> I don't know of a method to detect that until it progresses so far that
cracks are propagated to the surface. Anyone else know of one?
>
>cheers,
>
>John Lye
__________________________________________________________________
John,
Fatigue cracks start at the surface and work their way into the material.
Think about where the loads are carried in a steel cylinder. They are
carried near the surface, that is why a pipe is approximately as strong.
Consequently, the fatigue crack will start at the surface and slowly work
inward., Each time the part is stressed the crack will progress further
inward to relieve the stress. This will result in a part with "beach
marks.", ie, the fatigued surface will have half circle lines emminating
from the start of the fatigue crack. Fatigue failure cracks "point" back
to the place where the crack started. Of course, on a crankshaft, if it
goes far enough to break the two surfaces will probably rub together and
destroy all the good evidence anyway, so.........
Anyway, magnaflux is acceptable for external or fatigue crack detection.
If there is any fatigue cracking it will be detected.
BTW - John, I finally got the shocks off, I had to loosen one spring
pedestal only. More later when I get the links off. Now where did I put
my 20 Ton press?
Jack Brooks
BSE Mechanical Engineering/Material Science
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