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No rating yet Subject: Re: [Other] GKH modulus Author: Monte McGlaun Date: 2008-05-06 20:24:25Another observation related to scatter. Every material I have had tested to obtain stress strain data has had variations from test to test in Young's modulus. This occurred at different labs and with different materials. Up to 30% variation! So much for constants.
What this means for a critical, dynamically tuned structure is that it is possible to see big differences between our calculations and the performance of the production assembly. Or we may see differences from one assembly to the other if they are made from different material lots.
Monte A. McGlaun, Staff Engineer Bell Helicopter Textron, Inc., Fort Worth, TX
-----Original Message----- From: xansys-bounces_at_xansys.org [mailto:xansys-bounces_at_xansys.org] On Behalf Of Chris_Masterson_at_Toyota.com Sent: Tuesday, May 06, 2008 2:34 PM To: ANSYS User Discussion List Subject: Re: [Xansys] [XANSYS][Other] GKH modulus
The interesting thing is that for this material we have been buying what
are supposedly Aircraft Quality certified mill runs directly from the mill to try and eliminate material defect problems and we are still stuck with about 25% rejection due to defects. The mill has worked up a new process that they claim will eliminate the problem, but the turn around time is so long for a new run that I have been forced to consider alternate materials with compromised specific stiffnesses. Apparently even aerospace certification isn't always good enough.
We do actually coupon test each delivery lot of certain stress critical parts to ensure that the full heat treat cycle was correct...and it is abolutely necessary to prevent failures as we fairly regularly catch heat treat errors and inconsistencies that would cause catastophic failures.
On the density front, I do at times add drawing requirements to verify mass upon receipt and allow for stock removal in non-critical areas if possible to allow the vendor to correct for material and machining variations. The nominal density error was only important for my up front design study not for the final production solution.
Regards, Chris Masterson Toyota Racing Development
"Carlos Shultz" Sent by: xansys-bounces_at_xansys.org 05/06/2008 10:54 AM Please respond to ANSYS User Discussion List
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Subject Re: [Xansys] [XANSYS][Other] GKH modulus
Paris,
>>The ultimate is to test the material at hand, sampling many batches & suppliers BUT who has the time and $$$ for that.
That's the aerospace solution. Coupon test every lot and put specifications on prints requiring specific properties.
Chris,
It might be possible to find already certified materials when someone else only buys a partial mill run...it wouldn't hurt to ask your vendors. Also, density shouldn't be too hard to determine (weigh and then displace some volume of water).
Carlos PADT
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