What we call the
implicit corotational method is proposed as a tool to obtain
geometrically exact nonlinear models for structural elements, such as beams or shells,
undergoing finite rotations and small strains, starting from the basic solutions for
the three-dimensional Cauchy continuum used in the corresponding linear
modelings.
The idea is to use a local corotational description to decompose the deformation
gradient in a stretch part followed by a finite rigid rotation. Referring to this
corotational frame we can derive, from the linear stress tensor and the deformation
gradient provided by linear elasticity, an accurate approximation for the
nonlinear stress and strain tensors which implicitly assure frame invariance. The
stress and strain fields recovered in this way as functions of generalized stress
and strain resultants are then used within a mixed variational formulation
allowing us to recover an objective nonlinear modeling directly suitable for
FEM implementations through a black-box process which maintains the
full details of the linear solutions, such as shear warping and other subtle
effects.
The method is applied to the construction of three-dimensional beam and plate
nonlinear models starting from the Saint-Venant rod and Kirchhoff and
Mindlin–Reissner plate linear theories, respectively.
Keywords
geometrically exact beam and shell theories, corotational
description, postbuckling analysis