Incompatible Mode Elements
Incompatible Mode Elements
(OP)
Hello everyone.
Simple question: what are incompatible mode elements and how are they used? I'd like to get a general idea of the difference between this type of elements to the others (reduced, fully-integrated etc) and why are they so powerful for bending analyses - without going into too much maths.
Google search for 'incompatible mode elements' have produced unsatisfactory results. At least, none that are not riddled with too much technical/mathematical details.
Thanks y'all.
jo
Simple question: what are incompatible mode elements and how are they used? I'd like to get a general idea of the difference between this type of elements to the others (reduced, fully-integrated etc) and why are they so powerful for bending analyses - without going into too much maths.
Google search for 'incompatible mode elements' have produced unsatisfactory results. At least, none that are not riddled with too much technical/mathematical details.
Thanks y'all.
jo





RE: Incompatible Mode Elements
This is related to the use of low-order elements. In NX Nastran, when using CHEXA 8-nodes & CPENTA 6-nodes solid elements with no midside nodes, reduced shear integration with bubble functions is the default. This is recommended because it minimizes shear locking and Poisson's ratio locking and does not cause modes of deformation that lead to no strain energy.
The effects of using non default values are as follows:
• "IN = 3" produces an overly stiff element.
• If "IN = 2" and the element has midside nodes, modes of deformation may occur that lead to no strain energy.
• Standard isoparametric integration (ISOP = "FULL" or 1 and IN = 2 or 3) produces an element overly stiff in shear. This type of integration is more suited to nonstructural problems.
For geometric nonlinear analysis, it is recommended not to use incompatible modes by setting IN=2 or 3. If bending behavior is significant, it is highly recommended to use elements with midside nodes.
Best regards,
Blas.
RE: Incompatible Mode Elements
Use of incompatible mode elements can provide significant reduction of run times and results improvement in both 2 and 3-D where bending is present..
Hope this gives you a bit more of what you were looking for....
Ed.R.