Shell-Solid interaction

[spyros_ar]

Dear Abaqus users,

I am modeling a sandwich structure in Abaqus with conventional shell elements for the face sheets and solid elements for the core. The face sheets include reinforced patches, leading to variations in thickness and ply sequence. The top and bottom surfaces of the shells have been chosen as the reference surfaces. The shell and solid elements are connected using tie constraints. However, I noticed that the thickness of one face sheet appears to 'penetrate' the solid core. I am unsure how Abaqus handles shell thickness and whether this penetration affects the stiffness matrix of the structure. Should I leave a gap between the core and the face sheets to account for their thickness, or does Abaqus handle this internally? Any clarification on this would be greatly appreciated.

 

[FEA way]

If you are using shell section offsets then gaps shouldn't be necessary. By default, tie constraints take into account shell thicknesses and offsets for element-based surfaces.

 

[spyros_ar]

If you are using shell section offsets then gaps shouldn't be necessary. By default, tie constraints take into account shell thicknesses and offsets for element-based surfaces.

Alright. But how about the overlapping area between shell thickness and solid core. How abaqus threats this?

 

[SWComposites]

FE codes including Abaqus pay no attention to whether elements are overlapping each other or if there are gaps; the element stiffness matrices are calculated relative to the connected nodes, then the full stiffness matrix is built up.

If you have relatively thin facesheets compared to the core thickness, then using tie constraints and worrying about exact placement of the facesheet thickness is a complete waste of time and additional unnecessary complexity. Just attach the shell elements to the surface nodes of the core solid elements and be done with it. That's the way thousands of aircraft sandwich parts have been successfully modelled for decades.

 

[FEA way]

Alright. But how about the overlapping area between shell thickness and solid core. How abaqus threats this?

With properly defined offsets and tie constraints, there should be no overlaps. That's one of the purposes of shell section offsets. Enable shell thickness rendering to see if you have overlaps.