Why we use different types of meshes in abaqus like triangular element type,square element type etc,what is the significance of each element type ?

Dear Aamir:

There are many reasons why various kinds of elements are used. Shall give a simple example. Let us say we would want to mesh a simple 3D structural problem with general purpose solid elements. FE offers us at least the following choices:

Tetrahedral element with four nodes. This is the simplest element possible. It is a linear element. Good if you have no other choice. We use this element when the geometry is so complex that becomes otherwise difficult to mesh. It is a robust element that does not give you problems while solving. It could be beaten to shapes as sharp as a needle and the solver does not complain much except to throw-up a warning or two and continue solving. The disadvantages are it is too stiff in bending and your mesh size should be large. This means, you would consume more memory and solution time. This element does not capture stress gradients adequately. There is also another problem. When the mesh density is high, a single node is shared by too many elements. Now nodal stresses are averages of the nodal contribution of each element. Each nodal contribution is extrapolation from gauss points. We end-up getting unwieldy nodal stresses. But the element centroidal stresses could be still acceptable. So, what do we do? We go to the next better element.

Tetrahedral element with 10 nodes. This element is the same as the above but has mid-side nodes. Good when you import solid models from CAD and create a quick FE mesh. This element could also be used to mesh complex geometries but is a bit finicky. FE uses serendipity (commonly iso-parametric) elements where every element is mapped to a master element. This makes the numerical integration through Gaussian quadrature easier. When we do this, we run into what are called as Jacobians (involves a simple matrix and some basic differentiation). When any element matches well with the master element, the transformation functions are robust. If the master element and the finite element differ greatly, the mapping becomes quite fragile, for example when you have folded elements, kinked edges, etc. FEA does not like bent edges in elements even with mid-side nodes simply because the master element does not have kinked edges. While such problems are almost nonexistent in a linear tetrahedral element, it starts to show-up when you have mid-side nodes. However, since these elements have mid side nodes, they are a lot flexible than item #1. But still, the stress gradients at sharp corners, crack tips, etc. are not adequately captured. The number of nodes and elements and hence the computational time is even larger than item #1. So, what do we do? We go to the next better element.

Tetrahedral element with 10 nodes but mid nodes of a vertex moved close to an apex. These are called as Barsoum’s quarter point (or one-third) element. By moving the mid nodes towards the apex, we bend the stresses sharper and this approaches stress singularity in sharp edges better, as in a crack tip. However, this is only a desperate attempt to capture stress singularity. You could either use this element to capture steep stress gradients or use many elements to capture similar effect. Barsoum’s elements just offer us some extra convenience instead of huge mesh density in crack tips. Nothing more and nothing less!

Brick element with 8 nodes called as a hex element due to its six faces. A simple, but excellent element. Creating a good-looking mesh with this element is an art. Quite a flexible and well-behaved element and if you have a hex mesh, enjoy!

Brick element with 20 nodes, called as hex element with mid nodes. Same as above, but with mid nodes. Naturally flexes like a snake, but hogs on computer time. You don’t use it unless you would have to.

Then you have special general purpose elements, which are the same as above, but takes care of shear and volumetric locking. Shear and volumetric locking are easy to understand but have been irritants.

Only the very bests to you!

-Sathya Prasad

Messaoud Saïdani

Dear Aamir

The existence of different shapes of elements, such as square o triangular, is in order to allow more refined mesh were needed, for example in areas of high stress concentration where greater accuracy is needed, especially if the shape of modelled structures is complex. In such cases it is very common to combine square and triangular elements. Also, the number of nodes on each element may also affect the results.

Best wishes

Martin Baeker

Please read the analysis and the getting started manual on element choice. There are a lot of issues to think about in choosing the correct element type (you can give a full-semester course on this), so this is not something to be answered easily.

Sabeel Mehmood

The wide range of elements in the ABAQUS element library provides flexibility in modeling different geometries and structures. Kindly visit the following link for more details:

https://mashayekhi.iut.ac.ir/sites/mashayekhi.iut.ac.ir/files/u32/presentation10.pdf

Yalew Mekonnen Fenta

Different mesh element types are used in Abaqus in order to use them according the geometry of the model (Structure) you have for analysis. Use of appropriate mesh element type will make your approximation close to the theoretical result of your problem. You will reduce the percentage of error between your simulation and the theoretical results.

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