Solid elements vs Continuum shell elements for modelling a core in a sandwich structure

[spyros_ar]

Dear all,

I am performing a linear buckling analysis of a sandwich structure, specifically a tapered cylindrical shell with reinforced patches. The face sheets are modeled using conventional S4R shell elements and are tied to the core vie TIE constraints. For the core, I used two different approaches:

1. Solid C3D8I elements (4 elements across the thickness).
2. Continuum shell elements.

However, I observed that the linear buckling analysis produces significantly different results between the two cases. For instance, in case (2), the critical buckling load is three times lower than in case (1), and the buckling position is also different for the same applied load. What could be the reasons for these discrepancies?

 

[SWComposites]

can you show the buckling mode shapes?
the continuum shells are only for the core?
what core properties are used with each element type?

 

[spyros_ar]

can you show the buckling mode shapes?
the continuum shells are only for the core?
what core properties are used with each element type?

Yes the continuum shells are only for the core and again are tied to the face sheets (S4R). For both cases, the core is anisotropicand I assign material orientation via "Material Orientation Modulus"

 

[SWComposites]

Looks like it is a core shear crimping buckle mode. Which is why it is core element sensitive. Make a cut thru the thickness thru the buckle pattern area lengthwise, and show the mode shapes (zoom in on the buckle area).
Is the loading non uniform on the part?