Blakmax
Thanks for all the info, yes, I finally read the paper.
So I wanted to clarify a couple things and just make sure I have this right.
1. We are basically talking about adhesion and mixed failures if the bond is the problem? Because if we are talking about cohesion failures then the bond remained strong and the disbond failure was most likely a result of something else loading the blade beyond the design limit?
2. If the blade passed some kind of initial structural or NDI test out of the factory then it is assumed that for a non-cohesive failure, the bond degraded over time due to hydration?
The rate of strength loss depends upon a number of factors, the most important of which is the process used to prepare the surface during the factory bonding process. If the process produces chemical bonds which resist hydration. then the bond will last a long time. If not, then a shorter life will result. Other factors include higher operating temperatures and humidites, both of which will accelerate the hydration process and hence shorten the service life of the component.
Now, of all the tip disbonding examples I have seen there is a high percentage of adhesion failure. Erosion by itself can not cause adhesion or mixed mode failure in otherwise sound adhesive bonds. Hence, the entire discussion about which tape to apply is meaningless unless the bond failures are confirmed as pure cohesion failures.
3. Hydration can be slowed down but not eliminated and you are saying that the most important way to slow this down is proper surface prep? But you are saying that the paint covering the bond line does very little to prevent hydration? And are you also saying that an exposed bond line will not appreciably accelerate hydration of a well prepared and executed bond?
Please make sure that I am thinking of all this correctly.