Modeling of load responses for natural fiber reinforced composites under water absorption

Based on the continuum mechanics, a constitutive model has been developed to describe the swelling-elastic deformation behavior of natural fiber reinforced composites when considering the mechanical deterioration caused by water absorption and external loadings. Two internal variables are employed to measure the effects of damages caused respectively by water absorption and by external loadings. The Helmholtz free energy function and the evolution equations of these two internal variables are investigated in detail and given explicitly for short natural fiber reinforced composites. This proposed theoretical model is then applied to analyze the mechanical performance of swollen sisal fiber reinforced composites under uniaxial tension. Theoretical estimations on the evolutions of elastic modulus as well as tensile strength are found in good agreement with corresponding experimental results.