Abstract
Based on the characteristics of the Gibbs elastic potential for reversible isothermal deformation processes of orthotropic elastic materials, this paper has built a complete second-order nonlinear model to describe the dependence of deformation on stress in the tensile, compression and shear processes. This model contains 18 material parameters, including 9 parameters of the linear component similar to Hooke's law and 9 additional parameters in the second-order nonlinear component. The paper also provides the necessary experimental diagram to determine all the stated parameters of the model. From the published experimental data for organic glass materials, the parameters of the model are calculated.