The present paper is the first part of a work that aims at building a dissipative model of microcrack friction in quasi-brittle energetic materials. The latter is viewed as an assembly of elementary cells containing the most salient features of the heterogeneous microstructure of an energetic material. It is intended here to build an analytical model describing the mechanical and energetic response of such an elementary cell under confined tension. This is achieved by applying a previously published theory that allows for the determination of the amount of dissipated and stored energies in heterogeneous dissipative structures containing microcracks and other dissipative components.