Adhesion durability mechanical aspects

Additional work must be completed before these hydration inhibitor treatments will be widely used. However, it appears that combined FPL/inhibitor pretreatments have the potential of producing water stable aluminum oxides with structures that promote mechanical aspects of adhesion in a relatively simple manner. Since mechanical adhesion mechanisms are not greatly affected by water, these pretreatments show promise as a means of increasing the durability of metal/polymer adhesion systems in wet environments. 

On that basis, the book intends to bridge current issues, aspects and interests from fundamental research to technical apphcations. In seven chapters, the reader will find an arrangement of latest results on fundamental aspects of adhesion, on adhesion in biology, on chemistry for adhesive formulation, on surface chemistry and pretreatment of adherends, on mechanical issues, non-destructive testing and durability of adhesive joints, and on advanced technical applications of adhesive joints. Prominent scientists review the current state of knowledge about the role of chemical bonds in adhesion, about new resins and nanocomposites for adhesives, and about the role of macromolecular architecture for the properties of hot melt and pressure sensitive adhesives. Thus, insight into detailed results and broader overviews as well can be gained from the book. 

Another chemical treatment that has resurged recently due to improvements made in its formulation is the hydroxymethylated resorcinol (HMR). HMR has been used successfully with several timbers and adhesives, to promote the exterior durability of their bonded joints [65, 71]. Consequently, this technique seems ready for industrial application, at least for the species and adhesives tested. Nevertheless, studies to clarify some aspects of its action mechanism are still needed [20]. 

Durability is one of the most important aspects of the performance of a structural adhesive. The durability of an adhesive joint is the sum total of its responses to environmental effects such as heat, moisture, other chemicals, radiation, and mechanical stresses. Cyanoacrylate-based adhesives have a reputation for poor durability, especially when bonding metals... 

The interfacial regions have been highlighted as the regions where moisture may attack adhesive joints and the various mechanisms of environmental attack which have been postulated to explain the loss of durability are considered below. It should be emphasised that they should not necessarily be viewed as mutually exclusive mechanisms. Certainly there is ample evidence that no single mechanism can explain all the different examples which have been reported and which one is operative in any situation does depend upon the exact details of the adhesive system and the service environment. Also, it is noteworthy that the exact details of the mechanism of environmental attack may be dependent upon the timescale, temperature and stress level which the bonded Joint experiences, and these aspects are also discussed below. 

As discussed below, the classic example of the problem of oxide stability upon exposure of bonded joints is with aluminium and its alloys and this aspect has therefore been investigated in detail by the aerospace community. Particularly, the fundamental micro-mechanisms have been studied in order to explain observations such as those shown in Fig. 8.10, which reveals the effect of three common aerospace surface pretreatments upon the subsequent durability of the adhesive joints. The three treatments which have been studied in some detail are chromic acid etch (CAE), chromic acid anodize (CAA) and phosphoric acid anodize (PAA), and details of the processes were given in Section 4.3.4.5. 

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