Plate and Beam composite

[Jag2003]

I have a sanwhich structure made of two beams inbetweem two flat plates welded. This structure was pressurized and after some time ( 50 PSI) I hear a pop noise..this continued as the pressure was increased upto 300 psi. Then when the pressure on the plate was reduce slowely, still heard a pop noise. Can some one explain what caused this noise? Thanks for any suggestions.

Jag

 

[ishvaaag]

If I understand well you have say an WF at left, one at right, then one plate covering all atop and one doing the same thing below.

Now a guess on the pops. It may be that the plates have initial out of plane deformations, some of them in the form of depressions toward the interior. Even if the general shape of the edges is quite undeformed, these depressions may turn unto bulging ones when some specific inner pressures are reached. The pops you may be hearing would be then the claps of elastic buckling, not unlike the one we hear when agitating sheets of silverfoil around chocolat.

 

[Jag2003]

The plates are 1" thick and the beams are 6x6x1/4 hollow. beams are connected to the plate by 3 continuous longitude welds at 3 corners. ( Due to acces, 4 th corner inside is not welded)

Plates were flat before welding. It is possible small deflections after weld. Still, can it act like agitating sheets?Also could this popnoise ( high pitch metal to metal knocking noise)could be due to shear slippage between plate and beam on the unwelded 4 th corner?

Thanks


Jag

 

[ishvaaag]

I don't think at your thicknesses then elastic buckling is the culprit. Might it be some kind of resonances with the pressure from the pump device input yes clapping the inner unwelded corners against the plate?

 

[RiBeneke]

Perhaps your welders tacked the inner 4th edge of your beams where they could reach into the box from the ends. If they did, then the tacks would have cracked under pressure, and perhaps 'clicked' together when the pressure was released.

I am also concerned about the wisdom of applying internal pressure at 300 psi to a structure like this ??

 

[ishvaaag]

I was thinking during a walk, has the structure as such been checked?

Consider these things:

In code NBE EA-95 of Spain welding a 1/4 thing to one 1 inch thick is really not allowed since the weld exceeds the maximum for the thinner element and the minimum for the thicker, whichever the way. This is not to say there won't be instances where such problems appear and welds are made but surely other codes are called unto place for justification.

Coundn't be that the strength concentration provoked by the lack of the inner welds in one of the plates has initiated failure, and you have heard two instances of which during inflation? Think for a moment, to the exten it can resist moment, the sole weld will try to fix the plate, and the stress concentration start cracking through the weld or heat affected zone.

 

[Jag2003]

Just to clarify, pressure was applied on one side(not internally). Think of a both end fixed plate pressurized (loaded) in the middle.

In this case, instead of using a flat plate of 4", this built up structure provides adequate resistance to deflection due to pressure load.

The structure was checked using FEA and shear calculation was carried out to specify the weld thickness. It is interesting to know about Spanish welding code. But I believe weld like that is pretty common. ( for instance in tube to shell weld in a pressure vessel)

 

[ishvaaag]

Then what comes to my mind is the differential displacement at the free non welded inner corner overcoming steel-steel friction. You would be seeing two instances of the relative displacement.

 

[Jag2003]

ishvaag & Ribenke,

Thanks a lot for you input. Steel to Steel friction Vs Shear slippage will be my guess too. Anyhow, do you know of any research work / text / code spec to look up more on this topic.

Thanks again

Jag

 

[ishvaaag]

really not, but look Google

http://www.google.com/search?q=Noises+Steel+Structures&hl=es&lr=&ie=UTF-8&oe=UTF-8&start=20&sa=N

There are some promising links.

Also comes to my mind that the tubes will have the corners round. Upon application of pressure this may induce curvature in the webs of your composite structurem this being concomitant to what said.

 

[Jag2003]

ishvaag,

Thanks for the info. Carried out a test today and results are quite interesting. Assuming it was metal to metal friction, applied lubricant between the metal and then pressurized. There was no poping sound !! Looks like infact the differential displacement overcomming the friction created the noise.

Wonder anyone did (sureley there should be!!) research on this topic !!

Jag

 

[ishvaaag]

Thank you for the feedback, Jag.