You can use preintegrated general shell sections (SECTYPE,,GENS) when using the SHELL181 or SHELL281 element, provided that linear elastic material behavior is acceptable. Compared to standard shell usage with independent material and section definitions, preintegration requires fewer system resources because numerical integration through the thickness of the shell is not required.
The behavior of shell elements is governed by the generalized-stress/generalized-strain relationship of the form:
where:
{
N
} = {N
11, N
22, N
12} are membrane stress resultants per unit length |
{
M
} ={M
11, M
22, M
12} are bending stress resultants per unit length |
| {ε} = {ε11 , ε22, ε12} are membrane strains |
| {κ} = {κ11,κ22,κ12} are curvatures |
{
S
} = {S
1, S
2} are transverse shear forces per unit length |
| {γ}={γ1,γ2 } are transverse shear strains |
[
A
], [
B
], [
D
], and [
E
] are the section-stiffness matrices for membrane, coupling, bending, and
shear behavior, respectively |
{
M
T
} are stress resultants caused by a unit rise in temperature on a
fully constrained model |
{
B
T
} are bending-related stress resultants caused by a unit rise in
temperature on a fully constrained model |
T
I is the stress-free initial temperature |
T is the current temperature |
| (Subscripts 1 and 2 denote shell surface coordinates as employed by the shell element.) |
The preintegrated form of input enables you to import homogeneous section-stiffness
constants evaluated in other analyses or by third-party, special-purpose software tools.
For example, defining preintegrated section stiffnesses [
A
], [
B
], and [
D
] is common in analyses of layered composites, corrugated shells, or other
complex section construction.
Each of the following commands specifies a particular component quantity necessary for defining a preintegrated shell section:
Table 13.2: Commands for Specifying Preintegrated Shell Section Data
| Command | Quantity Defined and Data Specified |
|---|---|
| SSPA |
Membrane stiffness -- Symmetric part of submatrix [
A
11, A
21, A
31,A
22,A
32,A
33, T
|
| SSPB[a] |
Coupling stiffness -- Symmetric part of submatrix [
B
11, B
21, B
31,B
22,B
32,B
33, T
|
| SSPD[a] |
Bending stiffness -- Symmetric part of submatrix [
D
11, D
21, D
31,D
22,D
32,D
33, T
|
| SSPE[a] |
Transverse shear stiffness -- Symmetric part of submatrix
[
E
11, E
21, E
22, T
|
| SSMT |
Membrane thermal effects -- {
M
T
11, M
T
22, M
T
12, T
|
| SSBT[a] |
Bending thermal effects -- {
B
T
11, B
T
22, B
T
12, T
|
| SSPM |
Mass density of the shell section (assuming a unit thickness) DENS, T
|
Temperature dependencies (T) — You can define each of the preintegrated shell section data as
temperature-dependent. It is possible to specify up to six temperatures
(T) by reissuing any command as necessary. If you
issue a command for a temperature specified earlier, the most recent data
supersedes the previous value.
You can define preintegrated shell sections only when using the SHELL181 or SHELL281 element. When using preintegrated shell section data, the following conditions apply:
The section data defined by each command listed in Table 13.2: Commands for Specifying Preintegrated Shell Section Data is associated with the section most recently defined via the SECTYPE command.
You cannot use the shell element with heat-transfer shells.
Shell stresses are not available for output; however, the stress resultants are available as ETABLE quantities.
The thickness of the shell is assumed to remain constant even in a large-strain analysis.
Offset to midplane of the section or user defined location is allowed (SECOFFSET).
The preintegrated stiffness components must yield a positive definite section stiffness at analysis time.
If using preintegrated shell sections in a contact analysis, Ansys, Inc. recommends the pure Lagrange multiplier method.
For standard layered-shell sections, you can obtain
submatrices [
A
], [
B
], [
D
], and [
E
] via the SLIST command's FULL option or via the
*GET command (Entity =
SHEL).