Micromechanical viscoelastic characterization of fibrous composites

An efficient computational algorithm is proposed to evaluate the viscoelastic properties of fibrous composites. A repeating unit cell ( RUC) based on a pre-determined fiber packing is assumed to represent the microstructure of the composite. Finite element analysis of this unit cell under six specified loading conditions is carried out to study and quantify the time-dependent composite viscoelastic property of the unit cell. Volume averaging scheme is implemented to determine the averaged response as function of time in terms of stresses and strains. This time history analysis constitutes the data for characterization of the composite and determination of the viscoelastic parameters and coefficients. The individual viscoelastic properties of the constituents' materials as well as the composite are assumed to follow the Prony series definitions. To verify the algorithm certain examples are included. In these examples, the constituting fiber materials are assumed to be elastic and the matrix is assumed viscoelastic. Three different types of fiber packings; hexagonal ( HEX), square (SQR) and bidirectional crossed fibers (BCF), will be used and each packing will be examined for different fiber volume (V-f/V) fractions. The accuracy and verification of the results have been examined with known circumstances. The methodology is to be accurate and efficient so far the periodicity of the composite material rules. This micromechanics tool could make a powerful viable algorithm for determination of many linear as well as nonlinear properties in continuum mechanics material characterization and analysis.