Relative humidity and temperature dependence of mechanical degradation of natural fiber composites

Abstract

In this paper, the mechanical degradation of natural fiber composites is studied with the consideration of the relative humidity and the temperature. A nonlinear constitutive model is established, which employs an internal variable to describe the mechanical degradation related to the energy dissipation during moisture absorption. The existing experimental researches demonstrated that the mechanical degradation is an irreversible thermodynamic process induced by the degradation of fibers and the damages of interfaces between fiber and matrix, both of which depend on the variation of the relative humidity or the temperature. The evolution of the mechanical degradation is obtained through the determination of dissipation rates as a function of the relative humidity and the temperature. The theoretically predicted mechanical degradations are compared with experimental results of sisal fiber reinforced composites subject to different relative humidity and temperatures, and a good agreement is found. natural fiber, moisture absorption, mechanical degradation, relative humidity, temperature PACS number(s): 81,05.70.-a, 61.82.pv, 81.05.Lg Citation: Y. H. Pan, and Z. Zhong, Relative humidity and temperature dependence of mechanical degradation of natural fiber composites, Sci. China-Phys. Mech.

A two‐stage analysis for the role of fiber size in terms of length distribution on the performance under accelerated weathering tests of oil palm empty fruit bunch fiber‐reinforced vinyl acrylic composites

“…Since one of the major drawbacks of natural fibers is their considerable sensitivity to water, the microstructural changes in composites after salt‐fog exposure were expected to be more noticeable than those arising from the UV aging treatment; nevertheless, with regard to tensile mechanical performance, a similar behavior was observed. Then again, gradual damage of the interfacial region between the OPEFB fibers and the vinyl acrylic matrix took place resulting in the reduction of elongation at break due to matrix microcracking boosted by the continuous dimensional changes in both the fibers and the matrix during moisture cycling, the cutback in tensile strength and modulus of elasticity due to a combined effect of polymer plasticization and fiber softening leading to poor stress transfer efficiencies (viz., fibers pulled out and debonding, Figure 5), and the decline in toughness due to embrittlement coming from the overall effect of the aforesaid elements together with the reported action of salt ions and water molecules that decreases the hydrogen bonding between polymeric chains 68–70 . Moreover, it should be pointed out that leaching—evidenced by color fading—assisted fiber‐matrix debonding because of the development of osmotic pressure pockets at the composite interface 71 .…”

“…Then again, gradual damage of the interfacial region between the OPEFB fibers and the vinyl acrylic matrix took place resulting in the reduction of elongation at break due to matrix microcracking boosted by the continuous dimensional changes in both the fibers and the matrix during moisture cycling, the cutback in tensile strength and modulus of elasticity due to a combined effect of polymer plasticization and fiber softening leading to poor stress transfer efficiencies (viz., fibers pulled out and debonding, Figure 5), and the decline in toughness due to embrittlement coming from the overall effect of the aforesaid elements together with the reported action of salt ions and water molecules that decreases the hydrogen bonding between polymeric chains. [68][69][70] Moreover, it should be pointed out that leaching-evidenced by color fading-assisted fiber-matrix debonding because of the development of osmotic pressure pockets at the composite interface. 71 Comparatively, an alike phenomenon to that which occurred in the UV aging also happened in the salt fog aging; that is; the most prominent and statistically representative effects of the latter on elongation at break took place in the composites reinforced with the widest length distribution of OPEFB fibers.…”

Modeling of mechanical behaviors for natural fiber reinforced composites under hygrothermal ageing

“…On the basis of the non-equilibrium thermodynamic framework, Pan and Zhong [3][4][5][6][7] have conducted a series of research on modeling the effect of moisture absorption on the mechanical properties of natural fiber reinforced composites. In their analyses, the internal variables are introduced into the Helmholtz free energy to describe the mechanical degradation during the water absorption stage in the hygrothermal ageing process, and the relation between the amount of the water absorbed by the composites and the volumetric swelling of the composites is formulated on the hypothesis of the elastic incompressibility.…”

“…It is proved by the experimental observations that the micromechanical model is capable of predicting the modulus loss with the increasing water concentration. Pan and Zhong [3][4][5][6][7] have built a series of theoretical models to analyze the mechanical behaviors of natural fiber reinforced composites during the moisture absorption process from both macro and micro aspects.…”