lagrangian formulation

Please have look 
http://arxiv.org/abs/1110.5321
 
This paper presents the theory for the Lagrange co-rotational (CR) formulation of finite elements in the geometrically nonlinear analysis of 3D structures. In this paper, strains are assumed to be small while the magnitude of rotations from the reference configuration is not restricted. A new best fit rotator and consistent spin filter is derived. 

Regards,
Lukasz