Models and criteria of destruction of composite materials at the stage of macrocrack initiation

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The analysis was carried out and the limits of the use of modern damage models and criteria for the failure of composite materials (CM) at the stage of macrocrack initiation were established. The classification of CM and the main hypotheses and assumptions used in the development of the condition level are described. The main stage of the life cycle of a CM product is considered - the stage of nucleation and accumulation of scattered fractures at the micro and meso levels. The main principles of continuum damage mechanics, thermodynamics of irreversible processes and mechanics of a solid deformed body are used. The main mechanisms of microfailure of reinforced CM are described. It is shown that for them it is necessary to consider a set of phenomenological parameters that could assess the kinetics of the accumulation of diffused failures in the matrix, reinforcing fibers and the delamination between them. These complex processes in reinforced CMs require phenomenological modeling of damage in the form of tensor quantities with certain assumptions. Thus, the "mixture" hypothesis was widely used. It is shown that each component of the damage parameter is more expedient to determine from the hypothesis of the equivalence of specific energies. The method of conducting basic experiments to specify the regularities of damage accumulation in CM is detailed. A modified CM stiffness tensor is established, taking into account the degradation of the mechanical properties of the CM, regardless of the thermo-force parameters of the operating load. An analysis of modern criteria for the destruction of reinforced CMs and the limits of their use was carried out. The main directions of solving the problem of estimating the limit state of CM and the load-bearing elements made from them are shown.