ABSTRACT
The paper describes our improved 9-node quadrilateral shell element MITC9i, which is derived for the Reissner-Mindlin shell kinematics, the extended potential energy functional and Green strain.
The MITCi technique is used to avoid locking and it is based on the improved transformations proposed in (Wisniewski & Panasz 2013) for a membrane element. Here, these transformations are extended to bending/twisting and transverse shear shell strains.
To reduce the shape distortion effects, the so-called corrected shape functions (CSF) of (Celia & Gray) are used instead of the isoparametric ones, and we propose the method of computation the shift parameters for non-flat shell elements.
The drilling rotations are included via the drilling Rotation Constraint and the penalty method. This rotation is used in the multiplicative/additive update scheme valid for large (unrestricted) rotations.
The effect of the MITC9i technique and the CSF is that all three patch tests are passed, also for shifted side nodes along the straight edges and for arbitrary shifts of an interior node. The MITC9i shell element was subjected to a range of linear and non-linear numerical tests described in (Wisniewski & Turska 2017); here we provide additional examples illustrating its accurate and robust behavior.
