What are the possible origins of the nonlinear tensile behaviour of hemp fibres ?

International audienceIn recent years, there has been a growing renewal of interest in fibres derived from natural sustainable sources, as a result of their potential use in high performance composite materials. Because natural fibres are characterised by a large variability in their mechanical properties, the design of reliable structures based composites containing such natural fibres is a significant challenge for engineers, who are accustomed to the availability of consistent and accurate data for man-made fibres. In addition to their highly scattered mechanical properties, numerous fibres are characterised by a non-linear tensile behaviour. It has been observed by many authors in wood [1-5], and also in plant fibres such as flax [6-8] and hemp [9-12]. One of the typical nonlinear curve shape is plotted in Fig.1