A composite material outer duct engine case failure prediction method

Abstract

The application provides a composite material outer channel nacelle failure prediction method, comprising the following steps: ① adding main layers: according to the structure of the outer channel nacelle, main and auxiliary layers are arranged on the stress surface of the outer channel nacelle based on load proportion; ② adding additional auxiliary layers: according to the structure of the outer channel nacelle, additional auxiliary layers are arranged on the surface of the main and auxiliary layers; ③ nacelle strength calculation: the static strength of the nacelle is calculated under working load by adopting finite element simulation, and the maximum equivalent strain of the nacelle is calculated; ④ additional auxiliary layer load calculation; and ⑤ main and auxiliary layer failure calculation. The application can predict the fracture failure behavior of the composite material, take fracture as the criterion for the failure of the composite material outer channel nacelle, fully utilize the mechanical properties of the composite material, reduce the wall thickness of the composite material outer channel nacelle, and further realize the weight reduction effect of the composite material outer channel nacelle.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite material outer duct case failure prediction method. BACKGROUND

[0002] Composite materials belong to orthotropic anisotropic materials, have high specific strength, high specific stiffness and strong designability, are widely used in aerospace and other fields, and have good weight reduction effect. The outer duct case mainly bears the action of internal pressure load and axial force load, the principal stress direction of the working state remains basically unchanged, and the use of composite materials for design has great advantages. At present, a large number of aeroengines use composite materials to design the outer duct case. Composite materials are brittle materials, and there is no obvious sign before fracture failure occurs. Therefore, it is necessary to predict the failure of the composite material outer duct case.

[0003] In order to avoid the fracture failure of the composite material outer duct case in work, the commonly used method at present is to carry out nondestructive testing on the composite material outer duct case, and the specific steps are as follows:

[0004] 1. The initial defect of the composite material case is measured by using a nondestructive testing method;

[0005] 2. The initiation and expansion of the defect are measured periodically by using a nondestructive testing method;

[0006] The nondestructive testing method can detect the initiation and expansion of the defect of the composite material outer duct case. The defect may have little effect on the residual strength of the composite material outer duct case. Although the defect can be used as a criterion for the failure of the composite material outer duct case, the wall thickness of the composite material outer duct case needs to be increased, and the fracture failure reserve is usually 10-50, which leads to an insignificant weight reduction effect and does not play the advantages of composite materials. SUMMARY

[0007] To solve the above technical problems, the present application provides a composite material outer duct case failure prediction method, which can predict the fracture failure behavior of the composite material by using the mechanical properties of the composite material, and use the fracture as a criterion for the failure of the composite material outer duct case.

[0008] The present application is realized by the following technical solutions.

[0009] The present application provides a composite material outer duct case failure prediction method, which comprises the following steps:

[0010] ① Adding main plies: according to the structure of the outer duct case, setting main and auxiliary layers based on load proportion on the stress surface of the outer duct case;

[0011] ② Adding additional auxiliary layer: according to the structure of the outer casing, an additional auxiliary layer is arranged on the surface of the main auxiliary layer;

[0012] ③ Casing strength calculation: the static strength of the casing under the working load is calculated by using finite element simulation, and the maximum equivalent strain of the casing is calculated accordingly;

[0013] ④ Additional auxiliary layer load calculation: finite element simulation is used to solve the failure load of the additional auxiliary layer through parameterized design;

[0014] ⑤ Main auxiliary layer failure calculation: finite element simulation is used to solve the failure load of the main auxiliary layer through parameterized design.

[0015] Solving the failure load of the additional auxiliary layer is to take the load as a design variable, and take the maximum equivalent strain of the casing as a target function, when the target function is equal to the fracture strain of the additional auxiliary layer material, the corresponding load is the failure load of the additional auxiliary layer.

[0016] Solving the failure load of the main auxiliary layer is to take the load as a design variable, and take the maximum equivalent strain of the casing as a target function, when the target function is equal to the fracture strain of the main auxiliary layer material, the corresponding load is the failure load of the additional auxiliary layer.

[0017] After step ⑤, it also includes the step

[0018] ⑥ Load proportion checking: the proportional relationship of the working load, the failure load of the additional auxiliary layer and the failure load of the main auxiliary layer is checked, if the proportional relationship of the working load, the failure load of the additional auxiliary layer and the failure load of the main auxiliary layer does not meet the proportion setting, return to step ①.

[0019] The proportion setting is:

[0020] The working load is less than the failure load of the additional auxiliary layer, and the failure load of the additional auxiliary layer is less than the failure load of the main auxiliary layer, and,

[0021] 2.0<working load<additional auxiliary layer failure load, and,

[0022] 2.0<additional auxiliary layer failure load<main auxiliary layer failure load.

[0023] The performance of the additional auxiliary layer is weaker than that of the main auxiliary layer.

[0024] The finite element simulation uses Ansys Workbench.

[0025] In step ②, the cross-section connection performance between the additional auxiliary layer and the main auxiliary layer is also selected to ensure that the additional auxiliary layer and the main auxiliary layer are delaminated when the additional auxiliary layer fails.

[0026] The present application has the beneficial effect that the fracture failure behavior of the composite material can be predicted, the fracture is taken as the criterion for failure of the composite material outer duct nacelle, the mechanical properties of the composite material can be fully utilized, the wall thickness of the composite material outer duct nacelle is reduced, and the weight reduction effect of the composite material outer duct nacelle is realized. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a flowchart of at least one embodiment of the present application;

[0028] Figure 2 is a schematic diagram of the auxiliary layer structure in the present application;

[0029] Figure 3 is a schematic diagram of the load strain data in one embodiment of the present application. DETAILED DESCRIPTION

[0030] The technical solutions of the present application are further described below, but the scope of protection is not limited to the description.

[0031] Example 1

[0032] As shown in Figures 1 to 2 a composite material outer duct nacelle failure prediction method, characterized in that it comprises the following steps:

[0033] ① Add main plies: according to the structure of the outer duct nacelle, set the main and auxiliary layers on the stress surface of the outer duct nacelle based on the load ratio;

[0034] ② Add additional auxiliary layers: according to the structure of the outer duct nacelle, set additional auxiliary layers on the surface of the main and auxiliary layers;

[0035] ③ Calculate the strength of the nacelle: calculate the static strength of the nacelle under working load by finite element simulation, and calculate the maximum equivalent strain of the nacelle;

[0036] ④ Calculate the load of the additional auxiliary layers: use finite element simulation to solve the failure load of the additional plies by parameterized design;

[0037] ⑤ Calculate the failure of the main and auxiliary layers: use finite element simulation to solve the failure load of the main plies by parameterized design.

[0038] Example 2

[0039] Based on example 1, the solving of the failure load of the additional plies is to take the load as the design variable, and the maximum equivalent strain of the nacelle as the objective function, when the objective function is equal to the fracture strain of the additional plies, the corresponding load is the failure load of the additional plies.

[0040] Example 3

[0041] Based on the embodiment 1, the solving of the main layer failure load is to take the load as a design variable, and take the maximum equivalent strain of the casing as a target function. When the target function is equal to the main layer material fracture strain, the corresponding load is the additional layer failure load.

[0042] Embodiment 4

[0043] Based on the embodiment 1, after the step ⑤, it further includes a step

[0044] ⑥ Load proportion checking: the proportional relationship of the working load, the additional layer failure load and the main layer failure load is checked. If the proportional relationship of the working load, the additional layer failure load and the main layer failure load does not meet the proportion setting, it returns to the step ①.

[0045] Embodiment 5

[0046] Based on the embodiment 4, the proportion setting is:

[0047] The working load < the additional layer failure load < the main layer failure load, and,

[0048] 2.0 < the working load < the additional layer failure load, and,

[0049] 2.0 < the additional layer failure load < the main layer failure load.

[0050] Embodiment 6

[0051] Based on the embodiment 1, the additional layer performance is weaker than the main auxiliary layer.

[0052] Embodiment 7

[0053] Based on the embodiment 1, the finite element simulation adopts Ansys Workbench.

[0054] Embodiment 8

[0055] Based on the embodiment 1, in the step ②, the cross-section connection performance between the additional layer and the main layer is also selected to ensure that the connection interface between the additional layer and the main layer is delaminated when the additional layer fails.

[0056] Embodiment 9

[0057] Based on the above embodiments, the specific steps are as follows:

[0058] 1. Main layer design: according to the structure of the outer rotor casing and the main layer material selection, the main layer design is carried out; according to the load proportion of each direction, the layer proportion is set, the layer direction can be selected as 0°, 45°, 90° and 135°, and the thickness direction is set as symmetric layer.

[0059] 2. Additional layer design: according to the selection of additional layer material, an additional layer with weaker performance is added to the outer surface of the main layer, and the appropriate cross-section connection performance is selected, so that after the failure of the additional layer, the interface delamination between the additional layer and the main layer occurs, and stress concentration in the main layer is avoided.

[0060] 3. Casing static strength calculation: the finite element software Ansys Workbench is used to carry out the static strength calculation of the casing under the working load P1, and the maximum equivalent strain ε1 of the casing is calculated, which corresponds to Figure 3 point A in the middle;

[0061] 4. Additional layer failure load calculation: the additional layer failure load P2 is solved by parameterized design in the software Ansys Workbench, taking the load P as the design variable and the maximum strain ε of the casing as the objective function, and setting the objective function ε equal to the fracture strain ε 1t of the additional layer material, and the failure load P2 of the casing additional layer is solved, which corresponds to Figure 3 point B in the middle.

[0062] 5. Main layer failure load calculation: the main layer failure load P3 is solved by parameterized design in the software Ansys Workbench, and the load P is also taken as the design variable, and the maximum strain ε of the casing is taken as the objective function, and the objective function ε is set to be equal to the fracture strain ε 2t of the main layer material, and the failure load P3 of the main layer of the casing is solved, which corresponds to Figure 3 point C in the middle.

[0063] 6. Load proportion check: the relationship among the loads P1, P2 and P3 is checked, firstly P1 < P2 < P3 should be ensured, secondly P2 / P1 > 2.0 should be ensured, and finally P3 / P2 > 2.0 should be ensured. If the load proportion does not meet the requirements, repeat steps 1-5 to redesign, and when the load proportion meets the requirements, the final result is obtained.

Claims

1. A method of composite over-duct engine case failure prediction, the method comprising: The method comprises the following steps: ​ ①adding a main ply: according to the structure of the outer casing, a main ply is arranged on the stress surface of the outer casing based on the load proportion; ②adding an additional ply: according to the structure of the outer casing, an additional ply is arranged on the surface of the main ply; ③calculating the strength of the casing: the static strength of the casing under the working load is calculated by using finite element simulation, and the maximum equivalent strain of the casing is calculated accordingly; ④calculating the load of the additional ply: the failure load of the additional ply is solved by parameterized design through finite element simulation; ⑤calculating the failure load of the main ply: the failure load of the main ply is solved by parameterized design through finite element simulation; the failure load of the additional ply is solved by taking the load as a design variable and taking the maximum equivalent strain of the casing as a target function, and when the target function is equal to the fracture strain of the additional ply, the corresponding load is the failure load of the additional ply; the failure load of the main ply is solved by taking the load as a design variable and taking the maximum equivalent strain of the casing as a target function, and when the target function is equal to the fracture strain of the main ply, the corresponding load is the failure load of the additional ply.

2. The composite exhaust nozzle failure prediction method of claim 1, wherein: After step ⑤, the method further comprises the following step: ⑥checking the load proportion: the proportional relationship of the working load, the failure load of the additional ply and the failure load of the main ply is checked, and if the proportional relationship of the working load, the failure load of the additional ply and the failure load of the main ply does not meet the proportion setting, the method returns to step ①.

3. The composite exhaust nozzle failure prediction method of claim 2, wherein: the proportion setting is: working load < failure load of additional ply < failure load of main ply, and, 2.0 < working load < failure load of additional ply, and, 2.0 < failure load of additional ply < failure load of main ply.

4. The composite exhaust nozzle failure prediction method of claim 1, wherein: the performance of the additional ply is weaker than that of the main ply.

5. The composite exhaust nozzle failure prediction method of claim 1, wherein: the finite element simulation uses Ansys Workbench.

6. The composite exhaust nozzle failure prediction method of claim 1, wherein: in step ②, the cross-section connection performance between the additional ply and the main ply is also selected to ensure that the additional ply and the main ply are delaminated when the additional ply fails.

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