Study On The Dynamic Properties Of Airbag Fabrics

The permeability and deformation are the two principal factors influencing the safety of the airbag, especially for the uncoated airbag. In this regard, the material properties of the fabric can significantly contribute to the response of the vehicle occupant's interaction as he or she interacts with the airbag. The two properties that contribute to the energy absorbing capabilities of the fabric are its permeability and biaxial stress-strain characteristics. Currently, the accepted testing methods and standards have been recognized not ideal for testing the dynamic properties of airbag fabrics, as they are quasi-steady-state and the operating pressure of airbag fabrics is much higher than the conventional standards. Therefore, a new equipment is proposed based on the previous studies to measure not only the dynamic inflation but also the dynamic permeability of airbag fabrics meanwhile.Firstly, the central deflection of the airbag fabric subjected to penetration pressure from 0 to 50 kPa with an increment of 10 kPa was measured using a displacement transducer. Based on the experiment, the mathematical modeling of airbag inflation impacted by steady air pressure was constructed. Then the theory of membrane bending and the finite element method were used to solve this model respectively. The results showed that the latter one is more accurate. The numerical results indicated that the deformation surface of inflated airbag fabric under steady air pressure can be described as spherical cap, and the central deflection increases nonlinearly as the air pressure increases. The membrane stress at the fabric center is the maximum and becomes the minimum on the edge. Moreover, the membrane stress increases along with the increase of air pressure. The membrane stress in the radial direction is approximately equal to that in the tangential direction near the fabric center. The difference between the radial membrane stress and the tangential membrane stress is the biggest on the fixed edge, where the tangential membrane stress decreases to zero.Secondly, a new testing method of airbag dynamic inflation was proposed and the equipment was installed, which is composed of a high speed camera, a driver chamber and a driven chamber separated by a polyester diaphragm. At the end of the open driven chamber, the airbag fabric sample is clamped. This equipment can simulate the dynamic inflation of airbag by ruptured diaphragm. In order to screen the whole inflation process of airbag, the high speed camera trigger was designed and the trigger time is adjustable. Thus, the inflation height of airbag fabric at different time can be measured from the photographs.Thirdly, the mathematical modeling of airbag inflation impacted by high dynamic air pressure was constructed, and the deformation curve of inflated airbag fabric and the stress distribution were computed using the finite element method. The deflection height of the airbag fabric resulted from the simulation agreed well with the experiment data. The simulation results showed that the central region of deformation curve remains flat at the beginning of the inflation, then gradually disappears, and finally becomes arc as the pressure increases. In the dynamic inflation process, the stress of airbag, as well as the strain, nearly presents an annular distribution. Moreover, the strain at the fabric center is the maximum and becomes the minimum on the edge. The strain in the X direction is approximately equal to that in the Y direction, and both of them are the biggest at the fabric center. However, the strain in the Z direction has the opposite characters, which is the maximum on the edge and is lower than the one in the X, Y direction.Finally, the dynamic permeability of airbag fabrics were tested using the device proposed in this paper. It is found that the dynamic air flow rate increases linearly as the pressure drop increases. The relationship between the dynamic permeability and the deformation of airbag fabric was also investigated. It is found that the deformation is significantly minus-correlated with the dynamic permeability.