Microstructure,mechanical behaviour,damage mechanisms of polypropylene/short hemp fibre composites: Experimental investigations

This article is devoted to the study of mechanical behaviour of a polypropylene reinforced with short hemp fibres available industrially. The main objective of this study is to understand the major physical phenomena to be taken into account to propose, in an upcoming work, a relevant modelling of these composites. Important experimental investigations were performed and revealed quasi-isotropic microstructure at fibres scale in terms of spatial distribution and orientation using X-ray tomography. Influence of hemp fibres on behaviour of polypropylene/hemp composites was examined at controlled temperature upon monotonic and complex path uniaxial tensile loading at different strain rates (10⁻⁴, 10⁻³ and 10⁻² s⁻¹) and fibres weight fraction (0, 5, 10 and 20%w/w). Resulting stress–strain curves pointed out a reinforcing effect of hemp fibres at initial stage. Furthermore, the noted high strain rate sensitivity is accounted for quasi-brittle failure. Use of infrared thermography technique highlighted the presence of ‘two breaking modes’ depending on strain rate, i.e. at low strain rate one single damaged zone appeared, on the contrary at higher strain rate many damaged areas occurred in all calibrated zone. In accordance of all conducted experiments, non-linear behaviour of polypropylene/hemp composites is mainly attributed to matrix behaviour.