CN102622472A - Method for analyzing load and stress distribution and stress levels of composite mechanical connection pins - Google Patents

Abstract

The invention relates to a method for analyzing the nail load, stress distribution and stress level of the mechanical connection of composite materials. The technical feature is: establish a two-dimensional shell beam model to calculate the nail load distribution of the connector, and take out a rectangle near the target nail from the two-dimensional model Area bypass load; on the basis of the 2D shell beam model, according to the geometric information such as the size of the rectangular area and the bolt size, a new 3D solid model containing only target nails is created, and the bypass load extracted from the 2D model is used as the 3D model The force boundary condition can be applied, and the bolt preload can be applied, and the stress distribution and stress level of the area can be obtained by calculating the three-dimensional model. The invention of the method gives full play to the advantages of the two-dimensional modeling method and the three-dimensional modeling method in the finite element model, provides a fast and accurate calculation method for engineering calculation of multi-nail connection nail load distribution and stress analysis, and reduces design cost.

Description

Method for analyzing nail loads and stress distributions and stress levels in mechanical connections of composite materials

technical field

The invention relates to a method for analyzing the mechanical connection nail load, stress distribution and stress level of composite materials, which can be used in the fields of aerospace vehicle structure design, mechanical design and manufacturing. the

Background technique

Due to its high specific strength, high specific stiffness, good corrosion resistance and excellent designability, composite material structures have been more and more widely used in the field of aviation and aerospace in recent years, and have become one of the important materials for aircraft structures. The amount of composite materials is usually expressed as a percentage of the weight of the aircraft body structure, and has become one of the important indicators of the advanced level of aircraft structure design. the

The main load-bearing structures of composite materials are connected by a large number of bolts. This type of mechanical connection structure is the main connection structure and load transmission path in aircraft structures. Therefore, the mechanical connection joint of composite material has become a key part of the aircraft structure, and its connection mechanical properties, strength and life are worthy of attention. Due to the anisotropy of strength and stiffness of composite materials and lack of ductility, the load redistribution ability of each hole in the connection plate is poor in the multi-nail mechanical connection, and the load ratio of each connection hole varies greatly. Therefore, the problem of nail load distribution in multi-nail mechanical connections of composite laminates has always been highly valued in engineering design and application. At present, there are two types of methods available for application: experimental methods and finite element numerical analysis methods. The cost of the test method is high, the processing requirements of the specimen are strict, and it is difficult to conduct systematic research on many factors that affect the nail load distribution and strength, and the test results have a certain degree of dispersion; the finite element numerical analysis method is low in cost and can consider different parameters. Impact. the

Determining the bearing ratio, stress distribution and stress level of each nail in the multi-nail connection structure is the basis for calculating the strength of the multi-nail connection. The finite element methods widely used at home and abroad on the mechanical connection of composite materials include the following two types: one is the method of establishing a two-dimensional plate and shell model; the other is the method of establishing a three-dimensional solid model. The simple two-dimensional plate and shell model method is a simplified simulation method, which has a short calculation period and can obtain nail load distribution results that meet engineering accuracy; Preload, nail hole assembly clearance, friction and other factors, and the interlayer stress cannot be obtained. The method of establishing a three-dimensional solid model can take into account various influencing factors in the above-mentioned actual situation, but its disadvantages are that the modeling process is complicated, the calculation cycle is too long, and it is not universal. The convergence problem of nonlinear iterative calculation of contact problems often becomes a problem. Difficulties, not suitable for practical engineering applications. the

Contents of the invention

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a method for analyzing the nail load, stress distribution and stress level of the mechanical connection of composite materials, and utilizes the advantages of the two-dimensional modeling method and the three-dimensional modeling method in the finite element model, for In engineering, the calculation of multi-nail connection nail load distribution and stress analysis provide fast and accurate calculation methods, optimize the design of multi-nail connection structures, and reduce design costs. the

Technical solutions

A method for analyzing composite material mechanical connection nail load, characterized in that the steps are as follows:

Step 1: According to the actual length and width of each connected plate, establish the corresponding geometric plane at the respective mid-plane position, and establish the geometric line segment at the nail position; 

Step 2: On the geometric surface, divide the square area with each nail as the center and the row distance as the side length;

Step 3: Assign the geometric surface to the shell element attribute and divide it into a quadrilateral mesh; assign the geometric line segment to the beam element attribute and divide it into a line mesh, and the two end points of the beam element are on the grid nodes of the connected plate, There will be nodes on the side of the square; the grid division is completed to obtain a two-dimensional finite element plate and shell model;

Step 4: In the two-dimensional model, the fixed end of the connector is restrained by the fixed support, and the required load is applied to the loading end, and the load is transmitted between different connected plates through beam elements;

Step 5: Solve the calculation model through the finite element software. After the calculation is completed, extract the nodal force of the beam element from the obtained calculation results, and the magnitude of the nodal force is the nail load. the

A method for analyzing the surrounding stress distribution and stress level of the mechanical connection nail load of composite materials, characterized in that the steps are as follows:

Step 1: According to the actual length and width of each connected plate, establish the corresponding geometric plane at the position of the respective middle plane, and establish the geometric line segment at the position of the nail;

Step 2: On the geometric surface, divide the square area with each nail as the center and the row distance as the side length;

Step 3: Assign the geometric surface to the shell element attribute and divide it into a quadrilateral mesh; assign the geometric line segment to the beam element attribute and divide it into a line mesh, and the two end points of the beam element are on the grid nodes of the connected plate, There will be nodes on the side of the square; the grid division is completed to obtain a two-dimensional finite element plate and shell model;

Step 4: In the two-dimensional model, on any square area on the connected plate where any nail is the target nail, extract and save the bypass loads around the square area, and the bypass load includes force and bending moment;

Step 5: According to the side length of the square area in step 2 and the real thickness of each connected plate, establish a 3D geometric model of the connected plate; select any one of the connected plates, and extend one end of it in the axial direction to the length of the model 10% of the elastic prosthesis;

Step 6: Establish a three-dimensional geometric model of the fastener according to the size of the nail and washer, model the nail and washer as a whole, and use a cylinder to represent the thread shape;

Step 7: Assign the 3D geometric model obtained in Step 5 and Step 6 to the attribute of the solid unit, and scan to generate a hexahedral mesh; establish between nails and nail holes, between gaskets and connected plates, and between different connected plates Contact pairs to complete the establishment of the 3D solid model;

Step 8: Use one end of the elastic prosthesis in step 5 as a fixed support constraint;

Step 9: Use the bypass load taken out in step 4 as the force boundary condition on the corresponding surface of the 3D solid model, and the side of the elastic prosthesis is not loaded; the force is loaded in a uniformly distributed manner, and the bending moment is in accordance with the bending normal stress formula It is converted into stress and loaded gradiently on the surface, and the bolt pretightening force is applied on the nail through the pretightening force unit;

Step 10: use finite element software to solve and calculate the three-dimensional model, and obtain the stress distribution and stress level around the target nail. the

Take all the nails as the target nails in turn, and repeat steps 4 to 10 repeatedly to obtain the stress distribution and stress level around all nails. the

Beneficial effect

A method for analyzing the nail load, stress distribution and stress level of the mechanical connection of composite materials proposed by the present invention, establishes a two-dimensional shell beam model to calculate the nail load distribution of the connector, and takes out a side of a rectangular area near the target nail from the two-dimensional model road load; on the basis of the 2D shell-beam model, according to the geometric information such as the size of the rectangular area and the bolt size, a new 3D solid model containing only target nails is created, and the bypass load extracted from the 2D model is used as the force boundary of the 3D model Conditions, and the bolt pre-tightening force can be applied, and the stress distribution and stress level of the area can be obtained by calculating the three-dimensional model. the

Compared with the prior art, the present invention has beneficial effects: the advantages of the two-dimensional and three-dimensional finite element models are fully utilized, the applicability is strong, the calculation time is short, the calculation accuracy can be ensured, and the calculation efficiency is improved. In the method of the invention, the idea of combining the finite element analysis from the two-dimensional model to the three-dimensional model to analyze the problem is relatively novel, and can be used for other large and complex models. The method of the invention is applicable to the connection of composite material boards to composite material boards, metal boards to metal boards, and composite material boards to metal boards, and has strong universality. the

Description of drawings

Fig. 1: flow chart of technical scheme of the present invention;

Figure 2: A two-dimensional plate and shell model of a row of three-nail single-lap joints;

1-composite plate, 2-metal plate, I-the first nail, II-the second nail, III-the third nail;

Figure 3: Schematic diagram of joints shared by shell elements and beam elements in the 2D plate and shell model;

Figure 4: Schematic diagram of the grid form of the 3D solid model and its constraints;

Figure 5: Schematic diagram of the loading contents and methods of different types of plate bypass loads in the 3D solid model;

a: Loading content and method of fixed support plate; b: Loading content and method of non-fixed support plate. the

Detailed ways

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

The calculation process of the present invention is shown in Figure 1. In order to better understand the technical solution of the present invention, the above algorithm is applied to the common mechanical connection analysis of composite material plates and metal plates. The analysis content is: nail load distribution calculation, and maximum Stress field analysis around the nail loading hole. The connector is a single lapped plate with three nails, as shown in Figure 2. The following steps are based on the finite element software ANSYS:

Step 1. According to the actual length and width of different plates to be connected, establish a geometric surface at the position of the respective middle plane, move the origin of the working plane to the position of the nail, rotate the working plane, and move the plane along the X direction and the Y direction at two Keypoints are cut out of the geometry face. Connect the key points of the same nail on different boards with line segments, and record and save the key point numbers. The composite plate is plate 1 in Fig. 2a, and the metal plate is plate 2 in Fig. 2a;

Step 2. Take the nail as the center of the square, and the row distance as the side length, and use the working plane to divide the square area around each nail; as shown in Figure 2b;

Step 3 defines the material properties, and assigns SHELL99 shell element attributes to the composite material plate, and SHELL63 shell element attributes to the metal plate, and divides the geometric surface to generate a quadrilateral mesh. The line segment is assigned the beam element attribute of BEAM188, and is divided to generate a line mesh. The two end points of the beam element are on the grid node of the connected plate, that is, the beam element and the shell element share the node (as shown in Figure 3);

Step 4 applies the boundary conditions in Figure 2a to the connector;

Step 5 Apply the required load on the loading end of the connected plate, and calculate the two-dimensional plate and shell model in the Solution module;

After the calculation in step 6 is completed, save the model as a data file in 2D.db format. The nodal force of each common node is taken out in the post-processing module, and this value is the nail load;

In step 7, the I nail with the largest nail load distribution ratio is taken as the target nail. In the two-dimensional plate and shell model, select the square area near the target nail on each connected plate, that is, select the shaded area in Figure 2b;

Step 8 extracts the bypass loads around the square area. First select the elements in the shaded area, then select the nodes on the sides of the square, and enter the FSUM command in the command box to get the force of the selected elements on these nodes; use this command to extract the forces on the four sides of each square . The bypass loads extracted from the square sides perpendicular to the X axis include N _X , Q _Y , Q _Z , M _Y , M _Z ; the side loads extracted from the square sides parallel to the X axis include N _Y , Q _X , Q _Z , M _X , M _Z ; store the extracted bypass load into the data file;

Step 9 Create a new job, and establish the geometry of the connected plates according to the size of the square in the two-dimensional plate and shell model and the respective thicknesses of different connected plates. According to the actual size of the nail and washer, the geometry of the fastener is established, and the thread shape is ignored, and the nail and washer are regarded as a whole. Select a metal plate square, and extend its end along the X direction by 10% of the model length as an elastic prosthesis; the purpose of the elastic prosthesis is to eliminate the adverse effects of the strong constraint of the fixation on the stress distribution;

Step 10 assigns SOLID185 solid element attributes to the above-mentioned 3D geometric model, and scans to generate a hexahedral mesh. Define contact pairs between nails and nail holes, between gaskets and connected plates, and between different connected plates, and generate a three-dimensional solid model. The model grid is shown in Figure 4;

In step 11, the bypass load taken out in step 8 is added as a stress boundary condition to the corresponding surface of the three-dimensional solid model. Among them, the force is loaded in a uniform manner: the force perpendicular to the surface (N _X or N _Y ) is directly applied to the element surface, and the shear force is loaded by the surface effect unit SURF154; the bending moment is converted into a normal stress according to the bending normal stress formula, as The form of the gradient is added to the corresponding surface; the preload is applied using the preload element provided inside ANSYS. The side of the elastic prosthesis in the three-dimensional solid model does not contain stress boundary conditions, as shown in Figure 5a, only stress boundary conditions are applied to the shaded part;

Step 12 Calculate the 3D solid model in the Solution module. After the calculation is completed, the results of each layer in the respective unit coordinate system can be extracted in the post-processing module, and the stress cloud diagram can be drawn, and the overall deformation diagram can also be viewed. the

Step 13 If you want to change the target nail and re-analyze, you need to restore the 2D.db file saved in step 6, and then repeat steps 7 to 12. the

Claims (3)

1. A method for analyzing composite material mechanical connection nail loading, characterized in that the steps are as follows: Step 1: According to the actual length and width of each connected plate, establish the corresponding geometric surface at the position of the respective middle plane, and establish the geometric line segment at the position of the nail; Step 2: On the geometric surface, divide the square area with each nail as the center and the row distance as the side length; Step 3: Assign the geometric surface to the shell element attribute and divide it into a quadrilateral mesh; assign the geometric line segment to the beam element attribute and divide it into a line mesh, and the two end points of the beam element are on the grid nodes of the connected plate, There will be nodes on the side of the square; the grid division is completed to obtain a two-dimensional finite element plate and shell model; Step 4: In the two-dimensional model, the fixed support end of the connector is fixedly supported, and the required load is applied to the loading end, and the load is transmitted between different connected plates through beam elements; Step 5: Solve the calculation model through the finite element software. After the calculation is completed, extract the nodal force of the beam element from the obtained calculation results, and the magnitude of the nodal force is the nail load. 2. a method utilizing the described method of claim 1 to analyze the surrounding stress distribution and the stress level of the composite material mechanical connection nail load, it is characterized in that the steps are as follows: Step 1: According to the actual length and width of each connected plate, establish the corresponding geometric surface at the position of the respective middle plane, and establish the geometric line segment at the position of the nail; Step 2: On the geometric surface, divide the square area with each nail as the center and the row distance as the side length; Step 3: Assign the geometric surface to the shell element attribute and divide it into a quadrilateral mesh; assign the geometric line segment to the beam element attribute and divide it into a line mesh, and the two end points of the beam element are on the grid nodes of the connected plate, There will be nodes on the side of the square; the grid division is completed to obtain a two-dimensional finite element plate and shell model; Step 4: In the two-dimensional model, on any square area on the connected plate where any nail is the target nail, extract and save the bypass loads around the square area, the bypass loads include force and bending moment; Step 5: According to the side length of the square area in step 2 and the real thickness of each connected plate, establish a 3D geometric model of the connected plate; select any one of the connected plates, and extend one end of it in the axial direction to the length of the model 10% of the elastic prosthesis; Step 6: Establish a three-dimensional geometric model of the fastener according to the size of the nail and washer, model the nail and washer as a whole, and use a cylinder to represent the thread shape; Step 7: Assign the 3D geometric model obtained in Step 5 and Step 6 to the attribute of the solid unit, and scan to generate a hexahedral mesh; establish between nails and nail holes, between gaskets and connected plates, and between different connected plates Contact pairs to complete the establishment of the 3D solid model; Step 8: Use one end of the elastic prosthesis in step 5 as a fixed support constraint; Step 9: Use the bypass load taken out in step 4 as the force boundary condition on the corresponding surface of the 3D solid model, and the side of the elastic prosthesis is not loaded; the force is loaded in a uniformly distributed manner, and the bending moment is in accordance with the bending normal stress formula It is converted into stress and loaded on the surface gradient, and the bolt pretightening force is applied on the nail through the pretightening force unit; Step 10: use finite element software to solve and calculate the three-dimensional model, and obtain the stress distribution and stress level around the target nail. 3. The method according to claim 2, characterized in that in step 4, the target nails are changed, all nails are used as target nails in turn, and steps 4-10 are repeated repeatedly to obtain the stress distribution and stress level around all nails.

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