Formulation of Time-Dependent Thermal Strain in Composite Materials which are Composed of Elastic and Viscoelastic Solids

In this study, time-dependent behavior of thermal strain in composite materials which composed of elastic and viscoelastic solids is investigated. First, homogenized thermal expansion behavior of a unidirectional continuous CFRP is numerically analyzed using mathematical homogenization method. It is assumed to be orthotropic thermo-elasticity for carbon fiber. On the other hand, isotropic thermo-viscoelasticity based on generalized Maxwell model is assumed for base resin. It is shown to exhibit time-dependent thermal strain because of stress relaxation of base resin in the micro-scale (unit cell) of the CFRP. Second, the behavior of thermal strain is formulated by assuming that thermal strain is additively decomposed into equilibrium and non-equilibrium parts such as stresses in generalized Maxwell model. Non- equilibrium part of thermal strain is assumed to be dominated relaxation time of each Maxwell elements of the base resin. The resulting formulated thermal strain is shown to be perfectly successful for simulating the relaxation behavior of the unidirectional continuous CFRP.