Tensile deformation of a flax fiber

In this paper we investigate the tensile properties of a natural composite material: the flax fiber. The beginning of the stress-strain curve of a flax fiber upon tensile loading appears markedly non-linear. The hypothesis of a progressive alignment of the cellulose microfibrils with the tensile axis provides a quantitative explanation of this departure from linearity. This hypothesis is confirmed by the similar behavior which characterises hemp and ramie fibers. Besides, it has long been recognized that the natural character of flax fibers induces a large scatter of their mechanical properties. This scatter is shown not to be associated with the pronounced cross-section size variation observed along the fiber profiles. Two fiber size measurement methods are compared in order to check their influence on the property scatter and the decrease of the fiber mechanical properties as a function of the fiber diameter.