FEA corelation
FEA corelation
(OP)
Hello, I am analysing a sandwich panel as a plate and trying to corelate the displacment and stress with theoretical solution. I ran the analysis and the displacments conforms well with the theoretical solution but not the stresses. I don't understand why it works this way. i am comparing the vonmises stress. Any suggestions? Thanks.





RE: FEA corelation
RE: FEA corelation
RE: FEA corelation
Good Luck...
RE: FEA corelation
RE: FEA corelation
RE: FEA corelation
2) FEA is an approximate, numerical solution to a continuum mechanics problem; it will not give exact answers except for simple cases like statically determinate problems with boundary conditons and loadings that do not produce numerical singularities.
3) Please describe in detail your model and theoretical analysis.
RE: FEA corelation
1.) deflection
2.) Facing stress
3.)Core shear stress
What I observed was the deflection matches exactly with the theory.But the problem is with stresses. I checked the ply1 vonmises stress for the facing stress. but the error is 14%..could i compare the facing stress with the principal stress? it does compare well though.
Now with the core shear stress as i refine the mesh the shear stress is goin on increasing.
I am using Pcomp to analyse the sandwich panel.
So, swcomposites..how do i rectify the singularity condition..cause my boundary condition seems to be allright? Thanks for your suggestions..
RE: FEA corelation
2) What theoretical solutions are you comparing to? How do you know that they are correct?
3) Where are you comparing stresses? in the center? at an edge? at a corner? You have to compare streses from the modl at the same location as the hand solution. Start be comparing at the center of the plate.
4) I doubt the hand solultion predicts von mises stresses, so forget using them. Also, forget using principal stresses as they can be confusing and misleading for comparisons. Compare x and y direction stresses in the plate.
5) For which loading case do you get the "error"?
6) Simply supported plates loaded out-of-plane will typically have a stress singularity in the corners. Thisis due to the fact that the corners tend to deflect upwards under a downward pressure load.
7) Turn off ALL contour plot averaging. Make comparisons only using un-averaged element stresses (not nodal stresses). Nodal stresses are typically not accurate since they are extrapolated from the element streses calculated at integration points. Contour plot averaging of nodal stresses is even worse and often produces results that look good but are rubbish.
RE: FEA corelation
I am not getting any error. The analysis runs without any problem.I checked the normal stresses in the plies i.e the facing sheets but it ds nt ocmpare well wth theory whereas principal stress does.
How do i turn off the contour plot avergaing? Thanks for your patience.would u like to take a look at the problem?
RE: FEA corelation
The Hexcel beam example is analyzed using a beam formula; you are modeling it as a plate, therefore you will not get the same results.
The Hexcel plate example is analyzed using an old Mil-Handbook-23 approximate plate soluton using (I think) a truncated series solultion. It does not surprise me that you are getting different results in your FEM. The maximum stresses in the facesheet should be at the center of the plate, so compare your FEM results at that location (do not just look at the maximum values anywhere on the plate).
RE: FEA corelation
Have you checked that your constrainted points do not take load? Look at your "constraint forces", because it seems that part of the load of your model is being withstood by these point, which is wrong.
Good luck!