# Build Cross-section in Abaqus and Export to VABS

## Brief Instruction

Overall, the process is similar to creating [meshed beam cross-sections](https://help.3ds.com/HelpDS.aspx?V=2025&P=dssimulia_established&L=english&contextscope=all&F=simacaeanlrefmap/simaanl-c-meshedsection.htm) in Abaqus.

- Part:
  - Modeling space: 2D planar
  - Type: Deformable
  - Base feature: Shell
- Property:
  - Material: Any
  - Section: Solid (Homogeneous, Composite layup)
- Mesh: Any

Write the Abaqus model to an INP file.

Convert the INP file to a VABS input file using the command:

```bash
python -m sgio convert <filename>.inp <filename>.sg -ff abaqus -tf vabs
```

## Detailed Instruction

### Part module

As a cross-section of a slender structure, it is natural to create a "Deformable" "Shell" part in the "2D Planar" modeling space.

<!-- (See Figure {ref}`fig-abaqus-cs-part`) -->

```{figure} /images/abaqus_cs_create_part.png
:name: fig-abaqus-cs-part
:align: center
:width: 200
```

Composite structures can have different materials in different regions.
A useful tip is to create a base shape, such as a circle, large enough to cover
the entire cross-section.
Then, use the "Partition Face" tool to divide the base shape into regions.

```{figure} /images/abaqus_cs_partition_face.png
:align: center
:width: 500
```

### Property

Any type of material can be used for the cross-section, such as isotropic,
engineering constants, or orthotropic.
VABS requires local orientation data and allows additional in-plane rotations
(fiber angle) for each layer.
Hence, it is required to use the "Composite Layup" section type.
Here are instructions for setting up a "Composite Layup" section:

- Each section contains only one ply.
- Layer orientation is defined by assigning the local $y$ axis, while the local
  $x$ axis is always normal to the cross-sectional plane.
  For a composite layer, the local $y$ axis is usually set to be tangent to a
  base line.
- To set the fiber angle for each layer, use the column "Rotation Angle".

```{figure} /images/abaqus_cs_comp_section.png
:align: center
:width: 800
```

It is okay to use the "Composite Layup" section for all materials.
However, if a material is isotropic and no local orientation and fiber angle are needed, then it is also acceptable to use the "Solid" section.

```{figure} /images/abaqus_cs_solid_section.png
:align: center
:width: 500
```

### Mesh

There is no restriction on meshing.

```{figure} /images/abaqus_cs_mesh.png
:align: center
:width: 700
```

### File export

Create a job and write the model to an INP file.
Then use the command below to convert the INP file to a VABS input file:

```bash
python -m sgio convert <filename>.inp <filename>.sg -ff abaqus -tf vabs
```

By default, the Timoshenko beam model will be used.
To use the Euler-Bernoulli beam model, add the option `-m bm1`:

```bash
python -m sgio convert <filename>.inp <filename>.sg -ff abaqus -tf vabs -m bm1
```

To see help messages, use the command:

```bash
python -m sgio convert -h
```