ИСТИНА

Experimental investigations of mechanical properties of composite materials reveal different types of nonlinearity in their behavior. There is a variety of mechanisms of deformation of these materials, whichare dependent on the type of reinforcement, matrix properties, loading conditions, directions of loads with respect to reinforcement and some others. These mechanisms and their interactions determine the stress-strain behavior of materials. Physical nonlinearity of composite materials is that their mechanical properties are not invariant to the loading conditions but depend on the stress state type that is caused by heterogeneous structure of composite materials. Another type of nonlinearity is concerned the shear properties. Some features of the materials behaviors are analyzed and the corresponding phenomenological constitutive relations are formulated that can characterize them. The nonlinear models proposed in this research have a general form and they are suitable for any heterogeneous materials but mostly are directed to anisotropic laminate composites subjected to loadings under plane stress conditions. Two parameters are introduced into constitutive relations, one of which characterizes the stress state dependency of material properties and another one describes the nonlinear shear properties. The possibilities of proposed nonlinear elastic constitutive relations in describing of mechanical behavior of laminate composite materials are demonstrated on the base of experimental data, for laminate based on the glass cloth and polyether matrix.