Indentation-debonding of an Adhered Surface Layer

Abstract

In many technological applications (e.g. circuitboards), relatively thin, soft polymer layers are bonded to a harder (metal) surface. A new mechanical test for the adhesive bond strength between these layers using sharp, needle-like indenters, has been developed. This test and its experimental-analytical features are described in this paper. In the central indented region of the bonded polymer, compressive deformations of the top layer and subsurface take place. At the rim of the central indented area, however, a tensile stress is induced in the interfacial bond between the top layer and the substrate. Debonding occurs when this stress exceeds the bond strength. A debonded polymer surface layer displays Newton's rings because it diffracts light. Observations indicate that the debonded segment of the surface layer behaves as an elastic plate between the rim of indentation and the unfailed bonded region. The “peeling moment” capacity of adhesive at the bonded edge limits the bond resistance. Considering the latter as a constant parameter (a characteristic of the bond) a relation predicting the debonded radius in terms of the indenting force is derived.