Method of Fatigue Test

[lLouie]

Hi,

We produced two wings, one made of Al7075-T6 and the other made of composite. We want to do fatigue test of these wings, however we do not to know procedure. We know the loads applied for climbing, cruising and descending. For example, between 0-1g load in climbing, between 1-2g load in cruise and between 0-1g in descending. Can you share any documents for the fatigue test, please?

Sincerely,

 

[rb1957]

have you tried to help yourself ? have you google "fatigue test methodology" ?

there's lots of material available, but probably nothing that does all the work for you !?

Is this for certification, or "only" commercial/company testing ?

If for certification, talk to your local people (I have an idea you're in Poland ?). The certification people should be a good resource for you. They point you in the right direction.

You have a few load cases, ok, a start. You need to build a spectrum from these, a sequence of loads. You should create a "block" of loads, a sequence you'll repeat many times for the test. maybe a "block" of 1000 flights ? A document I use (to generate a spectrum) is ESDU 69023, but there are others.

What size plane ? I think you've talked abut a UAV in the past, so ESDU69023 may not be very relevant ... you may need to flight test ... go fly for a bunch of hours with an nz meter onboard and a cycle counter. Or just guess !!?? particularly if you're comparing two different wings. But composite and Aluminium are sensitive to different loads (Al is more sensitive to low loads, composite is more sensitive to high loads) so testing both with the same spectrum may not work "well".

"Wir hoffen, dass dieses Mal alles gut gehen wird!"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[lLouie]

Yes, I have googled it Many articles do not give the fatigue test process, so I asked for your help.
I can say that, they specify the block of loads, as you said 1000 flights. Our UAV flies between 1g and 1.8g. I should try to do fatigue test in this range. Shouldn't I?
Thanks to hydraulic piston, the axial load can be done between 1g and 1.8g.
I want to know if this method is correct. Yes, I have researched the articles but I don't know if I understood it correctly. In addition, how can I specify the ''block of loads''?
I am not ESDU's subscriber, so I can not see the documents

 

[goutam_freelance]

Aircraft fatigue test is very specialized field. You need to consult relevant experts from aerospace design industry.

For general reference see Wikipedia.
Link
"The International Follow-On Structural Fatigue Test Program (IFOSTP) was a joint venture between Australia, Canada and the U.S. to fatigue test the F/A-18 Hornet."

Now! Or it may be too late.

 

[rb1957]

Ok, I thought the links described a fatigue test quite well.

1) you need a test article (got that), that needs to be conformed to some set of engineering. You may want to install s/gauges to collect data at either control points (to verify the loading and your FEM) or at points where you have done analysis.

2) You need a load apparatus ... a hydraulic jack is the start of this, you also need a "whiffle tree" to distribute the load over the test specimen. Many other details like how to support the test article (will it be grounded, fixed to the ground at a point, or will it be "flying", with complete balanced set of loads and reactions) how to "tare" the test specimen (as weight is not part of the loading ... you could count it as part of the reaction but not typical practice). Many questions !

3) you need a test spectrum (I've said this repeatedly). Yes a test spectrum is different load levels, yes 1g and 1.8g many be representative; but how many load cycles to apply for 1 hr of flight, 1 flight cycle, whatever you choose.

4) Again repeatedly I've asked for certification or for company experience ? If for certification you need to talk to your local certification agency, and they can help but you'll need more technical support than you have demonstrated to date.

5) I think you've said this is for a UAV. I suggest that current spectrum generation tools are not appropriate for this type of airplane. I suggest that you measure the spectrum of loads your plane reacts to but doing flight test (with a loads monitoring system installed), collect data for several thousand hours to be somewhat confident. I'd also use this loads monitoring system on delivered airplanes, to gather more data, to verify the data you've collected.

6) I think you need professional help !

"Wir hoffen, dass dieses Mal alles gut gehen wird!"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.