Contamination rectification for structural adhesive bonding

Abstract

Structural adhesive applications have increased in popularity only recently even though they have been in existence for the past forty years. The largest single factor impeding a wider application of structural adhesives is the lack of confidence of the practicing engineer. This was due to the limited success adhesive applications enjoyed in their initial implementation. However, the advent of adhesives with better properties, better surface preparations and most of all, a better understanding of an adhesive joint has led to strong and durable bonds. So much so that the aircraft industry has invested substantially in structural adhesive applications. The fact that the aircraft industry has the highest safety factor in commercial industry and is second only to military and aerospace standards, should clearly show the integrity of adhesive bonding today. However, a lack of confidence still exists and this is due to lack of knowledge and its non-availability and not to its existence. The scope of this thesis is thus two-fold. The first scope is that of gathering relative theoretical information necessary to overcome the ignorance on the subject. This afterall was necessary as background knowledge to help a better interpretation of the results. The theoretical part is found in Part I of the thesis. The main scope however is that of examining the possibility of rectification measures for contaminated surfaces prior to structural adhesive bonding, which is covered in the second part of the thesis. The surface of the parts to be joined is perhaps the weakest link in an adhesive joint, this being due to probable surf ace contamination after the surf ace had been carefully pre-treated. The possibility of strong joints with contaminated surface is something that would be welcomed in engineering industry. This is especially true in workshops where the probability of contamination is much higher than that for a laboratory. What is contemplated here is the possibility of cleaning the prepared surface, now contaminated, without going through the whole procedure of retreating the surface from the beginning. This would not only save time and money but in most cases, retreatment of the surf ace is futile as the probability of contamination would still remain high. Such rectification measures would not only give bonds of a higher integrity but would open the fields of applications of structural adhesive bonding much wider.