Reliability analysis method of corrosion failure of carrier-based aircraft structure based on the shipboard service environment

Abstract

The present invention discloses a reliability analysis method for corrosion failure of a carrier aircraft structure based on a ship surface service environment, comprising the following steps: step 1: constructing a corrosion model of the carrier aircraft surface service environment to obtain a probability distribution of corrosion variables; step 2: constructing an initial damage model of the carrier aircraft surface service environment according to the corrosion model to obtain the value of the initial damage; step 3: establishing a cumulative fatigue damage model of the carrier aircraft structure considering the initial damage of corrosion according to the modified Chaboche fatigue damage model; step 4: establishing a finite element model of the carrier aircraft structure considering corrosion, and then calculating and obtaining the stress distribution on the surface of the structure; step 5: establishing a relationship model between initial damage, loading load and fatigue life based on the finite element calculation results, and then obtaining a relationship model between fatigue life and corrosion influencing factors; step 6: performing uncertainty analysis and life determination and extension analysis. The present invention provides a new method for safety assessment and life determination and extension of carrier aircraft structures.

Description

Technical Field

[0001] The present invention relates to the technical field of performance analysis, and in particular to a reliability analysis method for corrosion failure of a carrier-based aircraft structure based on a shipboard service environment. Background Art

[0002] Compared with land-based aircraft, carrier-based aircraft have a more severe service environment. When carrier-based aircraft serve on the deck of an aircraft carrier, the fuselage structure is in the marine atmosphere and the acidic salt mist atmosphere composed of exhaust gases from ships and aircraft engines, and the fuselage structure will be subject to severe corrosion. According to statistics, the service life of a certain type of carrier-based aircraft is less than 20% of that on land, and the attendance rate of a certain type of aircraft is less than 20% due to its inability to adapt to the high temperature and high humidity environment in the southern seas. These fully illustrate the severity of corrosion suffered by carrier-based aircraft in the marine environment. In addition, under the conditions of take-off and landing on the deck of the carrier-based aircraft, the fuselage structure is also subject to more impact load conditions. Impact loads will cause damage and cracks in the structural materials, and the corrosive environment will accelerate the expansion of cracks. Under the combined effects of impact loads and corrosive environments, the mechanical properties of the aircraft structure will accelerate the decline, resulting in a shortened structural life and a threat to aircraft safety. Therefore, in order to meet the reliability requirements of the carrier-based aircraft structure in the service environment of the deck, it is necessary to accurately predict the reliability of the corrosion failure of the carrier-based aircraft structure and improve the accuracy of the safety assessment and life extension of the carrier-based aircraft structure.

[0003] At present, the life prediction of carrier-based aircraft structures is mainly achieved by developing the environmental spectrum and load spectrum of the service environment and obtaining the fatigue life of the structure through laboratory tests. In essence, it assumes that the service environment and load of the carrier-based aircraft structure are constant, without in-depth analysis of the impact of fluctuations in the marine corrosion environment and take-off and landing load conditions of the ship deck on the reliability of the structure. If the service environment and load conditions change significantly, the life of the structure cannot be accurately predicted. Therefore, it is of great significance to analyze the corrosion failure laws of carrier-based aircraft structures under different mission environments and predict the reliability of corrosion failure of carrier-based aircraft structures based on the marine corrosion environment and load conditions of the ship deck, which is of great significance to improving the accuracy of safety assessment and life extension of carrier-based aircraft structures. Summary of the invention

[0004] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0005] The present invention proposes a reliability analysis method for corrosion failure of carrier-based aircraft structures based on the ship deck service environment. Based on the characteristics of the carrier-based aircraft ship deck service environment and the ship deck take-off and landing load conditions, the structural corrosion failure reliability of the carrier-based aircraft structure under the combined action of the ship deck marine atmospheric environment and the carrier-based aircraft take-off and landing impact load is evaluated, providing a new method for safety assessment and life determination and extension of carrier-based aircraft structures.

[0006] In order to achieve these purposes and other advantages according to the present invention, a method for analyzing the reliability of corrosion failure of a carrier aircraft structure based on a shipboard service environment is provided, comprising the following steps:

[0007] 1. Establishing a corrosion model for the service environment of carrier-based aircraft decks

[0008] When carrier-based aircraft are serving on the deck of an aircraft carrier, the aircraft structure will be subject to severe corrosion due to the influence of the marine atmospheric environment and the exhaust gas of ships and aircraft engines. Fatigue damage of structural materials usually originates from corrosion pits caused by corrosion, so the corrosion pits with the largest size on the surface of the structure are taken as the initial point of fatigue damage. In view of the characteristics of the carrier-based aircraft deck service environment, an acid salt spray atmospheric corrosion acceleration test is carried out on the structural materials of the carrier-based aircraft to obtain the maximum corrosion pit size under different corrosion time, pH value, salt concentration, temperature, humidity and other conditions. In this way, the corrosion time t, pH value p, salt concentration E and the maximum corrosion pit size under different corrosion time, pH value p and salt concentration E are established. c , temperature T, humidity H u Relationship with corrosion pit size c:

[0009] c=f(t,p,E c ,T,H u ) (1)

[0010] 2. Establish the initial damage model of the ship surface service environment:

[0011] The corrosion pits on the surface of the structure caused by corrosion are usually the starting point of fatigue damage to the structure. Therefore, the structural damage caused by corrosion is regarded as the initial damage. e .

[0012] According to the deck service environment of carrier-based aircraft and the load characteristics of carrier-based aircraft during take-off and landing, the deck service environment spectrum of carrier-based aircraft structure is compiled; using the compiled environment spectrum, the uncorroded and pre-corroded fatigue tests are carried out on the carrier-based aircraft structural materials; according to the obtained load fatigue life, the SN curve of the material under different corrosion conditions is calculated, and the initial damage D of the carrier-based aircraft structural material is obtained through numerical calculation. e .

[0013] For the isotropic material in the carrier aircraft structure, the damage variable D can be defined by the material modulus degradation, that is:

[0014]

[0015] Where E is the elastic modulus of the intact material; E d is the elastic modulus of the material after damage; D is a continuous variable between 0 and 1.

[0016] The initial damage D caused by corrosion can be obtained by theoretical deduction. e Relationship with fatigue parameters:

[0017]

[0018] Where γ, m and ξ are material constants; S max is the maximum stress; S th is the threshold value for materials without corrosion damage.

[0019] The three-parameter power function model of fatigue life SN curve is:

[0020] N(S max -S f ) H =C (4)

[0021] In the formula, S f is the fatigue limit strength; H and C are constants.

[0022] Based on the pre-corrosion fatigue test data of carrier-based aircraft structural materials, the initial corrosion damage D can be obtained by combining equations (3) and (4): e The value of corrosion pit size c and initial damage D are established. e The relationship between:

[0023] D e =g(c) (5)

[0024] 3. Establishing cumulative fatigue damage model:

[0025] Based on the cumulative damage mechanics theory and the modified Chaboche fatigue damage model, a cumulative fatigue damage model for carrier-based aircraft structures considering initial corrosion damage is established to estimate the fatigue life of carrier-based aircraft structures.

[0026] According to the distortion energy density theory, the Chaboche fatigue damage model is modified to consider multiaxial stress:

[0027]

[0028]

[0029] M(σ m )=M0(1-bσ m ) (8)

[0030] Where N is the number of fatigue loading; σ T is the equivalent stress of the structure; m is the average stress of fatigue load; σ a is the stress amplitude of fatigue load; σ0 is the fatigue limit strength; σ b is the ultimate tensile strength; β, a, M0 and b are material constants.

[0031] At the initial corrosion damage De If it exists, the corresponding life N under fatigue load can be obtained by integrating equation (6): f for:

[0032]

[0033] Then the damage amount after fatigue loading N times is:

[0034]

[0035] The parameters β, a, M0 and b in equations (6) to (8) can be calculated from the fatigue test data of standard smooth specimens. T It needs to be obtained through finite element simulation calculation.

[0036] 4. Establishing the Finite Element Simulation Model

[0037] The initial corrosion damage of the structural surface obtained by the ship surface service environment corrosion model is equivalent to the corrosion pits on the material surface, and a finite element model of the carrier-based aircraft structure considering corrosion is established in mechanical finite element simulation calculation software such as ABAQUS.

[0038] Through actual measurement and simulation calculation, the load distribution of the fuselage structure under different loading rates, flight attitudes, landing speeds, etc. during the take-off and landing phase of the carrier-based aircraft on the ship deck is obtained. The typical load spectrum is selected as the load input condition of the finite element simulation, and the stress distribution at the corrosion pits on the structure surface is calculated.

[0039] 5. Establishing a Corrosion Failure Model for Aircraft Carrier Structures

[0040] According to the finite element calculation results, the dangerous parts of the structural corrosion pits are determined, and the equivalent stress σ T 、Initial damage D e Substitute the data into the established cumulative fatigue damage model to obtain the fatigue life of the structure and establish the initial damage D e , loading load S and fatigue life N f The relationship between:

[0041] N f =F(D e ,S) (11)

[0042] Combining the corrosion model of the ship surface service environment and the initial damage model of the ship surface service environment, the fatigue life N can be obtained. f Relationship between corrosion factors

[0043] N f =G(t,p,E c ,T,H u ,S) (12)

[0044] 6. Conduct uncertainty analysis:

[0045] The corrosion variables and load variables of the selected carrier-based aircraft deck service environment are sampled by Latin hypercube according to their probability distribution to obtain n groups of sampling data. Using programming software such as Matlab, the sampling data are substituted into the ship deck service environment corrosion model and the carrier-based aircraft structure cumulative damage failure model for n calculations to obtain the probability distribution of carrier-based aircraft structure corrosion failure. Combined with the life standard of carrier-based aircraft structure, the reliability assessment of carrier-based aircraft structure corrosion failure can be achieved.

[0046] Conduct life extension analysis:

[0047] The probability distribution of corrosion failure of carrier-based aircraft structures obtained by uncertainty analysis can be further used to calculate the reliability of the life of carrier-based aircraft structures under different shipboard service environments and loads. This reliability achieves a quantitative assessment of the reliability of the life of carrier-based aircraft structures and can provide a reference for the life determination and extension of carrier-based aircraft structures.

[0048] In the reliability analysis of the present invention, a suitable sampling method is crucial to the sample quality. Compared with the traditional random sampling method, the Latin hypercube sampling method can make the obtained random samples more consistent with the input probability distribution. The Latin hypercube sampling method is a stratified sampling method that divides the probability distribution into equal intervals and randomly samples in each interval so that the extracted samples are consistent with the input probability distribution to the greatest extent.

[0049] The service environment of the aircraft carrier deck is mainly composed of the marine atmosphere and the exhaust gas of ships and aircraft engines, which is an acidic salt spray corrosion environment with a pH value of up to 3.5. In the service environment of the deck, the factors affecting the corrosion rate are mainly the corrosion time t, pH value p, salt concentration E c , temperature T, humidity H u Etc. The probability distribution of corrosion influencing factors can be obtained through laboratory accelerated corrosion tests and field exposure tests.

[0050] The loads borne by carrier-based aircraft when serving on an aircraft carrier mainly occur during the take-off and landing phases, including catapult take-off and arrested landing. The load variables of carrier-based aircraft during the catapult phase are mainly the loading rate of the catapult, the maximum catapult load, etc.; the load variables of carrier-based aircraft during the landing phase are mainly the landing speed, sinking rate, aircraft attitude, and aircraft carrier pitch and roll, etc. The probability distribution of load variables can be obtained through measured data and simulation of carrier-based aircraft structures.

[0051] The present invention has at least the following beneficial effects:

[0052] According to the characteristics of the marine atmospheric environment and take-off and landing load conditions on the deck of carrier-based aircraft, by constructing the deck service environment corrosion model, the structural cumulative damage failure model and the structural corrosion failure model, the reliability of the structural corrosion failure of the carrier-based aircraft under the combined action of the marine atmospheric environment on the deck and the take-off and landing loads of the carrier-based aircraft is evaluated, providing a new method for the safety assessment and life determination and extension of the carrier-based aircraft structure.

[0053] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a flow chart of the reliability analysis method of corrosion failure of carrier-based aircraft structures based on the shipboard service environment;

[0055] Figure 2 for the change of initial damage with service time;

[0056] Figure 3 is the stress distribution of the corrosion pit under the maximum stress load of 250MPa;

[0057] Figure 4 This is a life span distribution diagram. DETAILED DESCRIPTION

[0058] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0059] It should be understood that terms such as “having”, “including” and “comprising” used herein do not specify the existence or addition of one or more other elements or combinations thereof.

[0060] Aluminum alloy is a metal material widely used in carrier-based aircraft structures. This embodiment takes an aluminum alloy structure of a carrier-based aircraft as an example to verify the corrosion failure reliability analysis method of the carrier-based aircraft structure proposed in this article.

[0061] Corrosion model parameter acquisition:

[0062] The aluminum alloy structure test piece was subjected to a salt spray corrosion test in a DCTC 1200P salt spray corrosion test chamber. The corrosion solution was 5% NaCl solution with a pH value of 4.0. In order to simplify the test quantity, this paper only selected the corrosion time t as the corrosion model variable. The depth of the corrosion pits of the test piece after different corrosion cycles was measured using a stereo microscope to obtain the depth data of the corrosion pits under different corrosion cycles.

[0063] According to the equivalent conversion coefficient theory, it can be calculated that in a salt spray corrosion environment with 5% NaCl and pH value of 4.0, the aluminum alloy undergoes 7.9 days of laboratory accelerated corrosion, and its corrosion damage is equivalent to 1 year in the actual service environment. Therefore, the laboratory accelerated corrosion test results can be converted into the corrosion depth corresponding to different corrosion times of the carrier-based aircraft structure in the actual marine service environment, as shown in Table 1.

[0064] Table 1 Corrosion depth of specimens under different corrosion cycles

[0065]

[0066] The variation law of corrosion depth c of metal materials with corrosion time t can be expressed by power function. According to the corrosion test data in Table 1, the relationship between corrosion pit depth and corrosion time can be fitted: c = 56.21t 0.167 .

[0067] Initial damage model parameter acquisition:

[0068] Fatigue tests were carried out on aluminum alloy specimens without corrosion and after different corrosion cycles on a fatigue testing machine. According to the fatigue life data obtained from the fatigue test, the SN curves of aluminum alloy materials under different corrosion conditions were fitted. By combining equations (3) and (4) in parallel, we can get m = 1.6042, γ = 1.0006*10 -8 ,ξ=4.01,S th =125. Initial corrosion damage D e The curve of corrosion time is as follows: Figure 2 shown.

[0069] right Figure 2 By fitting the data in the figure, we can get the corrosion time t and the initial damage D e The relationship between:

[0070] D e =-0.1727e -0.4571t +0.1727

[0071] Accumulative fatigue damage model parameter acquisition:

[0072] The fatigue damage model parameters can be obtained by calibration based on the fatigue test data of static tensile test and non-corrosion test piece. The parameters β and The value of b can be obtained by fitting the fatigue test data under other stress ratios. Table 2 gives the fatigue damage model parameters of the structural parts.

[0073] Table 2 Fatigue damage model parameters

[0074]

[0075] Finite element simulation calculation:

[0076] The aluminum alloy structure specimen model of carrier aircraft was established in ABAQUS finite element simulation software, and the initial corrosion damage of the structure surface obtained by the ship surface service environment corrosion model was equivalent to a hemispherical pit on the specimen surface. A load was applied to the established specimen model to simulate the maximum tensile stress state of fatigue loading. Figure 3 The finite element calculation results of the corrosion damaged structural parts under the maximum stress load of 250MPa are shown. By changing the radius of the corrosion pit and the applied load, the equivalent stress σ under different corrosion depths and loads is calculated. T , as shown in Table 3.

[0077] Table 3 Equivalent stress under different corrosion depths and loads

[0078]

[0079] From the calculation results in Table 3, the equivalent stress σ can be calculated T Then the stress amplitude σ of the fatigue load a The relationship between:

[0080] σ T =(-15.1c 2 +8.273c+0.9592)σ a

[0081] Probability distribution of uncertain variables:

[0082] The service life of an aircraft is generally about 30 years. The loads borne by carrier-based aircraft when serving on an aircraft carrier mainly occur during the take-off and landing phases, including catapult take-off and arrested landing. Due to the frequent catapult take-off and arrested landing loads, the take-off and landing life of carrier-based aircraft often expires before the calendar life. Therefore, the service life of a certain structural component of a carrier-based aircraft is simplified to a uniform probability distribution.

[0083] The structural load of carrier-based aircraft during the catapult phase is affected by factors such as engine thrust, catapult loading rate, and catapult load; during the landing phase, the structural load is affected by factors such as landing speed, sinking rate, aircraft attitude, and carrier pitch and roll. Therefore, the load it bears during service can be simplified to a uniform probability distribution under its ideal take-off and landing load. The probability distribution of uncertain variables is shown in Table 4.

[0084] Table 4 Probability distribution of uncertain variables

[0085]

[0086] Reliability analysis:

[0087] The corrosion variables and load variables of the selected carrier-based aircraft deck service environment were sampled by Latin hypercube according to their probability distribution, and 100,000 sets of sampling data were obtained. The reliability analysis method proposed in this paper was implemented in the programming software, and the sampling data was substituted into the ship deck service environment corrosion model and the carrier-based aircraft structure cumulative damage failure model for 100,000 calculations to obtain the distribution of corrosion fatigue life of the carrier-based aircraft structure as shown in the figure. Figure 4 shown.

[0088] Depend on Figure 4 The failure probability of the carrier aircraft structure under different service lives can be calculated, as shown in Table 5. As can be seen from Table 5, the structure will not fail before the fatigue load it is subjected to reaches 40,000 times during service; but when the fatigue load it is subjected to reaches 50,000 times during service, its failure probability is 0.002%. Therefore, if you want to extend the life of the structure, the extended life should be less than 50,000 times without changing the structural state.

[0089] Table 5 Structural failure probability under different service life

[0090]

[0091]

[0092] As described above, the present invention aims at the characteristics of the marine atmospheric environment and take-off and landing load conditions of the carrier-based aircraft deck, and by constructing a ship deck service environment corrosion model, a structural cumulative damage failure model and a structural corrosion failure model, it is possible to evaluate the reliability of structural corrosion failure of the carrier-based aircraft structure under the combined effects of the ship deck marine atmospheric environment and the take-off and landing loads of the carrier-based aircraft, thereby providing a new method for structural safety assessment and life determination and extension of the carrier-based aircraft.

[0093] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A reliability analysis method for corrosion failure of carrier-based aircraft structures based on the shipboard service environment, characterized in that: The following steps are involved: Step 1: Construct a corrosion model for the service environment of the carrier-based aircraft deck and obtain the probability distribution of corrosion variables; Step 2: construct an initial damage model of the service environment of the carrier-based aircraft deck according to the corrosion model to obtain the value of the initial damage; Step 3: Based on the modified Chaboche fatigue damage model, a cumulative fatigue damage model of the carrier aircraft structure considering the initial corrosion damage is established; Step 4: Establish a finite element model of the carrier aircraft structure taking corrosion into account, and then calculate the stress distribution on the surface of the structure; Step 5: Based on the finite element calculation results, a relationship model between initial damage, loading load and fatigue life is established, and then a relationship model between fatigue life and corrosion influencing factors is obtained; Step 6: Conduct uncertainty analysis and life extension analysis; In step 1, the structural material of the carrier aircraft is subjected to an acid salt spray atmospheric corrosion acceleration test and an outdoor exposure test to obtain the maximum corrosion pit size under different corrosion time, pH value, salt concentration, temperature, and humidity conditions, thereby establishing the corrosion time t, pH value p, and salt concentration E c , temperature T, humidity H u The relationship between the corrosion pit size c, that is, the probability distribution of corrosion variables: c = f(t, p, E c ,T,H u ); In step 2, the initial damage D caused by corrosion e Relationship with fatigue parameters: Where γ, m and ξ are material constants; S max is the maximum stress; S th is the threshold value for materials without corrosion damage; The three-parameter power function model of fatigue life SN curve is: N(S max -S f ) H =C In the formula, S f is the fatigue limit strength; H and C are constants; Based on the pre-corrosion fatigue test data of carrier-based aircraft structural materials, the initial damage D caused by corrosion e The initial corrosion damage D is obtained by using the fatigue parameter relationship and the three-parameter power function model. e The value of corrosion pit size c and initial damage D e The relationship between: D e =g(c); In step 3, the Chaboche fatigue damage model is modified to a modified form that considers multiaxial stress conditions: Where N is the number of fatigue loading; σ T is the equivalent stress of the structure; m is the average stress of fatigue load; σ a is the stress amplitude of fatigue load; σ0 is the fatigue limit strength; σ b is the ultimate tensile strength; β, a, M0 and b are material constants; M(s m )=M0(1-bσ m ); At the initial corrosion damage D e If it exists, the corresponding life N under fatigue load can be obtained by integrating the above modified form f for: Then the damage amount after fatigue loading N times is: Among them, the parameters β, a, M0 and b can be calculated from the fatigue test data of the standard smooth specimen, and the equivalent stress σ T It needs to be obtained through finite element simulation calculation.

2. The method for reliability analysis of corrosion failure of carrier-based aircraft structure based on the shipboard service environment according to claim 1, characterized in that: In the step 4, the initial corrosion damage of the structural surface obtained by the ship surface service environment corrosion model is equivalent to the corrosion pits on the material surface, and a finite element model of the carrier aircraft structure considering corrosion is established in the mechanical finite element simulation calculation software.

3. The method for analyzing the reliability of corrosion failure of a carrier-based aircraft structure based on the shipboard service environment according to claim 2, characterized in that: In the step 4, the load distribution of the aircraft body structure under different loading rates, flight attitudes, and landing speeds during the take-off and landing phase of the carrier-based aircraft on the ship deck is obtained through actual measurement and simulation calculation, a typical load spectrum is selected as the load input condition of the finite element simulation, and the stress distribution at the corrosion pits on the surface of the structure is calculated.

4. The method for analyzing the reliability of corrosion failure of a carrier-based aircraft structure based on the shipboard service environment according to claim 3, characterized in that: In step 5, the dangerous part of the structural corrosion pit is determined by the finite element calculation results, and the equivalent stress σ at the location is calculated. T 、Initial damage D e Substitute the data into the established cumulative fatigue damage model to obtain the fatigue life of the structure and establish the initial damage D e , loading load S and fatigue life N f The relationship between: N f =F(D e ,S).

5. The method for analyzing the reliability of corrosion failure of a carrier-based aircraft structure based on the shipboard service environment according to claim 4, characterized in that: In step 5, the fatigue life N is obtained according to the comprehensive ship surface service environment corrosion model and the ship surface service environment initial damage model. f Relationship between corrosion factors and f =G(t,p,E c ,T,H u ,S).

6. The method for analyzing the reliability of corrosion failure of a carrier-based aircraft structure based on the shipboard service environment according to claim 5, characterized in that: In the step six, Latin hypercube sampling is performed on the selected corrosion variables and load variables of the carrier aircraft deck service environment according to their probability distribution to obtain n groups of sampling data. The sampling data are substituted into the ship deck service environment corrosion model and the carrier aircraft structure cumulative damage failure model by programming software to perform n calculations to obtain the probability distribution of carrier aircraft structure corrosion failure. Combined with the life standard of the carrier aircraft structure, the reliability evaluation of the carrier aircraft structure corrosion failure is realized.

7. The method for analyzing the reliability of corrosion failure of a carrier-based aircraft structure based on the shipboard service environment according to claim 6, characterized in that: In step six, the probability distribution of corrosion failure of the carrier-based aircraft structure obtained by uncertainty analysis is further calculated to obtain the reliability of the carrier-based aircraft structure life under different shipboard service environments and loads, and the reliability realizes quantitative evaluation of the reliability of the carrier-based aircraft structure life.

Images