Direct computation of stresses in linear elasticity

We present a new finite element method based on the formulation introduced by Philippe G. Ciarlet and Patrick Ciarlet, Jr. in Ciarlet and Ciarlet, Jr. (2005), which approximates strain tensor directly. We also show that the convergence rate of strain tensor is optimal. This work is a non-trivial generalization of its two dimensional analogue in Ciarlet and Ciarlet, Jr. (2009).