Nano-engineered composites: a multiscale approach for adding toughness to fibre reinforced composites

Fibre reinforced composites, and certainly carbon fibre composites (CFRP's), are champions in combining stiffness, strength and low weight. This unique set of properties has resulted in a strong increase of the use of composites in airplanes (up to 50% of their structural weight), and supports the expectation that CFRP's will soon make a breakthrough in automotive and other transport applications. One of the major limitations to the use of composites in primary structures is the rather low stress or strain threshold for damage initiation. Under static tensile loading, first matrix cracks in 0/90 or quasi-isotropic laminates appear at strains as low as 0.4%, whereas the final failure strain is as high as 1.5 to 2%. This early damage initiation can be further linked to the fatigue limit of UD-based laminates and, more generally, to the damage tolerance of textile based composites. In this research, different ways have been explored to increase the damage threshold of carbon and glass fibre reinforced composites by adding carbon nanotubes (CNT's) to either the matrix or the fibre sizing, or by growing them on the fibre surface. The effect of CNT's is not straightforward: some damage related properties are unaffected, but the interfacial shear strength, the interlaminar fracture toughness and the damage initiation threshold during tensile loading are strongly increased by adding CNT's. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11