Micromechanism based material models for natural fiber composites

The objective of Paper A was to develop a material model which includes all nonlinear viscoelastic phenomena observed in compressive tests on vinyl ester specimens using experimental data. The constitutive model developed by Schapery in the particular form previously presented by Megnis and Varna is used. The observed elastic behavior of thin specimens is explained based on parametric FEM analysis. The objective of Paper B was to use Schapery's model for nonlinear viscoelasticity and a power law for viscoelastic compliance to characterize the observed behavior for the material. The developed model has accuracy sufficient for practical applications. However, at high stresses the attempts to describe the viscoelastic compliance by a power law with a stress independent exponent were unsatisfactory and therefore stress dependence of this exponent was included in the data analysis. The objective of Paper C was to analyze the effect of geometrical parameters and constituent properties on effective properties of natural fiber composites. In order to do that we first develop an analytical model valid for orthotropic phase materials and for an arbitrary number of phases. This model is a straightforward generalization of Hashin's concentric cylinder assembly model and Christensen's generalized self- consistent approach.Godkänd; 2005; 20061213 (haneit