Anti-fatigue design method for auxiliary frame structure

Abstract

The invention belongs to the technical field of aircraft structure strength, and particularly relates to an anti-fatigue design method for an auxiliary frame structure. Comprising the steps of 1, obtaining a damaged auxiliary frame structure, and performing damage reason analysis on the damaged auxiliary frame structure; 2, determining an improvement scheme, and evaluating the improvement scheme; and step 3, carrying out test verification on the improved scheme. According to the anti-fatigue design method for the auxiliary frame structure, the structure damage reason analysis technology, the improved scheme evaluation technology and the test verification technology are fused, the stress concentration at the auxiliary frame stringer through hole is improved after the R angle of the stringer through hole is increased and changed, the maximum stress value at the hole opening position is also remarkably reduced after the height of the auxiliary frame is increased, and the anti-fatigue performance of the auxiliary frame structure is improved. And meanwhile, the rigidity of the hole of the auxiliary frame is increased, so that the whole auxiliary frame deforms more harmoniously under the airtight load, excessive deformation interference of the stringer and the auxiliary frame through holes is avoided, and the final scheme of the auxiliary frame meets the technical requirements of anti-fatigue design.

Description

Technical Field

[0001] This application belongs to the field of aircraft structural strength technology, and specifically relates to a fatigue-resistant design method for auxiliary frame structures. Background Technology

[0002] The auxiliary frame's stringer through-holes and other parts frequently exhibited premature cracking and other fatigue damage, severely impacting the test progress and aircraft operational safety. Based on the actual load conditions of this part during testing and a comparison of test data of the surrounding structure before and after the cracking of the auxiliary frame's stringer through-holes, it was decided to implement a structural fatigue resistance improvement design for the auxiliary frame.

[0003] Therefore, there is an urgent need for a technical solution to overcome or mitigate at least one of the aforementioned defects in the existing technology. Summary of the Invention

[0004] The purpose of this application is to provide a fatigue-resistant design method for auxiliary frame structures to solve the problem of premature damage to auxiliary frame structures and insufficient service life in the prior art.

[0005] The technical solution of this application is:

[0006] A fatigue-resistant design method for auxiliary frame structures includes:

[0007] Step 1: Obtain the damaged auxiliary frame structure and analyze the cause of damage to the damaged auxiliary frame structure;

[0008] Step 2: Determine the improvement plan and evaluate it.

[0009] Step 3: Conduct experimental verification of the improved scheme.

[0010] In at least one embodiment of this application, step one involves analyzing the cause of damage to the damaged auxiliary frame structure, including:

[0011] A macroscopic inspection was performed on the damaged auxiliary frame structure to determine the damaged areas;

[0012] The damaged auxiliary frame structure was stress-checked using finite element analysis to determine the location of maximum stress.

[0013] The cause of the damage is determined based on the damaged area and the location of the maximum stress.

[0014] In at least one embodiment of this application, the damage is caused by stress concentration due to repeated tensile loads superimposed on the stringer through the hole structure.

[0015] In at least one embodiment of this application, step two, determining an improvement scheme and evaluating the improvement scheme, includes:

[0016] Determine improvement directions based on the causes of the damage;

[0017] Determine the improvement plan based on the described improvement direction;

[0018] The improved scheme was stress-checked using finite element analysis to determine whether it met the design life requirements of the auxiliary frame.

[0019] In at least one embodiment of this application, the improvement is to enhance the fatigue resistance of the stringer through-hole.

[0020] In at least one embodiment of this application, the improvement is to increase the radius (R-angle) of the long stringer through hole and / or increase the height of the auxiliary frame based on the initial solution.

[0021] In at least one embodiment of this application, the improved scheme includes a first improved scheme, wherein the radius of the R-angle of the long stringer through hole in the first improved scheme is r, and the height of the auxiliary frame is H0+Δ2, wherein r is the radius of the R-angle of the long stringer through hole in the initial scheme, H0 is the height of the auxiliary frame in the initial scheme, and Δ2 is the height increment of the auxiliary frame.

[0022] In at least one embodiment of this application, the improved scheme includes a second improved scheme, wherein the radius of the R-angle of the long stringer through hole in the second improved scheme is r+Δ1, and the height of the auxiliary frame is H0, wherein r is the radius of the R-angle of the long stringer through hole in the initial scheme, Δ1 is the increment of the radius of the R-angle of the long stringer through hole, and H0 is the height of the auxiliary frame in the initial scheme.

[0023] In at least one embodiment of this application, the improved scheme includes a third improved scheme, wherein the radius of the R-angle of the long girder through hole in the third improved scheme is r+Δ1, and the height of the auxiliary frame is H0+Δ2, wherein r is the radius of the R-angle of the long girder through hole in the initial scheme, Δ1 is the increment of the radius of the R-angle of the long girder through hole, H0 is the height of the auxiliary frame in the initial scheme, and Δ2 is the increment of the height of the auxiliary frame.

[0024] In at least one embodiment of this application, the improved scheme includes a fourth improved scheme, wherein the radius of the R-angle of the long stringer through hole in the fourth improved scheme is r+Δ1, a part of the auxiliary frame height is H0, and another part of the auxiliary frame height is H0+Δ2, wherein r is the radius of the R-angle of the long stringer through hole in the initial scheme, Δ1 is the increment of the radius of the R-angle of the long stringer through hole, H0 is the height of the auxiliary frame in the initial scheme, and Δ2 is the increment of the auxiliary frame height.

[0025] In at least one embodiment of this application, step three involves experimental verification of the improved solution, including:

[0026] Component testing was conducted on the improved scheme;

[0027] Repair of testing machine;

[0028] The improved design was tested on a full-machine assembly.

[0029] The invention has at least the following beneficial technical effects:

[0030] The fatigue-resistant design method for the auxiliary frame structure in this application integrates structural damage cause analysis technology, improvement scheme evaluation technology, and experimental verification technology. By increasing the radius (R) of the long stringer through hole, the stress concentration at the long stringer through hole of the auxiliary frame is improved. Increasing the height of the auxiliary frame also significantly reduces the maximum stress value at the opening and increases the stiffness at the opening of the auxiliary frame. This makes the deformation of the entire auxiliary frame more coordinated under airtight load and avoids excessive deformation interference between the long stringer and the through hole of the auxiliary frame. The final auxiliary frame design meets the fatigue-resistant design technical requirements. Attached Figure Description

[0031] Figure 1 This is a flowchart of a fatigue-resistant design method for a secondary frame structure according to one embodiment of this application;

[0032] Figure 2 This is a schematic diagram of the initial design of the auxiliary frame structure according to one embodiment of this application;

[0033] Figure 3 This is a schematic diagram of the initial scheme model of the auxiliary frame structure of one embodiment of this application;

[0034] Figure 4 This is a schematic diagram of the stress distribution of the initial design of the auxiliary frame structure according to one embodiment of this application;

[0035] Figure 5 This is a schematic diagram of an improved auxiliary frame structure according to one embodiment of this application;

[0036] Figure 6 This is a schematic diagram of an improved auxiliary frame structure according to one embodiment of this application;

[0037] Figure 7 This is a schematic diagram of stress distribution in an improved auxiliary frame structure according to one embodiment of this application. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0039] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this application.

[0040] The following is in conjunction with the appendix Figures 1 to 7 This application will be described in further detail.

[0041] This application provides a fatigue-resistant design method for auxiliary frame structures, such as... Figure 1 As shown, it includes the following steps:

[0042] Step 1: Obtain the damaged auxiliary frame structure and analyze the cause of damage to the damaged auxiliary frame structure;

[0043] Step 2: Determine the improvement plan and evaluate it.

[0044] Step 3: Conduct experiments to verify the improved plan.

[0045] Specifically, firstly, in step one, the damage causes of the damaged auxiliary frame structure are analyzed, including:

[0046] A macroscopic inspection of the damaged auxiliary frame structure is conducted to determine the location of the damage; the macroscopic inspection includes force transmission analysis and deformation inspection.

[0047] The location of maximum stress was determined by stress examination of the damaged auxiliary frame structure using finite element analysis.

[0048] The cause of the damage is determined based on the location of the damaged area and the location of the greatest stress.

[0049] In one embodiment of this application, such as Figure 2-4 As shown, through macroscopic inspection of the initial design of the damaged auxiliary frame structure, an initial design model was constructed and finite element calculations were performed. The results showed that the damaged area was located at the girder through-hole, with the maximum stress located near the R-zone below the girder through-hole. In this embodiment, the damage was caused by repeated tensile loads combined with stress concentration in the girder through-hole structure. Based on the comprehensive damage investigation and the above analysis and calculations, it can be basically determined that the damage to the inter-frame auxiliary frame was caused by multiple factors, including high stress levels at the auxiliary frame opening, improper design of the girder through-hole R-angle, and insufficient stiffness of the auxiliary frame at the opening notch. The high stress concentration at the opening R-angle, coupled with a sudden change in auxiliary frame stiffness, caused deformation and continuous contact between the notch edge and the girder under airtight load, ultimately leading to premature cracking of the auxiliary frame opening edge.

[0050] Secondly, in step two, the improvement plan is determined and evaluated, including:

[0051] Determine improvement directions based on the cause of the damage;

[0052] Determine improvement plans based on the direction of improvement;

[0053] The improved scheme was stress-checked using finite element analysis to determine whether it met the design life requirements of the auxiliary frame.

[0054] In one embodiment of this application, the improvement direction is determined based on the cause of damage to improve the fatigue resistance of the girder through-hole. The improvement scheme is to increase the radius (R-angle) of the girder through-hole and / or increase the height of the auxiliary frame based on the initial scheme. Specifically, in this embodiment, the improvement scheme includes a first improvement scheme, a second improvement scheme, a third improvement scheme, and a fourth improvement scheme. In the first improvement scheme, the radius of the radius (R-angle) of the girder through-hole is r, and the height of the auxiliary frame is H0+Δ2; in the second improvement scheme, the radius of the radius (R-angle) of the girder through-hole is r+Δ1, and the height of the auxiliary frame is H0; in the third improvement scheme, the radius of the radius (R-angle) of the girder through-hole is r+Δ1, and the height of the auxiliary frame is H0+Δ2; in the fourth improvement scheme, the radius of the radius (R-angle) of the girder through-hole is r+Δ1, part of the auxiliary frame height is H0, and the other part of the auxiliary frame height is H0+Δ2; r is the radius (R-angle) of the girder through-hole in the initial scheme, Δ1 is the increment of the radius (R-angle) of the girder through-hole, H0 is the height of the auxiliary frame in the initial scheme, and Δ2 is the increment of the auxiliary frame height.

[0055] In this embodiment, the various improvement schemes are shown in Table 1. An improvement scheme model is constructed, and stress checks are performed on the improvement schemes using finite element analysis. Figure 5-7 As shown.

[0056] Table 1

[0057]

[0058] In one embodiment of this application, in the initial scheme, the radius of the R-angle of the girder through hole in the auxiliary frame structure is r, the frame height is H0, and the fatigue life of the initial scheme is n rises and falls. Under the same working conditions, constraints, and materials, stress analysis and life assessment were performed on different improvement schemes in Table 1. Among them, stress analysis and life assessment were performed on improvement scheme 2 in Table 1. After the radius of the R-angle of the girder through hole in the auxiliary frame structure was changed to 10mm, the frame height remained unchanged. The maximum stress value obtained through stress analysis is shown in Table 1. The fatigue life after the R-angle of the girder through hole was estimated. The DFR value of the structure before and after the change was calculated according to the notch fillet radius DFR curve. Based on the DFR value after the radius of the girder through hole was changed, the fatigue life N0 of the improved auxiliary frame structure can be obtained according to the standard S_N curve equation, which does not meet the fatigue life requirement.

[0059] Furthermore, stress analysis and life assessment were performed on improvement scheme 4 in Table 1. After changing the radius of the hole in the girder of the auxiliary frame structure to 10mm, the height of some frames was increased by 5mm. Comparing the finite element stress analysis results, it can be seen that partially increasing the height of the auxiliary frames between frames can effectively reduce its maximum principal stress, proving that the improvement scheme is feasible. According to improvement scheme 4 in Table 1, the maximum stress after partially increasing the frame height by 5mm is 287MPa; given the DFR value and the maximum stress, the number of takeoffs and landings N1 was calculated based on the standard SN curve equation, which meets the design life requirements of the auxiliary frame.

[0060] In the fatigue-resistant design method for the auxiliary frame structure of this application, step three involves experimental verification of the improved scheme, including:

[0061] Component testing was conducted on the improved design;

[0062] Repair of testing machine;

[0063] The improved design was tested on the entire machine.

[0064] The fatigue-resistant design method for the auxiliary frame structure presented in this application has been verified in relevant experiments and has been applied in engineering. After increasing the radius (R-angle), the stress concentration at the through-hole of the auxiliary frame stringer is improved. Increasing the height of the auxiliary frame also significantly reduces the maximum stress value at the opening and simultaneously increases the stiffness at the opening, making the deformation of the entire auxiliary frame more coordinated under airtight loads. At the same time, it avoids excessive deformation interference between the stringer and the through-hole of the auxiliary frame. The auxiliary frame structure with improved fatigue resistance design meets the fatigue design requirements.

[0065] The fatigue-resistant design method for the auxiliary frame structure proposed in this application can improve the fatigue performance of the auxiliary frame structure, ensure aircraft safety, reduce aircraft operating risks, prevent premature damage to the auxiliary frame structure, and extend the service life of the auxiliary frame.

[0066] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A fatigue-resistant design method for an auxiliary frame structure, characterized in that, include: Step 1: Obtain the damaged auxiliary frame structure and analyze the cause of damage to the damaged auxiliary frame structure; Step 2: Determine the improvement plan and evaluate it. Step 3: Conduct experimental verification of the improved scheme.

2. The fatigue-resistant design method for the auxiliary frame structure according to claim 1, characterized in that, Step one involves analyzing the causes of damage to the damaged auxiliary frame structure, including: A macroscopic inspection was performed on the damaged auxiliary frame structure to determine the damaged areas; The damaged auxiliary frame structure was stress-checked using finite element analysis to determine the location of maximum stress. The cause of the damage is determined based on the damaged area and the location of the maximum stress.

3. The fatigue-resistant design method for the auxiliary frame structure according to claim 2, characterized in that, The damage was caused by repeated tensile loads combined with stress concentration in the long stringer through the hole structure, leading to failure.

4. The fatigue-resistant design method for the auxiliary frame structure according to claim 3, characterized in that, Step two involves identifying improvement plans and evaluating them, including: Determine improvement directions based on the causes of the damage; Determine the improvement plan based on the described improvement direction; The improved scheme was stress-checked using finite element analysis to determine whether it met the design life requirements of the auxiliary frame.

5. The fatigue-resistant design method for the auxiliary frame structure according to claim 4, characterized in that, The improvement direction is to enhance the fatigue resistance of the stringer through-holes.

6. The fatigue-resistant design method for the auxiliary frame structure according to claim 5, characterized in that, The improved scheme is to increase the radius (R-angle) of the long stringer through hole and / or increase the height of the auxiliary frame, based on the initial scheme.

7. The fatigue-resistant design method for the auxiliary frame structure according to claim 6, characterized in that, The improvement scheme includes a first improvement scheme, in which the radius of the R-angle of the long stringer through hole in the first improvement scheme is r, and the height of the auxiliary frame is H0+Δ2, where r is the radius of the R-angle of the long stringer through hole in the initial scheme, H0 is the height of the auxiliary frame in the initial scheme, and Δ2 is the height increment of the auxiliary frame.

8. The fatigue-resistant design method for the auxiliary frame structure according to claim 6, characterized in that, The improved scheme includes a second improved scheme, in which the radius of the R-angle of the long girder through hole is r+Δ1 and the height of the auxiliary frame is H0, where r is the radius of the R-angle of the long girder through hole in the initial scheme, Δ1 is the increment of the R-angle of the long girder through hole, and H0 is the height of the auxiliary frame in the initial scheme.

9. The fatigue-resistant design method for the auxiliary frame structure according to claim 6, characterized in that, The improved scheme includes a third improved scheme, in which the radius of the R-angle of the long girder through hole is r+Δ1 and the height of the auxiliary frame is H0+Δ2, where r is the radius of the R-angle of the long girder through hole in the initial scheme, Δ1 is the increment of the radius of the R-angle of the long girder through hole, H0 is the height of the auxiliary frame in the initial scheme, and Δ2 is the increment of the height of the auxiliary frame.

10. The fatigue-resistant design method for the auxiliary frame structure according to claim 6, characterized in that, The improved scheme includes a fourth improved scheme, in which the radius of the R-angle of the long girder through hole is r+Δ1, the height of one part of the auxiliary frame is H0, and the height of another part of the auxiliary frame is H0+Δ2, where r is the radius of the R-angle of the long girder through hole in the initial scheme, Δ1 is the increment of the radius of the R-angle of the long girder through hole, H0 is the height of the auxiliary frame in the initial scheme, and Δ2 is the increment of the height of the auxiliary frame.

11. The fatigue-resistant design method for the auxiliary frame structure according to claim 6, characterized in that, Step three involves testing and verifying the improved solution, including: Component testing was conducted on the improved scheme; Repair of testing machine; The improved design was tested on a full-machine assembly.

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