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# 2nd order tetrahedral element vs First order hexahedral element

## 2nd order tetrahedral element vs First order hexahedral element

(OP)
Hi,
Between tet10 and brick, which of the above would be prefered for bolted joint analysis? Outside of a bolted joint, for other applications like crash analysis or for even a static stress analysis, which one would be better given meshing is not an issue? I understand that tet4 elements are stiffer in response compared to hexahedral elements, but wouldn't second order tetrahedrals bring out better accuracy or atleast comparable to that of hex elements? Would the math relating to shape functions would suffice to solve this question?

### RE: 2nd order tetrahedral element vs First order hexahedral element

Abaqus users are advised to choose linear hex elements for problems involving contact. If there’s also bending involved, then linear hex elements with reduced integration are recommended. For bending-only and stress concentration problems, one should use quadratic elements (possibly hex). For nonlinear dynamics like crash simulations, linear hex elements are good.

### RE: 2nd order tetrahedral element vs First order hexahedral element

Dear Pike12,
Not doubt here, if you can mesh with HEX 8-nodes elements not comparisson with TET10 ones, more accuracy and smaller model size (around 10 times smaller!!) when using the same elemet size.
When I need extremely accuracy in stress results (like in contact problems with curved geometry) you can use high-order HEX20 elements.

Tetrahedral elements can fit better any complex geometry, true, this is the strong point of TET meshing. But when you integrate the shape functions with Gauss points is less accurate than hexahedral elements. So the main limitation of HEX elements is the geometry.

BUT we have in FEMAP V2306 a new command named "HexMesh Bodies" that is able to mesh ANY CAD 3-D solid geometry, with little to no simplification or subdivision into smaller and simpler regions, as long desired by the finite element analysis community. Simcenter Femap has collaborated with other development organizations in the Siemens Simcenter Portfolio in order to offer this exciting technology to Femap users (the technology comes from the guys of FloEFD for SOLID EDGE CFD code), I love it & use a lot!!.

The hex-dominant mesher first fills a solid volume with as many hexahedral elements as possible, then fills the remainder of the volume with wedge, pyramid, and tetrahedral elements, as needed. This process creates high quality elements which can be sent directly to the Simcenter Nastran solver with no additional interaction from the user or manual refinement of the mesh.

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog de FEMAP & NX Nastran: http://iberisa.wordpress.com/

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