Originally Posted by chornedsnorkack
Does the aircraft aluminum, when subjected to excessive forces, fail by cracking, or by bending out of shape while remaining in one piece and keeping its strength?...
If loaded beyond its design strength, aluminum begins to deform. Aircraft that have been overstressed (hard landing, abrupt handling...) may have visible wrinkles in the aluminum skin and still be deemed safe for flight. On the wall of a classroom (back when I was in university) was a photo of a DC-6 static test with startlingly large wrinkles in the fuselage - but still in one piece.
Things may start breaking when the ultimate load is reached - usually 50% beyond design load. Or, a structure degraded by fatique may break - very unusual in airplanes, but it apparently happened to the Grumman Turbo Mallard
off Miami Beach in December.