Blade high-cycle fatigue limit prediction method considering corrosion damage

Abstract

The invention provides a blade high-cycle fatigue limit prediction method considering corrosion damage, which comprises the following steps: carrying out simulation modeling and processing according to a real blade to obtain a simulated blade, placing the real blade and the simulated blade in a constant-temperature corrosion solution to simulate the corrosion condition of the blade under a real working condition, obtaining blades with different corrosion durations, and carrying out high-cycle fatigue limit prediction on the blade after obtaining the blades with different corrosion durations. Performing stress-strain curve measurement and fatigue limit test on the blade, and fitting according to fatigue limit data to obtain a prediction curve of corrosion time and fatigue limit; the invention provides the method for simulating the blade corrosion condition and predicting the fatigue limit of the blade under the laboratory condition, and compared with the fatigue limit prediction of the traditional theoretical calculation and empirical formula, the fatigue limit of the blade closer to the real working condition can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of aeroengine blades, and in particular to a method for predicting the high-cycle fatigue limit of blades taking corrosion damage into consideration. Background Art

[0002] In today's civil aviation industry, safety has always been the primary goal of aircraft design. Aircraft not only have very complex structures, but also use a wide range of materials. Alloy materials account for the largest proportion of materials used in aircraft manufacturing. In recent years, air pollution has become increasingly serious, and the acidic components in the atmosphere have gradually increased. The corrosion problem of aviation alloy structures has become more and more serious. In a corrosive environment, corrosion pits or material shedding will appear on the surface of metal structures, resulting in local or even comprehensive damage, affecting the integrity of the structure. If the corrosion is severe, it will lead to a decrease in the cross-sectional area of ​​the component and an increase in local stress; corrosion may also form local defects, leading to stress concentration and fatigue fracture; corrosion will also accelerate the initiation of fatigue cracks, promote crack nucleation, and become the starting source of multiple cracks. If the corrosion situation is not considered in the maintenance plan of an aircraft in service, corrosion damage is likely to be ignored, thus becoming a potential threat to the aircraft's navigation. In addition, there are many types of metal materials used on aircraft. Electrochemical corrosion may occur when different materials cooperate with each other, especially for aircraft that often fly on cross-sea routes. The air humidity over the ocean is very high, and there are a large number of chloride ions. The effect of chloride ions on electrochemical corrosion is much greater than CO2 and SO2 in the air. Chloride ions can directly penetrate conventional antioxidant protective coatings and destroy aviation materials. With the extension of aircraft service time, the problem of aircraft structure corrosion has become more and more prominent, and has become an important factor restricting the normal use of military and civil aircraft today and in the future. In order to deal with existing and potential faults caused by structural corrosion damage, airline engineering maintenance personnel need to perform troubleshooting. Troubleshooting by airline engineering maintenance personnel is the main reason for flight delays, and most of the economic losses of airlines are caused by flight delays.

[0003] Engine blades are one of the most important alloy parts on aircraft. High cycle fatigue failure is a major technical issue in the development and use of engines. High cycle fatigue limit test is an important performance test for engine blades. Based on the experimental research on the characteristics and laws of the influence of notch geometry parameters and stress concentration on the high cycle fatigue strength of blade notches, the academic community has studied and evaluated the applicability of traditional fatigue notch coefficient empirical formula, critical distance theory, weakest link theory and other notch fatigue strength prediction methods for blade notch high cycle fatigue prediction. The study shows that the corrected critical distance theory has better prediction results for high cycle fatigue strength with a small notch root radius. The high cycle fatigue strength predicted by the weakest link theory is generally better than the uncorrected critical distance theory, but worse than the corrected critical distance theory for the notch root radius. However, the high cycle fatigue prediction results obtained by these notch fatigue strength prediction methods have large errors with the test values, low accuracy, and lack of simulation of blades with corrosion damage in actual working conditions. Summary of the invention

[0004] Purpose of the invention: The purpose of the invention is to provide a high-accuracy and high-reliability method for predicting the high-cycle fatigue limit of blades taking into account corrosion damage.

[0005] Technical solution: A method for predicting the high-cycle fatigue limit of blades considering corrosion damage, comprising the following steps:

[0006] (1) Establish a simulation model based on the morphology and size of the real blade;

[0007] (2) Selecting alloy material as the simulated blade material, and processing according to the simulation model to obtain a simulated blade with the same morphology and size as the real blade;

[0008] (3) The simulated blades and real blades are grouped and numbered respectively, and immersed in a corrosion solution, maintaining a constant temperature, and taking out a group of simulated blades and real blades at regular intervals to obtain simulated blades and real blades with different corrosion times;

[0009] (4) Measure the stress-strain curves of blades at different corrosion times, and measure the cross-sectional areas of the simulated blades and the real blade test sections, and calculate the ultimate tensile strength, yield strength, and yield strength ratio based on the maximum stress and yield stress;

[0010] (5) Given the stress ratio and maximum stress, fatigue tests are performed on blades with different corrosion times to measure the fatigue limit of the blades;

[0011] (6) Based on the fatigue limit data of blades with different corrosion times, a prediction curve corresponding to the fatigue limit of the blade and the corrosion time is fitted.

[0012] Specifically, the alloy material in step (2) includes stainless steel material.

[0013] Specifically, the etching solution in step (3) contains chloride ions.

[0014] Specifically, in step (4), an electronic universal testing machine is used to measure the stress-strain curve of the blade.

[0015] Specifically, in step (5), the stress ratio is the ratio of the minimum load to the maximum load in the alternating stress loaded in the fatigue test.

[0016] Specifically, in step (5), a high-frequency fatigue testing machine is used to perform fatigue testing on the blade.

[0017] Specifically, in step (5), the fatigue test includes: using the tensile strength obtained in step (4) as the initial maximum stress to perform a fatigue test, providing a stress step until an exceedance result occurs, and recording the fatigue limit of the blade.

[0018] Specifically, in step (6), the prediction curve corresponding to the blade fatigue limit and corrosion time is:

[0019] σ r =a*t -b

[0020] Where: r is the fatigue limit, t is the corrosion time, a and b are positive constants.

[0021] Preferably, step (3) further comprises: during the corrosion process, replacing the corrosion solution at fixed intervals.

[0022] Preferably, in step (3), the constant temperature is 50°C.

[0023] Beneficial effect: Compared with the prior art, the present invention has the following significant effects: first, a simulated blade with the same shape and size is manufactured using a real blade, a corrosive solution is used to simulate the blade corrosion in a real scenario, and blades with different corrosion times are obtained. Then, the stress-strain curves and fatigue limit tests are performed on the corroded blades. By analyzing the fatigue limits of blades with different corrosion times, curve fitting is performed to obtain a corrosion time-fatigue limit relationship that takes into account corrosion damage. Compared with existing theoretical calculations and empirical formulas, a blade fatigue limit prediction result that is closer to the actual working conditions can be obtained under laboratory conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the blade high cycle fatigue limit prediction method of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further explained below in conjunction with the accompanying drawings and specific implementation methods.

[0026] See also Figure 1As shown, a method for predicting high cycle fatigue limit of a blade considering corrosion damage is provided in one embodiment of the present invention, comprising the following steps:

[0027] (1) Establish a simulation model based on the shape and size of the real blade using simulation modeling software;

[0028] (2) Stainless steel material is selected as the simulated blade material, and a plurality of stainless steel simulated blades having the same shape and size as the real blades are obtained by using a simulation model through a CNC machining center;

[0029] (3) The simulated blades and the real blades are grouped and numbered respectively, and the simulated blades and the real blades of the same group are placed in a beaker, and a corrosion solution containing chloride ions is added to immerse the blades. The corrosion solution containing chloride ions can be hydrochloric acid or an inorganic salt containing chloride ions. In this embodiment, dilute hydrochloric acid is used for the experiment. The beaker is placed in a constant temperature water bath, and the heating temperature is set to 50°C. During the test, the corrosion solution is replaced every 48 hours to keep the concentration of the solution stable. A group of simulated blades and real blades with the same corrosion time are taken out at intervals to obtain simulated blades and real blades with different corrosion times to simulate the blade corrosion under real working conditions;

[0030] (4) An electronic universal testing machine was used to measure the stress-strain curves of blades at different corrosion times. It was observed that with the increase of corrosion time, the maximum stress and yield stress of the simulated blades and the real blades gradually decreased, and the mechanical properties of the materials decreased, but the degree of mechanical property degradation decreased with time.

[0031] The cross-sectional areas of the simulated blades and the real blade test sections were measured, and the ultimate tensile strength, yield strength and yield strength ratio of the current blade material were calculated based on the maximum stress and yield stress. Although the ultimate tensile strength and yield strength decreased, the yield strength ratio did not change significantly, proving that the blades still have strong resistance to deformation after corrosion and are not prone to plastic deformation.

[0032] (5) Given the stress ratio R and the maximum stress, the stress ratio R is the minimum load σ when the fatigue test is loaded with alternating stress. min With the maximum load σ max The ratio of the tensile strength of the blades with different corrosion times is obtained by selecting the appropriate tensile strength as the initial maximum stress. The blades with different corrosion times are subjected to fatigue tests using a high-frequency fatigue testing machine. The appropriate stress step is selected until an exceedance result occurs, and the fatigue limit of the corresponding blade is obtained.

[0033] (6) According to the fatigue limit data of blades with different corrosion times, data fitting is performed to obtain the prediction curve corresponding to the fatigue limit and corrosion time of the blade:

[0034] σr =569.8203*t -0.272

[0035] Where: r is the fatigue limit and t is the corrosion time.

[0036] It can be seen from the above prediction curve that with the increase of corrosion time, the fatigue limit continues to decrease, but the degree of decrease becomes smaller and smaller with time, and the corrosion resistance of the blade gradually improves. According to experience, after the passivation film is formed on the blade surface, the density is improved, which has a good protective effect on the specimen, and with the partial dissolution of stainless steel, the ratio of Cr and Ni elements increases, which improves the corrosion resistance of the blade.

[0037] (7) Under the same experimental conditions, the above steps (3)-(5) were repeated to obtain the fatigue limits of the blades under several other corrosion time periods. The corrosion time was substituted into the prediction curve in step (6), and the predicted fatigue limit was compared with the measured fatigue limit. Highly consistent results were obtained, which proved the reliability of the prediction curve. It further proved that this method is credible in predicting the high-cycle fatigue limit of blades considering corrosion damage.

Claims

1. A method for predicting high cycle fatigue limit of blades considering corrosion damage, characterized in that: The following steps are involved: (1) Establish a simulation model based on the morphology and size of the real blade; (2) Selecting alloy material as the simulated blade material, and processing according to the simulation model to obtain a simulated blade with the same morphology and size as the real blade; (3) The simulated blades and real blades are grouped and numbered respectively, and immersed in a corrosion solution, maintaining a constant temperature, and taking out a group of simulated blades and real blades at regular intervals to obtain simulated blades and real blades with different corrosion times; (4) Measure the stress-strain curves of blades at different corrosion times, and measure the cross-sectional areas of the simulated blades and the real blade test sections, and calculate the ultimate tensile strength, yield strength, and yield strength ratio based on the maximum stress and yield stress; (5) Given the stress ratio and maximum stress, fatigue tests are performed on blades with different corrosion times to measure the fatigue limit of the blades; (6) Based on the fatigue limit data of blades with different corrosion times, a prediction curve corresponding to the fatigue limit of the blade and the corrosion time is fitted.

2. The blade high cycle fatigue limit prediction method according to claim 1, characterized in that: In the step (2), the alloy material includes stainless steel material.

3. The blade high cycle fatigue limit prediction method according to claim 1, characterized in that: In the step (3), the etching solution contains chloride ions.

4. The blade high cycle fatigue limit prediction method according to claim 1, characterized in that: In the step (4), an electronic universal testing machine is used to measure the stress-strain curve of the blade.

5. The blade high cycle fatigue limit prediction method according to claim 1, characterized in that: In the step (5), the stress ratio is the ratio of the minimum load to the maximum load in the alternating stress loaded in the fatigue test.

6. The blade high cycle fatigue limit prediction method according to claim 1, characterized in that: In the step (5), a high-frequency fatigue testing machine is used to perform fatigue testing on the blade.

7. The blade high cycle fatigue limit prediction method according to claim 1, characterized in that: In the step (5), the fatigue test includes: using the tensile strength obtained in the step (4) as the initial maximum stress to perform a fatigue test, providing a stress step until an exceedance result occurs, and recording the fatigue limit of the blade.

8. The blade high cycle fatigue limit prediction method according to claim 1, characterized in that: In step (6), the prediction curve corresponding to the blade fatigue limit and corrosion time is: s r =a*t -b Where: r is the fatigue limit, t is the corrosion time, a and b are positive constants.

9. The blade high cycle fatigue limit prediction method according to claim 1, characterized in that: The step (3) also includes: during the corrosion process, replacing the corrosion solution at fixed intervals.

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