An algorithm is proposed to determine the effective deformation properties and stress-strain state of particulate composite materials with physically nonlinear components and complex stress state. The laws that govern the deformation of particulate composites are studied. A particulate composite is considered a two-component material of random structure. Its effective properties are determined by conditional averaging. The nonlinear equations that incorporate the physical nonlinearity of the components are solved by the method of successive approximations. The relationship between macrostresses and macrostrains is established. The effective deformation properties of a particulate composite as a function of the volume fractions of the components and stress state are studied Keywords: particulate composite, nonlinearity of deformation, complex stress state, effective deformation properties, stress-strain stateIntroduction. Under rather high loads, the macrostress-macrostrain relationship is nonlinear in many composite materials. This may be due to the physical nonlinearity of the components [3] or due to microdamages [6] appearing as microcracks or micropores during deformation [9][10][11][12][13][14][15]. The former type of nonlinearity is characteristic of composites based on plastic metal matrix or polymers at elevated temperatures. The latter type of nonlinearity is characteristic of brittle materials such as polymer composites at low temperatures, carbon-matrix composites, ceramic composites, etc.Extensive use is made of dispersion-reinforced composite materials, which are small solid quasispherical or quasispheroidal particles evenly distributed over a soft metal or polymer matrix. Such materials are usually subject to loading that induces a complex stress state. The dispersed particles are linearly elastic, and the matrix is nonlinear. The stress and strain interaction of the components results in the nonlinearity of the relationship between the macrostresses and macrostrains, which are determined by the volume fractions of the components and the shape and arrangement of particles. To predict the effective properties of such composites, it is necessary to solve a physically nonlinear elastic problem for a microinhomogeneous body. This problem is much more difficult to solve than the linear problem, especially for regular structures [1]. When the structure is stochastic, the ergodic property [7,8] allows us to use preliminary statistical averaging at one point instead of averaging of the final solution over a macrovolume, which considerably simplifies the formulation and solution of the problem. The singular [8] or single-point [7] approximation enables solution of the spatial nonlinear problem only for quasispherical structural elements [5]. The method of conditional moments [7] made it possible to predict the effective properties of physically nonlinear composites with arbitrary structural elements by solving a system of nonlinear algebraic equations.In the present paper, we outline a method and develop an ...