Measuring the interfacial shear strength of thin polymer coatings on glass

The interfacial adhesive shear strengths of four commercial polymer coatings on soda-lime glass were measured by the microindentation and single lap shear tests. The indentation interfacial shear strengths were over an order of magnitude greater and exhibited significantly less variability than those measured by lap shear. It is believed that the indentation test measures the “intrinsic” interfacial shear strength of the bonded coatings, whereas the lap shear strengths are controlled by large processing flaws (pores in this study) in the region of stress concentration near the overlap edge.