Effect of nanofiber diameter and arrangement on fracture toughness of out of autoclave glass/phenolic composites - Experimental and numerical study

In this study, the effect of (Polyvinyl butyral) PVB-nanofiber diameter and orientation on the mode II fracture toughness of laminated phenolic composite was investigated by means of experimental and numerical methods. The motivation was to explore the potential of nanofiber veils as an inter-laminar toughener of laminated composites in consideration of the importance of improving the inter-laminar fracture toughness of phenolic-based composites. As regards the experimental investigation, the fracture behavior of glass/phenolic composites was determined by end notched flexure (ENF) test taking into account four different nanofiber diameters (100, 165, 314 and 500 nm) and two fiber orientations: random and aligned. In addition, a finite element model including cohesive elements was applied to investigate numerically the fracture behavior of composites during mode II loading. The results indicate that there is an optimal value of nanofiber diameter that maximizes the initial fracture toughness (GIIC). The outcome also shows that aligned nanofibers are not able to improve the fracture toughness under mode II loading. The GIIC value of optimal sample (fiber diameter 165 nm and random orientation) is 26% higher than the reference laminates. On the other hand, it is proven that the bi-linear traction-separation law is a suitable method to model PVB-modified laminates under mode II loading. The effect of nanofiber diameter and orientation on cohesive parameters (K0, GIIC, σmax) was also studied.