A Thermoplastic Elastomeric Nanofibrous Membrane as CFRP Modifier to Boost Both Delamination and Damping Performance

In the present work, thermoplastic elastomeric nanofibers made up of a homogenous blend of nitrile butadiene rubber (NBR) and Ppolycaprolactone (CL), with 80% wt of rubbery component, are used to modify a carbon fiber reinforced polymer (CFRP) laminate with the aim of improving its delamination and damping behavior at the same time. Since the nanofibrous membrane is not chemically cross-linked, the fibrous morphology is lost during composite curing owing to its melting. Nonetheless, the nanomodified CFRP displays an impressive ability to improve the delamination resistance in mode I and also an enhanced damping capacity at low temperature. The use of nanofibrous membranes allows for modification of specifically selected areas, thus maximizing the toughening and damping behavior where most required, without necessarily affecting the whole bulk of the resin. Both PCL and NBR components contribute to the final performance; however, the very high amount of rubber leads to a membrane difficult to handle whose final performance in CFRP modification is not superior to membranes up to 60% wt NBR that are instead more stable and easier to deal with. Overall, the proposed results are nonetheless very promising, taking into account also that the improved delamination resistance in mode I and enhanced damping are obtained without significantly sacrificing the weight and overall dimension of the obtained composite

Polyamide Nanofibers Impregnated with Nitrile Rubber for Enhancing CFRP Delamination Resistance

Delamination is the main responsible for structural failure of composites having a laminar structure. In the present work, polyamide (Nylon 66) nanofibers, even impregnated with uncrosslinked nitrile butadiene rubber (NBR), are interleaved into epoxy-based carbon fiber reinforced polymer (CFRP) laminates with the aim to counteract the delamination phenomenon. The performance of nano-modified composites using both the nanofibrous mat types, that is, Nylon 66 and NBR-impregnated Nylon 66 membranes, is investigated. Mode I loading tests show a significant improvement of the interlaminar fracture toughness of rubber-modified CFRPs, especially in the G(I,)(R) (up to +151%). The improvement in the G(I,)(C) is less pronounced, but still significant (up to +80%). The achieved results are very encouraging and pave the way to the use of such Nylon-NBR hybrid mats for hindering delamination

Development and fracture toughness characterization of a nylon nanomat epoxy adhesive reinforcement

The potential of an electrospun nylon nanofibrous mat as adhesive carrier and reinforcing web in adhesive bonding has been proven by the authors in a previous work. In that work, a pre-preg nanomat was developed using a low-viscosity epoxy resin for composite hand lay-up, in order to favour wetting of the nanofibres and to minimize air entrapment. However, the resin for hand lay-up exhibited a poor bonding performance when compared to the one typical of epoxy adhesives. The present work is therefore aimed at developing a laboratory route to add an electrospun polymeric nanomat to a two-part epoxy adhesive joint. Three different adhesives with increasing viscosity have been preliminarily evaluated regarding the entrapment of air after curing. The most promising one has been used to manufacture a small-size, Al-alloy double cantilever beam joint and compare the performance with and without the nanomat. Three different precracking procedures have also been developed and evaluated, namely fatigue precracking (A), razor blade tapping (B) and nanomat exfoliation (C). The results indicate that the fracture toughness of the nanomat-reinforced adhesive joint is similar to the neat adhesive one at the beginning of the propagation but it becomes much higher as the crack advances

Nano-vascularized polymers: how nanochannels impact the mechanical behaviour at the macroscale

In recent decades, nature has inspired the engineering of many structural and smart materials. Nano-vascularization has been stimulating research on advanced materials for novel biomedical, orthopaedic, industrial, and aeronautical applications. The continuous development of nano-vascularized materials re-quires a more accurate understanding of their mechanical behaviour. This work provides a multiscale methodology to predict the macroscale properties of nano-vascularized materials. The methodology is experimentally validated for the case of a nano-vascularized epoxy resin manufactured using sacrificial electrospun nanofibers. It is based on the development of representative volume elements (RVEs) that encompass information about both the nanochannels distribution and on the mechanical properties of the material at different dimensional scales. The RVEs simulations allowed obtaining a homogenized model describing the nano-vascularized material properties and studying the most intimate failure mechanisms. A virtual stress tomographic investigation on the RVEs was adopted as a digital twin to reveal the damage evolution and the actual failure mechanisms of the nano-vascularized material: damage occurred mainly at the nanochannels intersections, particularly where the intersections become dense. Interestingly, the si-mulations revealed a correlation between the stress state and the formation of feather markings as well as local failures on the nanochannels linking directions, as evidenced by SEM analysis. (c) 2022 Elsevier Ltd. All rights reserved