/STACK (New!)

Block Format Keyword

/STACK - Stacking information for ply-based shell elements with multiple integration points through each layer

Description

This option is used to define the stacking sequence of a composite shell (/PROP/PCOMPP) in conjunction with the /STACK option.

Two possible input:

•	All elements may have different number of plies by associating a group of elements to the ply in a way similar to OptiStruct.

•	The layout is described by a sequence of substacks (“SUB”), which are comprised of several plies. The interface between substacks is defined with INT option line.

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

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/STACK/stack_ID/unit_ID
stack_title
Ishell	Ismstr	Ish3n	Idrill			Z0
hm		hf		hr		dm		dn
	Istrain	Ashear			Iint		Ithick
VX		VY		VZ		skew_ID	Iorth	Ipos

By ply

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
Pply_IDi			Zi
Blank

Or by substack

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
Sub	Nsub	Sub-plyn
Substack Name
Pply_IDi			Zi
Blank
Sub	Nsub	Sub-plyn
Substack Name
Pply_IDj			Zj
Blank

Optional:

INT

Pply_IDt

Pply_IDb

Field	Contents	SI Unit Example
stack_ID	Stack identifier (Integer, maximum 10 digits)
unit_ID	Optional unit identifier (Integer, maximum 10 digits)
stack_title	Stack title (Character, maximum 100 characters)
Ishell	Shell element formulation flag (Comment 3) (Integer) = 0: use value in /DEF_SHELL. = 1: 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 (Integer) = 0: use value in /DEF_SHELL = 1: small strain from time =0 (new formulation compatible with all other formulation flags) = 2: full geometric nonlinearities with possible small strain formulation activation in RADIOSS Engine (option /DT/SHELL/CST) = 4: full geometric nonlinearities (in RADIOSS Engine, option /DT/SHELL/CST has no effect)
Ish3n	3 node shell element formulation flag (Integer) = 0: use value in /DEF_SHELL = 1: standard triangle (C0) = 2: standard triangle (C0) with modification for large rotation = 30: DKT18 = 31: DKT_S3, which based on DTK12 of BATOZ (refer to the Theory Manual)
Idrill	Drilling degree of freedom stiffness flag (Integer) = 0: no = 1: yes
Z0	Distance from the shell element reference plane to the bottom surface of the shell (Real or blank). It should be considered, if Ipos =2. Default = 0.0 (Real)
hm	Shell membrane hourglass coefficient Default = 0.01 (Real)
hf	Shell out-of-plane hourglass Default = 0.01 (Real)
hr	Shell rotation hourglass coefficient Default = 0.01 (Real)
dm	Shell membrane damping (Real)
dn	Shell numerical damping (Real)
Istrain	Compute strains for post-processing flag (Integer) = 0: default set to value defined with /DEF_SHELL = 1: yes = 2: no
Ashear	Shear factor Default is Reissner value: 5/6 (Real)
Iint	Thickness integration formulation - through layer (ply) thickness (Comment 33) (Integer) = 0: default set to 1 = 1: Uniform integration scheme (uniformly distribution of the integration points through layer/ply thickness) = 2: Gauss integration scheme
Ithick	Shell resultant stresses calculation flag (Integer) = 0: default set to value defined with /DEF_SHELL = 1: thickness change is taken into account = 2: thickness is constant
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 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 Default = 0 (Integer) = 0: 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 (Comment 29) Default = 0 (Integer) = 0: layer positions are automatically calculated with regard to layer thicknesses. The coherence of global thickness with the sum of layer thicknesses is automatically checked. = 1: all layer positions in the element thickness are user-defined. Multiple layers may have the same special position. Global thickness is not checked in this case, since it needs to not be equal to sum of layer thicknesses. =2: the shell element reference plane is at Z0 from the bottom surface of the shell. =3: the top surface of the shell is considered as element reference plane. =4: the bottom surface of the shell is considered as element reference plane.
Pply_IDi Pply_IDj	Ply identifier for layer i (j) (Integer) i =1, 2, 3 …N j =1, 2, 3 …N
	Angle for layer i (j) (Comment 20) (Real)
Zi Zj	Z position of layer i (j) (Zi or Zj defines the position of the middle of the layer) Default = 0.0 (Real)
Sub	=SUB: Indicates the beginning of a substack definition (must be left justified) (Integer)
Nsub	Substack identification number (Integer)
Sub-plyn	Number of plies in substack (Integer)
Substack Name	Name of the substack (Maximum 100 characters)
INT	(Optional) Indicates the connection between 2 substacks (must be left justified). (Integer)
Pply_IDt	(Optional) Ply identification number of the top ply of the bottom substack (Integer)
Pply_IDb	(Optional) Ply identification number of the bottom ply of the top substack (Integer)

Substack definition for the ply layout with /DRAPE.

prop_type17_example

Using option def_orth =2 to define material direction for each ply.

stack_def_orth_option

1.	The stack is used in combination with /PLY to create composites properties through the ply-based definition. It is NOT compatible with /PROP/PLY option.

2.	Only compatible with Material Laws 25, 29, 30, 31, 35, 36, 42, 43, 44, 48, 52, 57, 60, 62, 63, 64, 65, 66, 69, 72, 73, 76, 78, 80, 82, 87 and user laws.

3.	Q4: original 4 nodes RADIOSS shell with hourglass perturbation stabilization.

QEPH: formulation with hourglass physical stabilization for general use.

QBAT: modified BATOZ Q4 24 shell with four Gauss integration points and reduced integration for in-plane shear. No hourglass control is needed for this shell.

DKT18: BATOZ DKT18 thin shell with three Hammer integration points.

4.	Small strain formulation is activated from time t = 0, if Ismstr =1. 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.

5.	If Ithick or Iplas are activated, the small strain option is automatically deactivated in the corresponding type of element.

6.	The hourglass formulation is visco-elastic for Q4 shells.

7.	If the small strain option is set to 1, the strains and stresses which are given in material laws are engineering strains and stresses; otherwise they are true strains and stresses.

8.	Flag Istrain is automatically set to 1 for Material Law 25.

9.	hm, hf, and hr are only used for Q4 shells. They must have a value between 0 and 0.05.

10.	For Ishell = 3, default values for hm and hr are 0.1.

11.	The default value of dm is 5% for Law 25.

12.	The same default value of dm is used in for QBAT shells, except:

•	the default value of dm for QEPH is 1.5% for Material Laws 36 and 43

For further information about dm coefficient, refer to the RADIOSS Theory Manual.

13.	Shell numerical damping dn is only used for Ishell =12 or 24:

•	for Ishell =24, dn is used for hourglass stress calculation

•	for QBAT, dn is used for all stress terms, except transverse shear

•	for DKT18, dn is only used for membrane

14.	The default value of dn is:

•	1.5% for Ishell =24

•	0.1% for QBAT

•	0.01% for DKT18

15.	Input components of global vector used to define direction 1 of local coordinate system of orthotropy. Alternatively, it may be defined by a local skew system.

prop_type9_v10

16.	Input components of global vector are defined in Line 6.

17.	Projection of vector on shell element plane becomes vector .

18.	Direction 1 of local coordinate system of orthotropy is defined with vector and angle (angle in degree).

19.	Input as many formats as number of layers (one format per layer, Line 7).

20.	is the angle between direction 1 of orthotropy and projection of vector on the shell for layer i.

21.	Layer positions must be defined if the Ipos flag is active. The Zi values are real layer positions in the local Z axis (negative and positive value are allowed and Zi defines the position of the middle of the layer).

22.	Different material laws could be defined for each layer (Comment 2).

23.	The material law number given in element input section will be used to define the mass and the sound speed of the composite, as well as the interface stiffness.

24.	Idrill is available for QEPH, QBAT (Ishell =12 or 24), and standard triangle (C0) shell elements (Ish3n= 1 or 2).

25.	Drilling DOF stiffness is recommended for implicit solutions especially for Riks method and bending dominated problems.

26.	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. The substack definition can only be used if N (the input number of layer) is equal to 0.

27.	All substacks must be defined before defining the INT connections.

28.	If an element contains plies belonging to several substack, the connection between the substacks is defined with an INT connection: the ply Pply_IDt of the first substack is connected to the ply Pply_IDb of the second substack.

29.	Ipos = 1 is not recommended unless the number of ply is constant for all elements.

The mid-surface of the shell is the surface defined by the nodes connected to the element. For an exact definition of this surface, refer to the Theory Manual.

30.

Ipos = 2:

prop_type17_ipos2

31.

Ipos = 3:

prop_type17_ipos3

32.

Ipos = 4:

prop_type17_ipos4

33.	Each layer (ply) of a shell element can contain a different (> 1) number of integration points through its layer thickness.