FEM Coincident Elements Bad?
FEM Coincident Elements Bad?
(OP)
Hi all,
I talked with an analyst recently about modeling up a composite preform joint, and after all the case studies he's done he told me that the nearest to actual results he got was to use coincident shell elements with different properties. After doing some searches, I wasn't able to find anything on coincident elements being an acceptable or unacceptable practice. I'm somewhat new to FEA, but I've taken a couple classes on the mathematical theory. After thinking about it for a while, I can't say it's necessarily wrong to do it that way from the theory, but my engineering "spider sense" tells me something's not quite right. Has anyone had experience with this or can anyone elaborate/correct me about this method?
Thanks!
Tim
I talked with an analyst recently about modeling up a composite preform joint, and after all the case studies he's done he told me that the nearest to actual results he got was to use coincident shell elements with different properties. After doing some searches, I wasn't able to find anything on coincident elements being an acceptable or unacceptable practice. I'm somewhat new to FEA, but I've taken a couple classes on the mathematical theory. After thinking about it for a while, I can't say it's necessarily wrong to do it that way from the theory, but my engineering "spider sense" tells me something's not quite right. Has anyone had experience with this or can anyone elaborate/correct me about this method?
Thanks!
Tim





RE: FEM Coincident Elements Bad?
Quando Omni Flunkus Moritati
RE: FEM Coincident Elements Bad?
RE: FEM Coincident Elements Bad?
Quando Omni Flunkus Moritati
RE: FEM Coincident Elements Bad?
If you have two or more coincident plate elements, for example, the total moment at an edge (or membrane force, or whatever) will be the sum of the moments in each of the coincident elements. If total force and moment resultants are of interest to you, you may need to write some sort of post-processor to find and sum the individual coincident plate element resultants.
Some FEA software systems have a "Composite" module which does the hard work for you - you specify your laminate build-up, and the software sums the individual lamina stiffness contributions to compose a single plate / shell element stiffness matrix. The structure is then solved using a single element, and then the post-processor takes the element force and moment resultants and back-substitutes to get the individual lamina force resultants.
http://julianh72.blogspot.com
RE: FEM Coincident Elements Bad?
RE: FEM Coincident Elements Bad?
Quando Omni Flunkus Moritati
RE: FEM Coincident Elements Bad?
However, if I was looking at something which is "thick-walled" and / or too irregular to model sensibly using plate-shell elements to capture the full geometry, I would typically model the "skins" using laminar-composite plate-shell elements, and fill the "core" with a mesh of solid elements. (You might even model "discrete" reinforcing components such as wire / cable, bar or strip pre-forms using linear "beam" elements.) You need to make sure you use a "compatible mesh" at the junction between the solid core elements and the "skin" plate-shell elements (and "beam" elements if applicable), to ensure full composite behaviour between the various components of the build.
Hope this helps!
http://julianh72.blogspot.com