Shell1.rst

Shell assembly with contact

Features

• Shell assembly
• Edge to face MPC contact
• Penalty contact between structure and indenter

Downloads

• Files on Github
• :download:`pre.fbd`
• :download:`post.fbd`
• :download:`tie.inp`

.. toctree::
  :maxdepth: 2

This example demonstrates the interaction between a minimal honeycomb sandwich structure and an indenter.

Preprocessing :download:`pre.fbd` > cgx -b pre.fbd The plot shows the shell meshes of the individual bodies, Note that you see the element edges on the negative side of the shell elements because view back was used.
Solving :download:`tie.inp` > ccx tie > ,,/,,/Scripts/monitor.py tie The solution converges with the default settings in a single step. The convergence plot shows, that the initial penetration creates more than 2000 contact elements, This number then stabilizes at approximately 100 elements.
Post-processing :download:`post.fbd` > cgx -b post.fbd
Shaded plot of the deformed system	Plot of the worst principal stress

pre.fbd

.. literalinclude:: pre.fbd :start-after: # parameters :end-before: # core	rc: width of the core sheets tc: thickness of the core sheets hc: height of the core ls: length of the skin sheets ri: radius of the indenter xi: excentricity of the indenter ts: thickness of the skin sheets
.. literalinclude:: pre.fbd :start-after: # core :end-before: # skin	The core consists of three vertical plates, which are connected in the center. Point p0 at the origin is swept in x direction, the resulting line is copied and rotated by \pm 120°. These three lines form the set c_bottom, which we later use for contact definition. The lines are swept in z direction, the copy of the generating set is named c_top and also later used for contact. The resulting structure is stored in set core for later material and thickness assignment.
.. literalinclude:: pre.fbd :start-after: # skin :end-before: # edges	The bottom skin sheet (set bottom) is created from corner point ps1 by sweep in negative x and y directions. The top skin (set top) is created as a translated copy of the bottom skin. Both skins have their positive sides down, therefore we flip the bottom skin to make both skins face the core.
.. literalinclude:: pre.fbd :start-after: # edges :end-before: # indenter	Generate sets for the edges of the skins. These are used later for displacement constraints. The comp commands are required to include the corner points in the sets.
.. literalinclude:: pre.fbd :start-after: # indenter :end-before: # positioning	Generate the hemisherical indenter. First we define a quarter of the hemisphere by explicitly specifying points, lines and the surface. Note, that the resulting surface is only roughly spherical. In the given case this does not matter. The hemisphere is generated by two successive copy commands. The duplicate nodes are removed by the merg command.
.. literalinclude:: pre.fbd :start-after: # positioning :end-before: # meshing	Place the indenter into starting position. We first have to adjust the orientation, then we move the indenter to just touch the top face of the top skin (account for the invisible shell thickness). Last we move the indenter to a slightly excentric position.
.. literalinclude:: pre.fbd :start-after: # meshing :end-before: # surfaces	Increase the default division of the lines Mesh with qu8, these are written as S8R elements. Write the mesh and all set definitions. We don't need all but don't want to send them individually.
.. literalinclude:: pre.fbd :start-after: # surfaces :end-before: # image	Write the surface definitions, required for contact definition. A separate set for the negative side of the top skin is required, because the file name does not account for the - sign and both sides would be written to the same file.
.. literalinclude:: pre.fbd :start-after: # image	Create a representative view of the geometry. The element edges are visible on the negative side of the surfaces.

tie.inp

.. literalinclude:: tie.inp :start-after: ** includes :end-before: ** constraints	Include the files generated by CGX
.. literalinclude:: tie.inp :start-after: ** constraints :end-before: ** material	Constrain the displacement of the edge of the bottom skin and of the indenter
.. literalinclude:: tie.inp :start-after: ** material :end-before: ** sections	Define the material Aluminium with Young's modulus and Poisson's ratio. The density is provided for eventual modal analysis.
.. literalinclude:: tie.inp :start-after: ** sections :end-before: ** ties	Assign material and thickness to the shell element sets. An offset of 0.5 times the thickness is applied, this shifts the reference surface to the positive side.
.. literalinclude:: tie.inp :start-after: ** ties :end-before: ** penalty	Define MPC contact between the core and the skin sheets.
.. literalinclude:: tie.inp :start-after: ** penalty :end-before: ** step	Define penalty contact between the top skin and the indenter.
.. literalinclude:: tie.inp :start-after: ** step :end-before: ** load	Start a non-inear static step with default time stepping settings
.. literalinclude:: tie.inp :start-after: ** load :end-before: ** output	Move the indenter 2 mm down.
.. literalinclude:: tie.inp :start-after: ** output :end-before: ** endstep	Request output of the displacements (U) and the stresses (S) to the frd-file.
.. literalinclude:: tie.inp :start-after: ** endstep	End of the step

post.fbd

.. literalinclude:: post.fbd :start-after: # read :end-before: # view	Read the results (frd) and the input file (for the set definitions)
.. literalinclude:: post.fbd :start-after: # view :end-before: # def	Switch on the deformed geometry and element edges. Adjust the view orientation
.. literalinclude:: post.fbd :start-after: # def :end-before: # color	Shaded displacement plot
.. literalinclude:: post.fbd :start-after: # color	Plot of the worst principal stress