Failure of attachment points during RTCA DO-160 Vibration Testing

[rhlg75]

Hi folks,

Do you know if failure of attachment point (representative of actual installation and used to fix the equipment under testing) during Rtca DO160 Vibration testing is considered acceptable (attachment point can be replaced and testing can be resumed)or it constitutes a failure to meet DO-160 vibration test pass fail criteria? DO-160 does not contain any clarification on this aspect. I wonder to know if there are other standards thar provide guidance on this.

Thank you,

 

[GregLocock]

If you get no better response (I have never run DO-160, or indeed any fatigue test where I couldn't ask someone with vastly more experience), then I suggest that if the failure is on the fixture side of the fastener joining fixture to item under test then it is probably OK to document, repair and carry on. If the failure is actually in the item under test (any part of the whole thing) then it has failed the test. In that case it may be that your fixture doesn't accurately replicate the in-service boundary conditions, and so the test was too severe on the IUT near the attachments, but frankly it is a bit late to find out now.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[IRstuff]

However, I would think that your customer would want some proof that the failure wasn't induced by the UUT, i.e., that the UUT possibly was resonating so hard that it caused the failure, which would be bad if that were to happen after installation.

Generally, fixtures are typically strong enough that they should not fail during a test. As a customer I would very concerned, both about the failure, and your apparent lack of concern.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:

http://www.engineering.com/AskForum/aff/32.aspx

 

[amanuensis]

Other standards : GAM EG13, STANAG 4370

 

[rhlg75]

Thanks for all your reply.
I agree with IRstuff that the failure of the attachment point is a matter of concern - however, RTCA DO-160 is applicable to equipments and not structural elements. Therefore, my concern now is to validate that equipment will pass on vibration testing - verification of the attachment points ability to withstand the loads resulting from Vibration testing can be treated separately and redesigned if needed. Do you agree? Tks

 

[IRstuff]

Again, I would disagree with that last statement. You need to prove that the failure was not induced by your equipment and that the loads applied to the attachment points do not exceed what actual aircraft attachment point are designed for. I do not think that you can treat this as some sort irrelevant thing. I think you miss the point qualification tests; the EMI tests are perhaps a better analogy. In the EMI tests, you need to prove that your equipment does not fail in the EMI environment; likewise, you need to prove that your equipment does not create an EMI environment that would be deleterious to the aircraft, i.e., susceptibility vs. emission. An aircraft airworthiness qualification is all about protecting the aircraft from the equipment being installed within it. In fact, consider the crash worthiness test, where your analysis would demonstrate that it does not become detached from its mountings in a crash and fly through the compartment and kill or injure the occupants; there, a failure occurs whether you or the attachment points fail, because if the attachment points fail, you may not have a sufficient number of attachment points, or your installation was insufficient to protect the attachment points.

TTFN
faq731-376
Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:

http://www.engineering.com/AskForum/aff/32.aspx

 

[DHambley]

rhlg, Could you explain a little more about what these "attachments points" are? Do you mean the bolts themselves which attach the UUT to the aircraft which are "representative of actual installation"? or is it the test equipment that these bolts (or rivets or whatever) are attached to?

Darrell Hambley P.E.
SENTEK Engineering, LLC

 

[rhlg75]

Hi IRstuff

Thanks for your reply. I understand your position and fully agree with you - failure of the attachment points indicates design issues and needs to be resolved. Thanks again

 

[rhlg75]

Hi DHambley

The failed item is a tie rod - even though it did not break, the soft mount at its end cracked - this was noted due to the shift on the ressonance search at the end of the testing for one axis.

Thanks,