Effect of coating thickness on the stress profile at the epoxy/silicone interface subjected to pull-off loading: A finite element analysis

Abstract

Previous experimental studies of silicone coatings have shown three distinct types of release behavior in the tensile flat punch test, depending on coating thickness. The mechanical response in the punch test is highly dependent upon the Poisson's ratio of the coating and its confinement ratio (punch radius divided by coating thickness). This study developed a high accuracy finite-element model of the punch test using the adaptive p-method with extensive mesh refinement to produce smooth stress profiles up to the punch edge. Stress distributions were found for a wide range of confinement parameters and Poisson's ratios. At a typical Poisson's ratio of 0.49, the highest center stress occurred for the intermediate thickness coatings—not thin or thick. Also, the thickest coatings demonstrated steadily increasing high stress towards the edge, while other thicknesses showed the steep singularity at the edge with a protective stress depression bordering inside it. The results further help explain why the critical pull-off force continues to increase as the thickness decreases, even with different release mechanisms. The stress profiles for thick coatings have almost no sensitivity to Poisson's ratio, unlike other thicknesses which show high sensitivity. Edge peeling is most likely to occur for all thick coatings, while other debonding modes are most likely for thin and intermediate thickness coatings. Together, results show the stress mechanics of the flat punch test follow three distinct types of confinement.