nonlinear constitutive relations, anisotropic materials, identification, composites.

A second-order elasticity model for an orthotropic material is considered. The analysis shows that the quadratic part of the proposed model contains thirteen elastic constants, nine of which are linearly independent. The parameters of the model are determined from the data of experiments with composite plates. The model allows one to describe experimentally observed nonlinear dependences of stresses and strains in the processes of tension, compression, and shear, as well as the difference in resistance of anisotropic materials.

Nguyen Sy Toan, postgraduate student, Tula State Univercity, Tula, Russia.

Khristich Dmitrii Viktorovich, Dr. Sci. Phys. & Math., Professor, Tula State University, Tula, Russia.