peteroznewman
Subscriber

Hi Mani,

You mentioned orthotropic material properties in your original post, but when I look at your materials, they are all isotropic.

When I look at your Ansys project, you have modeled the hexagonal honeycomb cells using surface geometry and assigned a wall thickness and material properties for solid aluminum. By modeling it this way, you may not need an orthotropic material model.  However, your model has not captured an important feature of honeycomb core, the double wall thickness created as a result of the manufacturing process. Foil sheets of thickness t are bonded together with strips of adhesive of width h and the strips of adhesive are staggered on the odd and even layers of foil. When that stack of foil sheets is pulled apart, a honeycomb cell is created, but notice in the figure below that some of the walls of the hexagonal cell have a wall thickness of t while others have a wall thickness of 2t.

Carbon fiber reinforced plastics with aluminum honeycomb core design  methodology for space and surface mining applications - ScienceDirect

Your model does not represent that.

A simpler way to model a honeycomb core sandwich is to use orthotropic material properties. Instead of modeling the hexagonal cells with surfaces, the entire core is represented by a solid body assigned an orthotropic material. The manufacturer provides the critical material properties of this core on their webpage. The properties are orthotropic relative to directions in the core called L and W.  The L direction is horizontal in the figure above, and that is the length of the foil sheets.  The W direction is vertical and that is the direction the sheets were pulled to open up the cells. Once face sheets are bonded to the top and bottom of the core, and the sandwich panel has some bending applied, you would expect a higher modulus in the L direction because that is shearing the walls with the 2t thickness, while the lower modulus in the W direction is shearing the angled walls with the thickness t.  Below is a copy of a manufacturers data sheet. Notice that the Shear Modulus in the “L” direction is about twice as large as the “W” direction. The other critical property is the compressive modulus.

Ansys Orthotropic material models require more constants than those three, but those are the critical ones.

Composite facesheets can also be orthotropic, but if many layers are stacked at multiple angles, the sheet can end up with nearly isotropic properties, especially if the laminar are fabric and not uni-directional tapes.

The surfaces representing the composites would be modeled coincident with the top and bottom faces of the solid core. Use Shared Topology so that the mesh of shell elements shares the nodes on the solid elements that mesh the core. This avoids using any bonded contact.