#### Vol. 10, No. 1, 2015

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Mechanical degradation of natural fiber reinforced composite materials under constrained swelling

### Yihui Pan and Zheng Zhong

Vol. 10 (2015), No. 1, 79–91
DOI: 10.2140/jomms.2015.10.79
##### Abstract

Natural fiber reinforced composite materials (NFRCMs) have found more and more applications because of their excellent performances over traditional fiber reinforced composites. However, mechanical properties of these materials may be dramatically degraded in a humid environment, whether subject to mechanical loading or not. A nonlinear constitutive model is established for unidirectional natural fiber reinforced composites under large swelling deformation based on nonequilibrium thermodynamics, in which an internal variable is incorporated in the Helmholtz free energy to consider the irreversible energy dissipation induced by moisture absorption. The Helmholtz free energy is further decomposed into the base free energy of the isotropic matrix, the reinforcing energy of fiber stretching and the free energy of volume expansion. Two kinds of reinforcing energy (the ${I}_{4}$-dependent model and the ${I}_{5}$-dependent model) are employed to predict the degradation of the elastic modulus for the cases of free swelling and constrained swelling. It is found that the predictions from these two models are identical for the case of free swelling and agree well with available experimental data. As for the case of constrained swelling, these two models yield obviously different results.

##### Keywords
natural fiber, moisture absorption, mechanical degradation, swelling, energy dissipation
##### Milestones
Received: 2 August 2014
Revised: 10 November 2014
Accepted: 21 November 2014
Published: 6 May 2015
##### Authors
 Yihui Pan School of Aerospace Engineering and Applied Mechanics Tongji University Shanghai, 200092 China Zheng Zhong School of Aerospace Engineering and Applied Mechanics Tongji University Shanghai, 200092 China