Strength Behavior of Metal-To-Metal and Metal-To-Composite Joints 2001-01-3083

The use of composites in automotive applications necessarily leads to investigating the effects of attachment (joining) on the overall strength of the new configuration. Traditional joining methods used for metal-to-metal (welding) and composite-to-composite are not directly applicable in metal-to-composite structures. A testing program was initiated to examine the relative strengths of typical roof structure welded joints with alternative roof structure designs involving composites attached to metal by threaded fasteners. Frequently the attachment of a composite roof to the metal body of a vehicle includes the introduction of a gap joint with an intervening seal. Lap-shear testing was used to determine comparisons of relative joint strength between the various methods. The results of this testing are presented. The use of threaded fasteners to attach composites to sheet metal was found to dramatically reduce the joint strength relative to the welding of metal-to-metal. The expected negative effects of attachment with gap joints and intervening seals were also confirmed by the results of this study.