Hello, I'm trying to program a quadrangular shell user element in Abaqus.

Could anybody show me how to process the rotation dofs? Because the rotation is not like displacement with additive decomposition. In the manual, it says that the Quaternion parametrization is used for finite rotation in abaqus, but I still can't find out how it works.

If I use the incremental rotation passed from abaqus to calculate the bending and transverse shear strain, I'll get severe distortion deformations during the simulations. For pure tension, it works well because the rotation has little contributions to the internal forces.