Evaluation of Residual Thermal Stresses of Fibrous Composites

A micromechanical model for fibrous materials is used for determination of thermoelastic properties and the residual stresses of continuous fiber composites with straight or wavy fibers. The fibrous composite material is assumed to be of periodic type and is composed of circular fibers distributed within the matrix. Following a thermoelastic finite element analysis of the unit cell under a temperature change, the stress and strain components are volume-averaged to obtain the continuum components of the thermal stress and strain at a typical material point represented by the unit cell. The coefficient of thermal expansion (CTE) is then measured using the constitutive relations. In the numerical examples, the fiber is assumed transversely isotropic and the matrix is taken as an isotropic material. The composite is therefore, transversely isotropic with straight fibers, but becomes orthotropic for the case of wavy fibers. The thermal residual stresses generated per unit temperature change are studied in detail by volume averaging over slices (to be called sub-volumes) of the representative volume element (RVE) along the length of the fiber. The sub-volume averaging scheme shows the variation of the internal stresses and strains within the RVE. It is shown the created thermal stresses will play a significant role on the composite failure.