Solid Elements (/PROP/SOLID)

Linear elements are better in terms of time and memory consumption, especially due to the low number of integration points and a larger time step ( $\text{Δ}t=\frac{L}{c}$ ):

• TETRA4: $L=a\sqrt{\frac{2}{3}}=0.816a$
• TETRA10: $L=a\frac{\sqrt{5/2}}{6}=0.264a$
• BRICK8: $L=\frac{Volume}{l\text{}\arg \text{}estfacearea}$
• BRICK20: $L\approx \frac{thickness}{2}$

Table 1 summarizes the differences between theses elements. For BRICK8, the use of co-rotational formulation is explained in Element Library the Radioss Theory Manual; which can avoid the accumulation of an error, due to the updating process, especially when elements undergo large shear deformation. The formulation is not used by default for this element and should be activated by you.

Figure 1. Solid Finite Element Meshes in Radioss

Solid elements can be degenerated to overpass some meshing problems. Degenerated elements can be obtained by merging nodes on a same edge (hexahedron) or suppressing a middle node in a TETRA10. The use of degenerated elements is not recommended, but if they cannot be avoided due to complex geometry, it is important to respect the element symmetry to keep a homogenous mass distribution. Some examples of degenerated solid elements are shown in Figure 2.

Figure 2. Solid Elements Degeneration Examples