“The finite element method is widely used in mechanical structure modal, strength and stiffness analysis due to its high calculation accuracy, especially in the linear range of material stress-strain.
The finite element method is widely used in mechanical structure modal, strength and stiffness analysis due to its high calculation accuracy, especially in the linear range of material stress-strain.
Through the establishment of high-performance computer-aided engineering analysis systems by OEMs and automotive design companies, their professional CAE teams and product development have carried out extensive CAE applications simultaneously, and they have played an increasingly significant role in guiding design, improving quality, reducing development costs and shortening development cycles. The role of.
The mature aspects of CAE applied to car body development mainly include: modal, stiffness, strength, NVH analysis, mechanism motion analysis, etc.; and the accuracy of vehicle crash simulation analysis, sheet metal stamping simulation analysis, fatigue analysis and aerodynamic analysis It has been further improved, has been put into practical use, and can be used for qualitative analysis and improved design.
Not long ago, the author originally launched the joint simulation of modal stiffness and strength of the whole vehicle structure on the simulation show platform. It uses Hypermesh software as a finite element pre-processing tool and Nastran software as a simulation tool for modal, stiffness, strength and vibration analysis. Femfat software is used as a vibration fatigue simulation tool for battery packs to establish a finite element simulation analysis model. Finally, Hyperview software is used to view and evaluate the modal, stiffness, strength, and vibration fatigue results of auto parts. The course is explained in detail and helpful Yu scholars can quickly grasp the key points of finite element learning. Take this opportunity to share with you the process and cases of the joint simulation of the modal stiffness and strength of the vehicle structure.
1. Geometry cleanup
Use Hypermesh software to pre-process the model:
For structural rigidity simulation, the components in the model have less impact on the system and can be discarded; the geometric features of the parts with greater impact on the system can be appropriately simplified, such as chamfered structure, structural alignment, etc. After the simplification is completed, check whether the entire model has interference and other problems. If there are any problems, you can use Hypermesh software to repair them. If there are no problems, you can use the midplane extraction tool to extract the midplane of the model. Geometry cleanup is required after the midplane is extracted:
1. For sensitive parts such as bolt holes and chamfers, the side length of the unit is not less than 3mm, the number of units between 3-5mm is less than 3% of the total unit, the average size of the solid unit is 3mm (2-4mm), and the hexahedral unit is used.
2. Unit quality
The number of triangular elements in the entire model is ≤15%. Except for structural restrictions, no more than two triangular elements are allowed to be adjacent;
3. The mounting holes below R4 are simulated with 4 nodes, and at least 6 nodes above R4;
4. The chamfer below R5 is ignored and expressed by one-layer unit; the width is greater than 8mm, and it is expressed by two-layer or more units;
5. The solder joints are established with connectors and contain the information of each layer of soldering, and the soldering side has at least 2 rows of units;
6. The projections of the nodes of each layer of the solder joints are aligned, and the solder joint type is acm;
7. The welding seam is connected by rbe2 unit, and the upper and lower layers are two;
8. The chassis sheet metal parts are modeled by 5*5 SHELL, and the unit nodes are aligned;
9. Hemming: the initial connection of the outsourcing part and the part being wrapped share the same node, and the hemming has only the middle layer of elements;
10. Bolt connection: RBE2 and BAR unit are simulated together/or only rbe2 is used
11. Adhesive: the upper and lower elements are aligned with the nodes of the connecting parts, and the solid elements are adhesive
13. MASS quality points are used for centralized quality;
14. Contact thickness (interference check)
15. Normal and free edge inspections should be carried out for each part, the normal direction is the same, and there can be no free edges;
16. The buckle of the instrument panel and the interior of the closure is simulated by RBE2.
After the above processing, the unconnected finite element model can be obtained. At this time, each component in the model exists independently, and the connection relationship has not been resumed, as shown in the following figure:
2. Model assembly connection
By analyzing the structural composition of the digital model and the role of each component to determine the retention, simplification, and connection of the components, while ensuring the simulation accuracy as much as possible, simplifying and reducing the number of grids while improving the quality of the grid and improving the calculation Efficiency, but the connection relationship between the components can have a great effect and influence on the simulation results, so it is necessary to accurately set the connection of the model. The figure below is the connected model. Common connections include solder joints, glue, seam welding and bolts.
3. Setting of finite element boundary conditions
In order to make the simulation results more reasonable, the finite element model must establish scientific boundary conditions. There are mainly the following boundary conditions: constraints (single-point constraint SPC, multi-point constraint MPC), load (concentrated force, uniform force, moment), etc.
Fourth, simulation analysis
Nastran software was used as a simulation tool for modal, stiffness, strength and vibration analysis, and Femfat software was used as a vibration fatigue simulation tool for battery packs to establish a finite element simulation analysis model. Finally, Hyperview software was used to realize the modal, stiffness, and strength analysis of auto parts. View the analysis results of working conditions such as vibration and fatigue.
Five, case screenshots
1. Front suspension restraint mode (as shown in the figure below):
2. Free modal analysis of the body-in-white (as shown in the figure below):
3. Car door restraint modal analysis Car door torsion, window frame and mounting point stiffness analysis (as shown in the figure below)
4. Analysis of body-in-white stiffness including stiffness curve drawing (as shown in the figure below)
5. Strength analysis of hydraulic workbench (gravity field) (as shown in the figure below)
6. Strength analysis of hydraulic drag support (concentrated force) (as shown in the figure below)
7. Frequency response intensity analysis of heavy truck air conditioner bracket (frequency response intensity) (as shown in the figure below)
8. Strength analysis of the lower swing arm (inertia release) (as shown below)
9. Random vibration analysis of power battery pack and vibration fatigue analysis of power battery pack (vibration fatigue) (as shown below)
10. Front suspension transient response analysis and front longitudinal beam buckling analysis (transient response and buckling analysis) (as shown below)