CN106021701B - Consider coachbuilt body beam framework collision modeling and the analysis method of plastic hinge characteristic - Google Patents

Abstract

The invention relates to a collision modeling and analysis method of a car body beam skeleton considering the characteristics of plastic hinges, and belongs to the field of car body design. First solve the cross-sectional area and moment of moment of inertia characteristics of the complex shape of the car body beam skeleton, then create the car body beam skeleton model, and then generate the plastic hinge model characteristics of the thin-walled beam element, and assign it to the material of the Belytschko-Schwer (BS) beam element Characteristics, the material characteristics select the MAT No. 29 material type of the LS-DYNA software; finally generate a keyword text file that can be solved by the LS-DYNA software, and call the LS-DYNA software to solve the collision. The beam unit is used to build the body skeleton model, and the plastic hinge model simulates the bending, torsion, and crushing deformation of the beam for collision analysis. The solution results are reliable, user-friendly, and greatly reduce the modeling cycle, which will be of great importance to the car body design. guiding role.

Description

Modeling and Analysis Method of Car Body Girder Skeleton Collision Considering Plastic Hinge Characteristics

technical field

The invention relates to the field of automobile body design, and relates to a collision modeling and analysis method of a car body beam skeleton, in particular to a car body beam skeleton collision modeling and analysis method considering the characteristics of plastic hinges. It is mainly used to quickly solve the static mechanical properties and dynamic plastic hinge mechanical properties of thin-walled beam elements, so as to realize the rapid modeling and solution of car body beam skeleton.

Background technique

The collision design of automobile body structure is one of the core technologies in the automobile industry. In order to shorten the design cycle and test costs, computer-aided design and analysis techniques have been widely used in the automotive industry. Computer simulations of car crashes usually use finite element analysis. The car body structure is stamped from sheet metal and spot welded. In the finite element simulation analysis, the thin plate structure is first divided into planar quadrilateral plate elements, and then the boundary conditions are applied, and the commercial software LS-DYNA or ABAQUS is used to solve the problem. Due to the large number of quadrilateral plate elements and the structural degrees of freedom are about 1 million, the calculation of the solution is large, which seriously affects the design cycle. At present, there is only linear finite element analysis of the body structure created by beam elements, that is, calculation of static bending and torsional stiffness and frequency dynamic stiffness. There is no dynamic nonlinear finite element analysis to simulate the collision of the body structure.

Contents of the invention

The object of the present invention is to provide a collision modeling and analysis method of car body girder skeleton considering the characteristics of plastic hinges, which solves the above-mentioned problems in the prior art. The invention solves the above-mentioned difficult problem of collision analysis of the beam skeleton of the car body, adopts the beam unit to create the body structure, the number of structural degrees of freedom is within about 1000, and the calculation time is short, thereby accelerating the collision design of the car body.

Above-mentioned purpose of the present invention is achieved through the following technical solutions:

The collision modeling and analysis method of car body girder skeleton considering the characteristics of plastic hinge includes the following steps:

1) First draw the geometric shape of the complex section, including open section, closed single-chamber section, closed double-chamber section, closed three-chamber section, and the above three closed sections with flanging, that is, the closed + open situation. Seven types of section shapes; then solve the static mechanical properties and dynamic plastic hinge properties of the above seven types of sections. The static mechanical properties include: static bending moment of inertia, static torsional moment of inertia, and static cross-sectional area; dynamic plastic hinge properties include: dynamic plastic pressure collapse characteristics, dynamic plastic bending characteristics and dynamic plastic torsion characteristics;

2) Create the body beam skeleton model of the car, and use the Belytschko-Schwer (BS) beam to build the body skeleton model. The BS beam uses the Belytschko-Schwer beam unit of the LS-DYNA software;

3) Generate the plastic hinge model properties of the thin-walled beam unit and assign it to the material property of the BS beam unit. The material property selects the MAT No. 29 material type of LS-DYNA;

4) Generate a keyword text file that can be solved by LS-DYNA software, and call LS-DYNA software to solve the collision.

In the described step 1), the solution method of the static torsional moment of inertia of the closed three-chamber section shape is:

Among them, q ₁ , q ₂ and q ₃ can be solved by the following equations:

in F ₁ , F ₂ and F ₃ are the areas enclosed by the first room, the second room and the third room of the section respectively; Lu _u , L _l , L _m and L _r are the upper plate, the lower plate and the middle plate respectively and the length of the reinforced plate; L′ _u and L′ _m are the lengths of the upper plate and the middle plate respectively; t _u , t _l , t _m and t _r are the thicknesses of the upper plate, the lower plate, the middle plate and the reinforced plate respectively.

The definition and solution method of the dynamic plastic crushing characteristics described in step 1): Divide the finite element plate element grid for each thin-walled beam, and collide the thin-walled beam with the rigid wall, so as to obtain the relationship between the collision support reaction force and the crushing amount, That is, plastic crushing characteristics;

The definition and solution method of dynamic plastic bending characteristics: Divide the finite element plate element grid for each thin-walled beam, fix one end of the thin-walled beam, and bend the other end around the Y-axis or Z-axis, so as to obtain the relationship between the bending moment and the bending angle, that is, the plasticity bending properties;

Definition and solution method of dynamic plastic torsion characteristics: Divide finite element plate element mesh for each thin-walled beam, fix one end of the thin-walled beam, and twist the other end around the X axis, so as to obtain the relationship between torque and torsion angle, that is, plastic torsion characteristics.

The creation method of the plastic hinge model in the step 3) and the composition of the plastic hinge model, the plastic hinge model is composed of 4 kinds of springs, including 1 kind of compression spring, 2 kinds of bending springs in Y direction and Z direction respectively, 1 A torsion spring around the X direction; assign the plastic hinge model to the MAT No. 29 material type of LS-DYNA, and then assign the material to the BS beam unit, so that the BS beam unit can be used to create the body skeleton; the plastic hinge The spring unit and the BS beam unit are condensed through the degree of freedom and reduced to a super unit, the internal degree of freedom is hidden, and the external degree of freedom is developed by the user. The user only needs to model for the external degree of freedom, and does not need to pay attention to the plastic hinge unit and the BS beam unit. relationship, which can speed up the modeling process of the body skeleton.

The beneficial effect of the invention is that the combination of the beam unit and the plastic hinge unit can truly simulate the collision process of the car body. The beam element simulates the elastic deformation of the structure, and the plastic hinge element simulates the plastic deformation of the structure. The car body skeleton model can be created within 2-3 days by adopting the method of the invention, and the analysis time only needs about 10 minutes, which greatly improves the efficiency of car collision design, shortens the design cycle, and especially solves the problem of crashworthiness in the concept stage of car body structure Difficulties in the field of sex analysis.

The method of the present invention is different from other car body structure crashworthiness analysis methods: the beam unit is used to build the body skeleton model, and the plastic hinge model is used to simulate the bending, torsion and crushing deformation of the beam, and the speed of collision analysis, modeling and solution is fast , the post-processing is convenient, and the solution results are reliable; the traditional design method is the lumped mass spring (LMS) (Kamal, 1970) model, the model is too simplified to observe the deformation of important parts, and the accuracy is not enough; the existing method is to use plate and shell elements to divide The detailed body structure has more than 1 million degrees of freedom (in the 1980s), and the amount of collision calculation is large, and the structure is inconvenient to modify and optimize. It is very convenient for users to operate, greatly reduces the modeling cycle, and adds corresponding functions according to the needs of users, so that the crashworthiness analysis of the car body can be carried out conveniently, which will have an important guiding role in the design technology of the car body.

Description of drawings

The accompanying drawings described here are used to provide a further understanding of the present invention, and constitute a part of the application. The schematic examples and descriptions of the present invention are used to explain the present invention, and do not constitute improper limitations to the present invention.

Figure 1 shows the complex cross-sectional shape of the frame beam unit of the car body;

Figure 2 shows seven types of cross-sectional shapes;

Fig. 3 is the schematic diagram of plastic hinge model;

Figure 4 is the definition and characteristic curve of plastic crush deformation;

Figure 5 is the definition and characteristic curve of plastic bending deformation;

Figure 6 is the definition and characteristic curve of plastic torsional deformation;

Fig. 7 is a car body skeleton model;

Fig. 8 is an exploded view of a car body frame assembly;

Fig. 9 is 16 kinds of sectional shapes of the beam unit of the car body skeleton assembly;

Figure 10 is a schematic diagram of the deformation of the body frame at different times;

Fig. 11 is energy curve with time;

Fig. 12 is the curve of rigid wall support reaction force with time;

Fig. 13 is the curve of node displacement with time;

Figure 14 is the curve of energy variation with the displacement of key nodes;

Figure 15 is the curve of collision force changing with key node displacement.

Detailed ways

The detailed content of the present invention and its specific implementation will be further described below in conjunction with the accompanying drawings.

The car body girder frame collision modeling and analysis method considering the plastic hinge characteristics of the present invention comprises the following steps:

1) First draw the geometric shape of the complex section, including open section, closed single-chamber section, closed double-chamber section, closed three-chamber section, and the above three closed sections with flanging, that is, the closed + open situation. Seven types of section shapes; then solve the static mechanical properties and dynamic plastic hinge properties of the above seven types of sections. The static mechanical properties include: static bending moment of inertia, static torsional moment of inertia, and static cross-sectional area; dynamic plastic hinge properties include: dynamic plastic pressure collapse characteristics, dynamic plastic bending characteristics and dynamic plastic torsion characteristics;

2) Create the body beam skeleton model of the car, and use the Belytschko-Schwer (BS) beam to build the body skeleton model. The BS beam uses the Belytschko-Schwer beam unit of the LS-DYNA software;

3) Generate the plastic hinge model properties of the thin-walled beam unit and assign it to the material property of the BS beam unit. The material property selects the MAT No. 29 material type of LS-DYNA;

4) Generate a keyword text file that can be solved by LS-DYNA software, and call LS-DYNA software to solve the collision.

In the described step 1), the solution method of the torsional moment of inertia of the closed three-chamber section shape is:

Among them, q ₁ , q ₂ and q ₃ can be solved by the following equations:

in F ₁ , F ₂ and F ₃ are the areas enclosed by the first room, the second room and the third room of the section respectively; Lu _u , L _l , L _m and L _r are the upper plate, the lower plate and the middle plate respectively and the length of the reinforced plate; L′ _u and L′ _m are the lengths of the upper plate and the middle plate respectively; t _u , t _l , t _m and t _r are the thicknesses of the upper plate, the lower plate, the middle plate and the reinforced plate respectively.

The definition and solution method of the dynamic plastic crushing characteristics described in step 1): divide the finite element plate element grid for each thin-walled beam, and collide the thin-walled beam with a rigid wall, so as to obtain the relationship between the collision support reaction force and the crushing amount, That is, plastic crushing characteristics;

The definition and solution method of dynamic plastic bending characteristics: Divide the finite element plate element grid for each thin-walled beam, fix one end of the thin-walled beam, and bend the other end around the Y-axis or Z-axis, so as to obtain the relationship between the bending moment and the bending angle, that is, the plasticity bending properties;

Definition and solution method of dynamic plastic torsion characteristics: Divide finite element plate element mesh for each thin-walled beam, fix one end of the thin-walled beam, and twist the other end around the X axis, so as to obtain the relationship between torque and torsion angle, that is, plastic torsion characteristics. The creation method of the plastic hinge model in the step 3) and the composition of the plastic hinge model, the plastic hinge model is composed of 4 kinds of springs, including 1 kind of compression spring, 2 kinds of bending springs in Y direction and Z direction respectively, 1 A torsion spring around the X direction; assign the plastic hinge model to the MAT No. 29 material type of LS-DYNA, and then assign the material to the BS beam unit, so that the BS beam unit can be used to create the body skeleton; the method plastic hinge The spring unit and the BS beam unit are condensed through the degree of freedom and reduced to a super unit, the internal degree of freedom is hidden, and the external degree of freedom is developed by the user. The user only needs to model for the external degree of freedom, and does not need to pay attention to the plastic hinge unit and the BS beam unit. relationship, which can speed up the modeling process of the body skeleton.

Implementation case:

(1) Calculation of static mechanical properties of beam element section

Figure 1 shows the cross-sectional shape of three chambers + opening, which is the most complex among the seven cross-sectional shapes, and it is used as an example for calculation and derivation. The section shape is described by node coordinates (X, Y) and sheet metal thickness t. During the body design process, some nodes on the section can be moved; in addition, due to the limited design space, some nodes cannot be moved and are fixed points. The movable points and fixed points in Figure 1 are only examples. Along the axial direction of the beam, the stamped sheet metal parts of the closed section are formed by spot welding, and the hexahedral solid finite element element is used to simulate the welding spots. Each metal sheet can be approximated as consisting of small rectangular segments. Therefore, the cross-sectional area A can be expressed as

Among them, n and m are the number of metal sheets and the number of rectangular segments of each metal sheet, respectively, A _i and t _i are the area and thickness of the i-th metal sheet, l _ij is the j-th rectangle of the i-th metal sheet The length of the fragment.

The moment of inertia and product of inertia of the section with respect to the x-axis and y-axis can be defined as

Among them, (x _ij , y _ij ) is the center of the j-th rectangular segment of the i-th metal sheet, and θ _ij is the angle between the j-th rectangular segment of the i-th metal sheet and the x-axis.

The principal moment of inertia formula of the section can be deduced through I _x , I _y and I _xy , namely

The formula for calculating the torsional moment of inertia of thin-walled sections depends on the type of section shape, as shown in Figure 2, where the formula for the torsional moment of inertia J _o of the opening part can be expressed as

Single chamber torsional moment of inertia Dual Chamber Torsional Moment of Inertia and the torsional moments of inertia of the three compartments are

Among them, q ₁ , q ₂ and q ₃ can be solved through the equation group (11).

in F ₁ , F ₂ and F ₃ are the areas enclosed by the first, second and third rooms of the section; _Lu , L _l , L _m and L _r are the upper, lower and middle plates respectively and the length of the reinforced plate; L′ _u and L′ _m are the lengths of the upper plate and the middle plate respectively; t _u , t _l , t _m and t _r are the thicknesses of the upper plate, the lower plate, the middle plate and the reinforced plate respectively.

When the closed section has flanging, as shown in (c), (e) and (g) of Figure 2, it is also called the combined section of opening + closing, the torsional stiffness can be defined as

where k is the number of cross-section chambers.

Therefore, the bending moment of inertia formulas I _x and I _y are the same for the seven cross-sectional shapes. However, the torsional moment of inertia formula J is different for the seven cross-sectional shapes.

(2) Calculation of beam element crushing, bending and torsion characteristics

When the car collides, the beam unit of the car body skeleton will be crushed, bent and torsionally deformed. In order to simulate the deformation of the beam unit well, a plastic hinge model is added at the connection of the beam unit. As shown in Figure 3, the plastic hinge model is It consists of 4 types of springs, including 1 type of compression spring, 2 types of bending springs in Y direction and Z direction, and 1 type of torsion spring, so these characteristics of various beams need to be calculated before crash analysis. The present invention calculates these characteristics through the method of finite element, so as to improve the precision of collision solution.

The definition and solution method of crushing characteristics: Divide the finite element plate element grid for each thin-walled beam, and collide the thin-walled beam with a rigid wall, so as to obtain the relationship between the collision support reaction force and the crushing amount, that is, the plastic crushing characteristic, as shown in Fig. 4.

Definition and solution method of bending characteristics: Divide finite element plate element mesh for each thin-walled beam, fix one end of the thin-walled beam, and bend the other end around the Y-axis or Z-axis, so as to obtain the relationship between bending moment and bending angle, that is, plastic bending characteristics , as shown in Figure 5.

Definition and solution method of torsional characteristics: divide each thin-walled beam into a finite element plate element grid, fix one end of the thin-walled beam, and twist the other end around the X axis, so as to obtain the relationship between torque and torsion angle, that is, plastic torsion characteristics, as shown in Figure 6 shown.

(3) Generate K-file collision solution in LS-DYNA format

After creating the finite element model, generate a keyword text file in LS-DYNA format, and call LS-DYNA to solve the collision. After the solution is completed, post-processing and data analysis are carried out in the self-developed software, including the curve of system energy changing with time, the curve of collision force and time, and the displacement curve of key nodes.

This embodiment takes a car body frame as an example to introduce the implementation effect of the present invention.

Taking a certain car as an example to simplify the body frame, omit some non-load-bearing structures such as the skin, and create the finite element model of the car body beam frame shown in Figure 7. The model has a total of 48 beam units, and these 48 beam units belong to 16 components. The division of these 16 components is shown in the exploded view in Figure 8. All beams in each component share a cross-sectional shape, and the cross-sectional shape of 16 is shown in Figure 9, so the car body structure is a component model. The crashworthiness analysis of the car structure shown in Figure 2 is carried out. The solved body skeleton deformation is shown in Fig. 10. The curve of energy changing with time is shown in Figure 11, the curve of rigid wall support reaction force changing with time is shown in Figure 12, the curve of node displacement changing with time is shown in Figure 13, and the curve of energy changing with key node displacement is shown in Figure 14 The change curve of collision force with the displacement of key nodes is shown in Fig. 15.

The above descriptions are only preferred examples of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made to the present invention shall be included within the protection scope of the present invention.

Claims (4)

1. a kind of coachbuilt body beam framework collision modeling considering plastic hinge characteristic and analysis method, it is characterised in that：Including with Lower step：

1) geometry of compound section is drawn first, including open section, silent single chamber section, silent dual chamber section, silent Three Room sections and the silent section of three of the above carry the case where flange, that is, the situation of silent+opening, totally seven types Section configuration；Then the static mechanical characteristics and dynamic plasticity for solving above seven kinds of sections cut with scissors characteristic, and static mechanical characteristics include： Static buckling the moment of inertia, static twist the moment of inertia and static cross-sectional area；Dynamic plasticity cuts with scissors characteristic：Dynamic plasticity is crushed Characteristic, dynamic plasticity flexural property and dynamic plasticity torque characteristic；

2) coachbuilt body beam framework model is created, body frame model is built using BS beams, the BS beams are using LS-DYNA softwares Belytschko-Schwer beam elements；

3) the plastic hinge model characteristics for generating thin-walled beams, are assigned to the material property of BS beam elements, which chooses No. 29 material types of MAT of LS-DYNA；

4) the keyword text file that LS-DYNA softwares can solve is generated, LS-DYNA softwares is called to carry out collision solution；

The definition of dynamic plasticity crush characteristics described in step 1) and method for solving：Finite element plate is divided to each thin walled beam Thin walled beam is collided rigid wall by unit grid, and the relationship namely plasticity conquassation to obtain collision support reaction and conquassation amount are special Property；

The definition of dynamic plasticity flexural property and method for solving：Finite element plate unit grid is divided to each thin walled beam, it will be thin Wall beam one end is fixed, and the other end is bent around Y-axis or Z axis, and the relationship namely plastic bending to obtain moment of flexure and bending angle are special Property；

The definition of dynamic plasticity torque characteristic and method for solving：Finite element plate unit grid is divided to each thin walled beam, it will be thin Wall beam one end is fixed, and the other end is reversed around X-axis, to obtain the relationship namely Plastic Torsion characteristic of torque and windup-degree.

2. the coachbuilt body beam framework collision modeling according to claim 1 for considering plastic hinge characteristic and analysis method, It is characterized in that：In the step 1), the method for solving of the static twist the moment of inertia of silent three Room section configuration is：

Wherein q₁, q₂And q₃It is solved by following equation group：

WhereinF₁, F₂And F₃Respectively the first Room of section, second The area that room and third room are surrounded；L_u, L_l, L_mAnd L_rRespectively upper plate, lower plate, middle plate and reinforcing plate length；L′_mFor in The partial-length of plate；t_u, t_l, t_mAnd t_rRespectively upper plate, lower plate, middle plate and reinforcing plate thickness.

3. the coachbuilt body beam framework collision modeling according to claim 1 for considering plastic hinge characteristic and analysis method, It is characterized in that：

4. the coachbuilt body beam framework collision modeling according to claim 1 for considering plastic hinge characteristic and analysis method, It is characterized in that：The composition of the creation method of plastic hinge model and plastic hinge model in the step 3), plastic hinge model are Be made of 4 kinds of springs, including a kind of compressed spring, 2 kinds be respectively Y-direction and Z-direction flexural spring, a kind of torsion around X-direction Turn spring；The plastic hinge model is assigned to No. 29 material types of MAT of LS-DYNA, the material is then assigned to BS beams again Unit, so as to create body frame using BS beam elements；Plastic hinge spring unit is agglomerated with BS beam elements by degree of freedom, It is reduced to a hyperelement, internal degree of freedom is hidden, and to User Exploitation, user only needs to be directed to external freedom external freedom degree Degree modeling, it is not necessary to the relationship for paying close attention to plastic hinge unit and BS beam elements, so as to accelerate the modeling process of body frame.