Thermal Stresses in Pyrotechnic Initiators Used in Automotive Supplemental Restraint Systems
Airbags were responsible for saving 14,772 lives in the US between 1975 and 2003. Currently, over 146 million vehicles are equipped with airbags that are expected to function properly during a long vehicle life span. The airbag’s pyrotechnic initiator is responsible for its deployment in crash situations. Cracks have been observed in the insulating glass that potentially can allow moisture to penetrate the initiator and degrade the pyrotechnic and bridgewire; degradation of the pyrotechnic or bridgewire can result in the initiator not functioning. The goal of this work was to determine the cause of the cracks with respect to the manufacturing process and to compare the results of this model to cracks observed in actual initiators returned from field service. Closed form solutions were used to determine basic stress magnitudes. A three-dimensional, finite element analysis was used to determine more exact stresses including the effects of transient cooling. The analysis showed that if the manufacturing process involves pouring molten glass into the initiator, the likelihood of cracking is high. Further, if the surface of the initiator cools faster than the center, cracking could result.