Method for high cycle fatigue damage evolution of helicopter metallic moving parts considering load sequence

Abstract

The application belongs to the field of structural strength design, and relates to a helicopter metal moving part high-cycle fatigue damage evolution method considering load sequence. The method comprises the following steps: according to a high-cycle fatigue damage model considering stress ratio and load sequence effect, based on finite element theory, evaluating a high-cycle fatigue damage evolution process of a helicopter rotor metal structure under variable amplitude loading, and predicting a high-cycle fatigue life.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of structural strength design, and relates to a helicopter metal moving part high-cycle fatigue damage evolution method considering load sequence. BACKGROUND

[0002] Fatigue problems are significant during the service process of a helicopter, fatigue damage of a helicopter rotor metal structure under cyclic loading reduces the service life and affects the safety of the structure. Flight loads during the service of the helicopter rotor metal structure are variable amplitude loads, and load sequence effects have influences on fatigue damage rate and fatigue life. SUMMARY

[0003] The application aims to accurately predict the high-cycle fatigue life of a helicopter rotor metal structure, evaluate the damage evolution process, and obtain the high-cycle fatigue performance S max -R-N surface model of the rotor metal structure considering the influences of stress ratio and load sequence effects, and a high-cycle fatigue damage model of the metal structure considering the load sequence effects is introduced. On this basis, a high-cycle fatigue damage evolution evaluation method of the structure under variable amplitude loading is given based on the finite element theory, which provides help for the design and failure analysis of the helicopter rotor.

[0004] The technical scheme of the application is as follows:

[0005] A helicopter metal moving part high-cycle fatigue damage evolution method considering load sequence, comprising:

[0006] According to the high-cycle fatigue damage model considering the influences of stress ratio and load sequence effects, the high-cycle fatigue damage evolution process of the helicopter rotor metal structure under variable amplitude loading is evaluated based on the finite element theory, and the high-cycle fatigue life is predicted.

[0007] The high-cycle fatigue damage model is as follows:

[0008]

[0009]

[0010]

[0011]

[0012] In the formula, R eff,i and S max,i are the effective stress ratio and the maximum stress of the i-th stress cycle under variable amplitude loading, respectively; ΔD i is the fatigue damage increment corresponding to the i-th stress cycle in the variable amplitude loading history; β is a stress ratio correction coefficient; R 0.2 is the yield strength limit of the material; S max is the maximum fatigue stress; and S∞ The safe fatigue limit of the material; R eff is the effective stress ratio, representing the stress change at the fatigue crack tip in the overload plastic zone under cyclic loading; S res is the residual stress; is the maximum fatigue stress in the overload stress cycle; μ and γ are the crack closure coefficient and the overload cutoff ratio, respectively, which are determined by tests; λ is a predetermined linear interpolation parameter.

[0013] According to the high-cycle fatigue damage model considering the stress ratio and load sequence effect, the high-cycle fatigue damage evolution process of the helicopter rotor metal structure under variable amplitude loading is evaluated based on the finite element theory, and the high-cycle fatigue life is predicted, including:

[0014] A finite element model of the helicopter metal moving part is established, and the fatigue load cycle number K when the structure fails under variable amplitude loading is initially set to 0, at which time the initial value of the high-cycle fatigue damage D i,j of each element in the structure finite element model is set to 0; i is the current stress cycle number; j is the finite element number of the rotor metal structure;

[0015] The fatigue load is applied according to the load spectrum sequence, and the working stress of each finite element is calculated and recorded in turn. Then, the high-cycle fatigue cumulative damage of each element is analyzed according to the high-cycle fatigue damage model considering the stress ratio and load sequence effect, and the high-cycle fatigue cumulative damage D i,j of the jth element of the structure under the ith fatigue load cycle in the load spectrum is obtained. i,j D i-1,j = D i,j + ΔD i-1,j ; D i,j is the high-cycle fatigue cumulative damage of the jth element of the structure under the i-1th last cycle.

[0016] The Palmgren-Miner linear cumulative damage theory is used to determine whether each element of the structure fails. When the cumulative damage D i,j of an element is greater than or equal to 1, the element fails and is killed; when the cumulative damage D i,j of an element is less than 1, the element does not fail, and the cumulative damage of the element is calculated and recorded, and the next fatigue load cycle is applied, and K is set to K+1, and the stress calculation of the structure finite element and the element failure analysis are performed.

[0017] This cycle is repeated until the helicopter rotor metal structure fails as a whole or the load spectrum ends, at which time the failure process of each element corresponds to the high-cycle fatigue damage evolution process of the structure.

[0018] The method further comprises:

[0019] The high-cycle fatigue life T of the structure under variable amplitude loading is obtained according to the final failure cycle number K, and the calculation formula is:

[0020] Methods for obtaining high-cycle fatigue damage models include:

[0021] The Stromeyer model is used to characterize the high-cycle fatigue performance of the helicopter rotor metal structure under a specified stress ratio. The model is modified to account for the influence of the stress ratio R, and the high-cycle fatigue performance S characterizing the rotor metal structure is obtained. max -RN surface model;

[0022] The simple and effective Palmgren-Miner linear cumulative damage theory is used to evaluate the high-cycle fatigue life of the structure under variable amplitude loading.

[0023] The high-cycle fatigue performance of rotor metal structures S max By combining the RN surface model and the Palmgren-Miner linear cumulative damage theory, an expression for the high-cycle fatigue damage rate is obtained.

[0024] The effective stress ratio R eff The expression for fatigue damage rate is introduced to describe the stress change at the fatigue crack tip in the overloaded plastic zone under variable amplitude loading, to account for the effect of loading sequence on fatigue damage, thus obtaining the high-cycle fatigue damage increment ΔD for the i-th stress cycle under variable amplitude loading. i This refers to the high-cycle fatigue damage model.

[0025] Characterizing the high-cycle fatigue performance of rotor metal structures S max The -RN surface model is:

[0026]

[0027] N is the failure life cycle number of the structure; A and α are preset fatigue performance parameters; R is the preset loading stress ratio.

[0028] High cycle fatigue damage rate Representation methods:

[0029]

[0030] λ = 2 / 3.

[0031] The beneficial effects of this invention are as follows: a surface model of the high-cycle fatigue performance of a helicopter rotor metal structure is obtained by considering the influence of stress ratio; the concept of effective stress ratio is introduced; a high-cycle fatigue damage model of the structure considering the load sequence effect is proposed; based on this, a method for evaluating the evolution of high-cycle fatigue damage of the structure under variable amplitude loading is given by using the finite element method; the high-cycle fatigue damage process and fatigue life of the structure are predicted, providing assistance for helicopter rotor design and failure analysis. Attached Figure Description

[0032] Figure 1 Technical flow chart of the method of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work are within the protection scope of the present application.

[0034] A helicopter metal moving part high-cycle fatigue damage evolution method considering load sequence, as shown in Figure 1 The specific steps of the method are as follows:

[0035] Step one, helicopter rotor metal structure high-cycle fatigue performance characterization model considering stress ratio.

[0036] The Stromeyer model is used to characterize the high-cycle fatigue performance of the helicopter rotor metal structure under the specified stress ratio, the influence of the stress ratio R is considered for correction, and the high-cycle fatigue performance S max -R-N surface model:

[0037]

[0038] In the formula, N is the failure life cycle number of the structure; A and a are preset fatigue performance parameters; β is a stress ratio correction coefficient, usually β = 1 for aluminum alloy structure, β = 2 for alloy steel structure, and β = 0.65 for titanium alloy structure; R 0.2 is a preset material yield strength limit; S max and R are the maximum fatigue stress and the loading stress ratio respectively; S ∞ is a preset material safety fatigue limit. Formula (1) is a three-parameter surface model of the rotor metal structure, which can characterize the high-cycle fatigue performance of the structure considering the stress ratio effect.

[0039] Step two, helicopter rotor metal structure high-cycle fatigue damage model considering load sequence.

[0040] The simple and effective Palmgren-Miner linear cumulative damage theory is usually used to evaluate the high-cycle fatigue life of the structure under variable amplitude loading, and the Palmgren-Miner linear cumulative damage theory can be expressed as:

[0041]

[0042]

[0043]

[0044]

[0045] In the formula, D represents fatigue damage; dD / d n ΔD represents the fatigue damage rate, indicating how quickly the structure develops fatigue damage. i N represents the fatigue damage increment corresponding to the i-th stress cycle in the variable amplitude loading process; i Let be the number of cycles corresponding to the fatigue failure of the structure under the i-th stress cycle loading; K is the number of stress cycles when the structure fails under variable amplitude loading; L is the number of stress cycles contained in 1 flight hour; T is the number of flight hours when the structure fails under fatigue loading, i.e., the high-cycle fatigue life of the structure under variable amplitude loading.

[0046] The high-cycle fatigue performance of rotor metal structures S max Substituting the RN surface model (Equation 1) into Equation (2), we can obtain a representation of the high-cycle fatigue damage rate:

[0047]

[0048] In fact, the load sequence effect in variable amplitude loading has a significant impact on the high-cycle fatigue damage rate and high-cycle fatigue life, but this is not considered by conventional fatigue performance characterization models and cumulative damage theories. In the semi-linear Willenborg model, by introducing the effective stress ratio R... eff The concept characterizes the effect of loading sequence on crack propagation behavior, describing the stress change at the crack tip within the overloaded plastic zone under cyclic loading. Similarly, the effective stress ratio R... eff Introducing the fatigue damage rate expression (6) to describe the stress change at the fatigue crack tip in the overloaded plastic zone under variable amplitude loading, and considering the influence of the load sequence effect on fatigue damage, the modified expression for the high-cycle fatigue damage rate is as follows:

[0049]

[0050] in:

[0051]

[0052]

[0053]

[0054] In the formula, R eff The effective stress ratio represents the stress change at the fatigue crack tip within the overloaded plastic zone under cyclic loading; S res This is residual stress; is the maximum fatigue stress in the overload stress cycle obtained from the fatigue load spectrum; μ and γ are the preset crack closure coefficient and overload cutoff ratio, respectively; λ is the linear interpolation parameter, and generally, λ = 2 / 3 is calculated according to the crack arrest condition after overload. It can be seen that formula (7) considers the influence of load sequence effect on high-cycle fatigue damage and can represent the high-cycle fatigue performance under variable amplitude loading.

[0055] Substituting formula (7) into formula (3), the high-cycle fatigue damage increment ΔD of the i th stress cycle under variable amplitude loading is obtained as follows: i

[0056]

[0057] In the formula, R eff,i and S max,i are the effective stress ratio and the maximum stress of the i th stress cycle under variable amplitude loading, respectively, and the calculation method of R eff,i is shown in formulas (8) to (10).

[0058] Step three, a method for evaluating the high-cycle fatigue damage evolution and predicting the life of a rotor metal structure under variable amplitude loading.

[0059] According to the high-cycle fatigue damage model considering the stress ratio and load sequence effect in step two, based on the finite element theory, the high-cycle fatigue damage evolution process of a helicopter rotor metal structure under variable amplitude loading is evaluated, and the high-cycle fatigue life is predicted, and the specific process is as follows:

[0060] 1) A finite element model of a helicopter rotor metal structure is established, and the fatigue load cycle number K = 0 is set, at this time, the high-cycle fatigue damage D of each element in the structure finite element model (element number j = 1, 2, 3,...) is set to 0; K,j

[0061] 2) The fatigue load is applied according to the load spectrum sequence, the working stress of each element of the rotor metal structure is calculated and recorded, and then the high-cycle fatigue cumulative damage of each element is analyzed according to the high-cycle fatigue damage model considering the stress ratio and load sequence effect (formulas (8) to (11)), and then the high-cycle fatigue cumulative damage of the j th element of the structure under the i th fatigue load cycle loading in the load spectrum is:

[0062] D i,j = D i-1,j + ΔD i,j (12)

[0063] In formula (12), ΔD is calculated by formula (11), D and D are obtained by cycle-by-cycle calculation. i,j i,j i-1,j

[0064] ​​​​​3) using Palmgren-Miner linear cumulative damage theory to judge whether each unit of the structure is failed, when the cumulative damage D i,j ≥1, the unit is failed, and the failed unit is killed; when the cumulative damage D i,j <1, the unit is not failed, the cumulative damage of the unit is calculated and recorded. The next fatigue load cycle is applied, and the load cycle number K=K+1 is set, and the finite element stress calculation and unit failure analysis of the structure are carried out.

[0065] 4) thus repeatedly, until the whole helicopter rotor metal structure is failed or the load spectrum is ended, at this time, the failure process of each unit corresponding is the high cycle fatigue damage evolution process of the structure; further, according to the final failure cycle number K and formula (5), the high cycle fatigue life T of the structure under variable amplitude loading can be obtained.

[0066] The key points of the present application are:

[0067] 1) Stromeyer model is modified by considering the influence of stress ratio, and S max -R-N surface model representing the high cycle fatigue performance of the rotor metal structure is obtained.

[0068] 2) based on the semi-linear Willenborg model, the effective stress ratio R eff is introduced to describe the stress change of the fatigue crack tip in the plastic zone under overloading, a high cycle fatigue damage model of the rotor metal structure considering the load sequence effect is proposed, and the high cycle fatigue damage increment ΔD i of the i-th stress cycle under variable amplitude loading is obtained.

[0069] 3) according to the proposed high cycle fatigue damage model considering the stress ratio and the load sequence effect, based on the finite element theory, an evaluation method of the high cycle fatigue damage evolution of the rotor metal structure under variable amplitude loading is given, the high cycle fatigue damage process of the structure can be obtained, the high cycle fatigue life can be predicted, and help is provided for the helicopter rotor design and failure analysis.

[0070] The above is only a specific embodiment of the present application, which is described in detail, and the part not described in detail is the conventional technology. However, the protection scope of the present application is not limited to this, any changes or replacements within the technical range disclosed by the present application can be easily thought by those skilled in the art, which should be covered in the protection scope of the present application. The protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for high-cycle fatigue damage evolution of helicopter metal moving parts considering load sequence, characterized in that, include: Based on the high-cycle fatigue damage model that considers stress ratio and load sequence effects, and using finite element theory, we evaluate the high-cycle fatigue damage evolution process of helicopter rotor metal structures under variable amplitude loading and predict high-cycle fatigue life. The high-cycle fatigue damage model is as follows: ； ； ； ； In the formula, A and α These are preset fatigue performance parameters; and The first under variable amplitude loading i Effective stress ratio and maximum stress for each stress cycle; To correspond to the first in the variable amplitude loading process i The fatigue damage increment per stress cycle; β This is the stress ratio correction factor; R 0.2 The yield strength limit of the material; S max This represents the maximum fatigue stress. S ∞ The safe fatigue limit of the material; The effective stress ratio represents the stress change at the tip of the fatigue crack in the overloaded plastic zone under cyclic loading. This is residual stress; This represents the maximum fatigue stress during an overload stress cycle. μ and γ These are the crack closure factor and the overload cutoff ratio, respectively, which were determined through experimental testing. λ These are the predetermined linear interpolation parameters.

2. The method according to claim 1, characterized in that, Based on a high-cycle fatigue damage model considering stress ratio and load sequence effects, and using finite element theory, the high-cycle fatigue damage evolution process of a helicopter rotor metal structure under variable amplitude loading is evaluated, and the high-cycle fatigue life is predicted, including: A finite element model of the moving metal components of a helicopter is established, and the fatigue load cycle number is calculated for fatigue failure of the structure under variable amplitude loading. K Initialize the value to 0. At this point, the high-cycle fatigue damage of each element in the structural finite element model is... The initial value is set to 0; i This represents the current stress cycle number. j This refers to the finite element number of the rotor metal structure; Fatigue loads were applied sequentially according to the load spectrum, and the working stress of each finite element was calculated and recorded in turn. Then, the high-cycle fatigue cumulative damage of each element was analyzed using a high-cycle fatigue damage model considering stress ratio and load sequence effects, yielding the first element in the load spectrum. i The structure under fatigue load cycle loading is the first j Accumulated high-cycle fatigue damage in each unit , ; For the first i -1 cycle loading structure j Accumulated high-cycle fatigue damage in each unit; The Palmgren-Miner linear cumulative damage theory is used to determine whether each element of the structure has failed. When the element accumulates damage... When the value is ≥1, the element fails and is killed; when the element accumulates damage... When the value is less than 1, the element has not failed. Calculate and record the cumulative damage of the element, continue applying the next fatigue load cycle, and set... K = K +1, perform structural finite element stress calculation and element failure analysis; This cycle repeats until the entire metal structure of the helicopter rotor fails or the load spectrum ends. At this point, the failure process of each unit is the high-cycle fatigue damage evolution process of the structure.

3. The method according to claim 2, characterized in that, The method further includes: Based on the final failure cycle number K To obtain the high cycle fatigue life of the structure under variable amplitude loading T The calculation formula is as follows: , in, L This represents the number of stress cycles contained in one hour of flight.

4. The method according to claim 1, characterized in that, Methods for obtaining high-cycle fatigue damage models include: The Stromeyer model is used to characterize the high-cycle fatigue performance of helicopter rotor metal structures under a specified stress ratio, considering the stress ratio. R The influence of these factors is corrected to obtain high-cycle fatigue performance characterizing the rotor metal structure. Surface model; The simple and effective Palmgren-Miner linear cumulative damage theory is used to evaluate the high-cycle fatigue life of the structure under variable amplitude loading. High-cycle fatigue performance of rotor metal structure By combining the surface model with the Palmgren-Miner linear cumulative damage theory, an expression for the high-cycle fatigue damage rate is obtained, where, N The number of cycles in the failure lifetime of the structure; Effective stress ratio The expression for fatigue damage rate is introduced to describe the stress change at the fatigue crack tip in the overloaded plastic zone under variable amplitude loading, so as to consider the influence of the loading sequence effect on fatigue damage, and thus obtain the first... i High-cycle fatigue damage increment per stress cycle This refers to the high-cycle fatigue damage model.

5. The method according to claim 4, characterized in that, Characterizing the high-cycle fatigue performance of rotor metal structures The surface model is as follows: ； N The number of cycles in the failure lifetime of the structure; A and α These are preset fatigue performance parameters; R This is the preset loading stress ratio.

6. The method according to claim 4, characterized in that, High cycle fatigue damage rate Representation methods: 。 7. The method according to claim 1, characterized in that, λ = 2 / 3.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-7.

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