Multiscale Toughening of Composites with Carbon Nanotubes—Continuous Multiscale Reinforcement New Concept

Abstract

Strengthening composite structures for advanced industries such as offshore wind generation is a real issue. Due to the huge dimensions expected for next generation wind-blades, composites based on glass fibers can no longer be used due to the lack of stiffness, whereas composites based on carbon fibers are expensive. Therefore, switching to alternative structural solutions is highly needed. This might be achieved by appropriate use of carbon nanotubes (CNTs) either as fillers of epoxy matrices, especially in inter-plies, or as fillers of epoxy glues used in structural bonding joints. As an example, trailing edges of offshore wind-blades are addressed in the current article, where monolithic bonding holds together the two structural halves and where the risk of sudden and brittle separation of edges while wind-turbines are in service is quite high. This can lead to tedious and very expensive maintenance, especially when keeping in mind the huge dimensions of new generation wind turbine blades that exceed lengths of 100 m. Bond joints and composites inter-plies of the final CNT-reinforced structures will exhibit stiffness and toughness high enough to face the severe offshore environment. In this article, multiscale Finite Element (FE) modeling is carried out to evaluate mechanical properties following the addition of CNTs. To achieve an optimal reinforcement, the effect of inclination of CNTs vs. mechanical loading axis is studied. Two innovations are suggested through this numerical study: The first consists of using homogenization in order to evaluate the effects of CNT reinforcement macroscopically. The second innovation lies in this forward-looking idea to envisage how we can benefit from CNTs in continuous fiber composites, as part of a deep theoretical rethinking of the reinforcement mechanisms operating at different scales and their triggering kinetics. The presented work is purely numerical and should be viewed as a “scenario” of structural composite materials of the future, which can be used both in the offshore industry and in other advanced industries. More broadly and through what is proposed, we humbly wish to stimulate scientific discussions about how we can better improve the performances of structural composite materials.