Tension-tension fatigue behaviour of woven hemp fibre reinforced epoxy composite: A multi-instrumented damage analysis

The purpose of this work is to characterise the tensile-tensile fatigue behaviour of a woven hemp fibre reinforced epoxy composite, adding up analysis of fatigue damage mechanisms by combining different techniques: optical microscopic and X-ray micro-tomography observations, temperature field measurement by infrared camera, and acoustic emission monitoring (AE). Two different stacking sequences: [0°/90°] and [±45°] are compared. A power law based model is used to fit S-N curves of experimental results. [±45°]7 layups show better fatigue strength than [0°/90°]7 ones, in relative terms. This is explained by the difference of their damage behaviour, in concordance with the local shear stresses developing in [±45°]7 laminates. Moreover, high resolution micro-tomography pictures allow one to clearly visualise the yarn/matrix interface damage in these materials. The obtained results give a complete description of fatigue damage mechanisms, and a damage scenario during fatigue tests is proposed for these eco-composite materials.