Thick or Thin? Shell element formulation option for SOLIDWORKS Simulation

   By Suman Sudhakaren on April 11, 2023

When simulating components that have thin geometry, it is difficult to use very small solid element size to meet the criteria of minimum of two rows of high quality or four rows of draft quality solid elements in the through thickness direction.  We don’t recommend using large element size as this would deteriorate mesh quality and not capture intricate geometric features accurately.  Also, using large number of small size solid elements to capture stresses in the thickness direction would result in higher number of degrees of freedom leading to increased computational costs. This is where shell meshing is beneficial and is the natural choice for sheet metal and thin parts.

A linear triangular shell element is defined by three corner nodes connected by three straight edges. A parabolic triangular element is defined by three corner nodes, three mid-side nodes, and three parabolic edges. Shell elements are 2D elements capable of resisting membrane and bending loads, i.e. shell elements allow us to evaluate membrane and bending stresses.

actual deformation

For studies using sheet metals, the thickness of the shell is automatically extracted from the geometry of the model.

When using surfaces or solid bodies, users must input thickness and select either the thick or thin shell formulation.

To determine whether to use Thin or Thick shell formulation, we need to consider the thickness to span ratio of the model.  Depending on this ratio, the shear deformation can become negligible compared to the bending deformation.  For a relatively long yet thin solidbody with this ratio less than 5% (0.05), the thin shell formulation that does not take shear deformation into account is used.  This is based on Kirchoff’s theory where shear deformation in thickness direction is ignored.

actual part vs modeled with a shell

For cases where the thickness to span ratio is higher than 0.05, the shear deformation is not negligible compared to bending deformation. Thick shell formulation takes shear deformation into account and is based on Mindlin theory.

shell definition

To summarize, for span to thickness ratio greater than 20 opt for Thin shell elements and for a span to thickness ratio between 10 and 20 use the Thick shell elements.  While we are limited to triangular elements in SOLIDWORKS Simulation, we have options for rectangular (quad) element and more in advanced simulation using Simulia roles on 3DEXPERIENCE platform.

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Suman Sudhakaren

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