Characterization, modeling, and design of airbags and woven expansible fabrics

Air-bag technology relies on woven fabrics as the material of construction. Knowledge pertaining to the fabric's permeabihty as a function of pressure drop and inflating gas temperature under biaxial stretching condhions is crucial from an energy dissipation point of view. An expansible fabric, stretched biaxially, wiU open up and bbecome more permeable. The extent to which fabric porosity changes with temperature, pressure drop, the source of fiber used in the fabric, fabric weave, fabric finish and fabric denier is impossible to determine a priori. In this regard, it is the material properties of the fabric which significantly contribute to the safety of the vehicle occupant as he/she interacts with the deployed airbag.

In order to quantify fabric characteristics and airbag behavior, a novel blisterinflation technique was developed to deform a fabric biaxially. At least three different types of polymeric fabrics woven from nylon 66, nylon 6 and high strength polyester fibers with various construction and finish were investigated in this study. The biaxial deformation of fabrics are modeled with non-linear finite element (FEA) based approach with the assumption of continuity. The latter assumption is highly questionable. Moreover, these models fail to adequately mcorporate the effects of temperature and pressure drop on deformation. In this study, a more rehable fabric-material response model (FMRM) for biaxial deformation was developed based on the semi-empirical approach called artificial neural networks.

With respect to airbag behavior, four different mechanisms for overall energy dissipation were modeled. This approach was based on the kinetic energy considerations which arise when the occupant interacts with the airbag (KEAM). The KEAM model highlights the various energy adsorption mechanisms and defines potential synergistic roles they play on energy dissipation. Finally, energy dissipation of an airbag made from a particular fabric was related to the properties of the fabric and the required volume of the airbag for reliable operation.

These two models, FMRM and KEAM, were then integrated with a passenger restraint action model (PRAM) in order to investigate the restraint action on the occupant during impact. PRAM is a model of numerical simulation for investigating the restraint achieved whh airbags. A detailed analysis of the interaction forces experienced after impact between the airbag and the occupant can be carried out with this model.