The Section Stiffness material model provides a way of directly entering the stiffness or compliance of a shell without direct knowledge about the cross-section thickness and material distribution. Its main purpose is for entering homogenized properties of for example perforated or corrugated sheets.

In many cases, the properties of the shell cross section are anisotropic. All input data are interpreted along the local directions specified in the Coordinate System Selection section.

By adding the following subnodes to the Section Stiffness node you can incorporate other effects:

From the Specify list, select Effective stiffness or Effective flexibility in order to specify the representation of the section stiffness.

For Effective stiffness, enter the Extensional stiffness matrix, DA; Bending-extensional stiffness matrix, DB; Bending stiffness matrix, DD; and Shear stiffness matrix, DAs.

For Effective flexibility, enter the Extensional flexibility matrix, Da; Bending-extensional flexibility matrix, Db; Bending flexibility matrix, Dd; and Shear flexibility matrix, Das.

If required, enter also the Translational inertia, I0; Rotational-translational inertia matrix, I1; and Rotational inertia matrix, I2. The translational inertia is the average mass per unit area. As long as the shell is not thick or shear flexible, the two latter contributions to the inertia can usually be ignored. If the mass distribution of the shell is symmetric with respect to the midplane, then I1 is identically zero.

The default for all section properties is to take the values From material. Any one of the matrices can also be User defined.

Enter an In-plane force factor, SN. This is a matrix which transforms the local membrane force (N11, N22, N12) into a local in-plane stress (s11, s22, s12).

Enter a Moment factor, SM. This is a matrix which transforms the local bending moment (M11, M22, M12) into a local in-plane stress (s11, s22, s12).

Enter an Out-of-plane force factor, SQ. This is a matrix which transforms the local shear force (Q1, Q2) into a local transverse shear stress (s13, s23).

Enter the shear correction factors for transverse shear k23 and k13.

When computing the contribution from shear stiffness to the total virtual work, it is necessary to take into account that the shell approximation assumes that shear stresses and strains in the thickness direction are constant, whereas in reality the distribution is more complicated. The shear correction factors are used to compensate for this, so that the total strain energy density is correct. When operating with stiffness and flexibility matrices, this correction can also be built directly into the matrices DAs and Das. Is so, set both shear correction factors to 1.

Select a Formulation — From study step (default), Total Lagrangian, or Geometrically linear to set the kinematics of the deformation and the definition of strain. When From study step is selected, the study step controls the kinematics and the strain definition.

To have full control of the formulation, select either Total Lagrangian, or Geometrically linear. When Total Lagrangian is selected, the physics will force the Include geometric nonlinearity check box in all study steps.

Select a Strain decomposition — Automatic (default), Additive, or Multiplicative to decide how the inelastic deformations are treated. This option is not available when the formulation is set to Geometrically linear.

The Strain decomposition input is only visible for material models that support both additive and multiplicative decomposition of deformation gradients.

Physics tab with Shell selected:

Physics tab with Plate selected: