Context:
The midsurface modeling process relies on an accurate solid model as the
starting point. Midsurface modeling is best suited to thin solids or
thin-walled solids where wall thickness is constant or where reasonable
approximations of the wall thickness at each point can be made easily. You can
apply midsurface modeling to any solid cell within a model; you need not apply
it to the entire model. If you apply midsurface modeling to only a portion of a
solid model,
Abaqus/CAE
automatically creates shell-to-solid coupling constraints to couple the motion
of the midsurface shell edges to that of the remaining solid model faces.
Shell-to-solid coupling constraints will not be created if the angle between
the shell surface and the solid face deviates significantly from 90°.
Besides reduced expense, you might use a midsurface model in place of a
solid model to better account for bending response in thin sections of the
model. Shell elements are designed to manage bending loads within the thickness
of a single element, whereas a single solid element will have little or no
resistance to bending.
Creating a midsurface model in
Abaqus/CAE
is a manual process. The procedure presented below provides an overview of the
general steps involved. The tasks within each step may vary depending on the
complexity and completeness of the original solid model and the analysis
requirements. Some steps, such as Step 4 below, may not be required or may be
completed in a different order from what is presented here.
Assign midsurface regions on the solid part. Use the Assign
Midsurface Region tool to select one or more cells from the solid
part to begin creating a midsurface model. For more information, see
Assigning a midsurface region.
Abaqus/CAE
removes the selected cells from the active representation and creates a
reference representation containing the selected cells.
Create new shell faces to replace the solid geometry that you moved to
the reference representation.
You can use tools in the
Geometry Edit toolset
or the shell feature creation tools to add shell features to the midsurface
model. For more information, see
The Geometry Edit toolset
and
Adding a shell feature,
respectively. The offset faces tool in the
Geometry Edit toolset
is the most common face creation method for midsurface models. The offset
process creates new faces based on selected geometry and automatically assigns
a shell thickness based on the offset parameters.
Assign thicknesses to the new shell features.
The Assign Thickness and Offset tool allows you
to assign shell thicknesses to the new midsurface geometry (for more
information, see
Assigning thicknesses and offsets).
The tool allows you to assign thicknesses to individual faces, and you can also
use it to edit thicknesses that
Abaqus/CAE
assigned automatically for faces created using the offset process. You must
still assign a section to the new faces in the
Property module.
During the section assignment process you can make a final decision whether to
use the thickness defined with the section properties or to use the definition
from the geometry. You can toggle the shell thickness display in all part and
assembly-based modules to see the thickness in the viewport (for more
information, see
Visualizing shell thicknesses).
Revise any analysis attributes that were associated with the solid
geometry that was used to create the reference representation.
Analysis attributes such as loads, boundary conditions, or
interactions cannot be applied to geometry in the reference representation. Any
attributes that were associated with the solid geometry before it was moved to
the reference representation will be associated with an empty region if the
geometry is no longer part of the active representation. For more information,
see
Understanding the reference representation.