On Mar 4, 10:57pm, "Dunst, Mordecai" wrote:
>> Q) Conventional wisdom dictates that a magnafluxed piece of
>> ferrous metal is OK to use. Suppose that piece of metal has been
>> used for MANY hours...under hard loads. i.e. a buddy of mine has
>> an older airplane. About 8,000 hrs on the engine. He has the
>> standard annual and has the crank magnafluxed-"OK". He says the
>> FAA says its ok to re-use. Is it?
>> It seems that magnafluxing is an operator dependant task i.e. someone
>> can spend a little time or a lot of time on the procedure.....
John Lye replied
>I'm by no means an expert, but my understanding is that magnafluxing
>will only detect surface cracks. X-raying will detect internal
>flaws .. I guess what you need to
>be worried about is fatigue, and I don't know of a method to
>detect that until it progresses so far that cracks are propogated
>to the surface. Anyone else know of one?
I won't say that I am an expert but I do make a living as a mechanical
engineer analyzing structures (not engine internal components though).
In a crank, fatigue cracks would start as surface flaws and propagate
inward. I believe the highest stress in a crank would be due to
bending and bending stress is a maximum at the surface. Checking for
surface cracks with Magnaflux is the right thing to use in this case.
The process is operator dependent but not terribly difficult. A
skilled operator would know precisely where to look for cracks, e.g. at
cross-sectional changes near the crank arms. Just my opinion. Will
deny any responsibility if the crank breaks at 10 kft.
Pat Willems
p-willems@ti.com
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