Prestress-variable thermal fatigue test device and method

Abstract

The invention discloses a variable prestress thermal fatigue test device and method. The test device comprises a sample clamping unit, an induction heating unit, a cooling unit and a power control unit, the sample clamping unit is used for fixing a test piece and applying variable prestress; the induction heating unit adopts a high-frequency induction heating technology, and heats the test piece to a set temperature within a set time; the cooling unit is communicated with the test piece air inlet channel, and cold air is discharged into the air inlet channel for rapid cooling; and the power control unit is used for adjusting the prestress and cooperatively clamping the test piece. The device can accurately control the prestress in the thermal fatigue test process and simulate the thermal fatigue failure condition in a real service environment. The test method comprises the steps of prestress application, heating, heat preservation, cooling, cyclic testing and crack observation, and the test requirements under different working conditions can be met. The method is suitable for fatigue performance evaluation of materials or structures bearing complex thermal mechanical loads, such as steam turbine cylinders and aero-engine hot end components.

Description

Technical Field

[0001] The present invention relates to the fields of mechanical engineering, aviation and aerospace science and technology, and in particular to a thermal fatigue test device and method with variable prestress. Background Art

[0002] A thermal fatigue test apparatus is a device used to simulate fatigue failure of materials caused by cyclical temperature fluctuations in actual operating environments. Thermal fatigue testing involves repeatedly heating and cooling a material within a set temperature range until failure occurs, while simultaneously recording changes in the material's mechanical properties. This provides a basis for predicting the material's service life in the corresponding temperature environment. This testing method is widely used to assess the lifespan of key components in high-temperature environments, such as aircraft engines and steam turbines, providing an important reference for material selection and structural optimization in engineering applications.

[0003] However, existing thermal fatigue testing equipment still has the following limitations:

[0004] 1. Lack of prestress control: In actual operating conditions, components often experience a certain amount of prestress. However, existing thermal fatigue testing equipment typically simply fixes the test piece without applying or adjusting varying prestress, making it impossible to accurately simulate actual operating conditions. This testing method, which ignores prestress, results in significant deviations from actual service conditions, making it difficult to directly apply experimental data to engineering design and life prediction.

[0005] 2. Single test conditions and poor flexibility: Existing test equipment can usually only perform fixed temperature cycle tests, making it difficult to flexibly adjust key test parameters (such as prestress, heating temperature, and holding time). This limitation leads to overly idealized test conditions that cannot cover the complex temperature-stress environment under actual working conditions, thereby reducing the applicability of the test and the engineering reference value of the data.

[0006] 3. Irrational test piece design: Existing test piece designs are often overly simplified, failing to fully consider the structural characteristics of key components, such as the localized stress concentration areas of steam turbine cylinders or aircraft engine hot end components. Consequently, the test piece structure differs from the deformation, thermal expansion, and failure modes of actual components under service conditions, making it difficult to directly apply test results to engineering practice.

[0007] To address these issues, the present invention proposes a variable prestress thermal fatigue testing device and method. This device, utilizing an adjustable prestress clamping system, a programmable induction heating device, and a precisely controlled cooling system, simulates the thermal fatigue failure process of components under actual operating conditions. This device not only applies and adjusts prestress during the test, enhancing test authenticity, but also allows for flexible configuration of test conditions to accommodate the testing requirements of diverse materials and structures. Furthermore, the test piece structure of the present invention better aligns with actual service environments, thereby improving the reliability of test data and its engineering applicability. Summary of the Invention

[0008] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0009] Therefore, to solve the above technical problems, the present invention provides the following technical solution: a thermal fatigue testing device with variable prestress, which is mainly used to perform thermal fatigue tests on a test piece, wherein the test piece includes an upper clamping end, a test area, and a lower clamping end; the test device is characterized in that it includes:

[0010] The specimen clamping unit is used to fix the test piece and apply prestress to the test piece according to given requirements;

[0011] Induction heating unit, used to heat the test piece at a set temperature field at a set time;

[0012] A cooling unit is connected to the air inlet of the test piece through a pipeline, and is used to discharge cold air into the air inlet after the test piece reaches a set temperature field and maintains it for a set time;

[0013] A power control unit, used to control the magnitude of the prestress applied to the test piece and to control the clamping of the test piece;

[0014] The sample clamping unit works in conjunction with the power control unit to apply variable prestress.

[0015] As a preferred solution of the variable prestressed thermal fatigue testing device described in the present invention, the sample clamping unit includes a base, a lower column and a lower clamp. The base is arranged at the bottom of the lower clamp for fixing the clamp, the column is used to connect the base and the lower clamp, the lower clamp is made of high-temperature resistant material, and a slide rail for moving the lower column is arranged on the lower column. The lower clamp is used to clamp the test piece.

[0016] As a preferred solution of the variable prestressed thermal fatigue testing device described in the present invention, wherein: the lower clamping end of the test piece is fitted with the lower fixture; the area to be tested is heated by an induction heating unit, cooled by cooling gas, and serves as an observation area for fatigue cracks; the upper clamping end is used to fit the power control unit.

[0017] As a preferred embodiment of the variable prestressed thermal fatigue testing device of the present invention, the induction heating unit includes a high-efficiency power supply, a high-frequency transformer and an induction heater. The high-efficiency power supply is used to provide a high-frequency power supply. The high-frequency transformer is connected to the high-frequency power supply to adjust the voltage and current set by the high-frequency power supply output. The induction heater is connected to the output end of the high-frequency transformer to heat the test area of the test piece at a set temperature at a set time.

[0018] As a preferred solution of the variable prestressed thermal fatigue testing device of the present invention, the cooling unit includes a cooling air path connected to the air inlet in the test piece, for discharging cold air into the air inlet.

[0019] As a preferred solution of the variable prestressed thermal fatigue testing device described in the present invention, the power control unit includes an upper clamp, a movable column, a load sensor and a measuring device, the upper clamp is used to clamp the upper clamping end of the fixed test piece; the movable column is used to pull the test piece to a certain position after the upper clamp clamps the test piece, so as to add prestress that meets the test requirements; the load sensor and the measuring device are used to display and set the preload that meets the test requirements.

[0020] This solution also discloses a test method for the above-mentioned variable prestress thermal fatigue test device, which is characterized in that the test method includes the following specific steps:

[0021] S1: Fix the test piece and set the control system according to the number of cycles and heating temperature required by the test;

[0022] S2: Configure the induction heating device to meet the requirement of heating the test piece according to the preset conditions;

[0023] S3: heating the test piece to a set temperature using an induction heating device and maintaining the set temperature for a certain period of time;

[0024] S4: injecting cold air into the test piece through the cooling unit to cool the test piece for a certain period of time;

[0025] S5: Repeat steps S3 to S4 for a set number of times or until cracks appear on the test piece, and then end the test.

[0026] Beneficial effects of the present invention:

[0027] 1. The present invention can accurately simulate actual working conditions, as follows:

[0028] Variable prestress control: The power control unit of this invention precisely controls and dynamically adjusts the prestress applied to the test piece through the coordinated action of the upper fixture, movable column, and load sensor. This innovative design overcomes the limitation of existing technologies that cannot simulate prestressed environments, ensuring that test results are more consistent with the stress conditions of components in actual service environments, thereby improving the engineering applicability of test data.

[0029] 2. The present invention can create a variety of test conditions, as follows:

[0030] Flexible temperature control: The present invention adopts an induction heating unit, which can accurately control parameters such as heating temperature, heating rate, and holding time through the cooperation of high-frequency power supply, high-frequency transformer and heating coil, so as to meet the test requirements under different materials and working conditions, making the test method more flexible and diverse.

[0031] Efficient cooling system: The cooling unit is connected to the external duct, which can quickly inject cold air into the test piece to achieve rapid cooling. This not only improves test efficiency, but also ensures the stability and repeatability of the temperature cycle test, thereby improving the accuracy and reliability of the test.

[0032] 3. The present invention can improve test accuracy and efficiency, as follows:

[0033] Real-time monitoring and data recording: This device is equipped with load sensors and high-precision measuring equipment, which can monitor and record prestress and temperature changes in real time during the test, ensuring that all key parameters of each test are accurately recorded, providing a reliable experimental basis for subsequent data analysis and material life prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0035] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0036] Figure 2 Schematic diagram of the specific structure of the test piece of the present invention. DETAILED DESCRIPTION

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0039] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0040] Furthermore, the present invention is described in detail with reference to schematic diagrams. For ease of illustration, when describing the embodiments of the present invention, cross-sectional views illustrating device structures may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely illustrative and should not limit the scope of protection of the present invention. Furthermore, in actual production, the three-dimensional dimensions of length, width, and depth should be included.

[0041] Reference Figures 1-2 , an embodiment of the present invention provides a variable prestress thermal fatigue testing apparatus, particularly suitable for simulating the thermal fatigue process of a test specimen 200 of a steam turbine component. The test specimen 200 comprises an upper clamping end 201, a test area 202, and a lower clamping end 203. The upper clamping end 201 and the lower clamping end 203 are hollow cylinders with closed upper and lower ends, respectively, and are welded to the test area 202. The test area 202 is designed based on the local structure of the failure location of the steam turbine and is hollow, truncated, and has multiple column holes for exhausting gas during cooling.

[0042] The device mainly includes a sample clamping unit 100, an induction heating unit 300, a cooling unit 400 and a power control unit 500, wherein the sample clamping unit 100 and the power control unit 500 work together to apply variable prestress;

[0043] The main structure of the device is as follows:

[0044] The specimen clamping unit 100 is designed to secure the test piece 200 and apply prestress according to given requirements. The unit is secured to the ground by a base 101 through a fixing device to ensure overall stability. The lower column 102 connects the base 101 and the lower fixture 103, providing support and guidance. The lower fixture 103 is made of high-temperature resistant material and can move within the slide rail of the column 102 to clamp the lower clamping end 203 of the test piece 200.

[0045] The induction heating unit 300 is used to heat the test area 202 of the test piece 200 according to the set temperature field at the set time; the unit is powered by a high-frequency power supply, and the output voltage and current are adjusted by a high-frequency transformer, and finally the test piece 200 is heated by the induction heater (heating coil); the transmission signal of the high-frequency transformer is connected to the industrial computer to realize remote control; the power control unit of the present invention can be controlled by an industrial computer, and can realize the automation of the test process, which not only reduces human errors, but also improves the stability and repeatability of the test, making the experimental data more reliable.

[0046] The cooling unit 400 is connected to the air inlet of the test piece 200 through the cooling air path 401, and is used to discharge cold air into the air inlet after the test piece 200 reaches the set temperature field and maintains it for a set time; the cooling unit 400 is designed as a countersunk screw hole, which is convenient for connection with an external duct to inject cold air.

[0047] The power control unit 500 is used to control the magnitude of the prestress applied to the test piece 200 and clamp the test piece 200; the unit includes an upper clamp 501, which is made of high-temperature resistant material and can move in the slide rail of the movable column 502, and is used to clamp the upper clamping end 201 of the fixed test piece 200; the movable column 502 is used to pull the test piece 200 to a certain position to add prestress that meets the test requirements; the load sensor and measuring equipment 503 is used to display and set the preload that meets the test requirements, and is controlled by an industrial computer.

[0048] This embodiment also discloses a specific application embodiment of the test method of the above-mentioned variable prestress thermal fatigue test device, and the test steps are as follows:

[0049] First, the test piece 200 is placed in the sample clamping unit 100, and the lower clamp 103 is controlled by an industrial computer to clamp the lower clamping end 203 of the test piece 200, and the control system is set according to the test requirements; then, the induction heating device 300 is configured to meet the requirements of heating the test piece 200 according to preset conditions, and the transmission signal of the heater is connected to the industrial computer for remote control; then, the induction heating device 300 is used to heat the test piece 200 to a set temperature (such as 400°C) and maintain the set temperature for a certain time (such as 15 minutes); after the test piece 200 reaches the set temperature and maintains the set time, the cooling unit 400 begins to introduce cold air, and the cooling time reaches 50 minutes, and one cycle is completed; finally, the heating and cooling steps are repeated a set number of times (such as 1000 times) or until cracks appear on the test piece 200, and the test is terminated.

[0050] The present invention integrates technologies such as variable prestress control, induction heating, high-efficiency cooling and automatic control to form a complete and innovative thermal fatigue test solution, which can accurately control the test temperature and make the test results more accurate; it has a variable prestress function, which makes up for the shortcomings of existing thermal fatigue test devices in this regard, making the test results and data more accurate and more in line with actual conditions; it provides a more diverse selection of test conditions; the design of the test piece 200 is simplified according to the local structure of the failure position of the turbine. Specifically, the geometric structure of the test piece 200 is based on the local structure of the turbine cylinder or the hot end component of the aircraft engine, and especially adopts a hollow frustum-shaped test area and column hole design to more realistically simulate the stress distribution and thermal expansion characteristics of actual components, so that the test results are closer to the failure mode under the actual service environment.

[0051] The above-mentioned device and method can effectively simulate the thermal fatigue process under actual working conditions and provide more accurate test data. It can be widely used in thermal fatigue testing of key components in high-temperature working environments such as aircraft engines and steam turbines, and has high practical value and promotion prospects.

[0052] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A thermal fatigue test device with variable prestress, the thermal fatigue test device being mainly used for performing a thermal fatigue test on a test piece (200), the test piece (200) comprising an upper clamping end (201), a test area (202) and a lower clamping end (203); characterized in that: The test device includes: A specimen clamping unit (100) is used to fix the test piece (200) and apply prestress to the test piece (200) according to given requirements; An induction heating unit (300) is used to heat the test piece (200) at a set temperature field at a set time; a cooling unit (400) connected to an air inlet of the test piece (200) through a pipeline, and configured to discharge cold air into the air inlet after the test piece (200) reaches a set temperature field and maintains it for a set time period; A power control unit (500) is used to control the magnitude of the prestress applied to the test piece (200) and to control the clamping of the test piece (200); The sample clamping unit (100) works in conjunction with the power control unit (500) to apply variable prestress.

2. The variable prestress thermal fatigue testing device according to claim 1, characterized in that: The sample clamping unit (100) includes a base (101), a lower column (102) and a lower clamp (103), wherein the base (101) is arranged at the bottom of the lower clamp (103) for fixing the clamp, the column (102) is used to connect the base (101) and the lower clamp (103), a slide rail for moving the lower column (102) is arranged on the lower column (102), and the lower clamp (103) is used to clamp the test piece (200).

3. The variable prestressed thermal fatigue testing device according to claim 2, characterized in that: The lower clamping end (203) of the test piece (200) is fitted with the lower fixture (103); the area to be tested (202) is heated by an induction heating unit (300), cooled by cooling gas, and serves as an observation area for fatigue cracks; and the upper clamping end (201) is used to fit the power control unit (500).

4. The variable prestress thermal fatigue testing device according to claim 3, characterized in that: The induction heating unit (300) comprises a high-efficiency power supply, a high-frequency transformer, and an induction heater. The high-efficiency power supply is used to provide a high-frequency power supply. The high-frequency transformer is connected to the high-frequency power supply and is used to adjust the voltage and current set by the high-frequency power supply output. The induction heater is connected to the output end of the high-frequency transformer and is used to heat the test area (202) of the test piece (200) at a set temperature at a set time.

5. The variable prestress thermal fatigue testing device according to claim 4, characterized in that: The cooling unit (400) includes a cooling air path (401) which is in communication with an air inlet duct in the test piece (200) and is used for discharging cold air into the air inlet duct.

6. The variable prestressed thermal fatigue testing device according to claim 5, characterized in that: The power control unit (500) comprises an upper clamp (501), a movable column (502), and a load sensor and a measuring device (503). The upper clamp (501) is used to clamp the upper clamping end (201) of the fixed test piece (200); the movable column (502) is used to pull the test piece (200) to a certain position after the upper clamp (501) clamps the test piece (200) to add a prestress that meets the test requirements; the load sensor and the measuring device (503) are used to display and set the preload that meets the test requirements.

7. The test method of the variable prestress thermal fatigue test device according to any one of claims 1 to 6, characterized in that: The test method comprises the following specific steps: S1: Fixing the test piece (200) and setting the control system according to the number of cycles, heating temperature, etc. required by the test; S2: configuring the induction heating device (300) so as to meet the requirement of heating the test piece (200) according to preset conditions; S3: heating the test piece (200) to a set temperature using an induction heating device (300), and maintaining the set temperature for a certain period of time; S4: injecting cold air into the test piece (200) through the cooling unit (400) to cool the test piece (200) for a certain period of time; S5: Repeat steps S3 to S4 for a set number of times or until cracks appear on the test piece (200), and then end the test.

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