Structure anti-fatigue optimization design method based on life-stress conversion

Abstract

The invention belongs to the field of helicopter rotor system strength design, and relates to a structure anti-fatigue optimization design method based on life-stress conversion. The method comprises the following steps: acquiring static strength and high-low cycle fatigue design load of a certain structure of the helicopter; and performing structure anti-fatigue optimization by taking the static strength stress constraint, the cycle fatigue stress constraint and the cycle fatigue stress constraint related to the target life as cycle fatigue stress constraints.

Description

Technical Field

[0001] The invention belongs to the field of strength design of helicopter rotor systems and relates to a structural anti-fatigue optimization design method based on life-stress conversion. Background Art

[0002] The strength design of traditional rotor systems adopts the manual iterative design of "design-check-modify design", which has the disadvantages of large design workload and long R&D cycle. Topological optimization design is an important means to improve design efficiency. In the fatigue optimization design of structures, the commonly used finite element software cannot directly realize the life as a constraint condition. Therefore, how to integrate the life index into the optimization design is the key to the fatigue design of structures. Summary of the invention

[0003] Purpose of the invention: To propose a structural anti-fatigue optimization design method based on life-stress constraints. The present invention is based on the life-stress conversion relationship, corresponds the life index with the structural stress, and through preliminary data analysis, the structural optimization stress constraint conditions that meet the fatigue strength can be obtained, providing a method for structural anti-fatigue design.

[0004] Technical solution:

[0005] Provides structural fatigue optimization design methods based on life-stress transformation, including:

[0006] Obtain the static strength, high and low cycle fatigue design loads of a helicopter structure;

[0007] Static strength stress constraints, cyclic fatigue stress constraints, and cyclic fatigue stress constraints related to target life are used as cyclic fatigue stress constraints to perform structural fatigue optimization.

[0008] Furthermore, the static strength, high and low cycle fatigue design loads of a structure are obtained, including:

[0009] According to the load spectrum, the load F that has the greatest impact on the structural stress distribution and size is selected as the characteristic load, and the load value covering the proportion t state is selected as the static strength and low-cycle fatigue design load F max ;

[0010] The maximum static load in the load spectrum is selected as the high cycle fatigue design static load F ys ;

[0011] According to the damage accumulation criterion, the working conditions in the load spectrum are synthesized, and the load fatigue limit corresponding to the target life is selected as the high-cycle fatigue design dynamic load F yd .

[0012] Furthermore, the static strength stress constraints include:

[0013] Static strength requires that the limiting stress of the structure is less than the yield limit of the material, and the ultimate stress is less than the strength limit of the material.

[0014] Furthermore, high cycle fatigue stress constraints include:

[0015] High cycle fatigue strength requires that the equivalent stress of the structure is less than the safe fatigue limit of the material.

[0016] Furthermore, low cycle fatigue stress constraints include:

[0017] Low-cycle fatigue strength requires that the equivalent stress of the structure is less than the stress limit value corresponding to the target life.

[0018] Furthermore, the structure is under the maximum load F max The limiting stress under action σ limit Need to meet:

[0019] σ limit <σ 0.2

[0020] Ultimate stressσ ult =σ limit Need to meet:

[0021] σ limit <σ 0.2

[0022] σ ult =σ limit ×K safe <σ b

[0023] In the formula, K safe is the structural safety factor.

[0024] Furthermore, under high cyclic static load F Hs The high cyclic static stress under the action is σ Hs , high cyclic dynamic load F Hd The high cyclic dynamic stress under the action is σ Hd , equivalent stress σ after linear Goodman correction Heq for:

[0025]

[0026] In the formula, α is 1, σ sp =σ s / J p is the safe fatigue limit of the material.

[0027] The ratio of high-cycle static stress to dynamic stress is consistent with the ratio of static / dynamic load in the load calculation spectrum, that is,

[0028]

[0029] High cycle static and dynamic stresses should meet the following requirements:

[0030]

[0031] Furthermore, at the maximum load F max The maximum stress under action is the low-cycle stress σ max , low-cycle static and dynamic stresses are σ Ls =σ Ld =σ max / 2, equivalent stress σ after linear Goodman correction Leq for:

[0032]

[0033] High cycle static and dynamic stresses should meet the following requirements:

[0034]

[0035] Beneficial effects:

[0036] The present invention obtains the stress constraint condition of the structure with respect to the target life through the corresponding relationship between life and fatigue stress, and the structure designed according to this condition meets the fatigue strength requirement. The present invention provides a life-stress conversion method for structural anti-fatigue design, improves the efficiency of structural design, and makes it meet the fatigue strength requirement, which is of great significance to the structural anti-fatigue design of helicopter rotor systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of static strength loading.

[0038] Figure 2 Schematic diagram of high cycle fatigue loading.

[0039] Figure 3 Schematic diagram of low cycle fatigue loading. DETAILED DESCRIPTION

[0040] The present invention provides a structural anti-fatigue optimization design method based on life-stress conversion, and the specific steps are as follows:

[0041] [1] Determine the load input

[0042] According to the load spectrum, the load F that has the greatest impact on the structural stress distribution and size is selected as the characteristic load, and the load value covering the proportion t state is selected as the static strength and low-cycle fatigue design load F max The maximum static load in the load spectrum is selected as the high cycle fatigue design static load F ys ; According to the damage accumulation criterion, the working conditions in the load spectrum are synthesized, and the load fatigue limit corresponding to the target life is selected as the high-cycle fatigue design dynamic load F yd .

[0043] [2] Static Strength Stress Constraint

[0044] Static strength requires that the limiting stress of the structure is less than the yield limit of the material, and the ultimate stress is less than the strength limit of the material.

[0045] [3] High cycle fatigue stress constraint

[0046] High cycle fatigue strength requires that the equivalent stress of the structure is less than the safe fatigue limit of the material.

[0047] [4] Low cycle fatigue stress constraint

[0048] Low-cycle fatigue strength requires that the equivalent stress of the structure is less than the stress limit value σ0 corresponding to the target life.

[0049] [5] Stress constraint conditions

[0050] The stress constraint condition that meets the structural fatigue strength requirements is the stress that meets the requirements of steps 2, 3, and 4.

[0051] [6] Optimized design

[0052] Commercial finite element software is used to optimize the design based on the stress constraints in step 5.

[0053] Example 1

[0054] The following is a further explanation of the design method of this specification with reference to an example. The structural material of this example is aluminum alloy, and the material yield limit is σ 0.2 =300MPa, the ultimate strength is σ b =500MPa, the average fatigue limit is σ s =200MPa, reduction factor is J p =2, structural safety factor K safe The specific steps for life-stress constrained structural fatigue optimization design are as follows:

[0055] [1] Determine the load input

[0056] The load F that has the greatest impact on the structural stress distribution and magnitude is selected as the characteristic load, and the maximum value is selected as the static strength and low-cycle fatigue design load F max = 10000N (t = 100%). The maximum static load in the load spectrum is selected as the high cycle fatigue design static load F Hs =7500N; According to the damage accumulation criterion, the working conditions in the load spectrum are synthesized, and the load fatigue limit corresponding to the target life is selected as the high-cycle fatigue design dynamic load F Hd =5000N, the ratio of static / dynamic load in the load spectrum is p=1.5.

[0057] [2] Static Strength Stress Constraint

[0058] The structure is under maximum load F max Under the effect (such as Figure 1 ) of the limiting stress σ limit Need to meet:

[0059] σ limit <σ 0.2

[0060] Ultimate stressσ ult =σ limit Need to meet:

[0061] σ limit <σ 0.2

[0062] σ ult =σ limit ×K safe <σ b

[0063] In the formula, K safe is the structural safety factor.

[0064] σ limit <min{300,500 / K safe}

[0065] [3] High cycle fatigue stress constraint

[0066] At high cyclic static load F Hs Under the effect (such as Figure 2 ) is σ Hs , high cyclic dynamic load F Hd Under the effect (such as Figure 2 ) is the high cyclic dynamic stress σ Hd , equivalent stress σ after linear Goodman correction Heq for:

[0067]

[0068] In the formula, α is 1, σ sp =σ s / J p =100MPa is the safe fatigue limit of the material.

[0069] The ratio of high-cycle static stress to dynamic stress is consistent with the ratio of static / dynamic load in the load calculation spectrum, that is,

[0070]

[0071] High cycle static and dynamic stresses should meet the following requirements:

[0072]

[0073] [4] Low cycle fatigue stress constraint

[0074] At maximum load F max Under the effect (such as Figure 3 ) is the low-cycle stress σ max , low-cycle static and dynamic stresses are σ Ls =σ Ld =σ max / 2, equivalent stress σ after linear Goodman correction Leq for:

[0075]

[0076] High cycle static and dynamic stresses should meet the following requirements:

[0077]

[0078] [5] Stress constraint conditions

[0079] The stress constraint conditions that meet the structural fatigue strength requirements are:

[0080]

[0081] [6] Optimized design

[0082] Commercial finite element software is used to optimize the design based on the stress constraints in step 5.

[0083] Furthermore, in the step 1, t is usually not less than 95%.

[0084] Furthermore, in step 2, K safe Generally, 1.5 is recommended.

[0085] Furthermore, in step three, α is related to the material and can be 1 for aluminum alloy.

Claims

1. A structural fatigue optimization design method based on life-stress transformation, characterized in that: include: Obtain the static strength, high and low cycle fatigue design loads of a helicopter structure; Static strength stress constraints, cyclic fatigue stress constraints, and cyclic fatigue stress constraints related to target life are used as cyclic fatigue stress constraints to perform structural fatigue optimization.

2. The method according to claim 1, characterized in that Obtain static strength, high and low cycle fatigue design loads of a structure, including: According to the load spectrum, the load F that has the greatest impact on the structural stress distribution and size is selected as the characteristic load, and the load value covering the proportion t state is selected as the static strength and low-cycle fatigue design load F max ; The maximum static load in the load spectrum is selected as the high cycle fatigue design static load F ys ; According to the damage accumulation criterion, the working conditions in the load spectrum are synthesized, and the load fatigue limit corresponding to the target life is selected as the high-cycle fatigue design dynamic load F yd .

3. The method according to claim 2, characterized in that Static strength stress constraints include: Static strength requires that the limiting stress of the structure is less than the yield limit of the material, and the ultimate stress is less than the strength limit of the material.

4. The method according to claim 2, characterized in that: High cycle fatigue stress constraints include: High cycle fatigue strength requires that the equivalent stress of the structure is less than the safe fatigue limit of the material.

5. The method according to claim 2, characterized in that: Low cycle fatigue stress constraints include: Low-cycle fatigue strength requires that the equivalent stress of the structure is less than the stress limit value corresponding to the target life.

6. The method according to claim 3, characterized in that The structure is under maximum load F max The limiting stress under action σ limit Need to meet: s limit <s 0.2 Ultimate stressσ ult =σ limit Need to meet: s limit <s 0.2 s ult =s limit ×K safe <s b In the formula, K safe is the structural safety factor.

7. The method according to claim 4, characterized in that At high cyclic static load F Hs The high cyclic static stress under the action is σ Hs , high cyclic dynamic load F Hd The high cyclic dynamic stress under the action is σ Hd , equivalent stress σ after linear Goodman correction Heq for: In the formula, α is 1, σ sp =σ s / J p is the safe fatigue limit of the material. The ratio of high-cycle static stress to dynamic stress is consistent with the ratio of static / dynamic load in the load calculation spectrum, that is, High cycle static and dynamic stresses should meet the following requirements:

8. The method according to claim 5, characterized in that At maximum load F max The maximum stress under action is the low-cycle stress σ max , low-cycle static and dynamic stresses are σ Ls =σ Ld =σ max / 2, equivalent stress σ after linear Goodman correction Leq for: High cycle static and dynamic stresses should meet the following requirements:

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