DESIGNING RELIABLE POLYMER-COATINGS

A method to predict the ultimate adhesion performance of coatings subj ected to biaxial, tensile stress is presented. A set of equations is d eveloped to predict the onset of failure when the locus of failure is cohesive in the coating. The equations also have been extended to pred ict fatigue lifetime when a coating is cycled from a low temperature t o room temperature. To test these equations, the Edge Liftoff Test (EL T) was developed. It consists of fabricating coatings of various heigh ts on a rigid substrate and dicing the latter, so that the edges are 9 0 degrees to the interface. The parts are cooled and the temperature o f debonding is recorded. For thermal fatigue validation, cycles at whi ch the first debond is observed are recorded. ELT results have been co llected for a typical epoxy for both monotonic and cyclic cooling. The predictions are in agreement with results.