While both Q8 (Quadratic Quadrilateral Element) and T6 (quadratic triangular element) are widely used for domains composed of quadratic elements, due to my investigation for problems containing high plastic deformation zones in stress concentration regions yield same results. Unlike the Q8 is mostly used than T6, T6 usually gives more controllable mesh density distribution, as well as lower analysis time and finer convergence (in the case of equal number of nodes for Q8 meshed and T6 meshed model). Altogether, is there still any advantage in Q8 respect to T6?
The fact that you get shorter cpu time with T6 is because you have only 2 Gauss points in triangular element instead of 8. So the total Gauss points in a triangular mesh results in half (order of magnitude) Gauss points if the nodes distribution is exactly the same, requiring less cpu time.
The fact that final results are identical means that your mesh is thick enough to get good results even with half nodes.
G.
Hi Pejman,
Excerpt from http://mihanbana.com/dl/matlab-Abaqus-mihanbana.com.pdf , page 305:
"...The 8-nodded quadrilateral element has curved sides, which makes it very useful in modeling structures with curved edges (Figure 9.69)...."
Excerpt from http://ziaeirad.iut.ac.ir/sites/ziaeirad.iut.ac.ir/files//files_course/10-linear_strain_triangle_and_other_types_of_2d_elements.pdf , page 15:
"...Q4 and T3 are usually used together in a mesh with linear elements.
Q8 and T6 are usually applied in a mesh composed of quadratic elements.
Quadratic elements are preferred for stress analysis, because of their high accuracy and the flexibility in modeling complex geometry, such as curved boundaries..."
Regards
For stress analysis, especially for finding stress concentrations near small features, for examples, holes, corners, etc., it is a recommended to use quadrilateral elements instead of triangular elements. The main reason behind this is the fact that, with quadrilateral elements, you can create streamlined meshes around those small features (see the attached figure) which will capture normal stress gradients more accurately when compared with unstructured triangular meshes. For the accurate evaluation of stress concentration factors, and estimation of fatigue life thereafter, getting the accurate value of stresses only on the surface is not enough. You also need to capture the gradients in normal direction accurately and this can be done efficiently using quadrilateral elements.
Triangular meshes are easy to generate when compared to those filled with quads, and such models run faster as well. However, faster is not always better and accurate. For some specific problems, for example, evaluating stress concentrations, accuracy is more important than speed. For such problems, you have to use quad elements and carefully generate the streamlined meshes around intricate features. If you want to stick to triangular elements, then you have to have extremely fine meshes, therefore spend more resources, in order to capture accurate gradients.
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