Detecting defects in adhesion between a metal hemisphere and a polymer base

Detecting localized defects in adhesion on a spherical shell is challenging, especially if one has access only to its rim. Our group previously quantified the spatial average of the adhesion between a metal hemisphere and a polymer base [1]. Here we report on progress towards determining the presence of localized defects, their position, size, and strength. Tests were performed on a 5 cm diameter metal hemisphere attached to a UHMWPE (Polyethylene, PE RCH 1000 D150×2000 Etralene) base. Defects in adhesion were generated by machining hexagonal holes (5 to 17.5 mm) into the polymer base prior to fixing by adhesive. These known areas without adhesion were remotely characterized with a guided ultrasonic wave (Lamb quasi-modes) generated by a Nd:YAG (1064 nm, 8 ns pulse duration) pulse from one rim of the shell and detected with a laser Doppler vibrometer. We detected the presence and position of the defects.