The Durability of Lap-Shear Adhesuve Bonds Following Accelerated Environmental Testing

Poor durability of steel/adhesive bonds in the presence of moisture has inhibited widespread structural use of this joining technology. The durability of metal/adhesive bonds can be influenced by a number of variables. Effects on durability due to substrate, surface preparation, and environmental exposure were examined using single lap-shear adhesive joints. Cold rolled steel, galvanized steel, and Zincro-metal adherends were untreated, alkaline cleaned, lubricated or zinc phosphated prior to bonding. All samples using treated bare steel exhibited higher initial bond strength but poor to fair durability. However, samples prepared from Zincrometal adherends actually retained most of their initial strength even in accelerated environments. The reported results suggest that simply cleaning adherend surfaces prior to adhesive bonding is inadequate to insure long term durability. Rather, a moisture resistant barrier layer must be deposited between the steel/adhesive interface in order to significantly improve the durability of structural adhesive bonds.