/PROP/TYPE17 (STACK)

Description

The input can be either "substack" or by ply, but not both.

Format

Definition

Comments

1. The stack property is used in combination with /PROP/TYPE19 (PLY) to create composites properties through the ply-based definition.
   • The ply defined with /PROP/TYPE19 used in option Pply_ID_i or Pply_ID_j. in this stack property.
   • Only 1 integration point can be defined per ply that is, Npt_ply =1 in /PROP/TYPE19 (PLY).
2. 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.
   • I_shell = 12 (QBAT): modified BATOZ Q4 y24 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.
   • The hourglass formulation is visco-elastic for Q4 shells.
3. 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 $\text{Δ}t<\text{Δ}{t}_{\min }$ can be switched to a small strain formulation by Radioss Engine option /DT/SHELL/CST, except if I_smstr = 4.
   • If the small strain option is set to 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.
4. 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.
5. d_n - Shell numerical damping coefficient
   • I_shell = 12, 24:
     • for I_shell = 24, 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.
6. I_thick - Shell resultant stresses calculation flag
   • If I_thick = 1, the small strain option is automatically deactivated in the corresponding type of element.
7. I_plas - Shell plane stress plasticity flag
   • I_plas is available for material LAW27
   • It is recommended to use I_plas =1, if I_thick =1.
   • If I_plas =1, the small strain option is automatically deactivated in the corresponding type of element.
8. 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 or 24), and standard triangle (C0) shell elements (I_sh3n = 1 or 2).
9. 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 3. 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 4. 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 shell element normal direction $n$ . Local coordinate system Skew_ID is ignored.

     
     
     Figure 5. 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 6.

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

   • shell element ( ${\varphi }_s$ > 0 in either /SHELL or /SH3N)
   • 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 is derived from direction m1 with the angle ${\alpha }_i$ (defined in /PROP/TYPE19).

   If ${\alpha }_i=90°$ , the layer is orthotropic.

10. I_pos - ply position
    • In this property, ply position defined with Z_i and option I_pos.
    • Z_i values are real ply positions in the local Z axis (negative and positive value are allowed and Z_i defines the position of the middle of each ply).
    • Z₀ only used with I_pos=2, it indicated distance from the shell element reference middle surface to the bottom surface of the whole ply or stack. For more information, see I_pos=2
    • I_pos= 0: ply positions are automatically calculated with regard to ply thicknesses.
      • The input thickness “Thick” may be equal to zero as the true shell thickness is always calculated from the ply thicknesses and positions of ply defined by Z_i.
      • If the input thickness “Thick” is different from 0.0, a warning will be displayed if the calculated thickness from the plies is different from the input thickness.

        
        
        Figure 7.

    • I_pos= 1: All ply positions and thickness in the element are user-defined (with $t_i$ in /PROP/PLY and Z_i).
      • Global thickness “Thick” is not checked, as it does not need to be equal to the sum of ply thickness.
      • Multiple plies are allowed to have the same space position.
      • This option is not recommended unless the number of ply is constant for all elements.
    • I_pos= 2: the shell element mid-surface is at Z₀ from the bottom of the ply layout.

      
      
      Figure 8.

    • I_pos = 3: the top of the ply layout is coincident with the element mid-surface

      
      
      Figure 9.

    • I_pos = 4: the bottom of the ply layout is coincident with the element mid-surface

      
      
      Figure 10.

11. Define by substack
    • If the substack definition is used, each substack definition begins with the keyword “SUB” and the substack identification number.
    • All the plies until the next keyword “SUB” or the keyword “INT” is encountered belong to the same substack.
    • All substacks must be defined before defining the “INT” connections.
    • If an element contains plies belonging to several substacks, the connection between the substacks is defined with an “INT” connection: the ply Pply_ID_t of the first substack is connected to the ply Pply_ID_b of the second substack.
    • For more details, refer to the above examples for this property.
12. Material for each ply
    • Material for each ply defined with mat_ID in /PROP/TYPE19.
    • Material between each ply defined with Minterply inside this property. It used for Plyxfem formulation.
    • This property is only compatible with Material Laws 25, 27, 36, 60, 72, 93 and user laws.
    • Material law type for ply must be the same for each ply
    • The material law number given in /PART will be used to define the mass and the sound speed of the composite, as well as the interface stiffness.
    • The material law type input in the /PART definition must be identical to the material law type used in mat_ID in /PROP/TYPE19.
13. Plyxfem formulation
    • The plyxfem formulation is activated using the Plyxfem flag. It used to describe the delamination between plies.
    • Once plyxfem is activated (Plyxfem=2), then an interply material (Minterply) must be defined between each ply.
    • This interply material must use LAW1 with Ladeveze failure criteria (/FAIL/LAD_DAMA) for delamination.
    • This option is in the beta stage.
14. 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 element global 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 layers 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.