Mathematical predictions of gas permeability for automotive air-bags

Abstract

The mathematical relationship combining an applied pressure drop and the resultant gas velocity through a woven fabric is important to the air-bag industry to predict the performance of new materials before they are woven. The main difficulty in formulating a mathematical solution is the complexity of the woven fabric structure. In available publications, fabric pores had normally been represented as a series of cylindrical pipes. This article considers the same approach and analyzes some of the equations to review their industrial applicability. Because none of the equations have been found adaptable in predicting the permeability behavior of air-bag fabrics, experimental data have been used to generate empirical equations. The data were generated using a dynamic air permeability tester that was used to project air at high pressure through a variety of air-bag fabrics. A static permeability tester was also used to generate results through the same fabrics at lower pressures. The final equations combine the fabric cover factor and the pressure differential to give the resultant gas velocity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2104–2112, 2000