HyperCrash

# Simple Fold — the Shape

In order to create an intermediate zone close to the fold line, the surfaces are also cut to be two planes parallel to the symmetry plane and are obtained by shifts in positive and negative directions.

The three planes divide the airbag into four main zones. Zone 0, in which the distance of the points from the symmetry + plane is positive, is not modified. The node in the Zone 1, situated between the symmetry + plane and the original symmetry plane, are moved toward the mean plane. The points located initially on the symmetry plane (number 2 on the Figure 23) are moved on the mean plane. This movement preserves the parallelism of the airbag layers. The third zone becomes symmetrical to Zone 1 with respect to the mean plane. Finally, the fourth zone is rotated without distortion (angle ) around the intersection line of the mean and symmetry planes.

Figure 23: The shape of the fold. |

The final shape of the folded airbag depends on three numerical parameters:

• | Minimum element size — This parameter determines the distance between the symmetry plane and its two children when the airbag is very thin. |

• | Minimum gap — this parameter defines the minimum distance between the two pieces of the "internal'' layer that is created after folding. |

• | Maximum slope — when the airbag becomes thick, after a few folds, it is impossible to keep the distance between the three planes constant, because the slope of the rotated parts becomes too significant and the distortion of the "internal'' layers gets too big. To limit this slope (angle on the Figure 23), a maximum alpha tangent is requested by the program. This means that when the airbag is thick, the distance between the three cutting planes depends on the airbag's thickness and on this parameter. |