NASGRO High Humidity Air (HHA) for Material Crack Growth Properties

[SAITAETGrad]

I guess the crux of my question is "are all high humidity air environments equal" or, at least in terms of NASGRO database HHA, is the definition of HHA sufficient to cover civil aircraft without a further environmental knockdown factor? Assume of course the affected area of analysis does not involve sump, fuel, saltwater, etc. environments.

 

[SAITAETGrad]

Since my question is not gathering much interest, I will open it up into something more general.

How do you validate the real world environment relative to the specified laboratory environment for crack growth curves, particularly NASGRO database material data?

 

[FastMouse]

I don't use the NASGRO database, although the materials I usually deal with are the normal aerospace aluminium alloys. As a general rule, the da/dN data that I use are generated in lab ambient conditions and no adjustment for actual operating environment is performed. In terms of civil aircraft, I can imagine that most operating environments are not totally dissimilar to the lab ambient conditions, and in any case, feedback from the fleet-wide scheduled inspection program will (should) detect any undesirable trends.

Early in my career I queried my then-employer about the fact that we did not take into account the (approx) +20C to -40C to +20C thermal cycle that external structural components, like wing skins, would experience. I never really got much of an explanation and did not pursue it. In any case, it can be argued that this thermal cycle is of little significance.

Short answer: No knockdown factor.