Dear Community,

I’m currently working on my MSc thesis, where I need to simulate a stiffened panel in Abaqus. At the moment, I’m using shell elements (S4R); my concern is mainly about how to set up the model correctly.

I’m facing two difficulties:

1) Shell section offset and stringer foot representation
When modelling the skin and the stringer foot with shell sections, there is an overlap in thickness.

• If I keep the section offset = 0, the foot region is not correctly represented in the geometry (see the second image).
• If I apply an offset (±0.5 depending on the shell normal), the foot sits in the correct physical position, but then the reference surface is no longer the midsurface. This leads to secondary bending effects under in-plane loading, which should not be present.

2) Applying combined biaxial compression and shear using displacement control
I need to apply a combination of biaxial compression and in-plane shear. Using direct edge displacements, the corners become over-constrained since each corner belongs to two loaded edges. This creates conflicts even though I’m aiming for a uniform in-plane strain field.

In short:

• How can the stringer foot be represented without creating artificial bending from the offset?
• How can a uniform combined biaxial + shear loading be applied via displacements without corner conflicts?

I will attach figures to illustrate the geometry. Any guidance on how to approach these issues would be greatly appreciated.

Best regards,
Daniel