Modelling the influence of fibre internal structure on the measured modulus of technical natural fibres

The internal structure, cross section area (CSA) and mechanical properties of palm and coir fibres were investigated using SEM on cryotome cut samples, tensile measurements of single technical fibres at three gauge lengths and optical microscopy of fibre cross sections. The measured technical fibre modulus was significantly dependent on gauge length and CSA. Two theoretical approaches were developed to fit the observed modulus dependence on fibre CSA. These calculated the measured technical fibre modulus as a function of the dimensions of the technical and elementary fibres combined with modulus of the elementary fibres and the efficiency of the inter-level interface to transfer stress across consecutive levels within the fibre. Palm fibre results gave good correlation between experimental observations and theoretical predictions. The modulus dependence of coir fibres on CSA was less well defined due to a higher level of property variability which led to poorer correlations with fitting model values.