How do second-order elements affect contact analysis?

Second-order elements, such as C3D20R, can present unique challenges in contact analysis due to their behavior in certain discretization methods. Here are the key considerations:

1. Discretization method matters:
   • When using second-order elements, the choice between node-to-surface and surface-to-surface discretization significantly impacts results. For example, node-to-surface contacts may introduce additional mid-face nodes (e.g., converting C3D20R to C3D27R), which can alter nodal force distributions and increase computational complexity.
2. Force distribution behavior:
   • Second-order elements can produce tessellated or irregular force distributions (e.g., CNORMF values) when subjected to uniform pressure. This is due to the way nodal forces are calculated, especially in the absence of mid-face nodes.
3. Performance and accuracy:
   • First-order elements (e.g., C3D8I) are often preferred for contact regions as they simplify calculations, reduce solve time, and improve accuracy for nodal force outputs. If second-order elements are necessary, using surface-to-surface discretization is recommended to avoid additional mid-face nodes.
4. Model requirements:
   • The suitability of second-order elements depends on your specific model and output needs. If precise nodal force values are not critical, the irregularities in force distribution may not significantly affect other outputs like stress or pressure.
5. For optimal results:
   • Use first-order elements for slave surfaces in contact.
   • Opt for surface-to-surface discretization when second-order elements are unavoidable.
   • Evaluate whether the CNORMF behavior impacts your analysis goals.