The design of aerospace structures from composites requires modeling of their stress-strain state, based on experimentally determined values of the characteristics of the materials used in their production. To calculate the thermoplastics molding process, information on the rheology, thermophysics, and shrinkage, mechanical and other properties of the material is needed. The properties of the composite are nonlinear and depend on the orientation of the reinforcing fibers; therefore, it is necessary to create high-precision models of the anisotropy of the mechanical characteristics of the material reinforced by short fibers. The choice of the shape of nonlinear material parameters approximation curve can significantly affect the results of mathematical modeling of the stress-strain state of a composite product.

The paper compares the plasticity models of a composite reinforced by short fibers. For verification, tensile tests of flat samples were carried out according to ISO 527 with various share of reinforcing fibers cut at different angles to the molding direction. The use of plasticity models to verify the multilevel model of composites allows one to increase the accuracy of modeling nonlinear problems of static stiffness and strength of structures made of composite materials reinforced by short fibers.