A thermoviscoplastic theory for composite materials by using a matrix-partitioned unmixing-mixing scheme

A thermo-elasto-viscoplastic constitutive theory for fiber-reinforced composite materials is suggested by extending the existing unmixing-mixing scheme which is based upon some micromechanical observations. A new technique, which is called the "matrix-partition method," is introduced in the model development. By this method, deformation states in the matrix phase can be represented with a set of mechanical variables for the respective parts of the partitioned matrix. As material parameters, which explain the three-dimensional microstructural effects resulting from kinematic compatibilities in the boundaries of the fibers and the matrix, the stress variation factors and the strain contribution factors are defined. The strain component of thermal expansion due to temperature changes is also included for the mathematical formulation. To verify the derived constitutive equations, the representative volume element of a unidirectionally fiber-reinforced lamina is discretized and analysed by the developed finite element code. The overall stress-strain curves are obtained through the finite element analyses subject to various loading conditions, and compared with the predicted curves by the constitutive equations based on the matrix-partioned unmixing-mixing model. The numerical results illustrate the validity and the usefulness of the proposed theory on composite thermoviscoplasticity.