Contribution for a better characterization of the tensile mechanical behaviour of flax/PP biocomposite materials

Abstract

This work aims to characterize the mechanical behaviour in tension of biocomposite (polypropylene/flax fibres), using a digital image correlation device The preliminary results show that the strain level at the surface of the tested specimen is not uniform. It also appears that the position of the observation area greatly affects the measured strain level. This is attributed to both the inhomogeneity in the internal structure in the woven fabric composite materials and the change in the local damage process from one area to another within the loaded specimen, as confirmed by the microscopic observations of fracture facies of broken specimens. To overcome these drawbacks, the observation area is enlarged to the entire surface of the loaded specimen. In this case, the results clearly indicate that the tensile stress strain curves of the woven flax/PP specimen loaded in wrap and weft directions show a bi-linearity mechanical behaviour, characterized, as generally reported in the literature, with a knee point at 20 MPa in stress and 0.2% in strain. In the shear plan direction, however, a nonlinear behaviour is obtained. Finally, based on the SEM observations, the dominating damage mechanisms in tension of this composite (kink bands, splitting cracks at flax bundles, fiber failure, and matrix cracks) are identified.