Element Size v Stresses 5

[ellas1]

I am very rusty with FEA. To check the effects of the mesh size with the accuracy of the results, I analyzed two 1/2"x4"x10" simply supported plates loaded with 10 psi on the local Z axis. The first plate was meshed with 1"x1" elements and the second with 1/4"x1/4". The stresses on the 1/4"x1/4" element are double than the stresses on the 1"x1". Based on my hand calculations the bending stresses are close to the results of the 1"x1" mesh.Can anyone explain the differences?

Note: I always thought that smaller elements produce better or more accurate results.

Thank you

 

[JoshPlumSE]

EngAddict -

I was limiting my discussion to plate elements only since that was the nature of the OP's question. With most plate elements there is a thickness to least width ratio beyond which the element formulation begins to degrade and results do not improve with further sub-meshing. In fact, the results are supposed to degrade.

 

[EngAddict]

Thanks for the clarification.

I don't have any references that support this, perhaps you could list some for my own understanding?

All my testing on plates elements show the stress converging then not increasing any discernible amount, but not degrading..

These stresses at my convergence point match very accurately the hand calculations too.

Therefore I can only conclude that the mesh should be refined until the stress converges, regardless of whether using solid elements or plate elements. Any further refinement will not compromise the results but will only waste computational time.

Maybe the observation of stress degradation is limited to a particular plate element type with a few select codes? Perhaps now outdated with newer code revisions?..

 

[inline6]

when modelling spot welds in a plate model using beam elements node to node connected a fine mesh can lead to stiffnesses that are too low due to local bending deformation.

Also if you are talking about a 20mm thick plate you wouldn't use a 1mm mesh size.