the fields of aviation and mechanical processing in which metal materials are subjected to tensile tests. However, the operation is relatively complicated. The heating furnace consists of two hinged parts, left and right, and is hung on a bracket. When in use, the bracket must be adjusted so that the furnace chamber of the heating furnace is at the same height as the test piece to be heated. The heating furnace must be closed before the test piece can be covered. Once misaligned, the fatigue tensile machine module may be seriously damaged. In addition, it can only perform fatigue tensile tests, while in actual working conditions, bending stress is more harmful to some key structures.A repeated bending fatigue testing machine disclosed in Chinese Patent No. 202310362101.2 includes: a base, a vertical plate is vertically arranged on the base, a rotating shaft is arranged on the vertical plate, the rotating shaft is vertically penetrated through the vertical plate and rotated with the vertical plate; a test bench, fixedly arranged on one side of the vertical plate, and a first clamp for clamping a metal wire is arranged on the test bench; a mounting plate is arranged on the same side of the vertical plate relative to the test bench, the mounting plate is fixedly connected to the rotating shaft and is parallel to the vertical plate, and a second clamp for clamping a metal wire is arranged on the mounting plate; a driving mechanism is arranged on one side of the vertical plate, and is used to rotate the rotating shaft; a counterweight mechanism is connected to the mounting plate, and is used to always apply tension to the metal wire in a direction away from the first clamp and the second clamp, and the direction of the tension is parallel to the axial direction of the metal wire at the part of the second clamp away from the first clamp. The structure includes a motor arranged on a vertical plate and a reducer connected to the output shaft of the motor, the output shaft of the reducer is connected to the rotating shaft, the counterweight mechanism includes a first guide rail horizontally fixedly connected to the mounting plate, a first guide pulley arranged on the first guide rail, a traction rope wound around the first guide pulley, a counterweight block connected to one end of the traction rope, and a third clamp arranged on the mounting plate, the third clamp is used to clamp the metal wire, the third clamp is slidably fitted to the mounting plate along the direction of the tension exerted on the metal wire, the end of the traction rope away from the counterweight block is connected to the third clamp, the first clamp is detachably provided with two clamping blocks, the first clamp can make the two clamping blocks simultaneously translate in the direction of moving away from or approaching each other, and the tops of the opposite sides of the two clamping blocks are both rounded; the second clamp is detachably provided with a sleeve, the sleeve is used for the metal wire to slide through, and the pipe mouth of the sleeve is rounded. The metal wire is bent to different angles by means of a counterweight mechanism and a driving mechanism, and the bending test is performed in two different directions to realize the repeated bending fatigue performance detection of the metal wire. However, the magnitude and frequency of the loading stress are limited. A bending fatigue testing machine disclosed in Chinese Patent 201210192707.8 includes: a driving device, a main shaft, a plurality of eccentric wheels, a main shaft support seat and a sample rack; the main shaft is rotatably mounted on the support seat; the driving device is connected to the main shaft and can drive the main shaft to rotate; the sample rack is used to fix the sample, and the height of the sample rack and the horizontal distance between the sample rack and the main shaft are adjustable; the eccentric wheel is mounted on the main shaft and can rotate with the main shaft, and the eccentric wheel can apply a periodic load to the sample mounted on the sample rack, the driving device includes a hydraulic motor and a reducer, the reducer is mounted between the hydraulic motor and the main shaft, and can transmit the power of the hydraulic motor to the main shaft, and also includes a roller matched with the eccentric wheel, the roller is mounted on the sample, and the eccentric wheel applies a periodic load to the sample through the roller, and also includes a counter, the counter is connected to the main shaft, and records the number of rotations of the main shaft.Its driving device drives the eccentric wheel installed on the main shaft to rotate with the main shaft through the rotation of the main shaft. The eccentric wheel cooperates with the sample, so that the sample is repeatedly bent under the action of alternating stress, and the sample is subjected to a bending fatigue test. However, it can only apply stress in a single bending direction, and the sample clamping and bending stress loading modules are relatively complicated, which is not suitable for introducing a heating module.

[0004] Therefore, how to realize bending fatigue testing under high temperature environment is a big problem. On the other hand, how to use relevant test equipment to evaluate the high temperature bending fatigue performance of equipment structure / material is also an urgent problem to be solved. It is necessary to determine the appropriate key parameters such as test temperature, loading stress and loading frequency. This comes from the actual service conditions of the equipment, and the actual operating parameters cannot be fully adopted. Because in many cases, when the actual operating parameters of the equipment are used for high temperature bending fatigue testing, fatigue cracks and fractures will not appear on the specimens for a long time or even permanently, resulting in unbearable time costs or test costs. Therefore, it is necessary to develop and design a high temperature bending fatigue test device and test method, which can strengthen the experimental parameters without changing the fatigue mechanism and development process, and realize the evaluation and verification of high temperature bending fatigue performance in a relatively short time. Summary of the invention:

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art, develop and design a high temperature bending fatigue test device and test method to load three-point or four-point reciprocating bending stress and reasonably determine the high temperature bending fatigue test parameters.

[0006] In order to achieve the above-mentioned purpose, the main structure of the high-temperature bending fatigue test device of the present invention comprises a fatigue testing machine and a heating furnace connected as a whole, and a dynamic fixture and a static fixture arranged in the heating furnace;

[0007] Wherein, the fatigue testing machine is connected with the moving fixture;

[0008] The heating furnace has at least a heating element and a temperature sensor, and the maximum heating temperature is 1500°C. There are a large number of threaded holes on the top of the furnace so that the static fixture can be installed in different positions as needed and the relative distance can be adjusted to meet the testing needs of samples of different specifications.

[0009] The movable fixture adopts an inverted "F" shape structure. The upper clamping plate is connected to the fatigue testing machine and moves up and down based on the control of the fatigue testing machine. The lower clamping plate is fixedly installed on the clamping rod. The relative positions of the upper clamping plate and the lower clamping plate are provided with several hemispherical protrusions to clamp several points above and below the middle part of the sample.

[0010] The static clamp is composed of two opposite inverted "F"-shaped components. The bottom adopts a threaded support rod design. The upper clamping end has a downward hemispherical protrusion, and the lower clamping end is provided with a threaded through hole. The tail of the equipped screw is a hemispherical structure corresponding to the position of the protrusion.

[0011] The specific process of the high temperature bending fatigue test method involved in the present invention is as follows:

[0012] (1) Determine the actual service conditions of the sample, including but not limited to temperature, main bending stress, form and vibration frequency;

[0013] (2) Determine the key parameters of the bending fatigue test, including but not limited to temperature and stress load, where the temperature is greater than the temperature under actual working conditions and the stress load is greater than the maximum stress under actual working conditions;

[0014] (3) Determine the test time and carry out high temperature fatigue bending test.

[0015] Compared with the prior art, the high-temperature bending fatigue test device of the present invention has a simple structure and is easy to operate. It simulates high-temperature conditions in the fields of aviation and mechanical processing, and measures the fatigue performance and fatigue life of metal materials subjected to repeated bending stress at different temperatures through three-point or four-point bending tests, thereby providing a basis for material selection and structural design of key parts such as equipment engines. The high-temperature bending fatigue test method reasonably determines the high-temperature bending fatigue test parameters based on corrosion fatigue equivalent conversion. Without changing the high-temperature fatigue mechanism and crack development history, the fatigue damage of equipment under long-term high-temperature service conditions can be quickly reproduced in a short period of time in the laboratory, thereby realizing rapid screening and assessment and verification of new equipment structures / materials, greatly shortening the test time and reducing the test cost. Description of the drawings:

[0016] Figure 1 It is a schematic diagram of the main structural principle of the present invention.

[0017] Figure 2 The figure is a side view of the main structure of the movable clamp involved in the present invention. Specific implementation method:

[0018] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0019] Embodiment 1:

[0020] The main structure of the high temperature bending fatigue test device involved in this embodiment is as follows Figure 1 As shown, it includes a fatigue testing machine 1, a heating furnace 2, a dynamic fixture 3 and a static fixture 4;

[0021] The fatigue testing machine 1 at the top is connected to the heating furnace 2 at the bottom to form a whole. The heating furnace 2 is provided with a heating element 21 and a temperature sensor 22, as well as a moving fixture 3 and a pair of static fixtures 4.

[0022] Specifically,

[0023] The heating furnace 2 adopts a square structure, and the maximum heating temperature is 1500°C. A circular furnace opening 23 is opened at the center of the top to allow the clamping rod 31 to pass through.

[0024] The main structure of the movable fixture 3 is as follows Figure 2 As shown, it includes a clamping rod 31, an upper clamping plate 32, a lower clamping plate 33 and a protrusion 34; the top of the clamping rod 31 passes through the furnace opening 23 opened at the top center of the heating furnace 2 and is connected to the fatigue testing machine 1, and the bottom is provided with an upper clamping plate 32 and a lower clamping plate 33 parallel to each other, and the lower surface of the upper clamping plate 32 and the upper surface of the lower clamping plate 33 are provided with a hemispherical protrusion 34 with corresponding positions;

[0025] The main structure of the static clamp 4 includes a mounting rod 41, an upper clamping end 42, a lower clamping end 43, a protrusion 34, a threaded through hole 44 and a screw 45; the top of the mounting rod 41 is arranged on the top of the heating furnace 2, and the upper clamping end 42 and the lower clamping end 43 are arranged on the bottom, and the protrusion 34 with a hemispherical structure is arranged on the lower surface of the upper clamping end 42, and the lower clamping end 43 is opened on the threaded through hole 44, and the screw 45 with a hemispherical structure on the top is arranged in the threaded through hole 44.

[0026] The furnace of the heating furnace 2 involved in this embodiment is made of ceramic, the furnace wall is made of titanium alloy, and a plug hole for inserting a temperature sensor 22 is provided on the upper part of the furnace body so that the probe of the temperature sensor 22 can detect the internal temperature. The heating element 21 is heated by an electric coil and an insulation layer is added, so that the heating furnace 2 has the advantages of fast heating and uniform temperature in the furnace.

[0027] The movable fixture 3 is connected to the fatigue testing machine 1 through the furnace opening 23;

[0028] The static clamps 4 are installed on both sides of the inner wall of the heating furnace 2 near the furnace opening 23 .

[0029] When the high temperature bending fatigue test device involved in this embodiment is used,

[0030] The dynamic clamp 3 clamps two points in the middle of the sample 100, and the paired static clamps 4 clamp both ends of the sample 100. In addition, limit baffles are installed on the front and rear sides of the static clamp 4 to prevent the sample 100 from slipping.

[0031] Through the reciprocating motion of the fatigue testing machine 1 , a four-point bending stress fatigue test is performed on the sample 100 .

[0032] Embodiment 2:

[0033] The high temperature bending fatigue test method involved in this embodiment is implemented based on titanium alloy materials of sensitive components of aircraft engines. The specific process includes the following steps:

[0034] (1) Based on the survey results, determine the actual service conditions of titanium alloy materials for sensitive components of aircraft engines, including parameters such as temperature, main bending stress, form and vibration frequency;

[0035] Among them, the flight time of an aircraft is 100 to 200 hours a year, and the working temperature of titanium alloy parts in the engine is -100 to 550°C. When used on the engine for a long time, the maximum temperature does not exceed 350°C. In actual use, the service temperature is below 250°C.

[0036] The engine components are mainly subjected to bending stress during operation, and the stress is maintained below 400MPa in flight state;

[0037] (2) Determine the key parameters of bending fatigue test

[0038] (a) Temperature

[0039] The test temperature is determined according to the temperature under the actual working conditions. In order to achieve accelerated testing, the test temperature is appropriately increased. It can be seen from the service environment in step (1) that the maximum temperature of the titanium alloy components in the engine under the service conditions does not exceed 350°C. By conducting high-temperature fatigue tests on titanium alloys at different temperatures, the fatigue life (number of cycles) of the titanium alloy components at each temperature is determined without changing the corrosion mechanism and process, and then the fatigue life equivalent conversion relationship at different temperatures is calculated;

[0040] Since high-temperature thermal corrosion is divided into high-temperature thermal corrosion (Type I) and low-temperature thermal corrosion (Type II), the temperature of Type I thermal corrosion is 850℃~950℃ (higher than the melting point of mixed salt), and the temperature of Type II high-temperature thermal corrosion is between 650℃~800℃ (lower than the melting point of mixed salt). When increasing the test temperature to accelerate the high-temperature fatigue failure process, the set test temperature should not cross the boundary temperature between high-temperature thermal corrosion (Type I) and low-temperature thermal corrosion (Type II) to avoid changes in the corrosion mechanism caused by changes in the state of deposited salt;

[0041] (b) Stress load

[0042] The stress load is determined according to the maximum stress under actual working conditions. To achieve accelerated testing, the stress load size is appropriately changed. On the basis of the service stress load of titanium alloy components, a stress load increase gradient is set, and high-temperature fatigue tests under different stress loads are carried out simultaneously. Under the premise of not changing the corrosion mechanism and process, the fatigue life (number of cycles) corresponding to each stress load is determined, and then the fatigue life equivalent conversion relationship of different stress loads is calculated;

[0043] The fatigue life of titanium alloy components under different temperature and stress load conditions is shown in Table 1:

[0044] 0℃ 250℃ 350℃ 650MPa <![CDATA[5.98×10 4 ]]> <![CDATA[3.95×10 3 ]]> / 600MPa <![CDATA[6.13×10 6 ]]> <![CDATA[2.37×10 4 ]]> / 550MPa <![CDATA[3.19×10 7 ]]> <![CDATA[1.98×10 4 ]]> / 500MPa <![CDATA[1.36×10 9 ]]> <![CDATA[2.79×10 6 ]]> / 450MPa / <![CDATA[6.55×10 6 ]]> <![CDATA[1.57×10 4 ]]> 400MPa / <![CDATA[1.41×10 7 ]]> <![CDATA[2.15×10 4 ]]> 350MPa / <![CDATA[>1.17×10 8 ]]> <![CDATA[1.97×10 7 ]]>

[0045] Taking 350℃ and 450MPa stress load as standard test conditions, the fatigue life equivalent conversion coefficient is shown in Table 2:

[0046] 0℃ 250℃ 350℃ 650MPa 0.2625 3.9747 / 600MPa 0.0026 0.6624 / 550MPa 0.0005 0.7929 / 500MPa 0.0000 0.0056 / 450MPa / 0.0024 1.0000 400MPa / 0.0011 0.7302 350MPa / 0.0001 0.0008

[0047] Since the SN curve of metals at high temperatures has no horizontal part, the maximum stress without fracture under 107-108 cycles is generally used as the high-temperature fatigue strength limit. At the same time, the stress load must be higher than the high-temperature fatigue limit to be used as an acceleration condition, because it has a significant impact on fatigue life. When the stress load increases, the high-temperature fatigue life decreases significantly.

[0048] (c) Other parameters

[0049] Since the stress waveform and cycle frequency have limited influence on the bending fatigue life, the relevant parameters can be kept consistent with the actual working conditions. For example, the loading waveform is selected as a sine wave, the loading frequency is 10Hz, and the stress ratio R is -1;

[0050] (3) Determine the test time and conduct high temperature fatigue bending test

[0051] Based on the service environment of step (1), the engine titanium alloy component is calculated to be in service for 200 hours in one year at 250°C and a stress load of 400 MPa. The fatigue test time converted to the standard test conditions (350°C, 450 MPa) according to Table 2 is: 200×0.0011=13.2 min;

[0052] A high-temperature bending fatigue testing machine 1 is used to control the temperature of the heating furnace 2 at 350°C. The titanium alloy component is clamped by a dynamic clamp 3 and a static clamp 4 for a bending fatigue test. The maximum bending stress is 450MPa, the stress ratio R=-1, the loading waveform is a sine wave, the loading frequency is 10Hz, and a bending fatigue test is performed for 13.2min. The high-temperature bending fatigue corrosion of the titanium alloy component after one year of actual service as an aircraft engine component is analyzed and studied.

[0053] Embodiment 3:

[0054] The main structure of the high-temperature bending fatigue testing device involved in this embodiment is the same as that of Embodiment 1, except that the heating furnace 2 adopts a sealed and waterproof design, into which seawater or salt mist is injected, and combined with waterproof heating components, it can realize in-situ bending fatigue testing under high-temperature salt mist or high-temperature seawater conditions, so as to be close to the actual working environment of some samples 100.

[0055] Embodiment 4:

[0056] The main structure of the high-temperature bending fatigue testing device involved in this embodiment is the same as that of Embodiment 1, except that the dynamic clamp 3 is composed of upper and lower matching clamping end components extending in three directions (with a spacing of 180°), and cooperates with the static clamps 4 at different positions to realize bending fatigue tests of three groups of parallel samples 100 at the same time.

Claims

1. A coating high temperature bending fatigue test device, characterized in that: The main structure includes a fatigue testing machine and a heating furnace connected as a whole, and a dynamic fixture and a static fixture arranged in the heating furnace; The fatigue testing machine is connected to the dynamic fixture; The heating furnace has at least a heating element and a temperature sensor; The movable fixture adopts an inverted "F" shape structure; The static clamp consists of two sets of opposite inverted "F" shaped components.

2. A coating high temperature bending fatigue test device according to claim 1, characterized in that: The upper clamping plate of the dynamic fixture is connected to the fatigue testing machine, and the lower clamping plate is fixedly installed on the clamping rod. A plurality of hemispherical protrusions are arranged at relative positions of the two to clamp the sample.

3. A coating high temperature bending fatigue test device according to claim 1 or 2, characterized in that: The bottom of the static clamp adopts a threaded support rod design. The upper clamping end has a downward hemispherical protrusion, and the lower clamping end is provided with a threaded through hole. The tail of the equipped screw is a hemispherical structure corresponding to the position of the protrusion.

4. The high temperature bending fatigue test device according to claim 1, characterized in that: The main structure of the dynamic clamp includes a clamping rod, an upper clamping plate, a lower clamping plate and a protrusion; the top of the clamping rod passes through the furnace opening opened in the center of the top of the heating furnace and is connected to the fatigue testing machine, and the bottom is provided with an upper clamping plate and a lower clamping plate parallel to each other, and the lower surface of the upper clamping plate and the upper surface of the lower clamping plate are provided with protrusions of hemispherical structures with corresponding positions.

5. The high temperature bending fatigue test device according to claim 1, characterized in that: The main structure of the static clamp includes a mounting rod, an upper clamping end, a lower clamping end, a protrusion, a threaded through hole and a screw; the top of the mounting rod is arranged on the top of the heating furnace, and the upper clamping end and the lower clamping end are arranged on the bottom, a protrusion with a hemispherical structure is arranged on the lower surface of the upper clamping end, a threaded through hole is opened on the lower clamping end, and a screw with a hemispherical structure on the top is arranged in the threaded through hole.

6. The high temperature bending fatigue test device according to claim 3, characterized in that: The heating furnace adopts a square structure, and the maximum heating temperature is 1500℃. A circular furnace opening is opened at the center of the top. The dynamic fixture is connected to the fatigue testing machine through the furnace opening, and the static fixture is installed on both sides of the inner wall of the heating furnace near the furnace opening.

7. A coating high temperature bending fatigue test device according to claim 6, characterized in that: The furnace chamber of the heating furnace is made of ceramic, the furnace wall is made of titanium alloy, a socket for inserting a temperature sensor is arranged on the upper part of the furnace body, and the heating element is heated by an electric coil with an external insulation layer.

8. The high temperature bending fatigue test device according to claim 3, characterized in that: The specific process during use is: (1) Determine the actual service conditions of the sample; (2) Determine the key parameters of bending fatigue test; (3) Determine the test time and carry out high temperature fatigue bending test.

9. The high temperature bending fatigue test device according to claim 6, characterized in that: The heating furnace adopts a sealed and waterproof design, which is injected with seawater or salt spray, and is equipped with waterproof heating components to carry out in-situ bending fatigue tests under high-temperature salt spray or high-temperature seawater conditions.

10. A coating high temperature bending fatigue test device according to claim 1 or 2, characterized in that: The dynamic fixture is composed of upper and lower matching clamping end components extending in three directions, and cooperates with static fixtures in different positions to carry out bending fatigue tests on three groups of parallel samples at the same time.

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