Solution

SOLUTION

STEP 1: Flat Bag Meshing

A typical passenger airbag (PAB) is taken from example models. 2D Shell Meshing is done in Hypermesh with an average element size of 5mm. The pleats are captured in the main panel of the PAB. The geometry lines shown below represent the flat shape of the passenger airbag. This is how an airbag will look before stitching. For airbags, modelling always starts from flat shape.

STEP 2: Stitching

The flat PAB is then stitched in Hypermesh using morphing techniques. Step by step stitching process is shown below.

STEP 3: Folding

Crush folding is done on the stitched bag, in order to fit it into the package using simfolder. During crush folding, tied contact is defined in pleats to prevent it from opening.

To represent the instrument panel and windscreen that make contact with the passenger airbag,an approximate meshing is done

STEP 4: Deployment Model

The folded bag is positioned in the IP mesh and a deployment model is prepared in LS Dyna, in which the contacts and constraints are as shown in the images below:

The segments with pleats are connected in the centre with Nodal Rigid Body (NRB). These NRB’s will hold the pleats from being opened during deployment.

Cross section of pleats after connected with NRB

The following materials are used in deployment model.

The airbag deployment is done using the corpuscular particle method (*AIRBAG_PARTICLE), in which the simulated gas particles will come out of the inflator according to a mass flow curve and hit the bag elements causing the airbag to open. This method will simulate the airbag deployment very close to reality.

Airbag Closed volume set defined in Particle

Vectors defined for guiding the gas particles

The following *AIRBAG_PARTICLE card and mass flow curve is used in deployment model.

Particle card

Mass flow curve

Two deployment models have been prepared and run fired. The first model has no NRB, so the pleat segments will open, while the second model has NRB, so the pleat segments will remainclosed throughout deployment. The fully deployed shape of both the models are compared below.

Fully deployed shape

The pressure comparison plot is shown below

The volume comparison plot is shown below

Maximum volume
Model 1 without NRB – 122 Litres
Model 2 with NRB – 118 Litres