Failure analysis of seat belt buckle inertial release

Failure not only occurs when components fracture or yield under stress; it is also characterized by components failing to perform a required action. One such mechanism involving automotive seat belt buckles is the phenomenon commonly referred to as inertial unlatching. Inertial forces and motions resulting from accelerations and decelerations accompanying real world collisions such as vehicle rollovers can trigger the unwanted release of certain side-release and end-release buckles, leading to occupant injury or death. This study demonstrates this failure mode of some commercially produced automotive end-release buckles, and presents laboratory testing correlating accelerations to unlatching. Case studies of forensic evidence of unwanted inertial unlatching in practice are given.