ADHEREND SURFACE-MORPHOLOGY AND ITS INFLUENCE ON THE PEEL STRENGTH OF ADHESIVE JOINTS BONDED WITH MODIFIED PHENOLIC AND EPOXY STRUCTURAL ADHESIVES

A detailed investigation of the interfacial region between the oxide and the adhesive/primer for aluminium peel test specimens, bonded with Redux 775 and AF163-2K/EC3960 and covering a range of peel strengths between about 1.8 to 12.3 N mm-1 has been undertaken. Transmission electron microscopy (TEM) and scanning electron microscopy examination has shown that increasing adherend roughness on scales of tens of micrometres and tens of nanometres correlates with increasing peel strength. Measurements of carbon, aluminium and oxygen on both sides of the fracture surface for in situ peeled AF163-2K specimens have been made using X-ray photoelectron spectroscopy. This was found to corroborate the TEM morphological evidence that enhanced peel strengths arise because of the presence of very fine scale whisker-like features at the surface of the oxide. Theoretical calculations are also presented which demonstrate one mechanism whereby roughness on a scale of tens of micrometres could give rise to enhanced peel strength.