We propose a structural model for a granular elastomeric composite. This model allows us to relate deformation and strength of composite with size of particles of the disperse phase, that is, to take into consideration the scale factor of strength. Studying theoretically stress-strain state of medium in the zone of two rigid inclusions in elastic incompressible matrix, we obtain the dependency of mathematical expectation of breaking strength on physical and mechanical characteristics of coupling agent, on size of particles, and on distance between particles. We propose new probabilistic criterion for generation of micro-fracture zones (delamination of the matrix out off particles) in composite structures. Using the criterion proposed, we performed model study of the processes of development of an internal zone of damage in composite systems depending on inclusion volume fraction and size of inclusions. We obtain corresponding graphs for tension and determine the values of limiting failure stress under macro-tension and corresponding values of macro-deformations.