Failure of automobile seat belts caused by polymer degradation

Abstract This paper analyzes the failure of a particular brand of automobile seat belts. The failures described were part of what nearly became the most expensive and widespread automobile recall in U.S. history, affecting about 8.8 x 10 6 vehicles and with a potential total cost of U.S. $10 9 . The failures were caused by the degradation and fracture of the seat belts’ polymeric release buttons. When fragments break away from the buttons, they can become lodged within the seat belt mechanism in a variety of locations, such that any one of three distinct failure mechanisms can result: (1) the belt fails to latch, (2) the belt will latch but will not unlatch, and (3) the belt appears to be latched but is not. The seat belt mechanism, and the ways in which the degraded button can cause it to fail, are described in detail. The buttons themselves were found to have been injection molded of ABS and to have undergone photo-oxidative degradation. This degradation process is documented and described. Conclusions from the analysis and lessons learned from the failures are described, along with the auto industry|s short- and long-term solutions to the problem. © 1998 Elsevier Science Ltd. All rights reserved.