TOWARDS DAMAGE RESISTANT COMPOSITES USING ELECTROSPUN NANOFIBERS: A MULTISCALE ANALYSIS OF THE TOUGHENING MECHANISMS

Fiber reinforced polymer composite laminates have become a standard material in applications were a high stiffness and high strength are required at minimal weight. Nevertheless, delamination between reinforcing plies and brittle matrix fracture remain the most important failure modes that are encountered in service for laminated composite materials. Although traditional solutions exist to toughen the interlaminar region between reinforcing plies, these systems often have important disadvantages which makes it too difficult to apply them to industrial scale. Recently, electrospun nanofibers have been suggested as an interlaminar toughening method which is much more viable as the electrospinning is relatively straightforward and scalable while the nanofibers do not affect the composite production process. Nevertheless, although the expected benefits are numerous, the research on composite laminates enhanced with electrospun nanofibrous veils is still very limited. A thorough understanding of the micromechanical fracture mechanisms and the parameters to obtain toughened composites have not been determined as of yet, but it is crucial in order to advance the research into these materials. In this presentation we would like to provides such insights by analyzing the nanofiber toughening effect on three different levels simultaneously for several nanofiber types: (i) the nano reinforced epoxy level, (ii) the interlaminar level and (iii) the laminate level. It was found that each level corresponds to certain (micro)mechanisms that result in a toughening effect. The bridging of microcracks by electrospun nanofibers is the main toughening mechanisms present on all levels. Nevertheless, the obtained increase in interlaminar fracture toughness on the interlaminar and laminate level is dependent on many more parameters which have been overlooked until now and are exposed by our multiscale analysis. In this presentation emphasis will be given on the effect of the mechanical properties of the nanofiber and how it influences the fracture toughness of the composites on these different levels