A method for calculating crack propagation under axial load with bushing lug

Abstract

This invention belongs to the field of aircraft strength calculation technology and discloses a method for calculating crack propagation under axial load of a bushing lug. First, the lug parameters are determined. Based on the bushing type, a detailed finite element model of the bushing lug is established to obtain the stress level at the first corresponding lug. Then, detailed finite element models of different lug combinations are established to obtain the stress level at the second corresponding lug. The stress levels at the two corresponding lugs are then combined to obtain the corrected working stress for crack propagation analysis. Finally, crack propagation analysis is performed on the bushing lug. This invention introduces a lug bending coefficient by considering lug thickness and hole diameter, and also considers the increase in local stress caused by bolt bending. A bushing coefficient is introduced according to different bushing types, and the influence of the bushing on the stress in the lug hole is considered, thus improving the calculation accuracy and efficiency of crack propagation analysis.

Description

Technical Field

[0001] This invention belongs to the field of aircraft strength calculation technology, and relates to a method for calculating crack propagation in an aircraft structure with bushing lugs, specifically a method for calculating crack propagation under axial load in a structure with bushing lugs. Background Technology

[0002] Lug structures are widely used in the connection between various parts of an aircraft. The safety of the aircraft structure is determined to a certain extent by the safety of these lugs. Currently, crack propagation analysis does not consider the influence of different lugs and lug bending on crack propagation analysis under axial load, resulting in a dangerous situation in crack propagation calculation, which brings potential safety hazards to the aircraft. In addition, the traditional lug stress intensity factor is obtained by looking up charts, which is inefficient and inaccurate. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for calculating crack propagation under axial load on lugs containing bushings, which can be used for calculating crack propagation under axial load on aircraft structural lugs.

[0004] The technical solution of the present invention is as follows: A method for calculating crack propagation of a bushed lug under axial load is proposed. The method involves determining the lug parameters, establishing a detailed finite element model of the lug with bushing based on the type of bushing, obtaining the stress level at the first corresponding lug, and then establishing detailed finite element models for different combinations of lugs to obtain the stress level at the second corresponding lug. The stress levels at the two corresponding lugs are then combined to obtain the corrected working stress for crack propagation analysis. Finally, crack propagation analysis of the bushed lug is performed based on the NASRO software lug analysis model and lug material data.

[0005] Furthermore, the specific steps include: S1, determine the parameters of the ear piece, including the ear piece thickness, the diameter of the ear piece hole, and the axial and radial length of the initial damage angular crack; S2, based on the bushing type in the detailed finite element model containing the bushing lug, determine the bushing coefficient K2 as the stress level at the first corresponding lug; S3. Based on the detailed finite element model of different combinations of ear pieces, determine the bending coefficient K1 of the ear piece as the stress level at the second corresponding ear piece. S4. Determine the fracture performance data of the ear piece based on the material of the ear piece structure; S5, determine the random load spectrum or constant amplitude load spectrum corresponding to the ear structure, and obtain the working stress of the ear; S6. The bushing coefficient and bending coefficient are used as correction factors to correct the working stress of the lug. Then, based on the CC19 model of the lug hole corner crack in the NASGRO software, the lug fracture performance data determined in S4 are input to perform crack propagation analysis.

[0006] Furthermore, in S2, the bushing coefficient K2 is determined according to the bushing type of the ear piece. When the bushing of the ear piece is a shoulder bushing, K2=1, and when the bushing is a non-shoulder bushing, K2=1.2.

[0007] Furthermore, in S3, when the ear piece is a single ear piece, K1=1; when the ear piece is a forked ear piece, the value of K1 is obtained through the ear piece bending coefficient curve.

[0008] Furthermore, in S3, the stress level is obtained based on the detailed finite element model, and the ear bending coefficient of the fork ear structure is calculated under different ear hole diameters and different ear thickness coefficients. The curve composed of the ear bending coefficients of the fork ear structure under all different ear hole diameters and different ear thickness coefficients is the ear bending coefficient curve.

[0009] Furthermore, in S5, the working stress of the lug is S=P / (Dt), where D is the diameter of the lug hole, t is the thickness of the lug, and P is the load borne by the lug.

[0010] Furthermore, in S6, the working stress of the modified lug is: S=K1K2P / (Dt), where D is the diameter of the lug hole, t is the thickness of the lug, and P is the load borne by the lug.

[0011] Furthermore, in S6, the CC19 model is selected according to NASGRO. Based on the crack propagation direction, the crack propagation length is divided into axial crack propagation length a and radial crack propagation length c. Based on the stress intensity factor, crack propagation rate curve, and load spectrum corresponding to the crack, the crack propagation length under a single cycle is obtained. Then, the crack length under the entire random load spectrum or constant amplitude load spectrum is calculated to complete the crack propagation analysis.

[0012] The beneficial effects of this invention are as follows: 1. This invention provides a method for evaluating crack propagation under axial load of a bushing lug. By considering the lug thickness and hole size, a lug bending coefficient is introduced, and the increase in local stress of the lug caused by bolt bending is also taken into account. A bushing coefficient is introduced according to different bushing types, and the influence of the bushing on the stress of the lug hole is considered.

[0013] 2. This invention overcomes the risky consequences of calculation results caused by neglecting the type of lug bushing and the bending of the lug. Furthermore, by using the NAGOR analysis software, selecting the corresponding material and analysis model, and performing crack propagation analysis, the calculation accuracy and efficiency are improved. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this invention, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the ear piece in an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of the ear plate bending coefficient curve in an embodiment of the present invention.

[0017] Figure 3 This is a schematic diagram of the ear piece analysis model in an embodiment of the present invention.

[0018] Figure 4 This is a schematic diagram of the crack propagation curve in an embodiment of the present invention. Detailed Implementation

[0019] This section describes embodiments of the present invention, used to explain and illustrate the technical solutions of the present invention. Unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating directions or positional relationships, are given in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or device referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include more than one of those features. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integrated connections; they can refer to mechanical connections or point connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] Example 1: A method for calculating crack propagation of a bushed lug under axial load is proposed. The method involves determining the lug parameters, establishing a detailed finite element model of the lug with bushing based on the type of bushing, obtaining the stress level at the first corresponding lug, and then establishing detailed finite element models for different combinations of lugs to obtain the stress level at the second corresponding lug. The stress levels at the two corresponding lugs are then combined to obtain the corrected working stress for crack propagation analysis. Finally, crack propagation analysis of the bushed lug is performed based on the NASRO software lug analysis model and lug material data.

[0023] Specifically, the following steps are included: S1, determine the parameters of the ear piece, including the ear piece thickness, the diameter of the ear piece hole, and the axial and radial length of the initial damage angular crack; S2, based on the bushing type in the detailed finite element model containing the bushing lug, determine the bushing coefficient K2 as the stress level at the first corresponding lug; S3. Based on the detailed finite element model of different combinations of ear pieces, determine the bending coefficient K1 of the ear piece as the stress level at the second corresponding ear piece. S4. Determine the fracture performance data of the ear piece based on the material of the ear piece structure; S5, determine the random load spectrum or constant amplitude load spectrum corresponding to the ear structure, and obtain the working stress of the ear; S6. The bushing coefficient and bending coefficient are used as correction factors to correct the working stress of the lug. Then, based on the CC19 model of the lug hole corner crack in the NASGRO software, the lug fracture performance data determined in S4 are input to perform crack propagation analysis.

[0024] In S2, the bushing coefficient K2 is determined according to the bushing type of the ear piece. When the bushing of the ear piece is a shoulder bushing, K2=1, and when the bushing is a non-shoulder bushing, K2=1.2.

[0025] In S3, when the ear piece is a single ear piece, K1=1; when the ear piece is a forked ear piece, the value of K1 is obtained through the ear piece bending coefficient curve.

[0026] In S3, the stress level is obtained based on the detailed finite element model, and the ear bending coefficient of the fork ear structure is calculated under different ear hole diameters and different ear thickness coefficients. The curve composed of the ear bending coefficients of the fork ear structure under all different ear hole diameters and different ear thickness coefficients is the ear bending coefficient curve.

[0027] In S5, the working stress of the lug is S=P / (Dt), where D is the diameter of the lug hole, t is the thickness of the lug, and P is the load borne by the lug.

[0028] In S6, the working stress of the modified lug is: S=K1K2P / (Dt), where D is the diameter of the lug hole, t is the thickness of the lug, and P is the load borne by the lug.

[0029] In S6, the CC19 model is selected according to NASGRO. Based on the crack propagation direction, the crack propagation length is divided into axial crack propagation length a and radial crack propagation length c. Based on the stress intensity factor, crack propagation rate curve, and load spectrum corresponding to the crack, the crack propagation length under a single cycle is obtained. Then, the crack length under the entire random load spectrum or constant amplitude load spectrum is calculated to complete the crack propagation analysis.

[0030] Example 2: Based on different bushing types—shouldered bushings and non-shouldered bushings—detailed finite element models were established to obtain the stress levels at the corresponding lugs and determine the bushing coefficients. Specifically, the stress on the lug hole compressive stress of different bushing types (shouldered and non-shouldered) was studied using finite element models to obtain the lug coefficient, which represents the influence of the bushing on the lug stress; it is suggested to modify this to a bushing coefficient. The lug bending coefficient, based on the fork lug structure, studies the influence of thickness bending on the lug hole stress under different thicknesses t and lug hole diameters D.

[0031] Detailed finite element models of different combinations of ear thickness t and ear hole diameter D were established to obtain the stress level of the ear hole, determine the ear bending coefficient, and finally give the working stress for ear crack propagation analysis. Based on the NASRO ear analysis model and relevant data of ear material, crack propagation analysis was performed.

[0032] The method for evaluating crack propagation under axial load with bushing lugs is based on the aircraft lug structure and a detailed finite element model.

[0033] A method for evaluating crack propagation under axial load on a bushing lug is proposed, which obtains the stress level of the corresponding lug, S = P / (Dt), where P is the axial load on the lug, D is the diameter of the lug hole, and t is the thickness of the lug.

[0034] Specifically, the ear plate stress was obtained based on different combinations of ear plate thickness t and ear plate hole diameter D. The ear plate bending coefficient K1 was obtained based on the variation law of the t / D coefficient. The stress level was obtained based on the detailed finite element model, and the ear plate bending coefficient of the fork ear structure under different t / D coefficients was calculated.

[0035] The described method for evaluating crack propagation under axial load on lugs with bushings establishes detailed finite element models for lugs of the same size, with and without bushings, for different conditions. The stress at the lug hole is obtained, and the bushing coefficient K2 is calculated by comparing the stress level of the bushing-bearing detail with that of the lug without bushings. When the bushing is a shoulder bushing, K2 = 1; when the bushing is a non-shoulder bushing, K2 = 1.2. The corresponding coefficient is obtained by comparing the stress level of the lug with a shoulder bushing with that of the lug of the same size without bushings, and the same applies to non-shoulder bushings. The shoulder bushing can locally reduce the stress in the lug hole.

[0036] A method for evaluating crack propagation under axial load on lugs with bushings, based on fracture performance data of lug materials from NASGRO.

[0037] A method for evaluating crack propagation under axial load with bushing lugs is based on the constant amplitude / random spectrum corresponding to the modified stress S=K1K2P / (Dt) at the lug of the aircraft structure.

[0038] A method for evaluating crack propagation under axial load with bushing lugs is proposed, based on the NASGRO CC19 model for corner cracks in lug holes, to analyze crack propagation. Where: W is the lug width, D is the lug hole diameter, and a and c represent the dimensions corresponding to the initial damage corner crack.

[0039] The above technical solution is described in steps, as follows: Step 1: Determine the relevant parameters of the ear piece, including the ear piece aperture D, ear piece thickness t, and initial damage angle cracks a and c; Step 2: Determine the bending coefficient K1 under this ear structure. When the ear is a single ear, K1=1. When the ear is a forked ear, refer to the ear bending coefficient curve. Step 3: Determine the bushing coefficient K2 based on the selected bushing type; Step 4: Determine the corresponding fracture performance data based on the material corresponding to the ear plate structure; Step 5: Determine the random / constant amplitude load spectrum corresponding to the ear structure, and calculate the working stress according to S=P / (Dt); Step 6: Determine the working stress of the ear piece correction S=K1K2P / (Dt), where the amplification factor of the random load spectrum or constant amplitude load spectrum is K=K1K2.

[0040] Step 7: Assuming the crack is a corner crack in the lug hole, select the CC19 model according to NASGRO. The corner crack is divided into two crack propagation directions, a and c. Based on the stress intensity factor, crack propagation rate curve, and load spectrum corresponding to the crack, obtain the crack propagation length under a single cycle, and then calculate the crack length under the entire random / constant amplitude load spectrum to complete the crack propagation analysis. Obtain the change of crack with the number of load cycles, that is, obtain the crack propagation curve; The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention shall still fall within the scope of the invention.

Claims

1. A method for calculating crack propagation under axial load with bushing lugs, characterized in that, The parameters of the lug are determined, and a detailed finite element model of the lug with bushing is established according to the type of bushing. The stress level at the first type of lug is obtained, and then detailed finite element models of different combinations of lugs are established to obtain the stress level at the second type of lug. The stress levels at the two types of lugs are then combined to obtain the corrected working stress for crack propagation analysis of the lug. Finally, crack propagation analysis of the lug with bushing is performed based on the lug analysis model and lug material data from NASRO software.

2. The method for calculating crack propagation under axial load with bushing lugs according to claim 1, characterized in that, Specifically, the following steps are included: S1, determine the parameters of the ear piece, including the ear piece thickness, the diameter of the ear piece hole, and the axial and radial length of the initial damage angular crack; S2, based on the bushing type in the detailed finite element model containing the bushing lug, determine the bushing coefficient K2 as the stress level at the first corresponding lug; S3. Based on the detailed finite element model of different combinations of ear pieces, determine the bending coefficient K1 of the ear piece as the stress level at the second corresponding ear piece. S4. Determine the fracture performance data of the ear piece based on the material of the ear piece structure; S5, determine the random load spectrum or constant amplitude load spectrum corresponding to the ear structure, and obtain the working stress of the ear; S6. The bushing coefficient and bending coefficient are used as correction factors to correct the working stress of the lug. Then, based on the CC19 model of the lug hole corner crack in the NASGRO software, the lug fracture performance data determined in S4 are input to perform crack propagation analysis.

3. The method for calculating crack propagation under axial load with bushing lugs according to claim 2, characterized in that, In S2, the bushing coefficient K2 is determined according to the bushing type of the ear piece. When the bushing of the ear piece is a shoulder bushing, K2=1, and when the bushing is a non-shoulder bushing, K2=1.

2.

4. The method for calculating crack propagation under axial load with bushing lugs according to claim 2, characterized in that, In S3, when the ear piece is a single ear piece, K1=1; when the ear piece is a forked ear piece, the value of K1 is obtained through the ear piece bending coefficient curve.

5. The method for calculating crack propagation under axial load with bushing lugs according to claim 4, characterized in that, In S3, the stress level is obtained based on the detailed finite element model, and the ear bending coefficient of the fork ear structure is calculated under different ear hole diameters and different ear thickness coefficients. The curve composed of the ear bending coefficients of the fork ear structure under all different ear hole diameters and different ear thickness coefficients is the ear bending coefficient curve.

6. The method for calculating crack propagation under axial load with bushing lugs according to claim 2, characterized in that, In S5, the working stress of the lug is S=P / (Dt), where D is the diameter of the lug hole, t is the thickness of the lug, and P is the load borne by the lug.

7. The method for calculating crack propagation under axial load with bushing lugs according to claim 2, characterized in that, In S6, the working stress of the modified lug is: S=K1K2P / (Dt), where D is the diameter of the lug hole, t is the thickness of the lug, and P is the load borne by the lug.

8. The method for calculating crack propagation under axial load with bushing lugs according to claim 2, characterized in that, In S6, the CC19 model is selected according to NASGRO. Based on the crack propagation direction, the crack propagation length is divided into axial crack propagation length a and radial crack propagation length c. Based on the stress intensity factor, crack propagation rate curve, and load spectrum corresponding to the crack, the crack propagation length under a single cycle is obtained. Then, the crack length under the entire random load spectrum or constant amplitude load spectrum is calculated to complete the crack propagation analysis.

Images