SURFACE PREPARATION FOR ADHESIVE BONDING.

Abstract

Results of an experimental program are presented which show that epoxy adhesive bonded joints with sandblasted surfaces are stronger than those with polished surfaces in the brittle temperature region. There is an optimum surface roughness, degree of chromate etching, and specimen size for maximum joint strength with aluminum adherends. A fracture mechanis is proposed in which the formation of microcracks under applied stress is concentrated at the adherend asperities. The coalescence of these to form one or more cracks of critical length leads to brittle fracture. The cracks are thought to form in the interfloccular phase of the epoxies rather than through massive carbon-carbon bond rupture. The higher strengths of roughened surfaces are attributed to the indered coalescence of the microcracks.