Effect of Gauge Length, Cross Sectional Area and Strain Measurement Methods on Stiffness Characterization of Fique Natural Fiber

Among different mechanical properties, stiffness of natural fibers is one of the most important and challenging properties to measure due to their irregular cross section area. In this paper, a direct strain measurement method is presented and applied to Fique (Fucraea andina) fibers. The results are compared against the conventional indirect strain measurement method commonly used in fiber characterization. The latter requires considering the system compliance, being particularly challenging for natural fibers with a wide variability among them. One solution to address this issue can be using gauge lengths of around 100 to 200 mm, which are longer than the ones typically used for the characterization of single fibers. Each fiber’s cross section has been measured precisely, and the assumption that fibers have a circular cross section is studied. The Young’s modulus of the tested Fique fibers is measured to be 17 GPa using indirect strain measurement, and it is found to increase with gauge length using direct strain measurement to 18 GPa for 100 mm length, for either area calculation approach. Fibers’ area values show differences from assuming circularity to measure the cross-sectional area, but its impact on the Young’s modulus is not significant when enough number of fibers is tested.