When adhesives are used for repairs, it’s extremely important to know what you can expect from the part repaired in such a way. Lack of trust in adhesives is often a consequence of wrong expectations.
Fact is, a repaired part cannot be expected to last forever, performing in the same way it always has. You must ask yourself why it failed in the first place. Was it put under forces too high to withstand? Did a high stress impact damage it?
You’ve all heard the saying that a chain is only as strong as its weakest link – it’s the same with any part: it will break on its weakest spot. Very likely, the design at the breaking point was less than perfect and presented a failure risk from the beginning. Once you’re forced to repair, you might want to consider slight changes in the design of the part. Perhaps you’re able to enlarge the area you want to bond, add some additional or reinforcing material. Only bonding the part back together without taking any additional actions to improve it will quickly result in a new failure, once put under the same forces that made it fail before. Even when the adhesive itself is strong enough, it doesn’t help with the material of the repaired part being too weak.
You have to be especially aware when you’re repairing high strength materials like metal. Adhesives are in their chemical basis plastic materials. Which makes them about ten times weaker than metals. So adapting the design of the part becomes crucial here as well.
And finally, it is possible that you’ve adapted the design and the adhesive is in principle strong enough, but the repair still doesn’t work. Well, then the reason for the failure may be in the one thing I keep hammering in most of my articles: surface preparation. Cleaning, cleaning and more cleaning. Roughening the surface can also help, when possible, because it basically enlarges the adhering surface area on micro level. And again – if you feel insecure about what to do, never hesitate to contact an expert.