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This work evaluates the effects of modified‐graphene oxide (M‐GNs) loading and graphene nanoplatelets (GNs) modification on the low‐velocity and high‐velocity impact (LVI and HVI) behaviors of aramid fiber/epoxy composites. Aminopropyltrimetoxysilane compound was used to modify the surface of the GNs. The epoxy resin was incorporated with 0.1, 0.3, and 0.5 wt% M‐GNs to fabricate the multiscale M‐GNs/aramid fiber/epoxy composites via the hand lay‐up route. The obtained results from the LVI and HVI tests revealed that the highest impact resistance was related to the multiscale specimen having 0.3 wt% M‐GNs. For example, under LVI conditions (impact energy of 60 J), the addition of 0.3 wt% M‐GNs enhanced the force peak and absorbed energy of the composite by 44% and 95%, respectively. The addition of 0.3 wt% M‐GNs increased the ballistic limit and absorbed energy of the composite (exposed to the HVI) by 23% and 52%, respectively. The fracture surface of the specimens was evaluated by scanning electron microscopy to find the dominant mechanisms. It was also found that the incorporation of the M‐GNs reduced the damaged area and enhanced damage tolerance. The results demonstrated that modification of the GNs enhanced the LVI and HVI properties of the multiscale composites.

Specialty optical fibers, in particular microstructured and multi-material optical fibers, have complex geometry in terms of structure and/or material composition. Their fabrication, although rapidly developing, is still at a very early stage of development compared with conventional optical fibers. Structural characterization of these fibers during every step of their multi-stage fabrication process is paramount to optimize the fiber-drawing process. The complexity of these fibers restricts the use of conventional refractometry and microscopy techniques to determine their structural and material composition. Here we present, to the best of our knowledge, the first nondestructive structural and material investigation of specialty optical fibers using X-ray computed tomography (CT) methods, not achievable using other techniques. Recent advances in X-ray CT techniques allow the examination of optical fibers and their preforms with sub-micron resolution while preserving the specimen for onward processing and use. In this work, we study some of the most challenging specialty optical fibers and their preforms. We analyze a hollow core photonic band gap fiber and its preforms, and bond quality at the joint between two fusion-spliced hollow core fibers. Additionally, we studied a multi-element optical fiber and a metal incorporated dual suspended-core optical fiber. The application of X-ray CT can be extended to almost all optical fiber types, preforms and devices.

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