Assessing the effect of a thickness gradient on the shear stress profile at the epoxy/silicone interface of thin coatings subjected to transverse shear loads with finite element analyses

Low surface energy materials are used as foul-release coatings (FRCs) to reduce the forces required to remove biofouling. Previous experiments observed the release behavior of epoxy studs (pseudobarnacles) from silicone coatings with a thickness gradient. The studs were loaded transversely in thick-to-thin and thin-to-thick directions, and the final decohesion always proceeded from the thin to the thick side of the coating. However, trends in the critical transverse forces required for removal were not apparent. In this study, finite element models (FEMs) were created to determine the peak shear stress at the interface of an epoxy stud bonded to a silicone coating with a thickness gradient in response to a transverse load. The effects of the average coating thickness, the thickness gradient of the coating, and the transverse loading direction were determined. At a given average coating thickness, increasing the thickness gradient produced higher peak shear stresses at the interface, which would reduce the critical force required to remove the epoxy stud (i.e., would improve the performance of the FRC). The influence of the increased thickness gradient waned as the average coating thickness increased. Therefore, moderately thin coatings with large thickness gradients would be optimal for FRC performance under transverse loading.