Large Deflexion analysis won't converge

[sandcd]

I'm trying to analyse a fairly simple flat plate under surface pressure (out of plane loading) using large deflexion theory. I have no problem down to a plate thickness of 2mm but as soon as I drop below about 1.6mm I get an error message saying that the iteration will not converge. I haven't given any value of yield strength, so the plate can't be actually failing. Now the maths shouln't care what thickness I use so I presume it is some sort of limit in a default setting. I have had a go at changing these but haven't got anywhere.

Has anyone got any ideas why I am having this trouble.

Thanks

 

[corus]

Large deflection problems can fail if your load is at the buckling point or snap-through point. Maybe that's happened when you reach a certain plate thickness. The yield stress doesn't come into it, but the problem is still non-linear dependent upon plate thickness.

Tata

 

[sandcd]

Thanks for your response. To be honest we normally assume that buckling has occurred when the iterations don't converge but in this case we can't see how the plate can buckle. It is restrained all round its perimeter and we are only applying an out of plane load so the plate should be in tension. We have simplified our actual model to be a simple rectangular plate but still get the same error message at low plate thicknesses. Is the difference in deflections from one iteration to the next related to plate thickness and if so can this somehow be changed.

Any suggestions would be welcome.

 

[rb1957]

i don't think it's a buckling issue ... do you specify the initial load step ? the thinner plate will experience large deflections earlier than the thicker one (sounds like motherhood when you write it out)

 

[crisb]

Does the program automatically reduce the load if it doesnt converge at your required loading, and/or have you tried to solve this under a reduced loading?
Have you tried altering numbers of iterations and any other available solution parameters?
Do the boundary conditions allow the plate to go into tension, when bending deflections get large?

 

[JohnyGluebag]

Check to see if the element is set for membrane behavior, might help.

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JohnyGluebag