Effect of Heat on the Properties of Automotive Airbag Materials

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Abstract

Automotive airbags are subjected to extreme temperatures (up to 900°C) during deployment which is achieved by using pyrotechnic inflators. Although the airbag fully inflates within a few milliseconds, the heat often causes physical damage to the airbags fabric and seams in this short period of time. In this study, the effects of heat on airbag yarns (highly drawn Nylon 6,6) and airbag fabrics were investigated with the goal of understanding whether or not high heat causes the internal structure of the material to change. The degree of crystallinity of the material was found to increase as the delta H values of the material increased with heat and heating rate in a Differential Scanning Calorimeter (DSC) for both unheated and heated fibres (extracted from airbag yarns) as well as unfired and fired airbag fabrics. The storage modulus of the material was also found to drop gradually as the material was heated from sub-zero temperature to melting point in a Dynamic Mechanical Analyzer (DMA) with sharp drops in the glass-transition and melting regions. The initial stiffness and the breaking strength of the material were found to decrease in a tensile tester as the temperature and heating rate at which the material was heated increased. This unusual behaviour, i.e. a reduction in stiffness and strength with a rise in the degree of crystallinity was found to be due to a reduction in the molecular orientation of the fibres as high levels of shrinkage were observed for both yarns and fabrics when the material was heated. The shrinkage increased with increasing temperature and heating rate which caused the diameter of the fibre to increase. Upon correlation with shrinkage, the initial stiffness and breaking strength of the material were found to be inversely proportional to shrinkage while the breaking strain was proportional to shrinkage.

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