A wind tunnel airfoil low-temperature reciprocating loading test method and device

Abstract

The application discloses a wind tunnel airfoil low-temperature reciprocating loading test method and device in the technical field of wind tunnel airfoil test, which comprises the following steps: firstly, strain gauge pasting and calibration are completed; then, a test piece is installed on a tool and placed in an insulation box; a low-temperature environment is established by gradient filling of liquid nitrogen; precise reciprocating stress load is applied by using an actuator cylinder; after the test is completed, the box is opened and static standing is carried out; finally, internal defect detection is carried out by table inspection and scanning, and the results are recorded and output. The application accurately realizes a stable low-temperature environment of-185 DEG C to-196 DEG C by setting a multilayer insulation structure and a liquid nitrogen filling system, and simulates uniform reciprocating stress and comprehensively detects structural damage by means of a high-precision actuator cylinder and monitoring equipment, so that the high accuracy and reliability of test results are ensured, a strong basis is provided for wind tunnel airfoil design optimization, repeated tests are effectively reduced, efficiency is improved, resources such as liquid nitrogen and test pieces are saved, and test cost is significantly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wind tunnel airfoil testing, in particular to a wind tunnel airfoil low-temperature reciprocating loading test method and device. BACKGROUND

[0002] In the field of aerospace, the performance of wind tunnel airfoils is crucial to the safety and efficiency of aircraft. With the development of technology, the demand for research on the performance of wind tunnel airfoils under extreme conditions is increasing, and the mechanical property testing under low-temperature environment has become a key link.

[0003] The existing technology faces many problems when conducting similar tests. In terms of temperature control, traditional low-temperature test equipment cannot accurately reach and stably maintain -185℃, a specific low temperature, with large temperature fluctuations. For example, some simple low-temperature boxes may have limited performance of insulation materials or unstable refrigeration systems, resulting in temperature control accuracy of only ±5℃ or even worse, which cannot meet the strict requirements of temperature accuracy for tests.

[0004] In the stress loading segment, the existing loading device has problems such as insufficient loading accuracy and uneven stress distribution when simulating 0~500Mpa reciprocating stress loading. This may be due to the design of the loading mechanism not being precise enough to accurately control the size and direction of the loading force, thereby affecting the simulation of the real stress conditions of the wind tunnel airfoil.

[0005] For airfoil structure damage monitoring, the commonly used methods are often not comprehensive and accurate. Traditional visual inspection can only detect obvious surface damage and cannot detect small cracks, internal delamination, and delamination defects. Some simple non-destructive testing methods, such as conventional ultrasonic testing, may not be able to accurately detect early small damage due to limited resolution, resulting in inaccurate assessment of the airfoil structure state, so we propose a wind tunnel airfoil low-temperature reciprocating loading test method and device. SUMMARY

[0006] To solve the technical problems in the prior art, the present application provides a wind tunnel airfoil low-temperature reciprocating loading test method and device, which integrates a test box capable of stably controlling -185℃~-196℃ ultra-low temperature, combines a servo loading system capable of accurately simulating 0~500MPa reciprocating load, and constructs an airfoil structure online monitoring system integrating high-resolution ultrasonic and optical fiber sensing technology.

[0007] The purpose of the present application is achieved by a wind tunnel airfoil low-temperature reciprocating loading test method, comprising the following steps:

[0008] S1, paste strain gauge: obtain the stress-strain distribution results of the test piece by finite element analysis, and paste strain gauges in key areas. After pasting, measure the resistance value of the strain gauge;

[0009] S2, calibration operation: invert the tooling and install the test piece. Hang the weight through the steel wire rope, gradually increase the weight, and detect the strain value synchronously. Record the weight after reaching the standard;

[0010] S3, connecting device: one end of the test piece is connected to the tooling, and the other end is connected to the steel wire rope through the lifting ring. The steel wire rope is coupled with the actuator cylinder to form a cantilever loading state, and the load parameter is set;

[0011] S4, heat preservation treatment: place the tooling in the heat preservation box, install the detection device, and close the box;

[0012] S5, temperature adjustment: use gradient filling strategy to fill liquid nitrogen into the heat preservation box, and intermittently detect and record the temperature of the test piece to construct a low temperature test environment;

[0013] S6, dynamic loading test: start the actuator cylinder, apply reciprocating motion to the test piece based on the load-time curve, and monitor the actuator cylinder parameters in real time through the monitoring system;

[0014] S7, post-detection: open the box at a speed of 5° / s, take out the test piece and stand for 10 minutes, detect the surface quality of the test piece, scan the internal defects of the test piece, and record and output the detection results.

[0015] Optionally, the key areas include areas with large strain, middle areas of the test piece, and loading end areas;

[0016] The resistance value of the strain gauge is within a predetermined range, specifically 120±0.5Ω;

[0017] Measure the insulation resistance, and the insulation resistance value is ≥100MΩ.

[0018] Optionally, the process of step S2 is specifically:

[0019] After inverting the work, one end of the test piece is fixedly connected to the tooling, and a steel wire rope is hung at the other end of the test piece, and a weight is hung through the steel wire rope;

[0020] When adding weights, each time a weight is added, stand for 2 minutes, then use a strain measurement instrument to read the strain value, until the strain value is 6450με, and the corresponding stress is 500Mpa;

[0021] Record the weight at this time, and note it as the load parameter of the subsequent actuator cylinder.

[0022] Optionally, before use, the heat preservation box is cleaned and dried, and a plurality of heat preservation structures are arranged on the outside.

[0023] The detection device is a temperature sensor, and the measuring head of the temperature sensor is tightly attached to the surface of the test piece during installation.

[0024] Optionally, in step S5, the gradient filling strategy is specifically:

[0025] The initial filling speed is 80 mL / min, and the filling is performed for 1 min;

[0026] If the temperature is greater than -185℃, the filling speed of 30 mL / min is used for filling;

[0027] At the same time, the temperature in the incubator is detected and recorded every 5 seconds until the temperature is stable at -185℃ and the fluctuation is within ±1℃ within 10 minutes;

[0028] In the test, the temperature is detected every 10 minutes, and if the temperature is greater than or equal to -184℃, liquid nitrogen is added at a speed of 20 mL / min until the temperature is less than or equal to -185℃, and the temperature change is continuously detected and recorded.

[0029] Optionally, in step S6, the monitoring system includes a high-precision laser displacement sensor and a force sensor.

[0030] The actuator parameters include motion displacement and loading force.

[0031] A wind tunnel airfoil low-temperature reciprocating loading test device for implementing the wind tunnel airfoil low-temperature reciprocating loading test method, comprising an incubator, a tool assembly, an actuator, a liquid nitrogen filling device, and a monitoring system.

[0032] The incubator is provided with a multi-layer insulation structure, a built-in temperature sensor, an external 8cm aerogel felt, and a hole in the wall for the temperature sensor to insert, and a hole at the upper end for inputting liquid nitrogen.

[0033] The tool assembly is connected to the test piece by 10.9 high-strength bolts.

[0034] The actuator is connected to the working assembly and connected to the test piece by a steel wire rope, and the control system is provided with a load parameter.

[0035] Optionally, the multi-layer insulation structure includes a stainless steel inner insulation box, inner insulation cotton, an outer insulation box, and outer insulation cotton.

[0036] The inner part of the inner insulation box is used to place the tool assembly.

[0037] The stainless steel inner insulation box, the inner insulation cotton, the outer insulation box, and the outer insulation cotton are sequentially sleeved.

[0038] The outer side of the outer insulation cotton is wrapped with aerogel felt.

[0039] Optionally, the incubator is further provided with a feedback controller linked with the temperature sensor.

[0040] When the temperature is greater than or equal to -184 DEG C, the liquid nitrogen filling device is automatically triggered, and the filling is carried out at a filling speed of 20 mL / min.

[0041] Optionally, the monitoring system further comprises:

[0042] An optical magnifying glass is used to detect surface cracks of the test piece.

[0043] An ultrasonic monitor is used to detect internal defects of the test piece.

[0044] Compared with the prior art, the present application has the beneficial effects that: the present application can accurately control the test environment temperature at -185 DEG C to -196 DEG C, the temperature fluctuation is very small, and the reciprocating stress loading of 0 to 500 Mpa is accurately simulated, the loading precision is high, and the stress distribution is uniform, which makes the test conditions highly consistent with the actual working conditions, the test results are more accurate and reliable, and provides a strong basis for the design optimization and engineering application of the wind tunnel airfoil.

[0045] Through the cooperative work of various high-precision monitoring equipment, comprehensive, in-depth and accurate monitoring of the structural damage of the test piece is realized, not only the small surface cracks can be found in time, but also the internal delamination, delamination and other defects can be accurately detected, and the overall evaluation of the quality and safety of the test piece is ensured.

[0046] The test process is designed scientifically and reasonably, and each step is closely linked to reduce the uncertainty and operation errors in the test process. The accurate temperature control, stress loading and monitoring means avoid repeated tests caused by unstable test conditions or inaccurate detection, greatly improving the test efficiency. At the same time, the efficient test process saves the test time, liquid nitrogen consumption and test resources such as test pieces, reduces the test cost, and improves the overall cost-effectiveness. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of the provided drawings.

[0048] Figure 1 is the flow chart of the wind tunnel airfoil low-temperature reciprocating loading test method provided by the present application.

[0049] Figure 2It is the schematic diagram of the whole structure of the wind tunnel airfoil low-temperature reciprocating loading test device provided by the application.

[0050] Figure 3 It is the schematic diagram of the calibration operation provided by the application.

[0051] Figure 4 It is the schematic diagram of the test piece and tool connection provided by the application.

[0052] Figure 5 It is the schematic diagram of the actuator loading curve provided by the application.

[0053] In the figure: 1, heat preservation box; 2, tool assembly; 3, actuator; 4, weight; 5, steel wire rope; 6, test piece. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0055] As Figures 1 to 5 shown in the figure, the wind tunnel airfoil low-temperature reciprocating loading test method comprises the following steps:

[0056] S1, paste strain gauge: obtain the stress and strain distribution results of the test piece through finite element analysis, and paste strain gauges in key areas. After the pasting is completed, the resistance value of the strain gauge is measured;

[0057] S2, calibration operation: invert the tool, and install the test piece. The weight is hung by the steel wire rope, the weight is gradually increased, the strain value is synchronously detected, and the weight quality is recorded after reaching the standard;

[0058] S3, connection device: one end of the test piece is connected with the tool, the other end is connected with the steel wire rope through a lifting ring, the steel wire rope is coupled with the actuator to form a cantilever hanging state, and the load parameter is set;

[0059] S4, heat preservation treatment: place the tool in the heat preservation box, install the detection device, and close the box body;

[0060] S5, temperature adjustment: the heat preservation box is filled with liquid nitrogen by using a gradient filling strategy, and the temperature of the test piece is intermittently detected and recorded to construct a low-temperature test environment;

[0061] S6, dynamic loading test: start the actuator, apply reciprocating motion to the test piece based on the load-time curve, and monitor the parameters of the actuator in real time through the monitoring system;

[0062] S7, post-detection: open the box at a speed of 5° / s, take out the test piece and stand for 10 min, detect the surface quality of the test piece, scan the internal defects of the test piece, and record and output the detection results.

[0063] It should be noted that the test principle of the present application is as follows: the present application is based on the principles of precise temperature control and stress loading, provides a stable low-temperature environment through a liquid nitrogen low-temperature test box, and applies reciprocating stress to the wind tunnel airfoil test piece according to a preset load-time curve by using an actuator to simulate the stress state under actual working conditions.

[0064] During the test process, the strain, temperature, structural damage and other parameters of the test piece are monitored in real time by means of strain gauges, temperature sensors, magnifying glasses, handheld ultrasonic detectors and other equipment, and the test piece is judged whether it meets the performance standard by comparing and analyzing the monitoring data with the design requirements.

[0065] Specifically, the key areas include areas with large strain, middle areas of the test piece and loading end areas;

[0066] The resistance value of the strain gauge is measured within a predetermined range, specifically 120±0.5Ω;

[0067] The insulation resistance is measured, and the insulation resistance value is ≥100MΩ.

[0068] Further, the areas with large strain are usually the parts with the most concentrated stress, which are the potential starting points of structural failure. These areas have characteristics such as large stress gradient, complex multi-directional stress state, etc.; the middle areas of the test piece are usually in a relatively ideal uniform stress field, and the data thereof are crucial for verifying the overall performance model of the material; the loading end areas are the only way for external load to be transmitted to the internal structure, and have obvious local effects, risks such as stress concentration and loading eccentricity, etc.

[0069] For example, when pasting, first place the test piece stably on a clean and dry table top, and according to the stress and strain distribution results obtained by finite element analysis or theoretical calculation in advance, accurately paste the strain gauges in the key areas with large strain, the middle areas of the test piece and the loading end areas; use special high-performance glue to ensure that the strain gauges are tightly attached to the surface of the test piece without bubbles, wrinkles and other defects.

[0070] After pasting, use a high-precision resistance measuring instrument to measure the resistance value of the strain gauge, which should be within the specified normal range, and measure the insulation resistance to ensure that the strain gauge can accurately measure the strain change.

[0071] Specifically, the process of step S2 is as follows:

[0072] After inverting the work, one end of the test piece is fixedly connected with the tooling, and a steel wire rope is hung at the other end of the test piece, and a weight is hung through the steel wire rope.

[0073] When adding the weight, each time a weight is added, the strain value is read by the strain gauge after 2 minutes, until the strain value is 6450με, and the corresponding stress is 500 Mpa;

[0074] The weight of the weight at this time is recorded and is used as the load parameter of the subsequent actuator cylinder.

[0075] Exemplarily, the test piece is firmly connected with the tooling in an inverted manner, the end of the stainless steel adjustable wire rope is adjusted to a suitable position, and the weight is carefully placed. When the weight of the weight is increased each time, the operation should be slow and smooth to prevent the weight from falling or the test piece from being impacted;

[0076] After the weight is added, the test piece strain is fully stabilized for 2 minutes, and then the strain value is read using a high-precision strain gauge. This process is repeated to gradually increase the weight of the weight. When the strain value is accurately displayed as 6450με, that is, the stress is 500 Mpa, the weight of the weight at this time is immediately accurately recorded using an electronic balance with a precision of 0.1 g. The weight will be used as the accurate setting value of the subsequent actuator cylinder 2 for reciprocating load.

[0077] Further, when connecting the test device, first, the left end of the test piece is tightly connected with the test tooling through a high-strength bolt. The tightening torque of the bolt should strictly reach 30 N·m according to the design requirements to ensure that the connection part is not loose or slippage. The right end is reliably connected with the steel wire rope that has undergone strict quality detection and pre-stretching treatment through a lifting ring screw. The size of the lifting ring screw should match the test piece and the steel wire rope. After connection, the fastening degree is checked. Then, the steel wire rope is accurately connected with the actuator cylinder, the positions of various parts are adjusted, and the test piece is in a precise cantilever hanging state. According to the weight of the weight obtained by calibration, the load parameter is accurately set in the actuator cylinder control system, and the setting error is controlled within ±0.5% to ensure the accuracy of stress loading.

[0078] Specifically, before use, the incubator is cleaned and dried, and multiple layers of insulation structure are provided on the outside.

[0079] The detection device is a temperature sensor. When installed, the measuring head of the temperature sensor is tightly attached to the surface of the test piece.

[0080] Further, the measuring head of the temperature sensor is tightly attached to the surface of the test piece, which is the key to realizing accurate temperature measurement. It can maximize the reduction of contact thermal resistance between the measuring head and the test piece, and ensure that the sensor can truly and quickly reflect the temperature change of the test piece itself, rather than the temperature of the environment or air, thereby effectively avoiding errors caused by temperature fluctuations or measurement lag on the test results.

[0081] For example, before use, use a lint-free cloth to dip a suitable amount of alcohol and carefully wipe the stainless steel inner insulation box inside to remove oil stains, dust and other impurities, then dry with dry compressed air, carefully and smoothly put the test piece connected with the test fixture into the insulation box to avoid collision with the inner wall of the insulation box;

[0082] After covering the insulation box cover, use a thickness of 8cm aerogel felt to tightly wrap the outside of the insulation box in multiple layers to ensure no heat leakage point, open a small hole with a diameter of 1.5cm at a distance of 15cm from the bottom of the side wall of the insulation box for installing a high-precision temperature sensor (such as a PT100 temperature sensor with an accuracy of ±0.1℃), insert the measuring head of the temperature sensor through the small hole and fix it with high-temperature resistant sealant to ensure that the measuring head is in close contact with the surface of the test piece and can accurately monitor the temperature change of the test piece;

[0083] Specifically, in step S5, the gradient filling strategy is as follows:

[0084] The initial filling speed is 80mL / min, and the filling is 1min;

[0085] If the temperature is greater than -185℃, the filling speed is 30mL / min;

[0086] At the same time, the temperature in the insulation box is detected and recorded every 5s until the temperature is stable at ≤-185℃ and the fluctuation is ≤±1℃ within 10min;

[0087] In the test, the temperature is detected every 10min, if the temperature is ≥-184℃ and above, the liquid nitrogen is added at a speed of 20mL / min until the temperature is ≤-185℃, and the temperature change is continuously detected and recorded.

[0088] Further, the initial rapid filling can quickly pull the environmental temperature to the target zone, shortening the test preparation time; then according to the real-time temperature feedback, switch to low-speed filling, and set the temperature control index, effectively avoid the temperature overshoot or large amplitude oscillation caused by the instantaneous violent vaporization of liquid nitrogen, prevent the unpredictable thermal shock to the test piece, the continuous monitoring and small, precise compensatory filling in the test process form a closed-loop control system, which can timely offset the temperature rise caused by environmental heat leakage or test piece heat generation, ensuring that the test piece is always in a stable, uniform low-temperature environment during the entire dynamic loading test period.

[0089] Specifically, in step S6, the monitoring system includes a high-precision laser displacement sensor and a force sensor;

[0090] The actuator parameters include motion displacement and loading force.

[0091] Further, the specific process of step 6 is: before starting the actuator, the actuator is comprehensively inspected, including the fastening of the connection part, the lubrication, the stroke accuracy and the control system parameter setting, etc.

[0092] After starting the actuator, the motion displacement and loading force of the actuator are monitored in real time by a monitoring system composed of a high-precision laser displacement sensor and a force sensor, so as to ensure that the actuator strictly reciprocates according to the load-time curve shown in the figure, and the motion cycle error is controlled within ±0.3s. Figure 5

[0093] During the whole 10h test process, the temperature sensor value is observed every 10min, if the temperature rises to-184℃ and above, liquid nitrogen is slowly added at a speed of 20mL / min to make the temperature quickly fall below-185℃, and the temperature change is continuously observed to ensure the temperature stability.

[0094] The specific process of step 7 is: after the 10h test is completed, the end cover of the insulation box is slowly opened at a speed controlled within 5° / s to avoid damage to the test piece due to rapid temperature change. The tooling and test piece are carefully taken out and placed on a stable table with a levelness error of not more than ±0.1mm / m, and are left for 10min.

[0095] The detection personnel use a high-definition optical magnifying glass with a magnification of 15 times to observe step by step at an interval of 3mm from one end of the test piece, to check whether there are structural damage signs such as delamination, debonding, buckling, obvious cracks, etc.

[0096] For any suspected damage site found, a measuring microscope with an accuracy of 0.02mm is used to measure the crack length to judge whether it exceeds the design requirement of 0.3mm, and the damage position, type and crack length, etc. are recorded in detail.

[0097] Subsequently, a handheld ultrasonic detector with a frequency of 8MHz and a resolution of 0.05mm is used to comprehensively scan and detect the test piece, the detection speed is controlled within 30mm / s, whether there are internal delamination, debonding and other defects is accurately judged according to the ultrasonic reflection signal, and the detection results are recorded and saved in the form of images and data

[0098] A wind tunnel airfoil low-temperature reciprocating loading test device for realizing the wind tunnel airfoil low-temperature reciprocating loading test method, comprising an insulation box, a tooling assembly, an actuator, a liquid nitrogen filling device and a monitoring system.

[0099] The insulation box is provided with a multi-layer insulation structure, a built-in temperature sensor, and an external 8cm aerogel felt, and the box wall is provided with a hole for inserting the temperature sensor and an upper end hole for inputting liquid nitrogen.

[0100] ​The tool assembly is connected with the test piece through 10.9-grade high-strength bolts;

[0101] The actuating cylinder is connected with the working assembly, the test piece is connected through a steel wire rope, and a load parameter is arranged in the control system.

[0102] Specifically, the multi-layer insulation structure comprises a stainless steel inner insulation box, inner insulation cotton, an outer insulation box and outer insulation cotton.

[0103] The inner part of the inner insulation box is used for placing the tool assembly.

[0104] The stainless steel inner insulation box, the inner insulation cotton, the outer insulation box and the outer insulation cotton are sequentially sleeved.

[0105] The outer side of the outer insulation cotton is wrapped with aerogel felt.

[0106] Specifically, the insulation box is further provided with a feedback controller linked with the temperature sensor.

[0107] When the temperature is greater than or equal to -184 DEG C, the liquid nitrogen filling device is automatically triggered, and filling is carried out at a filling speed of 20 mL / min.

[0108] Specifically, the monitoring system further comprises:

[0109] An optical magnifying glass is used for detecting surface cracks of the test piece.

[0110] An ultrasonic monitor is used for detecting internal defects of the test piece.

[0111] Further, the test device provided by the present application comprehensively and finely realizes the requirements of the foregoing low-temperature reciprocating loading method, wherein the multi-layer insulation structure (from inside to outside, a stainless steel inner box, inner insulation cotton, an outer insulation box and outer insulation cotton, and the outermost layer is wrapped with 8cm aerogel felt) forms an efficient low-temperature environment.

[0112] The tool assembly is connected with the test piece through 10.9-grade high-strength bolts, so as to ensure the connection stiffness and fatigue life of the test piece under the double actions of low temperature and reciprocating load, which is the basis for realizing accurate mechanical transmission.

[0113] The actuating cylinder is connected with the test piece through a steel wire rope, so as to provide stable, accurate and high-frequency reciprocating load excitation, and the load parameter arranged in the control system is accurate quantization of the loading process.

[0114] In addition, the device is provided with a feedback controller linked with the temperature sensor, which is in line with the core idea of "dynamic feedback" and "closed-loop control" in the gradient filling strategy, and can automatically trigger liquid nitrogen filling at a precise speed of 20mL / min when the temperature deviates from the stable threshold, realizing the automatic, unmanned and high stability maintenance of the low-temperature environment.

[0115] In summary: the present application can accurately control the test environment temperature at -185℃~-196℃, the temperature fluctuation is very small, and the reciprocating stress loading of 0~500Mpa is accurately simulated, the loading precision is high, and the stress distribution is uniform, which makes the test conditions highly consistent with the actual working conditions, the test results are more accurate and reliable, and provides a strong basis for the design optimization and engineering application of wind tunnel airfoils.

[0116] Through the cooperative work of various high-precision monitoring equipment, comprehensive, in-depth and accurate monitoring of the structural damage of the test piece is realized, not only the surface micro cracks can be found in time, but also the internal delamination, delamination and other defects can be accurately detected, and the comprehensive evaluation of the quality and safety of the test piece is ensured.

[0117] The test process is designed scientifically and reasonably, and each step is closely linked to reduce the uncertainty and operation errors in the test process. Precise temperature control, stress loading and monitoring means avoid repeated tests caused by unstable test conditions or inaccurate detection, greatly improving the test efficiency. At the same time, the efficient test process saves the test time, liquid nitrogen consumption and test resources such as test pieces, reduces the test cost, and improves the overall cost-effectiveness.

[0118] The above examples are only used to help understand the method of the present application and its core idea. It should be noted that for ordinary skilled persons in the art, without departing from the principles of the present application, the present application can be improved and modified, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A wind tunnel airfoil cryogenic reciprocating loading test method, characterized by, The method comprises the following steps: S1, pasting strain gauges: obtain the stress-strain distribution results of the test piece through finite element analysis, and paste strain gauges in key areas; after pasting, measure the resistance value of the strain gauges; S2, calibration operation: invert the tooling and install the test piece, hang the weights through the steel wire rope, gradually increase the weight, synchronously detect the strain value, and record the weight after reaching the standard; specifically: after inverting the work, one end of the test piece is fixedly connected with the tooling, a steel wire rope is hung at the other end of the test piece, and weights are hung through the steel wire rope; when the weights are added, each time one weight is added, the strain value is read by using a strain measuring instrument after standing for 2 min, until the strain value is 6450με and the corresponding stress is 500 Mpa; record the weight at this time, and mark it as the load parameter of the subsequent actuating cylinder; S3, connecting device: one end of the test piece is connected with the tooling, the other end is connected with the steel wire rope through a lifting ring, the steel wire rope is coupled with the actuating cylinder to form a cantilever hanging state, and the load parameter is set; S4, heat preservation treatment: place the tooling in the heat preservation box, install the detection device, and close the box body; S5, temperature regulation: use a gradient filling strategy to fill liquid nitrogen into the heat preservation box, and intermittently detect and record the temperature of the test piece to construct a low-temperature test environment; the gradient filling strategy specifically comprises: the initial filling speed is 80 mL / min, and the filling is performed for 1 min; if the temperature is greater than -185℃, the filling is performed at a filling speed of 30 mL / min; at the same time, the temperature in the heat preservation box is detected and recorded every 5 s until the temperature is stable at -185℃ and the fluctuation is less than or equal to ±1℃ within 10 min; in the test, the temperature is detected once every 10 min, if the temperature is greater than or equal to -184℃, liquid nitrogen is added at a filling speed of 20 mL / min until the temperature is less than or equal to -185℃, and the temperature change is continuously detected and recorded; S6, dynamic loading test: start the actuating cylinder, apply reciprocating motion to the test piece based on the load-time curve, and monitor the actuating cylinder parameters in real time through the monitoring system; S7, post-detection: open the box at a speed of 5° / s, take out the test piece and stand for a set time, detect the surface quality of the test piece, scan the internal defects of the test piece, and record and output the detection results.

2. The wind tunnel airfoil cryogenic reciprocating loading test method of claim 1, wherein: The key areas include areas with large strain, middle areas of the test piece, and loading end areas; The resistance value of the strain gauges is in a preset range, specifically 120±0.5Ω; The insulation resistance value is greater than or equal to 100 MΩ.

3. The wind tunnel airfoil cryogenic reciprocating loading test method of claim 1, wherein: Before use, the heat preservation box is cleaned and dried, and a plurality of heat preservation structures are arranged outside; The detection device is a temperature sensor, and when installed, the measuring head of the temperature sensor is closely attached to the surface of the test piece.

4. The wind tunnel airfoil cryogenic reciprocating loading test method of claim 1, wherein: In step S6, the monitoring system comprises a high-precision laser displacement sensor and a force sensor; The actuating cylinder parameters include motion displacement and loading force.

5. A wind tunnel airfoil cryogenic reciprocating loading test apparatus for implementing the wind tunnel airfoil cryogenic reciprocating loading test method of any one of claims 1-4, characterized by: The heat preservation box, tooling assembly, actuating cylinder, liquid nitrogen filling equipment and monitoring system are included; The heat preservation box is provided with a plurality of heat preservation structures, a temperature sensor is built-in, the outside is wrapped with 8 cm aerogel felt, the box wall is provided with a hole for the temperature sensor to insert, and the upper end is provided with a hole for inputting liquid nitrogen; The tool assembly is connected with the test piece through a 10.9 high-strength bolt connection test; The operating cylinder is connected with the working assembly, the test piece is connected through a steel wire rope, and a load parameter is arranged in the control system.

6. The wind tunnel airfoil cryogenic reciprocating loading test apparatus of claim 5, wherein: The multi-layer heat preservation structure comprises a stainless steel inner heat preservation box, inner heat preservation cotton, an outer heat preservation box and outer heat preservation cotton; The inside of the inner heat preservation box is used for placing the tool assembly; The stainless steel inner heat preservation box, the inner heat preservation cotton, the outer heat preservation box and the outer heat preservation cotton are sequentially sleeved; The outside of the outer heat preservation cotton is wrapped with aerogel felt.

7. The wind tunnel airfoil cryogenic reciprocating loading test apparatus of claim 6, wherein: The heat preservation box is further provided with a feedback controller linked with the temperature sensor; When the temperature is greater than or equal to -184 DEG C, the liquid nitrogen filling equipment is automatically triggered, and filling is carried out at a filling speed of 20 mL / min.

8. The wind tunnel airfoil cryogenic reciprocating loading test apparatus of claim 5, wherein: The monitoring system further comprises: An optical magnifying glass is used for detecting surface cracks of the test piece; An ultrasonic monitor is used for detecting internal defects of the test piece.

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