PARAM, CURVSHL2

Bulk Data Entry Activates a correction to strain and stress calculation for second order shell elements (CQUAD8, CTRIA6) that considers strong curvature of the shell (relative to shell thickness).

Parameter Values Description
CURVSHL2 <YES, NO, THICK>
YES
Activates a correction to strain and stress calculation for second order shell elements (CQUAD8, CTRIA6) that takes into account strong curvature of the shell (relative to shell thickness). 1 through 5
NO (Default)
THICK
Activates alternate stress recovery for curved second order shell elements (CQUAD8, CTRIA6). Recommended for very thick shells. 6

Comments

  1. The correction, when activated, is dependent upon relative "strength" of the curvature, hence it will be zero for flat shell elements.
  2. The correction is applied only to post-processing of the results (stress and strain calculation). The element stiffness matrix is not affected; hence the displacement solution and global forces remain unaffected.
  3. The correction is not applied to composite materials and shells with membrane-bending coupling (MID4 on PSHELL). Such entities may be present in the finite element model, yet their strain and stress calculation then, uses standard calculation for thin shells (and a warning message is issued).
  4. PARAM,CURVSHL2 is supported for optimization runs.
  5. It is essential that the individual shell element curvature matches the intended overall curvature of the model in the surrounding region. This is especially important when the element size is small relative to the shell thickness (in such cases, long format for nodal coordinates may be required to capture the curvature accurately).
  6. Internally, PARAM,CURVSHL2,THICK modifies the element stiffness matrix by introducing drill DOF constraints. This modification affects displacements.