Success in adhesive bonding of components requires careful control of the bonding process, surface condition and an understanding of the operating environment. Forensic analysis forms an important part both in the optimisation of bonding processes, understanding the factors that affect bond quality, and in the evaluation of bond failures.
The situations where forensic analysis may be used in practice include the following:
1. Failure investigations - Failure of bond
3. As part of design, procedure and method optimisation
4. Following inspection and monitoring to evaluate bond
The most common usuage of forensic analysis for adhesive joints is following failure or leakage of the joint. It is important to establish why the failure has occurred and what are the causes.
There are many variables in adhesion processes and optimisation is not always straightforward.
The most common reason for failure of a joint is inadequacies in the surface preparation methods used. Failure to properly carry out the bonding and application of the adhesive or to adequately cure are also important. In many bonding applications it is important to achieve uniform coverage of the adhesive as any unbonded areas may act as stress concentrators.
Even where bonding has been properly carried out failure may occur if the service loading, environment or temperature goes outside the limits for which the joint was designed.
Forensic analysis may be useful following proof testing either to ascertain a cause of failure or leakage or to identify any hidden damage that may be present within the joint.
In any new adhesive joint application there may be the need for a development programme to optimise the surface preparation, mix of adhesive, bonding procedure, curing and other conditions. This may include mechanical testing to verify the integrity and strength of join that is achieved.
In some applications it may be prudent to inspect or monitor the bond to give confidence in the current condition. At it’s simplest this may entail visual inspection. Non-destructive methods may also be deployed. If the inspections give rise to concern for example there was evidence of leakage or local disbonding it may be prudent to undertake a more detailed forensic investigation on selected joints.
Based on this analysis an appropriate maintenance strategy can be put in place. Such analysis may be useful where adhesively joined components have been in service for a significant fraction of their design life to give confidence in component integrity or provide a case for life extension or scheduled replacement of the joints.
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