In the Loop - Tech Tips Understanding Metal Fatigue

By Bill Freeman EAA #148597, Reprinted from the 1981 EAA Designee Newsletter
Technical Tips Manual Vol 2

In the aircraft community the term "metal fatigue" is often used without any explanation, usually in reference to some part which has failed an inspection or perhaps a part which has failed in service.

Some self-styled authorities will say that the metal "crystallized," which caused it to crack. You may envision the metal somehow getting "tired" and failing, and in some older aircraft it might seem that there was good reason to become tired, but these are far from the reality of metal fatigue. 

Fraction of Endurance Limit Allowable table

On any part of the surface finish is important if you want to avoid any stress concentrations. A highly polished surface finish has the best fatigue resistance. See the table above.

READ MORE in the attached PDF at the bottom of this page.