Practical adhesion - locus of failure

Clearly, from the above, practical adhesion depends on much more than just surface tensions  

Let us first examine the proper or ideal adhesive joints, an ideal situation with no flaws (cracks, etc.) and no contaminants (moisture, dirt, oH). Even for ideal adhesive joints, the real work of adhesion is often at least one order of magnitude lower than the theoretical value, or even less for poorly wetted systems. 

Not all adhesion problems are the same. The location of the locus of failure is quite important, as can 

Determination of the locus of failure is very important for obtaining a proper solution to the adhesion problem. It is not always easy to determine the locus of failure if the failure is at a place more than 100 nm from the interface it is rather easy to find the locus, but it may be more difficult at distances of 10-100 nm. 

If the failure is at the interface, then we may need to increase adhesive forces, e.g. via specific interactions, chemical bonds, enhanced entanglement, etc. If the failure is cohesive we may need to increase the strength of the materials. Finally, it is worth mentioning that the locus of failure may also depend on the rate of stress that is applied with fast stresses yielding often cohesive failure and slow ones adhesive failure. 

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