Steel, Al etc fatique

[dicer]

If memory serves the higher the heat treated strength of steel the more knotch sensitive it is, and is also more sensitive to low cycle fatique. How does Aluminum compair to different alloys and hardness of steels?
I know in the aircraft parts world we strive to keep down the stress risers on both types of materials. Is it really that important with Al?

 

[metengr]

dicer;
The fatigue behavior between aluminum and steel is very different. Instead of trying to summarize the differences, I have included a link to the site below. First, review the article on fatigue crack initiation and propagation for aluminum-aluminum alloys. After this, go back and navigate your way to the key to metals steel and review the various articles on fatigue of steel. The web site contains various articles that are worth reading.

http://nonferrous.keytometals.com/default.aspx?ID=CheckArticle&NM=197

 

[EdStainless]

Steels have a fatigue limit. If you are below a stress level you will have infinite life.
Al doesn't work that way. Even at very low loads you will eventually reach the fatigue limit.
Fatigue in these materials has to be managed differently.

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Plymouth Tube

 

[dicer]

Ed, that is interesting, but, from what I have seen Al has a very long fatique life. If it didn't we wouldn't see highly stressed aircraft parts still being used from many years ago say 60 to 90 years old, and gosh that was with old school metalurgy. I have always though that since Al has a very low knotch sensitivity that such things as corrosion and stress risers don't affect its fatique life, as much as steel correct? And as far as the low load deal I would think that is a steel related property. I have seen many more steel parts fail from low load cyclic stress than Al parts. So what alloys added to Al will increase the strength and fatique limits?