An aircraft structure fatigue test load optimization method based on damage accumulation

Abstract

The application discloses an aircraft structure fatigue test load optimization method based on damage accumulation, and comprises the following steps: calculating test loading point coordinates of an aircraft structure according to test loads and a load spectrum of each working condition; establishing shear force, bending moment and torque error coefficient matrixes of key sections of the aircraft structure according to the test loading point coordinates; calculating damage of the key sections of each working condition according to the shear force, bending moment and torque error coefficient matrixes of the key sections of each working condition; establishing an objective function according to a Miner linear damage method and damage error and minimum of the key sections of each working condition; establishing constraint conditions for solving the objective function according to test requirements; and obtaining loading point loads of each working condition based on the constraint conditions for solving the objective function. The method has clear ideas, simple processes and high calculation efficiency, and the optimized loading point loads can meet the error requirements of the key sections with high precision, thereby laying a good foundation for high-precision implementation of the aircraft structure fatigue test.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aircraft fatigue test, and particularly relates to an aircraft structure fatigue test load optimization method based on damage accumulation. BACKGROUND

[0002] Modern aircrafts have complex use conditions, resulting in a large number of load states. Some fighter aircrafts have more than a thousand load states, and it is impossible to simulate all the load states in full-size aircraft structure fatigue test. The conventional method is to optimize all the load states into the same load distribution, and a set of loading devices is used to apply the load of all working conditions throughout the test. Therefore, in order to truly reflect the actual load condition of the aircraft structure in use, it is a key link in fatigue test to convert the design load into test load. When the load error reaches 5%, the total damage error caused to the structure will exceed 20%. Therefore, ensuring the accuracy of the conversion from the design load to the test load is a key link that affects whether correct test data can be obtained.

[0003] The fatigue test load optimization in the prior art is all based on the load equivalence principle, but the cumulative damage of the load to the structure is the key to the structure examination in fatigue test. Therefore, the fatigue test load based on the load equivalence principle has low precision and large error. SUMMARY

[0004] The purpose of the present application is to provide an aircraft structure fatigue test load optimization method based on damage accumulation, so as to solve or alleviate at least one problem in the background art.

[0005] The technical solution of the present application is: an aircraft structure fatigue test load optimization method based on damage accumulation, comprising:

[0006] calculating the test loading point coordinates of the aircraft structure according to the test load of each working condition and the load spectrum;

[0007] establishing the shear force, bending moment and torque error coefficient matrix of the key section of each working condition of the aircraft structure according to the test loading point coordinates;

[0008] calculating the damage of the key section of each working condition according to the shear force, bending moment and torque error coefficient matrix of the key section of each working condition of the aircraft structure, and establishing an objective function according to the Miner linear damage method and the damage error and minimum of the key section of each working condition: In the formula, D jl is the damage of the lth key section in the jth flight working condition caused by the design load, is the damage of the lth key section in the jth flight working condition caused by the optimized test load;

[0009] establishing the constraint conditions of the objective function according to the test requirements,

[0010] Solving the objective function under the constraint condition to obtain the load of each working condition loading point.

[0011] Further, the shear error coefficient matrix of the key section of the aircraft structure under each working condition is:

[0012]

[0013] In the formula, Q p is the shear of the theoretical load at the pth section;

[0014] d pk is the load coefficient of the kth loading point to the pth section, and is 1 if there is contribution and 0 if there is no contribution.

[0015] Further, the bending moment error coefficient matrix of the key section of the aircraft structure under each working condition is:

[0016]

[0017] In the formula, M p is the bending moment of the theoretical load at the pth section;

[0018] l mpk is the bending moment arm of the kth loading point to the pth section.

[0019] Further, the torsional moment error coefficient matrix of the key section of the aircraft structure under each working condition is:

[0020]

[0021] In the formula, T p is the torsional moment of the theoretical load at the pth section;

[0022] l tpk is the torsional moment arm of the kth loading point to the pth section.

[0023] Further, the method further comprises optimizing the objective function, and the process comprises:

[0024] The S-N curve of the aircraft structure material is described in the form of a power function: N·S α =C, wherein N is the cycle life, S is the load, and α and C are parameters related to the material, stress ratio, loading mode, etc.;

[0025] Any load cycle (F min ,F max ) in the fatigue test is converted into the pulsating load of the maximum value P DL through equal damage conversion F min is the minimum cycle load, and F max is the maximum cycle load;

[0026] The linear cumulative damage is used to calculate the structural fatigue damage and life: In the formula, D is the total damage, n i is the i-th cycle, N i is the damage caused by the i-th load cycle;

[0027] Based on the damage contribution of each key section under single working condition, the objective function is simplified as:

[0028]

[0029] Based on the cumulative damage of the whole test, the objective function is simplified as

[0030]

[0031] In the formula, is the equivalent cumulative bending moment of the l-th section after optimization;

[0032] M ljDL is the equivalent cumulative bending moment of the l-th section under theoretical load.

[0033] Further, the parameter a takes a value of 4-8.

[0034] Further, the constraint condition is:

[0035]

[0036] In the formula, is the loading point load F1, F2…F k matrix to be solved;

[0037] e q , e M , e T are error matrices of shear force, bending moment and torque corresponding to each key section, respectively;

[0038] B 1×k is a matrix with all elements being 1.

[0039] The aircraft structure fatigue test load optimization method of the application constructs an objective function of fatigue test load calculation and optimization based on the Miner linear damage theory, and obtains the fatigue test load by determining the constraint condition of the objective function. The method has clear idea, simple process and high calculation efficiency. The optimized loading point load can meet the error requirement of key sections with high precision, and lays a good foundation for high-precision implementation of aircraft structure fatigue test. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions provided by the present application, the following will briefly introduce the drawings. Obviously, the drawings described below are only some embodiments of the present application.

[0041] Figure 1 For the aircraft structure fatigue test load optimization method flowchart of the present application. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present application clearer, the following will describe the technical solutions in the embodiments of the present application in more detail with the drawings in the embodiments of the present application.

[0043] In order to overcome the limitations of the load equivalence principle in fatigue load test, the present application proposes an aircraft structure fatigue test load optimization method considering damage effect based on the Miner linear damage accumulation theory, mainly including determination of test loading point position and optimization calculation of load.

[0044] As shown in Figure 1 , the aircraft structure fatigue test load optimization method based on damage accumulation provided by the present application includes the following steps:

[0045] S1, calculating test loading point coordinates under each working condition test load and load spectrum:

[0046] To minimize the error between the test load and the theoretical load of the aircraft structure node, the objective function is established to obtain the coordinates of each loading point, or a typical working condition is selected as the basis for the distribution of fatigue test load, and then the loading point coordinates are calculated.

[0047] S2, according to the loading point coordinates, establishing shear error coefficient matrix Q p×k , bending moment error coefficient matrix M p×k and torsional error coefficient matrix T p×k of the key section under each working condition, wherein the shear error coefficient matrix Q p×k , bending moment error coefficient matrix M p×k and torsional error coefficient matrix T p×k of the key section under each working condition are calculated as follows:

[0048]

[0049]

[0050]

[0051] In the formula, Q p is the shear of the theoretical load at the pth key section;

[0052] M pLet be the bending moment of the theoretical load at the p-th critical section;

[0053] T p Let be the torque of the theoretical load at the p-th critical section;

[0054] d pk The load factor of the k-th loading point on the p-th critical profile is 1 if it contributes and 0 if it does not.

[0055] l mpk Let f be the moment arm of the k-th loading point with respect to the p-th critical section;

[0056] l tpk Let be the torque arm of the k-th loading point relative to the p-th critical profile.

[0057] S3. Calculate the damage of the key sections under each working condition using the error coefficient matrix of shear force, bending moment, and torque. Based on Miner's linear damage theory, establish the following objective function to minimize the damage error of each key section:

[0058] In the formula, D jl The damage caused by the design load on the l-th critical profile in the j-th flight condition;

[0059] The damage caused by the optimized test load in the l-th critical profile under the j-th flight condition.

[0060] The objective function described above can be simplified, specifically including:

[0061] 1) The N·S curve of aircraft structural materials can be described by a power function: N·S α =C, where N is the cycle life, S is the load, and α and C are parameters related to material, stress ratio, loading method, etc.;

[0062] 2) Arbitrary load cycles (F) in fatigue testing min ,F max The damage caused by Odin can be transformed into a maximum value of P. DL The pulsating load, i.e. F min For the minimum cyclic load, F max Maximum cyclic load;

[0063] 3) Structural fatigue damage and life calculation adopts the linear cumulative damage (Miner) theory, that is, the total damage at the time of fatigue failure. In the formula, n i For the i-th iteration, N i The damage caused by the i-th load cycle.

[0064] 4) Based on the damage contribution of each key section under single working condition, the objective function is simplified as:

[0065]

[0066] Based on the cumulative damage of the whole test, the objective function is simplified as:

[0067]

[0068] wherein, is the cumulative bending moment of the lth section after optimization;

[0069] M ljDL is the cumulative bending moment of the lth section under theoretical load;

[0070] The value of parameter a is generally taken as 4-8.

[0071] S4, the constraint conditions for solving the objective function according to the test requirements, the constraint conditions include:

[0072]

[0073] wherein, is the loading point load F1, F2…F k to be solved;

[0074] e q , e M , e T are respectively the error matrixes of the shear force, bending moment and torque corresponding to each key section;

[0075] B 1×k is a matrix with all elements being 1.

[0076] S5, solving the objective function in step 3 based on the constraint conditions in step 4, to obtain the loading point load under each working condition.

[0077] The method of the application is based on the Miner linear damage theory to construct the objective function of fatigue test load calculation optimization, and provides the constraint conditions of the objective function, the test load optimization method of the application has clear idea, simple process and high calculation efficiency, the optimized loading point load can meet the error requirement of key section with high precision, which lays a good foundation for high-precision implementation of aircraft structure fatigue test.

[0078] The above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, any changes or replacements within the technical range disclosed in the application can be easily thought by those skilled in the art, which should be covered in the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A method for optimizing fatigue test loads for aircraft structures based on damage accumulation, characterized in that, The method includes: S1, calculate the coordinates of the test loading points of the aircraft structure based on the test loads and load spectra under each working condition; S2, Based on the coordinates of the test loading points, establish the shear force, bending moment and torque error coefficient matrix of the key sections of the aircraft structure under various working conditions; S3. Based on the shear force, bending moment, and torque error coefficient matrix of the key sections under various working conditions of the aircraft structure, calculate the damage of the key sections under each working condition. Establish the objective function based on the Miner linear damage method and the minimum damage error of the key sections under each working condition: In the formula, D jl For the damage caused by the design load on the l-th critical profile in the j-th flight condition, D * jl The damage caused by the test load after optimization of the l-th critical profile in the j-th flight condition, wherein the optimization process of the objective function includes: Describe the SN curve of aircraft structural materials in power function form: In the formula, N is the cycle life, S is the load, and α and C are parameters related to the material, stress ratio, and loading method. Arbitrary load cycles in fatigue testing ) is converted to the maximum value P through equal damage DL pulsating load F min For the minimum cyclic load, F max Maximum cyclic load; The fatigue damage and life of the structure are calculated using linear cumulative damage: In the formula, D represents the total damage, and n i For the i-th iteration, N i The damage caused by the i-th load cycle; Based on the damage contribution of each key profile under a single working condition, the objective function is simplified to: ； Considering the cumulative damage throughout the experiment, the objective function is simplified to ； In the formula, The equivalent cumulative bending moment of the l-th profile after optimization; The equivalent cumulative bending moment of the theoretical load on the l-th section; S4. Establish the constraints for solving the objective function according to the experimental requirements; S5. Based on the constraints, solve the objective function to obtain the load at each loading point under each working condition.

2. The method for optimizing aircraft structural fatigue test loads based on damage accumulation as described in claim 1, characterized in that, The shear force error coefficient matrix for key sections of the aircraft structure under various working conditions is as follows: ； In the formula, Q p Let be the shear force of the theoretical load at the p-th section; d pk The load factor of the k-th loading point on the p-th profile is 1 if it contributes and 0 if it does not.

3. The method for optimizing aircraft structural fatigue test loads based on damage accumulation as described in claim 2, characterized in that, The bending moment error coefficient matrix of the key sections of the aircraft structure under various operating conditions is as follows: ； In the formula, M p Let be the bending moment of the theoretical load at the p-th section; l mpk Let f be the moment arm of the k-th loading point with respect to the p-th section.

4. The method for optimizing aircraft structural fatigue test loads based on damage accumulation as described in claim 3, characterized in that, The torque error coefficient matrix for key sections of the aircraft structure under various operating conditions is as follows: ； In the formula, T p Let be the torque of the theoretical load at the p-th profile; l tpk Let be the torque arm of the k-th loading point relative to the p-th profile.

5. The method for optimizing aircraft structural fatigue test loads based on damage accumulation as described in claim 1, characterized in that, The parameter α takes a value of 4 to 8.

6. The method for optimizing aircraft structural fatigue test loads based on damage accumulation as described in claim 1, characterized in that, The constraints are as follows: ； In the formula, For the loading point loads F1, F2…F that need to be solved k matrix; e q e M e T These are the error matrices for shear force, bending moment, and torque corresponding to each key section; B 1×k It is a matrix with all elements being 1.

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