A method for predicting high-cycle fatigue limit of blade considering corrosion damage

Abstract

The application provides a kind of blade high-cycle fatigue limit prediction method considering corrosion damage, simulation modeling is carried out according to real blade, simulated blade is obtained by processing, real blade and simulated blade are placed in constant temperature corrosion solution, to simulate the corrosion condition of blade under real working condition, after obtaining blade of different corrosion time, stress-strain curve measurement and fatigue limit test are carried out on blade, and the prediction curve of corrosion time and fatigue limit is fitted according to fatigue limit data;The application provides a kind of method for simulating blade corrosion condition and predicting blade fatigue limit under laboratory conditions, compared with the fatigue limit prediction of traditional theoretical calculation and empirical formula, the blade fatigue limit closer to real working condition can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aero-engine blades, and particularly relates to a blade high-cycle fatigue limit prediction method considering corrosion damage. BACKGROUND

[0002] Safety has always been the primary goal of aircraft design in today's civil aviation industry, and the aircraft not only has a very complex structure, but also uses a wide range of materials, and 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, and the corrosion problem of aircraft alloy structures has become more and more serious. Under the corrosion environment, the surface of the metal structure will appear corrosion pits or material shedding, and then local or even overall damage will be caused, which will affect the integrity of the structure. If the corrosion is serious, it will cause the cross-sectional area of the component to decrease and the local stress to increase; corrosion can also form local defects, causing stress concentration and fatigue fracture; corrosion can also accelerate the initiation of fatigue cracks and promote crack nucleation to become the starting source of multiple cracks. If the corrosion condition is not considered in the maintenance plan of the aircraft in service, the corrosion damage may be ignored, thereby becoming a potential threat to the flight of the aircraft. In addition, there are many types of metal materials used on the aircraft, and during the mutual cooperation of different materials, electrochemical corrosion may occur, especially for aircrafts that often fly on transoceanic routes. The air humidity over the ocean is very high, and there are a large number of chloride ions, and the promotion effect of chloride ions on electrochemical corrosion is much greater than that of CO2 and SO2 in the air. Chloride ions can directly penetrate the conventional antioxidant protective coating and then damage the aircraft materials. With the extension of the service time of the aircraft, the corrosion problem of the aircraft structure becomes more and more prominent, and has become an important factor restricting the normal use of military and civil aircrafts today and in the future. In order to deal with the existing and potential failure problems caused by structural corrosion damage, the engineering maintenance of the aircraft needs to carry out fault elimination, and the fault elimination of the engineering maintenance of the aircraft is the main reason for the flight delay, and most of the economic losses of the aircraft company are caused by flight delays.

[0003] The engine blade is one of the most important alloy components on the airplane, and the high cycle fatigue failure is a major technical problem in the development and use of the engine. The high cycle fatigue limit test is an important performance test of the engine blade. On the basis of the test research on the influence characteristics and laws of the notch geometry parameters and stress concentration on the high cycle fatigue strength of the blade notch, the applicability of the traditional fatigue notch coefficient empirical formula, the critical distance theory, the weakest ring theory and other notch fatigue strength prediction methods for the high cycle fatigue prediction of the blade notch is researched and evaluated. The research shows that the modified critical distance theory is better for the high cycle fatigue strength prediction result of the small notch root radius, the high cycle fatigue strength predicted by the weakest ring theory is better than that by the unmodified critical distance theory, but worse than that by the modified critical distance theory. However, the error of the high cycle fatigue prediction result obtained by the several notch fatigue strength prediction methods and the test value is large, the accuracy is low, and the simulation of the blade with corrosion damage in the actual working condition is also lacking. SUMMARY

[0004] The purpose of the present application is to provide a high-accuracy, high-reliability blade high cycle fatigue limit prediction method considering corrosion damage.

[0005] Technical scheme: A blade high cycle fatigue limit prediction method considering corrosion damage comprises the following steps:

[0006] (1) Establish a simulation model according to the appearance and size of the real blade;

[0007] (2) Select an alloy material as the simulation blade material, and process the simulation blade with the same appearance and size as the real blade according to the simulation model;

[0008] (3) Group and number the simulation blades and real blades respectively, and immerse them in a corrosion solution, keep the temperature constant, take out a group of simulation blades and real blades every certain period of time, and obtain simulation blades and real blades with different corrosion times;

[0009] (4) Measure the stress-strain curves of the blades with different corrosion times, and measure the cross-sectional area of the test section of the simulation blades and real blades, and calculate the tensile ultimate strength, yield strength and yield strength ratio according to the maximum stress and yield stress;

[0010] (5) Given the stress ratio and the maximum stress, conduct a fatigue test on the blades with different corrosion times, and measure the fatigue limit of the blades;

[0011] (6) According to the fatigue limit data of the blades with different corrosion times, fit the prediction curve corresponding to the blade fatigue limit and the corrosion time.

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

[0013] Specifically, the corrosion 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 of the fatigue test loading.

[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 ultimate strength obtained in step (4) as the initial maximum stress to perform fatigue testing, giving a stress step, until the exceeding result appears, and recording the fatigue limit of the blade.

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

[0019] σ r =a*t -b

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

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

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

[0023] Beneficial effects: Compared with the prior art, the significant effects of the present application are: first, the same size and shape of the simulation blade is manufactured using the real blade, the corrosion solution is used to simulate the blade corrosion condition under the real scene, the blade with different corrosion time is obtained, then the stress-strain curve measurement and fatigue limit test are performed on the corroded blade, the fatigue limit of the blade with different corrosion time is analyzed, the curve fitting is performed, the corrosion time-fatigue limit relationship formula considering the corrosion damage is obtained, compared with the existing theoretical calculation and empirical formula, the blade fatigue limit prediction result closer to the real working condition can be obtained under the laboratory condition. BRIEF DESCRIPTION OF DRAWINGS

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

[0025] The present application will be further illustrated below in combination with the drawings and specific embodiments.

[0026] Please refer to Figure 1As shown, the method for predicting the high-cycle fatigue limit of a blade considering corrosion damage provided by one embodiment of the application comprises the following steps:

[0027] (1) According to the shape and size of the real blade, a simulation model is established by using simulation modeling software;

[0028] (2) Selecting stainless steel as the material of the simulation blade, the simulation model is processed by a numerical control machining center to obtain a plurality of stainless steel simulation blades with the same shape and size as the real blade;

[0029] (3) The simulation blades and the real blades are numbered respectively, the simulation blades and the real blades in 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 inorganic salt containing chloride ions, in this embodiment, dilute hydrochloric acid is used for experiment, the beaker is placed in a constant temperature water bath, the heating temperature is set to 50℃, the corrosion solution is replaced every 48h during the test to keep the concentration of the solution stable, a group of simulation blades and real blades with the same corrosion time are taken out at intervals to obtain simulation blades and real blades with different corrosion times to simulate the corrosion of the blades under real working conditions;

[0030] (4) The stress-strain curves of the blades with different corrosion times are measured by using an electronic universal testing machine, and it is observed that the maximum stress and yield stress of the simulation blades and the real blades gradually decrease with the increase of the corrosion time, the mechanical properties of the materials decrease, but the degree of decrease of the mechanical properties decreases with the increase of time.

[0031] The cross-sectional area of the test section of the simulation blade and the real blade is measured, the tensile ultimate strength, yield strength and yield strength ratio of the current blade material are calculated according to the maximum stress and yield stress, although the tensile ultimate strength and yield strength decrease, the yield strength ratio does not change significantly, which proves that the blade still has strong anti-deformation ability after corrosion and is not easy to deform plastically.

[0032] (5) Given the stress ratio R and the maximum stress, the stress ratio R is the ratio of the minimum load σ min to the maximum load σ max , according to the recorded tensile ultimate strength of the blades with different corrosion times, the appropriate tensile ultimate strength is selected as the initial maximum stress, the high-frequency fatigue testing machine is used to perform fatigue test on the blades with different corrosion times, the appropriate stress step is selected until the exceeding result appears, and the fatigue limit of the corresponding blade is obtained.

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

[0034] σr = 569.8203 * t -0.272

[0035] wherein σ is the fatigue limit, and t is the corrosion time. r

[0036] As can be seen from the above prediction curve, the fatigue limit continues to decline with the increase of corrosion time, but the degree of decline becomes smaller and smaller with the increase of time, and the corrosion resistance of the blade gradually improves. According to experience, after the formation of the passivation film on the surface of the blade, the compactness is improved, which plays a good protective role on the test piece. And with the partial dissolution of stainless steel, the proportion of Cr and Ni elements is improved, which improves the corrosion resistance of the blade.

[0037] (7) Under the same experimental conditions, repeat steps (3)-(5) to obtain the fatigue limit of the blade under several other corrosion times. Put the corrosion time into the prediction curve in step (6), compare the predicted fatigue limit with the measured fatigue limit, and obtain highly consistent results, which proves the reliability of the prediction curve and further proves the credibility of the method in predicting the high-cycle fatigue limit of the blade considering corrosion damage.​

Claims

1. A method for predicting the high-cycle fatigue limit of blades considering corrosion damage, characterized in that, Includes the following steps: (1) Establish a simulation model based on the morphology and size of the real blade; (2) Select alloy materials as simulated blade materials, and process simulated blades with the same shape and size as real blades according to the simulation model; (3) The simulated blades and real blades were grouped and numbered separately, and immersed in the corrosion solution. The temperature was kept constant. Every once in a while, a group of simulated blades and real blades were taken out 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 area of ​​the simulated blade and the test section of the real blade. Calculate the tensile strength, yield strength and yield ratio based on the maximum stress and yield stress. (5) Given the stress ratio and maximum stress, fatigue tests are conducted 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, the predicted curves corresponding to the fatigue limit of blades and corrosion time are obtained by fitting.

2. The method for predicting the high-cycle fatigue limit of blades according to claim 1, characterized in that: In step (2), the alloy material includes stainless steel.

3. The method for predicting the high-cycle fatigue limit of blades according to claim 1, characterized in that: In step (3), the corrosion solution contains chloride ions.

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

5. The method for predicting the high-cycle fatigue limit of blades according to claim 1, characterized in that: In step (5), the stress ratio is the ratio of the minimum load to the maximum load in the alternating stress applied during the fatigue test.

6. The method for predicting the high-cycle fatigue limit of blades according to claim 1, characterized in that: In step (5), a high-frequency fatigue testing machine is used to conduct fatigue tests on the blades.

7. The method for predicting the high-cycle fatigue limit of blades according to claim 1, characterized in that: In step (5), the fatigue test includes: using the tensile strength obtained in step (4) as the initial maximum stress for the fatigue test, giving a stress step until the result exceeds the limit, and recording the fatigue limit of the blade.

8. The method for predicting the high-cycle fatigue limit of blades according to claim 1, characterized in that: In step (6), the predicted curves for the fatigue limit of the blade and the corrosion time are as follows: s r =a*t -b In the formula: σ r t is the fatigue limit, t is the corrosion time, and a and b are positive constants.

9. The method for predicting the high-cycle fatigue limit of blades according to claim 1, characterized in that: Step (3) also includes replacing the corrosion solution at fixed intervals during the corrosion process.

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