Environmental durability of moisture-cured urethane adhesive joints

Hot-dipped galvanized steel was bonded to fiber-reinforced unsaturated poly ester (FRP) with a moisture cure urethane. Single lap shear joints were mad e with bondline thicknesses of 0.76 mm and bond areas of 25.4 mm x 25.4 mm. Single lap shear joints were aged by cataplasma, cyclic moisture, QUV(R), Weather-Ometer(R) and an oven at 60 degrees C. Cataplasma aging and cyclic moisture aging resulted in a 23 and a 28% drop, respectively, in lap shear strength of joints made with acetone-wiped surfaces. QUV(R) and oven aged j oints resulted in increased lap shear strength, and oven aged joints change d in failure mode from adhesive at the galvanized steel interface to cohesi ve failure. Weather-Ometer aged joints failed adhesively at the FRP interfa ce, but after closer inspection by environmental scanning electron microsco pe (ESEM) adhesive could be seen on the surface of the FRP. QUV(R) light ma y not always penetrate the adherend materials even though natural sunlight penetrates the same materials. When conducting accelerated aging of adhesiv e joints made with FRP adherends that allow light to penetrate to the joint , workers must carefully consider the light source and adherend material us ed in the design of accelerated aging experiments. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.