Failure Analysis of an Automobile Weldment

Abstract

A front-wheel drive hatchback automobile was involved in a severe front end impact. Failure analysis of the automobile revealed only a single sound spot weld in each of two 66 cm (26 in.) sections of both upper and lower floor sill flanges. Consequently, upon impact, the floor pan separated from the rocker panel, buckled and rotated upward and forward. This introduced slack in the seat belts since their retractors, being anchored to the floor pan, also rotated forward. Although not contributory to the accident itself, the faulty welds were responsible in part for the severity of the injuries sustained by the driver. The faulty welds in the unit body were apparently a consequence of improper settings of parameters on a multihead electrical resistance spot welding machine. Lack of appreciation of the hazard associated with failure of this weldment may have contributed to the low frequency of their physical inspection during production. A similar case involving faulty welds in a fuel delivery truck is also discussed.