In the last several years the Finite-Element Method has been successfully used in assessing and optimizing vehicle crash performance. Occupant modelling however, has remained the domain of gross motion simulators which make use of rigid body dynamics. New passive restraint systems like the airbag, have raised demands to mathematical modelling which cannot be satisfied with the existing models. The simulation of ‘out-of-position’ vehicle occupants is a prime example. A new approach to occupant simulation using the Finite Element Method is presented. The three-dimensional modelling of an airbag using the modified explicit dynamic FE-Code PAM-CRASH is the first step in this direction.
An airbag inflation model has been added to the PAM-CRASH code. It incorporates tabular input of the mass flow, calculation of the airbag's thermodynamics and gas flow out of the bag via vents and leakages. The airbag fabric is modelled with a newly implemented membrane element. This membrane element enables simulation of the highly orthotropic material behaviour of the airbag fabric. Although feasible, the gas inside the airbag has not been modelled with finite elements. Instead gas pressure and external forces resulting from contacts with the environment are applied to the membrane elements. This results in a model which is particularly useful in the simulation of the airbag's interaction with ‘in-position’, ‘out-of-position’ and ‘off-axis’ dummies, during and after inflation, and which can be used for the simulation of the unfolding process. The high quality of the airbag tissue material model also renders the approach useful in bag cutting pattern evaluation and optimization.
A series of test simulations have been carried out to demonstrate the capabilities of the model.