Side airbag folding method based on LS-DYNA and PRIMER
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In the passive safety restraint system of automobile, airbag plays a vital role. The deployment of the airbag provides protection for the occupants in the car, but it may also bring serious harm to the occupants who are not sitting normally. Therefore, it is of great significance to study the deployment process of airbag by finite element method.
Usually, the parameters of airbag (ignition time, air hole area, etc. ) is a set of optimal parameters set according to the dummy's normal sitting posture and the contact with the dummy after the airbag is deployed normally. In order to study the damage caused by the airbag to the detached component before it is fully deployed, it is necessary to ensure that the finite element airbag is as consistent as possible with the test from the beginning to the end, so the finite element airbag model must be folded according to the actual folding process. At the same time, it is necessary to avoid the penetration in the folding process, and prevent the airbag from losing energy in order to overcome the penetration in the deployment calculation process, which will lead to the weakening of the airbag stiffness, thus affecting the deployment shape and the damage value caused by the contact between the dummy and the airbag.
At present, the airbag model is simplified seriously, the gas generator in the airbag is also simplified and ignored, and even the airbag folding is simplified and set as a tiled model. The reason is that the airbag is complicated to fold, and HYPERMESH is difficult to restore the real mesh, or the folded mesh is calculated, but it is difficult to use effectively because of its serious penetration. Therefore, this paper takes RIMER software and LS-DYNA as examples to fold the side airbag.
1, model preprocessing
According to the actual 2D situation of airbag, the grid is divided into corresponding parts, including bolt fixing holes, and the exhaust holes also need separate parts. Because the airbag is to be folded, the position of the folding line needs to be handled in advance to facilitate later folding. As shown in the figure, the single-layer airbag is copied into two layers, which are offset by 0.3mm along the surface direction, and the nodes at the suture line merge. Check whether the outer surface of the original airbag model is a closed body.
2. Initial folding of airbag model.
There are several combinations of actual airbag folding methods (Z-shape, pleated folding, winding folding, etc. ). In the process of finite element folding, to keep the ID numbers of elements and nodes unchanged, import the mesh processed in the previous step into PRIMER software for folding. The initial folding is shown in the following figure:
3, the position of the generator matching
The folded airbag needs to install the generator into the initial folded airbag. At this time, the flexible boundary conditions and multi-parameter contact cards in DYNA software can be used to move the generator into the airbag. As shown in the figure, the generator can be duplicated into two, two contacts can be established, and the mobile generator can contact the upper and lower surfaces of the airbag respectively. The final shape is shown in Figure 2.
4. Press the airbag into the airbag box.
Finally, the airbag needs to be installed in the fixed space of the seat and does not interfere with the foaming of the seat and other parts such as the skeleton, so it needs to be installed in the airbag housing. When the initial folded airbag is put into the airbag box, there will be interference. It is necessary to enlarge the airbag box in XYZ direction to avoid interference, and then use the keyword * bound-ary _ declared _ final _ geometry in DYNA card to restore the airbag box to its original size. At this time, the airbag is completely confined in the airbag box, and the recommended solver is DYNA's R7. 1. 1. In LS-DYNA, the contact card has a card specially defined for airbag self-contact: * contact _ airbag _ single _ surface _ ID, the recommended self-contact parameter S0FT=2, and the friction coefficient (FS/FD) is set to 0. 1, so it is necessary to adjust the card items such as SFS/SST/SBOPT/DEPTH to avoid airbags during the calculation.
5. Gas marking grid penetrant inspection
The airbag squeezed into the box, the exit to hypermesh for interference inspection, basically did not penetrate.
6. Conclusion
Using the airbag folding tool in PRIMER software, combined with the powerful solution tool of Ls-dyna, a complex airbag model can be initially established, which lays the foundation for the later simulation benchmarking and simulation optimization of automobile side safety system.