The kinetics of crack growth in a viscoelastic orthotropic plate made of a composite material is analyzed. The external load is the superposition of a cyclic load and a constant tensile load. The level of the tensile load is assumed to exceed the amplitude of the cyclic load. The kinetic curves are compared with the constant tension curves. The effect of the cyclic component is studied.Keywords: viscoelastic composite material, operator continued fraction, crack growth, cyclic load 1. Viscoelastic Anisotropic Material. The stress-strain state of many polymers and polymeric composites is described by the linear rheological relations, even for high stress levels. Therefore, the stress-strain analysis of such materials is based on the linear theory of viscoelasticity. One of the alternatives of this theory that has recently received wide acceptance is based on the Boltzmann principle. According to this principle, the system of constitutive equations in the quasistatic theory of viscoelasticity is similar to the system of constitutive equations in the linear theory of elasticity, except for Hooke's law. The physical relations of linear viscoelasticity are similar to the physical relations of linear elasticity where the elastic anisotropy constants are replaced by integral operators. The stress-strain relationship for a linear viscoelastic medium are defined based on the Boltzmann principle aswhere ε kl and σ kl are the strain and stress components; and A ijkl * is the viscoelastic analog of the stiffness tensor. If the rheological characteristics of a viscoelastic composite are time independent (nonaging material), some viscoelastic operator M * acting on a time function has the following integral form (Volterra operator of the second kind):where M is the corresponding elastic constant; M(θ) is the relaxation function. Such functions are determined experimentally mainly for anisotropic media with certain symmetry. This reduces the number of independent creep functions.
Features of Modeling Cracked Composites.A typical feature of matrix composites of regular microstructure is the anisotropy of their macroscopic physicomechanical properties. Despite the variety of reinforcement schemes, the relationship between the strain and creep components is the main concern in describing the mechanical properties of the composite. The deformation mode of the composite can be predicted in two ways. One is to consider a reinforced material as a structure (microapproach). The complexity of the mathematical microstructural description of deformation is mainly due to inhomogeneity whose degree depends on the relative fractions of the phases and differences between their properties. Strongly