Influence of water on damage and mechanical behaviour of single hemp yarn composites

This study aims to investigate the influence of water ageing on local deformation around a yarn in a hemp/epoxy composite. Specific single yarn composites were manufactured with the yarn oriented at 90° with respect to the tensile direction and with two types of epoxy resin, one being fully synthetic and the other one partially bio-based. First, a quantification of damage due to the water ageing is realised and photoelasticimetry analysis is used to study the evolution of the state of stress. Then, dumbbell samples with or without water ageing were tested under an optical microscope, and strain fields around the yarn were measured with the Digital Image Correlation (DIC) technique. The experimental results showed an increase in the measured strain after the water ageing. The local constitutive behaviour of the different constituents of the specimens could be approached by local analyses, and the evolution of the apparent stiffness values are discussed.