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Damage tolerance in ductile woven silk fibre thermoplastic composites

A. Prapavesis 1, P. Kopana 1, Weijing Wu 2, J. Soete 1, Y. Mosleh 3, A.W. van Vuure 1

1 Department of Materials Engineering, KU Leuven, Heverlee, Belgium (
2 College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, China
3 Biobased Structures and Materials Group, Department of Engineering Structures, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, the Netherlands

In this study, the tensile and bending properties of silk fibre composites using three (0, 90) woven fabrics with different architectures are investigated. The tensile results show that the silk composites can achieve high strain to failure (more than 20%) and toughness (up to 13 MJ/m3), which can be further manipulated based on the architecture of the fabrics, thus providing more tailored properties and design freedom in applications. XCT and SEM characterization are used to investigate and explain the outstanding toughness of these composites. In tension, a high density of microcracking was observed away from the failed location, which could explain the intrinsic high ductility and energy absorption of silk fibre composites by means of damage spreading throughout its volume in contrast to inherently brittle materials. In bending, significantly lower properties were observed with the more striking being the strain at failure reaching only 30% of the tensile value, thus limiting the potential of silk fibres in bending-dominated loading configurations. XCT revealed that the lower performance is due to failure on the compressive side of the composites, where a clear characteristic kink-band was observed in all composites subjected to bending, while there was no visible damage on the side under tension. This behaviour is also linked to the soft HDPE polymer matrix used, which provides little resistance to fibre buckling.

Key words: Biocomposite, ductility, damage tolerance, X-ray computed tomography