Non-contact quantification of adhesion between a metal hemispherical shell and a polymer by guided acoustic waves

Guided acoustic waves (GAWs) are sensitive to delaminations between two materials. Certain modes can determine changes in adhesion for well-defined geometries. Considering the sensitivity of GAWs to detect delaminations, there is a paucity of attempts to quantify the adhesion between a hemispherical shell and a surrounding medium. The purpose of this study was to 1) quantify the average adhesion of a hemispherical metal shell to a polymer and 2) demonstrate that it is feasible to localize delaminations in the adhesion. A pair of custom made, needle-based transducers were used to launch GAWs into a 5 cm diameter, 1 mm thick hemispherical metal shell. The experiments were done in two parts: first, the average adhesion of a metal shell to a polymer was quantified by GAW attenuation. The shells were attached to a polymer (ultra-high molecular weight polyethylene) with various degrees of adhesion, ranging from a shell resting freely in a taylor-made polymer cavity to a shell which was adhered to the polymer with excess epoxy. In the second part, an artificial defect was generated in the interface between the metal shell and adhesive by drilling a hole into the polymer (to generate areas with no adhesion). Echoes of GAWs determined that defect localization on a curved surface is feasible. Finally, we determined that noncontacting laser ultrasonics could be used to replace the contacting needle-based transducers.