The yarn/matrix interface in composite materials: fragmentation tests and micro-CT based digital volume correlation
Résumé
Competing with glass-reinforced composites, natural fibre-reinforced composites are booming, and are of increasing interest to manufacturers for structural applications. A key issue of this kind of composite is investigated: the yarn/matrix interface behaviour. Different states of ageing and yarn treatments were studied through quantitative damage analysis and evaluation of the interfacial shear strength (IFSS). First, at the macroscopic scale of a hemp-based woven composite, damage rates were calculated from micro-CT image acquisitions before and after mechanical tests for different fibre orientations, matrices and hydrothermal ageing states. Results showed the predominant role of the yarn orientation in the development of interfacial damage. To further investigate the yarn/matrix interface, single yarn composites were manufactured and subjected to fragmentation tests. IFSS values were calculated for treated and untreated hemp yarn. Results showed that plasma treatment carried out at CANOE produced promising results. Finally, a damage scenario for a single yarn composite was established performing a fragmentation test coupled with micro-CT scans and digital volume correlation. This enabled the tracking of the full-field strain evolution at the yarn/matrix interface throughout fragmentation testing and a better understanding of the stress and strain redistribution that occurs when fibre breaks and debonding appear in the gauge length.
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