Any discolouration of the adhesive in the joint may well suggest that the assembly has been subjected to environmental attack. Excessive temperatures may burn or discolour the adhesive and water ingress can cause some adhesives to discolour or lose their hardness. Thicker bond lines are often more prone to environmental attack and joints that are subjected to peel or cleavage loads are also more likely to suffer from harsh environments. Analysing the failed surface often provides clues as to the root cause of failure. There are also some sophisticated surface analytical techniques available including X-ray photoelectron spectroscopy, Secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy [4]. These surface-analysis techniques are beyond the scope of this guide but all three are particularly useful for identifying surface contaminants to a depth of a few nanometres or even less with SIMS.
Adhesion problems, however, are usually complex and they are unlikely, in general, to be solved by the application of a single analytical technique, although these can provide very good directives as to the source of the problem.