7.2.3 ‘No adhesion’

The third (and probably the most common) failure mode is when the adhesive does not adhere properly. This may be due to several factors, including surface contamination, oxide layers, incompatible substrates, low surface energy substrates and/or excess moisture. The general cause of this failure is a mismatch of adhesive and substrate or lack of proper surface preparation (see Section 2 for further discussion of the basics of bonding and adhesion and Section 4 for surface preparation).

7.2.4 ‘No Performance’

One of the most important requirements of an adhesive joint is its ability to retain a significant proportion of its properties under the wide variety of expected environmental conditions encountered during an assembly’s service life. The factors that impact the performance, integrity and longevity of the adhesive after being fully cured, and assuming the other three factors (No Glue, No Cure, No Stick) have been addressed, are high humidity, extreme temperatures, chemical exposure, thermal cycling and UV exposure.

One of the most aggressive, hostile and damaging environments for any adhesive is the combination of high humidity and high temperature. Many manufacturers now demand performance after 1,000 hours at 85°C (185°F) and 85% RH, which is exceptionally challenging.

The durability of adhesives is the most difficult area to troubleshoot, as by its nature, it is likely to be observed quite some time after the component parts were assembled. If there are concerns that an adhesive has been subjected to environmental degradation, adhesive engineers should be engaged to assist in the analysis, as the parts may need to undergo laboratory analysis to determine the specific environmental factor or combination of factors that impacted its performance. It will be necessary to include investigations on the other three factors (No adhesive, No cure, No adhesion) when analyzing loss of performance is usually the last step of an investigation because it is the hardest to identify with certainty.

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