Using finite element analyses to assess the effect of a thickness gradient on the stress profile at the epoxy/silicone interface of thin coatings subjected to pull-off loading

Abstract

Silicone-based materials can be applied on ship hulls to serve as foul release coatings. Depending on the application, coatings are not likely to have a uniform thickness. Pull-off tests of epoxy studs from silicone coatings with a thickness gradient found that for the thickest coatings, release initiated at the edge and proceeded inward with no bias in the peeling direction, and as the thickness decreased the release initiated on the thin side of the coating. Release mechanism and critical pull-off force were also affected. In this work, finite element models were developed to predict the detailed stress field at the silicone/epoxy interface in silicone coatings with a thickness gradient. Average coating thickness, thickness gradient, and Poisson's ratio were varied to determine changes in the value and location of the peak interface stress and determine the properties that produce the highest peak interface stress, which should correspond to the lowest critical pull-off force. While the peak stress increased with increasing thickness gradients in all cases, the optimal geometric properties depended on the Poisson's ratio of the coating, so the specific material chosen is an important factor. The location of the peak stress was nearly always on the thin side of the coating when a thickness gradient was present, although the exact location (i.e., edge or interior) also depended on the Poisson's ratio.