Mathematical predictions of gas permeability for automotive air-bags

The mathematical relationship combining an applied pressure drop and the re sultant gas velocity through a woven fabric is important to the air-bag ind ustry to predict the performance of new materials before they are woven. Th e 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 co nsiders the same approach and analyzes some of the equations to review thei r industrial applicability. Because none of the equations have been found a daptable in predicting the permeability behavior of air-bag fabrics, experi mental data have been used to generate empirical equations. The data were g enerated using a dynamic air permeability tester that was used to project a ir at high pressure through a variety of air-bag fabrics. A static permeabi lity tester was also used to generate results through the same fabrics at l ower pressures. The final equations combine the fabric cover factor and the pressure differential to give the resultant gas velocity. (C) 2000 John Wi ley & Sons, Inc.