Аннотация:The results of recent studies of deformation softening and post-critical deformation
of steels are presented and the corresponding criteria are formulated for complex
loading conditions. The elastic and strength properties of different grades of
graphite materials as well as their fracture toughness properties are studied. The
method for the determination of crack length and the values of fracture toughness
characteristics of materials during stable equilibrium crack growth under bending
conditions is considered. The unstable or non-equilibrium crack growth from short
initial crack is observed in experiments, and corresponding theoretical explanation
is given. The process of unstable crack growth is analyzed for different loading
conditions. It has been shown that in the cases of short cracks, some part of stored
energy transforms into kinetic energy, which can be described by the equation of
energy balance during unstable crack growth.
Many structural materials, which are preferred for the developing of advanced
constructions, are inhomogeneous ones. These materials have complex internal
structure and properties, which make them to be more effectual in the solution
of special problems required for development engineering. On the other hand,
in consequence of this internal heterogeneity, they exhibit complex mechanical
properties. In this work, the analysis of some features of the behavior of composite
materials under different loading conditions is carried out. The dependence of
nonlinear elastic response of composite materials on loading conditions is studied.
Several approaches to model elastic nonlinearity such as different stiffness
for particular type of loadings and nonlinear shear stress–strain relations are
considered. Instead of a set of constant anisotropy coefficients, the anisotropy
functions are introduced. Eventually, the combined constitutive relations are
proposed to describe simultaneously two types of physical nonlinearities, one
of which characterizes the nonlinearity of shear stress–strain dependency and
another one determines the stress state susceptibility of material properties. The
method for experimental determination of material’s functions is proposed. Quite
satisfactory correlation between the theoretical dependencies and the results of
experimental studies is demonstrated.