Ftigue Information 3

[cirokos]

Hello there,

I am trying to find Wohlers curves or S-N curves for aluminum 5052. More specifically I want to calculate the fatigue life of a component made from this material with the Miners law but I cannot find fatigue information about the material.

Any help would be appreciated.

Thank you.

 

[dhengr]

Antonis25:
None of the people who have posted got angered or or particularly sarcastic, but the question was asked, answered quite nicely, by John, and then asked again; as though you didn’t bother the read the answers. The guys who have participated in this thread are top-of-the-class here on E-Tips, so you are getting darn good advice, from the creme of the crop here on E-Tiops. BTW your problem is really quite complex, and your problem presentation is really quite weak in terms of engineering details to start a meaningful discussion. So, in terms of our knowing what you are really trying to accomplish, how would we answer other than broadly, trying to draw you out, trying to get more details. If you think the small holes are causing the problem, can you eliminate the holes in the critical areas? Then, test that sample, or a few of them, and compare the results against the basic model. Anything you do with your design which adds stress raisers, like holes, bonding flaws, sharp geometry changes, etc. will probably outweigh the basic material properties unless you are using some really junky material.

 

[rb1957]

sorry, I don't think you really want a s/n curve for 5052, because as you (I think) rightly pointed out ... your form is quite "unusual" (compared to typical metals under fatigue, like airplane fuselages).

The endurance of the honeycomb is not well represented by the base material. does the weld (between the core and the facing) affect things ? most likely. If one portion of the core fails, does that failure entire panel ? unlikely. I'd've thought there were rules of thumb for designing a sandwich panel under fatigue which wuld give you a much better answer.

To answer your question a different way, why do you think your panel is sensitive to fatigue ? Is your fatigue load close to your design load (which is close to the panel allowable) ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Sparweb]

Just a side note: I did some digging on the chart that JohnBaker posted. That's for flame-sprayed Aluminum 5052. That process is completely different from rolled sheet or foil - to a degree that it is misleading to use that chart for a foil product at all. SN data must be based on tests, and the samples being tested must be of approximately the same form as the application in your interest. For instance, cladding has a drastic effect on the fatigue life of 2024 sheets with and without this treatment. There are two different charts to use. And that's just the difference between sheet cladding and not. The differences between rolled sheet and flame spray are beyond reach.

It is rare for 5052 sheet to be used in applications subject to fatigue, therefore I doubt any test data exists to support it. Just for fun I did a search through my electronic copy of Jaap Schijve's book on Fatigue, and "5052" doesn't even come up. Nothing in NASGRO either.

Last point: Your application is never subject to fatigue cracking. Honeycomb cells always fail by buckling (either shear or compression) or rupture. Besides, even if there is a "crack" (which would actually be a tear in the foil) it would grow to the next cell intersection and stop, permanently. You are chasing a wild goose, my friend.

 

[cirokos]

Here is my attempt to explain the subject a bit more clearly.

The problem is indeed a honeycomb panel subjected to shear fatigue stress. The core walls have some tiny perforation holes from which cracks appear in a very low number of cycles and lead to early fatigue failure. The material is Al 5052 with a yield strength over 300 Mpa. I am trying to find fatigue data of similar material with foil-like thickness to be representative of the one used in my experiments.

In my understanding, there is no actual data available to help me. Any guidance towards where to look that might be helpful would be great.

Thanks again and sorry for any trouble.

 

[LittleInch]

In my understanding, there is no actual data available to help me.

I think you have answered your own question.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cirokos]

LiitleInch
That was a conclusion I made from the answers I got!
I agree that's why I made that final comment with a bit more detail addressing everyone.

 

[rb1957]

it must be a really odd failure ... fatigue of honeycomb cell walls because of small "vent" holes. Have you considered other core materials ? maybe balsa wood ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[cirokos]

It is a really odd failure and happens too soon! I cannot do any changes just, my part is only to do some analysis and investigation.

 

[rb1957]

if it happens what are you investigating (if you can't change anything) ?

You think you understand the failure, then that gives you some ideas on what to attack.

I might talk to honeycomb panel people (like Hexcell) to see if they've ever seen something like this.





"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[cirokos]

I am investigating the stress concentration around these holes. Because these holes create a gap in the material it is expected to see a jump in stress, if the stress is significant it will alter the life o the panel. That's why I want the fatigue life of similar material, to find out approximately the life with those concentrated stresses.

If you have such connections and could do that it would be great!

 

[SWComposites]

He means you should contact Hexcel.

Do a search for Hexcel TSB-120 document. There is a very slight chance it has some info.

But you are very unlikely to find any useful public data. You will need to run your own tests.

What is the specific panel configuration?
What is the purpose of the holes? Size? Spacing?
What is the specific panel loading?

 

[rb1957]

Sorry, no such data. I'd commission a test program to determine the effect.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[cirokos]

Never imagined it would take such scale! There is no need to commission tests. we could discuss it somewhere else.

 

[cirokos]

SWComposites :

More general information is contained in that document. I am looking for fatigue data.

 

[rb1957]

how do you answer the question without any (readily available) data ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[cirokos]

rb1957 :
Which question you are referring to?

 

[rb1957]

I was replying to your observation ... "There is no need to commission tests."

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[cirokos]

firstly, I don't want to put you in any trouble.
Are you willing to carry out tests for a honeycomb panel or fatigue tests for the material?

If you want you I can provide my email to discuss it further.

 

[rb1957]

no.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Tmoose]

"The core walls have some tiny perforation holes from which cracks appear in a very low number of cycles and lead to early fatigue failure."

Who is doing the perforating, and how do they do it?

Please post some detailed pictures of the failed panels.