We present a mathematical framework for the so-called multidisciplinary free material optimization (MDFMO) problems, a branch of structural optimization in which the full material tensor is considered as a design variable. We extend the original problem statement by a class of generic constraints depending either on the design or on the state variables. Among the examples are local stress or displacement constraints. We show the existence of optimal solutions for this generalized free material optimization (FMO) problem and discuss convergent approximation schemes based on the finite element method.