On the quasiconvex hull for a three-well problem in two dimensional linear elasticity

We provide quantitative inner and outer bounds for the symmetric quasiconvex hull $Q^e(\mathcal{U})$ on linear strains generated by three-well sets $\mathcal{U}$ in $\mathbb{R}^{2\times 2}_{sym}$. In our study, we consider all possible compatible configurations for three wells and prove that if there exist two matrices in $\mathcal{U}$ that are rank-one compatible then $Q^e(\mathcal{U})$ coincides with its symmetric lamination convex hull $L^e(\mathcal{U})$. We complete this result by providing an explicit characterization of $L^e(\mathcal{U})$ in terms of the wells in $\mathcal{U}$. Finally, we discuss the optimality of our outer bound and its relationship with quadratic polyconvex functions.