Pull-off behavior of epoxy bonded to silicone duplex coatings

Flat-head studs, 7.2 mm diameter, were epoxied to 0.1-0.9 mm thick silicone layers attached to a rigid substrate. Pull-off tests were performed at nom inally 1.5 N/s to establish critical pull-off forces and detachment modes a t the epoxy-silicone interface. Most tests were performed on a two-layer co ating consisting of a silicone top coat and a stiffer silicone bond coat. A few tests were performed with a single layer of transparent silicone on a glass substrate, which allowed video analysis of the interface during pull- off. Critical pull-off force, P-c, decreased as the thickness of the coated layers increased. The thickness dependence of P-c was shown to be in good agreement with a model presented by Kendall for pulling a rigid cylinder fr om a elastomeric glue layer, but modified to account for a two-layer elasto meric coating; P-c varied as t(1/2)*, where t* is an effective thickness, w hich depends on the bulk moduli of the coatings as well as their thicknesse s. The observed pull-off mode was peeling, which occurred by nucleation, gr owth and coalescence of multiple voids initiated inside the contact area. ( C) 1999 Elsevier Science S.A. All rights reserved.