Residual properties and damage evolution of flax-epoxy composites subjected to fatigue loading

Flax fibre-based composites have seen increased use in recent years and new questions have arisen concerning their longevity. Thus, it is necessary to assess the long term properties such as fatigue and damage development. The present study focuses on the characterization of the residual properties of flax-epoxy composites subjected to fatigue loading as well as the damage development. Understanding these properties would allow easier prediction of long-term viability and durability of these materials and would as well facilitate their use. The fibre architecture was found to have a strong effect on the fatigue behaviour where higher strength and modulus composites have a postponed damage initiation, increased fatigue life, a reduced damage propagation rate as well as a higher energy dissipation due to high damage activity in the early stages. Residual properties were assessed on samples loaded for 500 000 cycles at 5Hz at a S/S0=0.3 stress level. It was found that the decrease in properties was around 15% as compared to the static properties. Furthermore, a slight increase of the slope of the stress-strain curve in the early cycles of the modulus degradation curves may be a sign of the stiffening phenomenon observed for cellulose-based composites where it is hypothesized that the reorientation of the microfibrils and elementary fibres movement within the technical fibres cause a brief increase in modulus.

Publication year:2015

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