Block Format Keyword This property set is used to define the sandwich shell property set. It is possible to define sandwich composite with several layers and each lay with individual material, thickness, layer position and orthotropic direction.

This property is only compatible with Material Laws 15, 25, 27, 36, 60, 72 and user laws and is compatible with XFEM (crack propagation) using /FAIL/JOHNSON, /FAIL/TAB1 and /FAIL/TBUTCHER.


(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/PROP/TYPE11/prop_ID/unit_ID or /PROP/SH_SANDW/prop_ID/unit_ID
Ishell Ismstr Ish3n Idril     P_thickfail    
hm hf hr dm dn
N Istrain Thick Ashear   Ithick Iplas  
VX VY VZ Skew_ID Iorth Ipos  
For each layer (integration point) per line
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
ϕ i ti Zi mat_IDi     F_weighti


Field Contents SI Unit Example
prop_ID Property identifier

(Integer, maximum 10 digits)

unit_ID Unit Identifier

(Integer, maximum 10 digits)

prop_title Property title

(Character, maximum 100 characters)

Ishell Shell element formulation flag. 1
= 0
Use value in /DEF_SHELL.
= 1 Default, if /DEF_SHELL is not defined
Q4, visco-elastic hourglass modes orthogonal to deformation and rigid modes (Belytschko).
= 2
Q4, visco-elastic hourglass without orthogonality (Hallquist).
= 3
Q4, elasto-plastic hourglass with orthogonality.
= 4
Q4 with improved type 1 formulation (orthogonalization for warped elements).
= 12
QBAT shell formulation.
= 24
QEPH shell formulation.


Ismstr Shell small strain formulation flag. 2
= 0
Use value in /DEF_SHELL.
= 1
Small strain from time = 0 (formulation compatible with all other formulation flags).
= 2 Default, if /DEF_SHELL is not defined
Full geometric nonlinearities with possible small strain formulation activation in Radioss Engine (option /DT/SHELL/CST).
= 3
Old small strain formulation (only compatible with hourglass type 2).
= 4
Full geometric nonlinearities (in Radioss Engine, option /DT/SHELL/CST has no effect).


Ish3n 3 node shell element formulation flag.
= 0
Use value in /DEF_SHELL.
= 1
Standard triangle (C0).
= 2 Default, if /DEF_SHELL is not defined
Standard triangle (C0) with modification for large rotation.
= 30
= 31
DKT_S3, which based on DTK12 of BATOZ (refer to Element Library in the Theory Manual).


Idril Drilling degree of freedom stiffness flag. 8
= 0
Use value in /DEF_SHELL.
= 1
2 Default, if /DEF_SHELL is not defined.


P_thickfail Percentage of layer thickness that must fail before the element is deleted. 12 13

0.0 P _ t h i c k f a i l 1.0


hm Shell membrane hourglass coefficient.

Default = 0.01

Default = 0.1 for hourglass type 3 (Ishell =3)


hf Shell out-of-plane hourglass.

Default = 0.01 (Real)

hr Shell rotation hourglass coefficient.

Default = 0.01

Default = 0.1 for hourglass type 3 (Ishell =3)


dm Shell Membrane Damping.

Default =0.0%

Default =1.5% for Ishell =24 (QEPH)+LAW 27

Default =5.0% for Ishell =1,2,3,4,12+LAW25 and 27


dn Shell numerical damping. 4

It only used for Ishell =12 and 24

Default =1.5% for Ishell =24 (QEPH)

Default =0.1% for Ishell =12 (QBAT)

Default =0.01% for Ish3n =30 (DKT18)


N Number of layers, with 1 ≤ N ≤ 100.

Default = 1 (Integer)

Istrain Compute strains for post-processing flag.
= 0
Use value in /DEF_SHELL.
= 1 Default, if /DEF_SHELL is not defined
= 2


Thick Shell thickness. 10


[ m ]
Ashear Shear factor.

Default is Reissner value: 5/6 (Real)

Ithick Shell resultant stresses calculation flag.
= 0
Use value in /DEF_SHELL.
= 1
Thickness change is taken into account.
= 2 Default, if /DEF_SHELL is not defined
Thickness is constant.


Iplas Shell plane stress plasticity flag.
= 0
Use value in /DEF_SHELL.
= 1
Iterative projection with three Newton iterations.
= 2 Default, if /DEF_SHELL is not defined
Radial return.


VX X component for reference vector.

Default = 1.0 (Real)

VY Y component for reference vector.

Default = 0.0 (Real)

VZ Z component for reference vector.

Default = 0.0 (Real)

Skew_ID Skew identifier for reference vector. 9

If the local skew is defined, its X-axis replaces the global vector V . VX, VY, and VZ coordinates are ignored.

Default = 0 (Integer)

Iorth Orthotropic system formulation flag for reference vector.
= 0 (Default)
The first axis of orthotropy is maintained at constant angle with respect to the X-axis of an orthonormal co-rotational element coordinate system.
= 1
The first orthotropy direction is constant with respect to a non-orthonormal system of deformed element.


Ipos Layer positioning flag for reference vector. 10
= 0 (Default)
Layer positions Zi are automatically calculated with regard to layer thicknesses.
= 1
All layer positions Zi must be user-defined.


ϕ i Angle for layer i. 9


[ deg ]
ti Thickness of layer i. 10


[ m ]
Zi Z position of layer I (Zi defines the position of the middle of the layer).

Default = 0.0 (Real)

[ m ]
mat_IDi Material identifier for layer i. 11


F_weighti Relative failure weight factor for layer i. 12 13  


3 layers (N=3) with different material, different material direction (fiber direction). Reference vector is taken from x-axis of skew.

Figure 1.
unit for prop
#              MUNIT               LUNIT               TUNIT
                  kg                  mm                  ms
New SKEW 1
#                 OX                  OY                  OZ
                 1.0                   0               100.0
#                 X1                  Y1                  Z1
                   0                   0                   1
#                 X2                  Y2                  Z2
                   0                  -1                   0
SH_SANDW example
#   Ishell    Ismstr     Ish3n     Idril                             Pthick_fail 
        12         0         0         0                                       0
#                 hm                  hf                  hr                  dm                  dn
                   0                   0                   0                  .1                  .1
#        N   Istrain               Thick              Ashear              Ithick     Iplas
         3         0                 1.6                   0                   1         1
#                 Vx                  Vy                  Vz   Skew_ID     Iorth      Ipos
                   0                   0                   0         1         0         0
#                Phi                   t                   Z    mat_ID                     F_weighti
                  45                  .5                   0         1                             0                              
                  90                  .6                   0         2                             0                              
                 -45                  .5                   0         1                             0                              


  1. Ishell, Ish3n – 4-node and 3-node shell formulation flag
    • Ishell=1,2,3,4 (Q4): original 4 nodes Radioss shell with hourglass perturbation stabilization.
    • Ishell=24 (QEPH): formulation with hourglass physical stabilization for general use (istotropic + LAW25 shells only).
    • Ishell=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.
    • Ish3n=30 (DKT18): BATOZ DKT18 thin shell with three Hammer integration points.
  2. Ismstr- Small strain formulation
    • Small strain formulation is activated from time t = 0, if Ismstr =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 Ismstr =4.
    • If Ismstr =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. hm, hf, and hr - Hourglass coefficients
    • hm, hf, and hr are only used for Q4 shells. They must have a value between 0 and 0.05.
    • For Ishell=3, default values of hm and hr are 0.1 with larger values possible.
  4. dn - Shell numerical damping coefficient
    • dn is only used for Ishell = 12 and 24.
      • for Ishell = 24, dn is used for hourglass stress calculation
      • for Ishell= 12 (QBAT), dn is used for all stress terms, except transverse shear
      • for Ish3n=30 (DKT18), dn is only used for membrane
  5. Ithick- Shell resultant stresses calculation flag
    • If Ithick=1, the small strain option is automatically deactivated in the corresponding type of element.
  6. Iplas- Shell plane stress plasticity flag
    • It is recommended to use Iplas =1, if Ithick =1.
    • Iplas=1 is available for Material Law 27.
    • If Iplas=1, the small strain option is automatically deactivated in the corresponding type of element.
  7. Output for post-processing
  8. Idril - Drilling degree of freedom stiffness flag
    • Drilling DOF stiffness is recommended for implicit solutions especially for Riks method and bending dominated problems.
    • Idril is available for QEPH, QBAT (Ishell =12, 24), and standard triangle (C0) shell elements (Ish3n = 1, 2).
  9. Orthotropy in local coordinate system.
    Two different ways to define the orthotropy with this property
    Orthotropic direction defined with global vector V (components defined in Line 6) and angle ϕ i (angle in degree) for each layer.
    Orthotropic direction defined with skew (X-axis in skew replaces the global vector V ) and angle ϕ i (angle in degree) for each layer.
    For both ways (with vector V or with skew), Projection of vector V (or x-axis of skew)on shell element plane becomes the vector V . Then for each layer, the orthotropic direction (direction 1) is vector V turn ϕ i degrees (turns positive direction coding to shell normal n ).

    Figure 2.

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

  10. Ipos – Layer position
    • Ipos = 0: layer positions are calculated automatically with "Thick".
      If T h i c k i N t i
      • A warning message is displayed.
      • And individual layer thickness will be adjusted to new layer thickness t i n e w with:
        T h i c k = i N t i n e w
        Here "Thick" and are the shell thickness and layer thickness which specified in input.

        Figure 3.
    • Ipos = 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.

  11. Mat_IDi- 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.
  12. P_thickfail parameter is not compatible with failure defined within the material law itself, such as plastic failure strain in LAW36.
  13. Element suppression rules used with /FAIL models:
    • Each single layer is turned OFF when all in-plane Gauss integration points in the layer are deleted.
    • The whole shell element is deleted when the following criterion is met:(2)
      i T h i c k i F _ w e i g h t i P _ t h i c k f a i l
      with (3)
      i = 1 , N l a y e r s

      Where, Thicki is relative thickness of failed layer i

    • When Ifail_sh parameters are defined locally in failure models associated to each layer material, the P_thickfail value is used by default and local parameter settings are ignored. Local failure model settings are only used when P_thickfail is not defined in the property which allows for backward compatibility with old models.