/PROP/TYPE11 (SH_SANDW)

This property is compatible with XFEM (crack propagation) using /FAIL/JOHNSON, /FAIL/TAB1 and /FAIL/TBUTCHER.

Format

Definition

Comments

1. I_shell, I_sh3n – 4-node and 3-node shell formulation flag
   • I_shell=1,2,3,4 (Q4): original 4 nodes Radioss shell with hourglass perturbation stabilization.
   • I_shell=24 (QEPH): formulation with hourglass physical stabilization for general use (istotropic + LAW25 shells only).
   • I_shell=12 (QBAT): modified BATOZ Q4γ24 shell with four Gauss integration points and reduced integration for in-plane shear. No hourglass control is needed for this shell.
   • I_sh3n=30 (DKT18): BATOZ DKT18 thin shell with three Hammer integration points.
2. I_smstr- Small strain formulation
   • Small strain formulation is activated from time t = 0, if I_smstr =1 or 3. It may be used for a faster preliminary analysis, but the accuracy of results is not ensured. Any shell for which can be switched to a small strain formulation by Radioss Engine option /DT/SHELL/CST, except if I_smstr =4.
   • If I_smstr =1 or 3, the strains and stresses which are given in material laws are engineering strains and stresses; otherwise they are true strains and stresses.
3. h_m, h_f, and h_r - Hourglass coefficients
   • h_m, h_f, and h_r are only used for Q4 shells. They must have a value between 0 and 0.05.
   • For I_shell=3, default values of h_m and h_r are 0.1 with larger values possible.
4. d_n - Shell numerical damping coefficient
   • d_n is only used for I_shell = 12 and 24.
     • for I_shell = 24 (QEPH), d_n is used for hourglass stress calculation
     • for I_shell= 12 (QBAT), d_n is used for all stress terms, except transverse shear
     • for I_sh3n=30 (DKT18), d_n is only used for membrane
5. I_thick- Shell resultant stresses calculation flag
   • If I_thick=1, the small strain option is automatically deactivated in the corresponding type of element.
6. I_plas- Shell plane stress plasticity flag
   • It is recommended to use I_plas =1, if I_thick =1.
   • I_plas=1 is available for Material Law 27.
   • If I_plas=1, the small strain option is automatically deactivated in the corresponding type of element.
7. I_drill - Drilling degree of freedom stiffness flag
   • Drilling DOF stiffness is recommended for implicit solutions especially for Riks method and bending dominated problems.
   • I_drill is available for QEPH, QBAT (I_shell =12, 24), and standard triangle (C0) shell elements (I_sh3n = 1, 2).
8. Anisotropy direction definition.
   The reference vector $\mathrm{V\text{'}}$ is projection of the input vector $V$ on the shell element surface and defined as following according to the flag I_P:

   • If I_P=0 and skew_ID = 0, the vector $V$ is defined with V_X, V_Y and V_Z.
   • If I_P=0 and skew_ID ≠ 0, the vector $V$ is the first direction (local X) of the local coordinate system skew_ID.
   • If I_P = 20, the vector $V$ is defined with the node N1 and N2 of the shell elements.

     
     
     Figure 2. I_P = 20

   • If I_P = 22, the vector $V$ is the first direction (local X) of the local coordinate system skew_ID. Vector components V_X, V_Y and V_Z are ignored.

     
     
     Figure 3. I_P = 22

   • If I_P = 23, the vector $V$ is defined with V_X, V_Y and V_Z. The reference vector $\mathrm{V\text{'}}$ is the product of vector $V$ and the shell element normal direction $n$ . Local coordinate system skew_ID is ignored.

     
     
     Figure 4. I_P = 23

   Then for each layer, the 1^st material direction (m1) is vector $V^{\prime }$ turned ${\varphi }_i$ degrees (turns positive direction around shell normal $n$ ).

   
   
   Figure 5.

   The hierarchy order to define the reference vector $V$ is:

   • initial state card (/INISHE/ORTHO)
   • shell property

   In case of reference metrics, the orientation for directions of anisotropy must be defined with the reference geometry, not the initial one.

   The 2^nd material direction m2 derived from direction m1 rotated 90 degrees (orthotropic).

9. I_pos – Layer position
   • I_pos = 0: layer positions are calculated automatically with "Thick".
     If $Thick\ne {\displaystyle \sum _i^N{t}_i}$

     • A warning message is displayed.
     • And individual layer thickness will be adjusted to new layer thickness $t_i^{new}$ with:
       (1)

       $$Thick={\displaystyle \sum _i^N{t}_i^{new}}$$
       Here Thick and $t_i^{}$ are the shell thickness and layer thickness which are specified in input.

       
       
       Figure 6.

   • I_pos = 1: all layer positions in the element thickness are user-defined (with $t_i$ and $Z_i$ ).
     • “Thick” is not checked, as it does not need to be equal to the sum of layer thickness.
     • Multiple layers are allowed to have the same space position.

     For more details, refer to “Layer thickness and layer position calculation” in the Property and Elements FAQs.

10. Mat_ID_i- Material for each layer
    • Each layer as well as the corresponding part must use the same material law type. But may have different material properties, hence material IDs. Radioss checks for this condition and errors out if it is not met.
    • Global material properties (membrane stiffness, bending stiffness, mass, and inertia) are calculated based on the material properties and layer (thicknesses …). They are used for stability, mass and interface stiffness.
    • A material is still required at part definition level but, is only used for pre- and post- (visualization “by material”) and its physical characteristics are ignored.
    • The previous formulation where stiffness and mass were calculated from the material associated to the part is still used if the version number of the input file is V13 or earlier.
11. Element deletion rules used with P_thick_fail and failure models:
    • Only P_thick_fail defined in the property is considered to trigger the element failure.
      • P_thick_fail > 0 defines a fraction of failed thickness. This uses the amount of thickness assigned to each layer.
      • P_thick_fail < 0 defines a ratio of failed layers. This uses the number of layers.
    • The P_thick_fail defined in failure model(s) (/FAIL) are not used.
    • For fully-integrated shells (I_shell=12), the rules described above for under-integrated shells applies to each Gauss point separately. P_thick_fail criterion is checked for all integration point thickness for each in-plane Gauss point. The element is deleted only when all Gauss points reach P_thick_fail criterion.
    • P_thick_fail rules are not used with failure models defined inside the material laws. It is used only for the failure model defined with /FAIL.