INFLUENCE OF PAINT BAKING EXPOSURE ON THE LAP-SHEAR PROPERTIES OF A POLYMER-CORED LAMINATED STEEL

Effect of thermal aging on the lap-shear properties of an acrylic-core d laminated steel was investigated by shear testing of specimens follo wing exposure in air to the paint bake temperature of 180 degrees C. T he laminated steel consists of two thin steel layers bonded to a polym er core. It was found that thermal aging caused an increase in shear m odulus and a decrease in ductility. Shear strength initially decreased , but then increased with aging time. Fractographic, thermal gravimetr ic, and differential scanning calorimetric analyses indicated that the decrease in shear strength and ductility is likely caused by void for mation resulting from evaporation of the volatiles in the acrylic. The se voids increased the local stresses. The subsequent increase in shea r strength is attributed to the increase in adhesive cross-linking fro m thermal curing which hardens the adhesive. The increase in shear mod ulus with increase in aging time is ascribed primarily to thermal curi ng.