Numerical Simulation And Experimental Research On The Permeability Of Airbag Fabrics

The permeability of airbag fabrics is one of the most important factors influencing the performance and safety of the airbag.If the permeability of airbag fabrics is too low,the airbag will receive a large impact loading and have a poor stability during the inflation;whereas if the permeability of airbag fabrics is too high,the airbag can not be quickly inflated,which increased the inflating time and made the airbag have a poor security.In order to ensure the security of the airbag,it is necessary to control and predict the permeability of airbag fabrics both accurately and regularly.The main research contents are given as following:Firstly,the airbag fabric was regarded as porous film based on the porous jump model.The static permeability of airbag fabrics was obtained by numerical simulation through exerting fixed pressure on the testing pipe.The results of numerical simulation show that:the static permeability of airbag fabrics increases as the pressure increases.The pressure in the testing pipe is unchanged before the airflow reaches the airbag fabrics and the pressure drops to atmospheric pressure when airflow is through the fabric.The inboard velocity of the syphon is larger than the outboard velocity.The velocity across the fabric changes largely,and two vortex areas are formed in front of the fabric,where the energy loses.Secondly,the results of numerical simulation of the static permeability were verified by static permeability testing.It is found that the difference between simulation results and testing data is small within a certain pressure,and the difference would increase as the pressure difference increases exceeding the pressure turning point.So,the results of numerical simulation don't fit to the tested data.By modifying the permeability of airbag fabrics with the trial & error method,the permeability considering the fabric deformation was obtained.Then the static permeability of airbag fabrics was computed over again.The static permeability of airbag fabrics resulted from the numerical simulation agrees well with the experiment data.In addition,through research on the relationship between modifying coefficient of the permeability and pressure,a way of predicting the modifying coefficient of the permeability by pressure is proposed.Thirdly,the airbag fabric was regarded as porous film based on porous jump model.The dynamic permeability of airbag fabrics was obtained by steady numerical simulation through exerting fixed pressure on the testing pipe.Then,the results of the steady simulation as an initial value,the unsteady numerical simulation was made by exerting dynamic pressure on the testing pipe.It is found that there is an apparently linear relationship between dynamic permeability of airbag fabrics and pressure.The separate vortex is formed in the step area of the testing pipe.It gradually decreases and moves to the step area as time increases.And the boundary layer is also moved to the step area.In addition,the pressure in the testing pipe gradually decreases with increase in time.The pressure between inlet and airbag fabrics is unchanged,but the pressure rapidly decreases to atmospheric pressure when the airflow is through the airbag fabrics.The results of numerical simulation of the dynamic permeability were verified by dynamic permeability testing.It is found that the dynamic permeability of airbag fabrics resulted from the simulation agrees well with the experiment data.Finally,the relationship between permeability and structure of airbag fabrics was investigated.The results show that the permeability coefficient of airbag fabrics increases linearly as the square of mean pore diameter of airbag fabrics increases.In addition,the permeability coefficient of airbag fabrics increases linearly as the porosity of airbag fabrics increases.The larger the square of mean pore diameter or the porosity of airbag fabrics is,the better the permeability of airbag fabrics is.