Aircraft duct fatigue crack growth analysis method and fatigue life prediction method

Abstract

The present invention discloses an aircraft duct fatigue crack propagation analysis method and a fatigue life prediction method, comprising the following steps: establishing a three-dimensional model of an aircraft duct; pre-processing the duct model to obtain a duct finite element model; establishing an initial crack on the duct finite element model; obtaining an enriched area related to the crack in the duct finite element model, and enhancing the enriched area by adding internal nodes in the enriched area; using a life cycle method and a cycle-by-cycle method to perform fatigue crack propagation analysis, and obtaining the distance between the crack tip point and the initial crack tip point when the crack propagation is completed and the corresponding number of cycles. The present invention performs fatigue crack propagation analysis of an aircraft duct based on XFEM, which can solve the problem that the traditional crack propagation analysis method needs to repeatedly insert the crack front during analysis and needs to continuously update the analysis model during the analysis process, resulting in iterative calculations.

Description

Technical Field

[0001] The invention belongs to the technical field of crack extension analysis, and in particular relates to an aircraft duct fatigue crack extension analysis method and a fatigue life prediction method. Background Art

[0002] Pipes are an important part of aircraft systems. Pipes and pipe joints usually account for 30%-50% of aircraft hydraulic systems. Therefore, the safety of the pipeline system directly affects the reliability and safety of the aircraft. For aircraft hydraulic pipelines in service, continuous and uninterrupted vibration will cause their structures to loosen, leak, wear, fatigue fracture, etc. With the gradual improvement of aircraft performance and weight reduction requirements, aircraft hydraulic systems are also developing in the direction of light weight, small size, high pressure resistance, high power, and variable pressure. This leads to a worse working environment for aircraft pipeline systems, and the pipeline system presents many problems such as high failure rate, multiple failure modes, and poor reliability. According to statistics, in aircraft system accidents, the failure rate of hydraulic pipeline systems accounts for 50%-60%, and it shows an increasing trend year by year, which directly affects the operational safety of aircraft. Among these hydraulic pipeline system failures, catheter fatigue fracture is the main source of pipeline system failures.

[0003] In aircraft duct structures, the presence and extension of fatigue cracks are usually extremely destructive, which will directly lead to a decrease in fatigue strength and load-bearing capacity, and even pose a great risk to the integrity and stability of the duct structure. Although the fatigue performance of the structure can be improved to a certain extent through regular inspection and maintenance, it will be difficult to formulate a reasonable dynamic health monitoring plan if the remaining life of the structure under a given crack defect cannot be quantified. These are indispensable in the implementation of new aircraft design concepts such as damage tolerance design.

[0004] Therefore, a reasonable evaluation of the fatigue performance of the duct structure based on the fracture mechanics method and an accurate prediction of the fatigue remaining life of key parts in the duct structure have important theoretical and engineering practical value for controlling pipeline system failures, improving the safety of the pipeline system, and ensuring the flight safety of the entire aircraft. Summary of the invention

[0005] The purpose of the present invention is to provide an aircraft duct fatigue crack growth analysis method to solve the problems of low efficiency and low accuracy when using existing analysis methods to perform crack growth analysis on aircraft ducts.

[0006] Another object of the present invention is to provide a method for predicting the fatigue life of an aircraft duct.

[0007] The present invention is achieved through the following technical solutions:

[0008] The aircraft duct fatigue crack growth analysis method includes the following steps:

[0009] Create a 3D model of the aircraft duct;

[0010] Pre-processing the catheter model to obtain a catheter finite element model;

[0011] Establishing initial cracks on the catheter finite element model;

[0012] The enriched area related to the crack is obtained in the finite element model of the catheter, and the enriched area is enhanced by adding internal nodes in the enriched area;

[0013] Fatigue crack growth analysis: The life cycle method and the cycle-by-cycle method are used to perform fatigue crack growth analysis to obtain the distance between the crack tip point and the initial crack tip point when crack growth is completed and the corresponding number of cycles.

[0014] As a further improvement to the above technical solution, establishing an initial crack on the catheter finite element model includes the following steps:

[0015] Generate a semi-elliptical crack surface on the catheter finite element model;

[0016] Divide the generated crack surface into crack surface meshes and divide them into three-dimensional triangular meshes;

[0017] A crack front node group is established, and the crack unit partially or completely cuts the finite element model of the conduit.

[0018] As a further improvement to the above technical solution, in the step of fatigue crack extension analysis, Parislaw is used to perform fatigue crack growth analysis.

[0019] As a further improvement to the above technical solution, the step of fatigue crack growth analysis includes a step of determining the load type by setting a stress ratio.

[0020] As a further improvement to the above technical solution, the step of fatigue crack growth analysis includes a step of numbering multiple cracks in the catheter finite element model.

[0021] As a further improvement to the above technical solution, in the step of fatigue crack growth analysis, a step of determining a stress intensity factor is included, and different values ​​are assigned to the stress intensity factor for different crack analysis methods;

[0022] The crack analysis method includes: plane stress auxiliary field is used for the end nodes of the open crack, plane strain auxiliary field is used for the internal nodes along the crack front, and the stress intensity factor at the end node of the crack front is copied from the adjacent node; plane stress auxiliary field is used for the entire crack front; and plane strain auxiliary field is used for the entire crack front.

[0023] As a further improvement to the above technical solution, the step of fatigue crack growth analysis includes a step of obtaining the contour number of the periphery of the crack tip.

[0024] As a further improvement to the above technical solution, before the step of fatigue crack growth analysis, a step of calculating a signed distance function of intersecting basic grid unit nodes in the catheter finite element model is included.

[0025] On the other hand, the present invention also provides a method for predicting the fatigue life of an aircraft duct. According to the crack growth increment and the corresponding number of cycles obtained in the duct fatigue crack growth analysis, the total crack growth increment and the total number of cycles are accumulated to predict the fatigue life of the duct.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] In the method adopted by the present invention for analyzing fatigue crack propagation of aircraft ducts, the analysis is performed based on the theory of extended finite element, which avoids the need to re-divide the grid in each calculation and analysis step in the existing traditional crack propagation analysis, thereby improving the efficiency of crack propagation simulation analysis.

[0028] The present invention performs fatigue crack growth analysis of aircraft ducts based on XFEM, which can solve the problems of traditional crack growth analysis methods that require repeated insertion of crack fronts during analysis and continuous updating of analysis models during the analysis process, resulting in iterative calculations. It can quickly and efficiently predict the crack growth path, and on this basis quickly obtain the fatigue life of the duct, which is of great significance in realizing rapid analysis and prediction of the fatigue life of aircraft piping systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 Schematic diagram of a three-dimensional model of an aircraft duct in an embodiment of the present invention.

[0031] Figure 2 Schematic diagram of the finite element model of the catheter in an embodiment of the present invention.

[0032] Figure 3 Schematic diagram of the finite element structural unit of the crack surface in the finite element model of the catheter in an embodiment of the present invention.

[0033] Figure 4 Schematic diagram of the crack tip node of the crack surface finite element structural unit in the catheter finite element model in an embodiment of the present invention.

[0034] Figure 5 Schematic diagram of a finite element model of a catheter with cracks in an embodiment of the present invention.

[0035] Figure 6 Schematic diagram of crack propagation on the outer wall of the conduit under the first load step in the fatigue crack propagation analysis in an embodiment of the present invention.

[0036] Figure 7 Schematic diagram of crack propagation on the outer wall of the conduit at the tenth load step in the fatigue crack propagation analysis in an embodiment of the present invention.

[0037] Figure 8 It is a schematic diagram of crack propagation in which the crack penetrates the inner wall of the conduit at the tenth load step in the fatigue crack propagation analysis in an embodiment of the present invention.

[0038] Fig. 9 Schematic diagram of the corresponding relationship between the number of cycles and the average crack extension depth in the fatigue crack extension analysis in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the present application clearer, the specific embodiments of the present application are further described in detail below in conjunction with the accompanying drawings. It is understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for the convenience of description, only the part related to the present application but not all the contents are shown in the accompanying drawings. Before discussing the exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flow charts. Although the flow chart describes each operation (or step) as a sequential process, many of the operations therein can be implemented in parallel, concurrently or simultaneously. In addition, the order of each operation can be rearranged. The process can be terminated when its operation is completed, but it can also have additional steps not included in the accompanying drawings. The process can correspond to a method, a function, a procedure, a subroutine, a subprogram, etc.

[0040] The fatigue crack growth analysis of the aircraft duct in the present invention is performed on the basis of XFEM, on this basis, it can avoid the need for repeated insertion of the crack front and continuous updating and iterative calculation of the analysis model during the analysis of the traditional crack growth analysis method, so that the crack growth path can be predicted quickly and efficiently in the fatigue crack growth analysis, and the fatigue life of the duct can be obtained, which is very important when analyzing the aircraft piping system composed of a large number of ducts, and can realize the rapid analysis and prediction of the fatigue life of the aircraft piping system.

[0041] The method for analyzing fatigue crack growth and predicting fatigue life of an aircraft duct of the present invention comprises the following steps:

[0042] Create a 3D model of the aircraft duct;

[0043] Pre-processing the catheter model to obtain a catheter finite element model;

[0044] Establishing initial cracks on the catheter finite element model;

[0045] The enriched area related to the crack is obtained in the finite element model of the catheter, and the enriched area is enhanced by adding internal nodes in the enriched area;

[0046] Fatigue crack growth analysis: The life cycle method and cycle-by-cycle method are used to perform fatigue crack growth analysis, and the distance between the crack tip point and the initial crack tip point when crack growth is completed and the corresponding number of cycles are obtained to realize the analysis of fatigue crack growth of aircraft ducts.

[0047] According to the crack growth increment and the corresponding number of cycles obtained in the fatigue crack growth analysis of the catheter, the total crack growth increment and the total number of cycles are accumulated, and the fatigue life of the catheter is predicted based on the obtained total crack growth increment and the total number of cycles.

[0048] In the analysis of fatigue crack propagation of aircraft ducts, the present invention modifies the command stream parameters of ANSYS analysis software and performs simulation calculations in combination with a finite element model established by Hypermesh software, which greatly improves both modeling and code running efficiency compared with traditional analysis methods.

[0049] In one embodiment, referring to Figures 1 to 9 As shown, the aircraft duct fatigue crack growth analysis method in this embodiment includes the following steps:

[0050] S01. Establish a three-dimensional model of the aircraft duct;

[0051] Here, according to the structural specifications of aircraft ducts and the relevant standard requirements of HB4-2-2002 expansion pipes, a three-dimensional model of aircraft ducts is established. Figure 1 shown.

[0052] S02. Pre-process the catheter model; including:

[0053] S021. Divide the finite element mesh of the catheter model;

[0054] The 2D-atuomesh function of Hypermesh software was used to define the mesh size to generate a 2D mesh on the model, and then the 3D-spin operation was used to generate a 3D mesh on the model;

[0055] S022. Define material properties;

[0056] Use the Utility-Material module in Hypermesh software to define the material properties of the catheter model;

[0057] S023. Define unit type;

[0058] In the Sensor module of Hypermesh software, select solid185 unit and assign this unit type to the catheter model to obtain the pre-processed catheter finite element model, as shown in the figure. Figure 2 shown.

[0059] S03. Establishing an initial crack on the catheter finite element model; including:

[0060] S031, establish crack surface;

[0061] Using the nodes, lines and surfaces functions in the Hypermesh software, a semi-elliptical crack surface was generated on the catheter finite element model, where the sizes of the semi-elliptical crack surface were a = 0.2 mm and c = 0.1 mm, a being the major axis size of the semi-elliptical crack surface, and c being the minor axis size of the semi-elliptical crack surface;

[0062] S032, split the surface grid;

[0063] The crack surface geometry is discretized using the MESH200 element and the crack surface element component M200EL is established. Here, for the three-dimensional crack surface, the element can be set to a three-dimensional triangular mesh defined by three nodes and KEYOPT(1) = 4, such as Figure 3 As shown;

[0064] S033. Establish a crack front node group;

[0065] Set up a separate node component MESHND for the crack front node, such as Figure 4As shown;

[0066] Specifically, the crack unit can partially or completely cut the catheter finite element model; Figure 5 .

[0067] S04. Define the crack extension enrichment zone;

[0068] The enriched regions associated with the cracks are defined in the conduit finite element model and enhanced by attaching internal nodes to support the enriched displacement function to support the required enriched displacement function.

[0069] To define the enrichment region in ANSYS software, the corresponding APDL command is:

[0070] XFENRICH,EnrichmentID,testcmp,,SING

[0071] Among them, EnrichmentID is the name specified to identify the enriched region, and testcmp is the group to which the enriched unit belongs.

[0072] S05. Define LSM value;

[0073] The LSM value defined here refers to the signed distance function of the intersecting basic mesh unit nodes in the catheter finite element model. The corresponding APDL command in ANSYS software is:

[0074] XFCRKMESH,EnrichmentID,M200EL,MESHND

[0075] S06, Fatigue crack growth analysis using Paris law;

[0076] Paris law is used here to analyze fatigue crack growth, where the Paris law can be expressed as:

[0077]

[0078] Where a is the crack length, N is the number of cycles, ΔK is the range of stress intensity factors at the crack tip, and C and m are the corresponding material parameters.

[0079] The fatigue crack growth law used here is set. The corresponding APDL command in ANSYS software is:

[0080] TB,CGCR,,,,PARIS

[0081] TBDATA,1,Value1,Value2

[0082] Among them, Value1 and Value2 represent the corresponding parameters C and m in Paris law respectively.

[0083] S07, fatigue crack growth analysis; reference Figure 6 , Figure 7 and Figure 8 ;

[0084] S071. Define load type;

[0085] The definition of load type here can achieve different working conditions by modifying the stress ratio. The corresponding APDL command in ANSYS software is:

[0086] CGROW,FCG,SRAT,Value

[0087] Wherein, Value represents the stress ratio, and in this embodiment, the Value value is -1;

[0088] S072, set the number of sub-steps;

[0089] In order to facilitate the subsequent extraction of the number of cycles under cracks of different depths / lengths, it is necessary to set the number of sub-steps for model calculation:

[0090] deltim,Value,Value,Value

[0091] Wherein, Value represents the inverse of the number of sub-steps, and in this embodiment, the Value value is 0.1;

[0092] S073. Number the cracks;

[0093] When there are multiple cracks in the catheter finite element model, each crack should be numbered separately; the corresponding APDL command in ANSYS software is:

[0094] CINT,new,ID

[0095] S074. Determine the stress intensity factor;

[0096] Here, the stress intensity factor is determined, and the corresponding APDL command in ANSYS software is:

[0097] CINT,TYPE,SIFS,Value

[0098] Among them, the value of Value can be 0, 1, and 2; different values ​​are assigned to the stress intensity factor for different crack analysis methods; here 0 means that the plane stress auxiliary field is used for the end nodes of the open crack, the plane strain auxiliary field is used for the internal nodes along the crack front, and the stress intensity factor at the end node of the crack front is copied from the adjacent node; 1 means that the plane stress auxiliary field is used for the entire crack front; 2 means that the plane strain auxiliary field is used for the entire crack front;

[0099] S075. Calculate the number of contours around the crack tip;

[0100] Here, the life cycle (LC) method and the cycle-by-cycle (CBC) method can be used for fatigue crack growth analysis. The life cycle (LC) method is often used for constant amplitude cyclic loads. By setting the crack growth increment Δa max , the number of cycles can be calculated according to the fatigue crack growth law of ΔN; the cycle-by-cycle (CBC) method is used for variable amplitude cyclic load and overload simulation. By setting the cycle increment ΔN, the crack growth increment Δa can be calculated according to the fatigue crack growth law;

[0101] S076. Obtain the distance between the crack tip point and the initial crack tip point when the crack propagation is completed and the corresponding number of cycles to complete the analysis of fatigue crack propagation of the aircraft duct.

[0102] In another embodiment, based on the above analysis of the fatigue crack propagation of the conduit, the fatigue life of the conduit can be predicted. The fatigue life prediction method includes the following steps:

[0103] According to the crack growth increment and the corresponding number of cycles calculated in each calculation sub-step, the total crack growth increment and the total number of cycles are accumulated to obtain the fatigue crack growth life, which can realize the prediction of the fatigue life of the catheter. Fig. 9 shown.

[0104] When the life cycle (LC) method or the cycle-by-cycle (CBC) method is used to calculate the crack growth life, the corresponding number of calculation sub-steps is set to obtain the number of cycles under each calculation sub-step. Usually, the number of calculation sub-steps can be set according to the analysis requirements.

[0105] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An aircraft duct fatigue crack growth analysis method, characterized in that: The following steps are involved: Create a 3D model of the aircraft duct; Pre-processing the catheter model to obtain a catheter finite element model; Pre-process the catheter model; including: dividing the catheter model finite element mesh, using the 2D-atuomesh function of the Hypermesh software to define the mesh size to generate a two-dimensional mesh on the model, and then using the 3D-spin operation to generate a three-dimensional mesh on the model; defining material properties; using the Utility-Material module in the Hypermesh software to define the material properties of the catheter model; defining the unit type, selecting the solid185 unit in the Sensor module of the Hypermesh software, and assigning the unit type to the catheter model to obtain the pre-processed catheter finite element model; Establishing an initial crack on the catheter finite element model; including: establishing a crack surface, using the nodes, lines and surfaces functions in the Hypermesh software to generate a semi-elliptical crack surface on the catheter finite element model; dividing the crack surface mesh, using the MESH200 unit to discretize the crack surface geometry and establish the crack surface unit component M200EL; establishing a crack front node group, setting a separate node component MESHND for the crack front node, and the crack unit can partially or completely cut the catheter finite element model; The enriched area related to the crack is obtained in the finite element model of the catheter, and the enriched area is enhanced by adding internal nodes in the enriched area; Fatigue crack growth analysis: Use the life cycle method and the cycle-by-cycle method to perform fatigue crack growth analysis, and obtain the distance between the crack tip point and the initial crack tip point when crack growth is completed and the corresponding number of cycles; In ANSYS software, APDL commands are used to define the enriched area, LSM value and the parameters of fatigue crack propagation analysis, including the fatigue crack growth law adopted, load type, the number of sub-steps of model calculation that need to be set, the number of each crack when there are multiple cracks, and the stress intensity factor.

2. The aircraft duct fatigue crack growth analysis method according to claim 1, characterized in that: In the step of fatigue crack extension analysis, Paris law is used to perform fatigue crack growth analysis.

3. The aircraft duct fatigue crack growth analysis method according to claim 1, characterized in that: The steps of fatigue crack growth analysis include a step of determining a load type by setting a stress ratio.

4. The aircraft duct fatigue crack growth analysis method according to claim 1, characterized in that: The step of fatigue crack growth analysis includes a step of numbering a plurality of cracks in the finite element model of the catheter.

5. The aircraft duct fatigue crack growth analysis method according to claim 1, characterized in that: The fatigue crack growth analysis step includes a step of determining a stress intensity factor, and assigning different values ​​to the stress intensity factor for different crack analysis methods; The crack analysis method includes: plane stress auxiliary field is used for the end nodes of the open crack, plane strain auxiliary field is used for the internal nodes along the crack front, and the stress intensity factor at the end node of the crack front is copied from the adjacent node; plane stress auxiliary field is used for the entire crack front; and plane strain auxiliary field is used for the entire crack front.

6. The aircraft duct fatigue crack growth analysis method according to claim 1, characterized in that: The step of fatigue crack growth analysis includes a step of obtaining contour data of the periphery of the crack tip.

7. The aircraft duct fatigue crack growth analysis method according to claim 1, characterized in that: Prior to the step of fatigue crack growth analysis, a step of calculating the signed distance function of the intersecting base mesh element nodes in the conduit finite element model is included.

8. A method for predicting fatigue life of an aircraft duct, characterized in that: According to the crack growth increment and the corresponding number of cycles obtained in the fatigue crack growth analysis of the catheter, the total crack growth increment and the total number of cycles are accumulated to predict the fatigue life of the catheter.

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