Aircraft composite material structure reuse performance evaluation method

Abstract

The invention belongs to the field of structural strength analysis, and relates to an aircraft composite material structure reuse performance evaluation method. The aircraft composite material structure reuse performance evaluation method mainly comprises the following steps: 1) an allowable value coverage design method based on a composite material building block type test; 2) a static force and vibration fatigue key component screening method based on aircraft structure strength analysis; 3) an aircraft composite material structure fatigue analysis method; 4) a composite material structure service life analysis method based on nondestructive testing; and 5) analyzing the calendar life of the composite material structure.

Description

Technical Field

[0001] The invention relates to a method for evaluating the reuse performance of aircraft composite material structures, and belongs to the field of structural strength analysis. Background Art

[0002] The service life of aircraft structures is an important design indicator that affects the overall mission benefits and the comprehensive performance of the aircraft. A high design life results in a low degree of structural lightweighting, while a low design life results in insufficient structural reuse reliability. For aircraft that have difficulty in rapid inspection of composite materials, the reuse performance evaluation of composite materials mainly relies on analytical methods and design assurance.

[0003] In order to meet the design requirements of light weight, high stiffness and low expansion, aircraft structures often use solutions with a high proportion of composite materials. The dispersion of fatigue performance of composite materials makes it difficult to design the life of the structure and evaluate its reuse performance. In addition, the low-cycle and high-load characteristics of aircraft make life assessment very different from the traditional methods. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies of the above-mentioned prior art, the present invention proposes a method for evaluating the reuse performance of aircraft composite structures, which realizes the reuse performance evaluation of aircraft composite structures with limited flight times and large load levels, including allowable value coverage design for composite structures, static and vibration fatigue key parts screening method for composite structures, low-cycle fatigue analysis of aircraft composite structures, composite structure life analysis method based on non-destructive testing, and composite structure calendar life analysis method.

[0006] (II) Technical solution

[0007] The present invention proposes a method for evaluating the reuse performance of aircraft composite material structures, comprising:

[0008] 1) Allowable value coverage design method based on building block test of composite materials;

[0009] 2) Static and vibration fatigue key parts screening method based on aircraft structural strength analysis;

[0010] 3) Fatigue analysis methods for aircraft composite structures;

[0011] 4) Composite material structure life analysis method based on non-destructive testing;

[0012] 5) Calendar life analysis method for composite structures.

[0013] (III) Beneficial effects

[0014] The beneficial effects of the present invention compared with the prior art are: the present invention proposes a method for evaluating the reuse performance of aircraft composite materials structures, which can realize the reuse performance evaluation of aircraft composite materials structures with limited flight times and large load levels, including the design of allowable value coverage of composite materials structures, static and vibration fatigue key parts screening methods for composite materials structures, low-cycle fatigue analysis of aircraft composite materials structures, composite materials structure life analysis methods based on non-destructive testing, and composite materials structure calendar life analysis methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flowchart of the inventive method of the present invention. DETAILED DESCRIPTION

[0016] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings.

[0017] The allowable value envelope of the composite material is constructed to include environmental factors such as temperature and moisture absorption state, taking into account the critical value of 80% long-term storage performance retention rate, and taking into account the effects of open holes, filled holes, delamination defects, impact damage, etc., to form a tensile, compression, and mechanical connection design allowable value system. The building block test of composite materials includes unnotched tensile and compression test, open hole tensile and compression test, filled hole tensile and compression test, post-impact tensile and compression test, and mechanical connection test.

[0018] The design allowable value contains data of different temperatures and moisture absorption states, where the temperature includes low temperature, room temperature and high temperature, and the moisture absorption state includes dry state and wet state. The low temperature is -70 degrees, the high temperature is 150 degrees for epoxy resin composite materials, and the high temperature is 180 degrees for bismaleimide composite materials; the dry state refers to the "manufacturing state", that is, after manufacturing, it is placed under laboratory atmospheric conditions without any moisture absorption treatment; the wet state requires special moisture absorption treatment, and the humidity is 85%.

[0019] The tensile design allowable value of the laminate is mainly determined by the performance of the fiber. It is necessary to consider the test data of open holes, filled holes, and delamination defects, and compare them with the unnotched tensile test data to form the tensile design allowable value defect influence coefficient K. t缺陷 ; According to the unnotched tensile test data of laminates under different environments, including low temperature, high temperature, and wet state, compared with the unnotched tensile test data at room temperature and dry state, the tensile design allowable value environmental impact coefficient K is formed t环境 The allowable tensile design value of the laminate is:

[0020] ε bt =ε btmax K t缺陷 K t环境

[0021] The allowable compression design value of the laminate is mainly determined by the performance of the matrix. It is necessary to consider the test data of the opening, filling and impact environment, and compare them with the unnotched compression test data to form the defect influence coefficient K of the allowable compression design value. c缺陷 ; Based on the unnotched compression test data of laminates under different environments, including low temperature, high temperature, and wet state, and compared with the unnotched compression test data at room temperature and dry state, the environmental impact coefficient K of the compression design allowable value is formed. c环境 The allowable design value of laminate compression is:

[0022] ε bc =ε bcmax K c缺陷 K c环境

[0023] The design allowable value of mechanical connection of laminates is mainly determined by the extrusion strength performance. It is necessary to consider the test data of flat head and countersunk head connection forms and compare them with the flat head tensile test data to form the design allowable value of mechanical connection and the connection form influence coefficient K. d连接形式 ; According to the mechanical connection test data under different environments, including low temperature, high temperature, and wet state, compared with the room temperature dry state mechanical connection test data, the environmental impact coefficient K of the mechanical connection design allowable value is formed d环境 ; According to the fatigue test data of mechanical connection in different ply forms, compared with the static test data of mechanical connection in dry state at room temperature, the fatigue influence coefficient K of the mechanical connection design allowable value is formed d疲劳 The allowable design value of the mechanical connection of the laminate is:

[0024] σ bd =σ bdmax K d连接形式 K d环境 K d疲劳

[0025] The allowable values ​​of structural design can cover the composite material system used, layup form, environmental factors, defect factors, and connection form.

[0026] Conduct nondestructive testing on composite materials after flight to obtain the degree of damage to composite materials, analyze the strength of aircraft composite materials, sort out structural margins, use life design methods for structural areas that are not covered by static fatigue, and select areas with a residual strength coefficient of less than 1.5 as fatigue key parts for fatigue life analysis. For vibration-sensitive structures, conduct high-frequency vibration fatigue life analysis.

[0027] The reusability analysis of key parts of laminate composite structure is carried out based on the SN curve of 0° laminate material. The fatigue performance of laminates mainly depends on the fatigue performance of 0° laminates in laminates, and the fatigue performance of 0° laminates in laminates is closely related to the fatigue performance of 0° unidirectional laminates. The SN curve of laminates is linked to the SN curve of 0° unidirectional laminates.

[0028] S p疲劳强度 =ηαS 0疲劳强度

[0029]

[0030] Using the building block test data, a parameter value α=0.17 with an envelope can be obtained.

[0031] The extended Tsai-Hill criterion is used to predict the fatigue life of one-way plates at any angle. The Tsai-Hill criterion is used to determine the failure of one-way plates under quasi-static loads, and its expression is:

[0032]

[0033] Where: It is the tensile or compressive strength of the unidirectional board along the fiber direction; It is the tensile or compressive strength of the unidirectional board along the direction perpendicular to the fiber; In-plane shear strength of the plate in the 1-2 direction.

[0034] Will As a function of fatigue cycle N, the above formula can be expanded to the failure criterion under fatigue load state:

[0035]

[0036] The layer-by-layer destruction method was used to perform fatigue analysis on composite materials with different ply ratios. The ply ratios of 0°, 45°, and 90° were changed respectively, and the parameter η value was calculated under different ply ratios. Considering the minimum ply ratio of 0°, the ply ratios of 0°, 45°, and 90° were 10%, 80%, and 10%, respectively, the parameter value η=0.17 with an envelope can be obtained.

[0037] The aging of carbon fiber performance is not affected much by the hot and humid environment, but mainly affects the aging of the matrix and the interface between the matrix and the fiber. Generally, the strength value of the composite material increases in the early stage of aging. This is mainly due to the post-curing cross-linking reaction of the resin matrix in the high-temperature aging environment, which improves the strength performance; in the middle stage of aging, the curing is basically complete and the strength no longer increases, but it is still higher than the strength value of the unaged sample. At this time, the post-curing cross-linking reaction of the composite material is better than the aging degradation effect; in the later stage, the plasticization degree of the material decreases, and the rigidity and brittleness increase, which causes the strength to decrease and stabilize. The Van't Hoff rule is used to conduct calendar life analysis, and a comprehensive evaluation of the reuse performance of aircraft composite structures is formed.

Claims

1. A method for evaluating the reuse performance of aircraft composite materials, characterized in that include: 1) Allowable value coverage design method based on building block test of composite materials; 2) Static and vibration fatigue key parts screening method based on aircraft structural strength analysis; 3) Fatigue analysis methods for aircraft composite structures; 4) Composite material structure life analysis method based on non-destructive testing; 5) Calendar life analysis method for composite structures.

2. The method for evaluating the reuse performance of aircraft composite material structures according to claim 1, characterized in that Includes a system of allowable values ​​for tension, compression, and mechanical connection design.

3. The method for evaluating the reuse performance of aircraft composite materials as described in any one of claims 1 or 2, wherein the structural design allowable value covers the composite material system used, the layup form, the environmental factors, the defect factors and the connection form.

4. The method for evaluating the reuse performance of aircraft composite materials as described in claim 1 or 2, wherein the composite material building block test includes an unnotched tensile and compression test, an open hole tensile and compression test, a filled hole tensile and compression test, a post-impact tensile and compression test, and a mechanical connection test.

5. The method for evaluating the reuse performance of aircraft composite material structures according to claim 1 or 2, characterized in that: The design allowable value includes data for different temperatures and moisture absorption states, where the temperature includes low temperature, room temperature and high temperature, and the moisture absorption state includes dry state and wet state.

6. The method for evaluating the reuse performance of aircraft composite material structures according to claim 5, characterized in that: The low temperature is -70 degrees. For epoxy resin composite materials, the high temperature is 150 degrees. For bismuth composite materials, the high temperature is 180 degrees. The dry state refers to the "manufacturing state", that is, after manufacturing, it is placed under laboratory atmospheric conditions without any moisture absorption treatment. The wet state requires special moisture absorption treatment, and the humidity is 85%.

7. The method for evaluating the reuse performance of aircraft composite materials as described in any one of claims 1 or 2, wherein nondestructive testing is performed on the composite material structure after flight to obtain the degree of damage to the composite material, the strength of the aircraft composite material structure is analyzed, the structural margin is sorted out, and the life design method is used for the structural area that does not cover the fatigue of static force, and the area with a residual strength coefficient of less than 1.5 is screened out as the fatigue key part for fatigue life analysis, and high-frequency vibration fatigue life analysis is performed on vibration-sensitive structures.

8. The method for evaluating the reuse performance of aircraft composite material structures according to claim 7, characterized in that: The layer-by-layer failure method was used to carry out fatigue analysis on composite materials with different ply ratios, and the ply ratios of 0°, 45°, and 90° were changed respectively.

9. The method for evaluating the reuse performance of aircraft composite material structures according to claim 1 or 2, characterized in that The extended Tsai-Hill criterion is used to predict the fatigue life of one-way plates with arbitrary angles.

10. The method for evaluating the reuse performance of aircraft composite material structures according to claim 1 or 2, characterized in that The calendar life analysis is carried out using the Van't Hoff rule to comprehensively form an evaluation of the reuse performance of aircraft composite materials structures.

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