Modeling of the mechanical degradation induced by moisture absorption in short natural fiber reinforced composites

This paper develops a constitutive model of short natural fiber reinforced composites (SNFRCs), with the consideration of nonlinear constitutive relation and large deformation induced by moisture absorption. This model accounts for the processes of moisture absorption and mechanical degradation in SNFRCs by a single internal variable, since these two thermodynamic processes are found correlated with each other. This internal variable is introduced to modify the Neo-Hookean model, from which the evolution equations of these two processes are derived by specifying a suitable energy dissipation function. Both the moisture absorption and the mechanical degradation are shown sensitive to the fiber content and could be enlarged with exposure time in a humid environment. Theoretical predictions of the evolution of the internal variable are compared with experimental results of short sisal fiber reinforced polypropylene and it is shown a good agreement between them. Moreover, this model is used to give a reasonable prediction of the degraded Young's modulus of SNFRCs.