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Re: Magnaflux

To: shop-talk@Autox.Team.Net
Subject: Re: Magnaflux
From: pbw@chong.dseg.ti.com (Pat Willems (@chong))
Date: Wed, 5 Mar 97 07:27:06 CST
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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