The present paper deals the possibility of obtaining stress-strain relation with a decreasing segment through considering two-component medium. The basic idea lies in the assumption that a crystalline structure consists of two lattices connected by nonlinear interaction force. This force depends on the relative displacement of the lattices. When the displacement reaches its critical value, the system passes to the unstable position leading to a complicated dynamics. In this article the problem of static loading of twocomponent medium is considered. The problem is limited to one space dimension. The analytic solution obtained by applying the Galerkin procedure is compared with results of numerical calculations.