ON DILATATION AND DIFFERENT RESISTANCE OF ISOTROPIC MATERIALS
Based on the fact that many composite and traditional structural materials do not obey the hypotheses of a «single deformation curve», and the laws of change in volume and shape, even in the case of the initial isotropy of the structure, are interrelated. The boundedness of the classical Hooke generalized law is shown. It is noted that approximations of experimental diagrams obtained under axial tension and compression with quasi-linear dependences are the most appropriate. That is, the use of nonlinear models of deformation of dilating materials and materials whose deformation and strength properties are determined by the type of stress state is recommended. We briefly analyze the well-known equations of state that determine the proportional deformations of initially isotropic bodies, taking into account the dependence of their stiffness on the qualitative picture of the realized stress state. Quasi-linear model approximations are considered. Physical equations with four, five, and six constants in the energy forms of deformation of weakly nonlinear initially isotropic materials were analyzed. The recommended methods for calculating the constants of materials from the simplest experiments for materials of different classes are considered. These parameters define the constants of the equations of state. At the same time, the greatest universality of the potential relations formulated in the spaces of normalized stresses is demonstrated. In addition, the physical validity of the general deformation laws of composite materials is confirmed and it is shown that the phenomena of dilatancy and diversity of resistance are two forms of manifestation of their special structure. The advantages of the accepted forms of potential are explained by the successful choice of harmonic stress functions, which are limited to the interval from -1 to +1. The sufficient universality of the strain potential formulated in the normalized stress spaces is shown.