Load Transfer Analysis in Short Carbon Fibers with Radially-Aligned Carbon Nanotubes Embedded in a Polymer Matrix

A novel shortfiber composite in which the microscopic advanced fiber reinforcements are coated with radially aligned carbon nanotubes (CNTs) is analyzed in this study. A shear-lag model is developed to analyze the load transferred to such coated fibers from the aligned-CNT reinforced matrix in a hybrid composite application. It is found that if the carbon fibers are coated with radially aligned CNTs, then the axial load transferred to the fiber is reduced due to stiffening of the matrix by the CNTs. Importantly, it is shown that at low loading of CNTs in the polymer matrix, there is a significant reduction in the maximum interfacial shear stress, e.g., at 1% CNTs, there is an ~25 % reduction in this maximum stress. Further, the modification in the load sharing between the fiber and the matrix plateaus at ~2% CNT matrix loading, indicating a small but critical window for engineering the interface in this manner. Effects of the variation of the aspect ratio of the fiber, CNT volume fraction and the application of radial load on the load transferred to such CNT coated fibers are also investigated

Thermal and Electrical Transport in Hybrid Woven Composites Reinforced with Aligned Carbon Nanotubes

Carbon nanotubes (CNTs) are a potential new component to be incorporated into existing aerospace structural composites for multifunctional (mechanical, electrical, thermal, etc.) property enhancement. Although CNT properties are extraordinary when measured individually, they tend to degrade by a large factor when integrated in system (often in polymer matrices). Mechanisms and effectiveness of nano-scale CNT implementation into macro-scale structural composites are not well understood. Non-mechanical aspects of these composites are the focus of this work. As a CNT hybridized fiber polymer composite, fuzzy fiber reinforced plastic (FFRP) is developed using a scalable fabrication method that achieves uniform CNT distributions for thermal and electrical conductive networks without requiring intensive mixing which can damage CNTs. At small CNT volume fractions (~0.5- 8% Vf), characterization shows significant enhancement in electrical conduction (x106-108) but limited enhancement in thermal conduction (x1.9). In addition, aligned-CNT polymer nanocomposites (A-CNT-PNCs) are being characterized as a representative volume element (RVE) of the FFRP. Experimentally obtained data on consistent A-CNT-PNC samples sets provide engineering knowledge and to achieve effective utilization of CNTs' multifunctional properties. Theoretical studies, both analytical and numerical, have been recently developed, suggesting interface effects may be a key to explaining the above limitations, including electron tunneling/hopping or phonon scattering at CNT-CNT and CNT-polymer interfaces. Multiple test techniques and property extraction methods for A-CNT-PNCs are developed and/or employed for cross-comparison. Applications of nano-engineered composites enhanced with CNTs can include lightning protection layers, electromagnetic interference shields, thermal management layers, and thermoelectrical sensor layers for airplane structures.Airbus IndustrieMassachusetts Institute of Technology (Richard and Linda Hardy Graduate Fellowship)Boeing CompanyEmpresa Brasileira de AeronáuticaLockheed MartinSpirit AeroSystems (Firm)Textron, inc.Composite Systems Technology (Firm)Toho Tenax Co., Ltd.Massachusetts Institute of Technology (Nano-Engineered Composite aerospace STructures (NECST) Consortium

Aligned Carbon Nanotube Reinforcement of Aerospace Carbon Fiber Composites: Substructural Strength Evaluation for Aerostructure Applications

https://www.aiaa.org/ProceedingsDetail.aspx?id=5776Vertically aligned carbon nanotubes (VACNTs) are placed between all plies in an aerospace carbon fiber reinforced plastic laminate (unidirectional plies, [(0/90/±45)2]s) to reinforce the interlaminar region in the z-direction. Significant improvement in Mode I and II interlaminar toughness have been observed previously. In this work, several substructural in-plane strength tests relevant to aerostructures were undertaken: bolt/tension-bearing, open hole compression, and L-shape laminate bending. Improvements are observed for the nanostitched samples: critical bearing strength by 30%, open-hole compression ultimate strength by 10%, and L-shape laminate energy (via increased deflection) of 40%. The mechanism of reinforcement is not compliant interlayer creation, but rather is a fiberstitching mechanism, as no increase in interlayer thickness occurs with the nanostitches. Unlike traditional (large-fiber/tow/pin) stitching or z-pinning techniques that damage inplane fibers and reduce laminate in-plane strengths, the nano-scale CNT-based ‘stitches’ improve in-plane strength, demonstrating the potential of such an architecture for aerospace structural applications. The quality of VACNT transfer to the prepreg laminates has not been optimized and therefore the noted enhancement to strength may be considered conservative. Ongoing work has been undertaken to both improve VACNT transfer and expand the data set.Massachusetts Institute of Technology (Nano-Engineered Composite aerospace STructures (NECST) Consortium

Self-powered pressure sensor based on the triboelectric effect and its analysis using dynamic mechanical analysis

Since 2012 there has been a rapid rise in the development of triboelectric nanogenerators due to their potential applications in the field of energy harvesting and self-powered sensors for vibrations, accelerations, touches, pressures and other mechanical motions. This study suggests a novel triboelectric nanogenerator based on the interaction between polyvinylidene fluoride and polyvinylpyrrolidone submicron fibers. Polyvinylpyrrolidone is introduced as a new material for the TENG because of its tendency of losing electrons easily, while polyvinylidene fluoride is selected for its strong-electron attracting ability. Electrospinning is suggested as a fabrication method for the nanofibers due to its simplicity, versatility and low-cost. Furthermore, the paper explores the possibility to use this triboelectric nanogenerator as a self-powered pressure sensor. For this purpose, the nanogenerator is subjected to dynamic mechanic analysis which produces controlled pressure forces applied with a certain frequency. This is the first work to suggest the use of dynamic mechanical analyzer to study the relation between the applied mechanical stimulus and the electric responses of the triboelectric nanogenerator. Eventually the sensitivity of the nanogenerator to different pressures is analyzed. A directly proportional relationship is found between the pressure applied and the resultant voltage and current amplitudes. The developed nanogenerator reacts to pressure in real time and as a sensor it exhibits a very high sensitivity and low experimental error for repeated measurements. The main contributions of this study are the development of a novel nanogenerator based on the triboelectric effect between polyvinylidene fluoride and polyvinylpyrrolidone electrospun fibers and the investigation for its potential use as a self-power pressure sensor. Eventually, the paper explores the advantages of dynamic mechanical analyzer for pressure analysis

Three-dimensional elastic constitutive relations of aligned carbon nanotube architectures

Tailorable anisotropic intrinsic and scale-dependent properties of carbon nanotubes (CNTs) make them attractive elements in next-generation advanced materials. However, in order to model and predict the behavior of CNTs in macroscopic architectures, mechanical constitutive relations must be evaluated. This study presents the full stiffness tensor for aligned CNT-reinforced polymers as a function of the CNT packing (up to ∼20 vol. %), revealing noticeable anisotropy. Finite element models reveal that the usually neglected CNT waviness dictates the degree of anisotropy and packing dependence of the mechanical behavior, rather than any of the usually cited aggregation or polymer interphase mechanisms. Combined with extensive morphology characterization, this work enables the evaluation of structure-property relations for such materials, enabling design of aligned CNT material architectures.NECST ConsortiumUnited States. Army Research Office (Contract No. W911NF- 07-D-0004)United States. Army Research Office (Contract No. W911NF-13-D-0001)United States. National Aeronautics and Space Administration (NASA Space Technology Research Fellowship Grant No. NNX11AN79H)National Science Foundation (U.S.) (Grant No. CMMI-1130437

An extended vascular model for less biased estimation of permeability parameters in DCEâ T1 images

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137317/1/nbm3698_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137317/2/nbm3698.pd

Bioinspired approaches for toughening of fibre reinforced polymer composites

In Nature, there are a large range of tough, strong, lightweight and multifunctional structures that can be an inspiration to better performingmaterials. Thiswork presents a review of structures found in Nature, frombiological ceramics and ceramics composites, biological polymers and polymers composites, biological cellular materials, biological elastomers to functional biological materials, and their main tougheningmechanisms, envisaging potential mimicking approaches that can be applied in advanced continuous fibre reinforced polymer (FRP) composite structures. For this, themost common engineering compositemanufacturing processes and current composite damage mitigation approaches are analysed. This aims at establishing the constraints of biomimetic approaches development as these bioinspired structures are to be manufactured by composite technologies. Combining both Nature approaches and engineering composites developments is a route for the design and manufacturing of high mechanical performance and multifunctional composite structures, therefore new bioinspired solutions are proposed.This research was funded by the project “IAMAT—Introduction of advanced materials technologies into new product development for the mobility industries”, with reference MITP-TB/PFM/0005/2013, under the MIT-Portugal program and in the scope of projects with references UIDB/05256/2020 and UIDP/05256/2020, exclusively financed by FCT - Fundação para a Ciência e Tecnologia

Continuous Growth of Vertically Aligned Carbon Nanotubes Forests

Vertically aligned carbon nanotubes are one of the most promising materials due their numerous applications in flexible electronic devices, biosensors and multifunctional aircraft materials, among others. However, the costly production of aligned carbon nanotubes, generally in a batch process, prevents their commercial use. For the first time, a controlled process to grow aligned carbon nanotubes in a continuous manner is presented. Uniform growth is achieved using 2D and 3D substrates. A significant reduction in time, gases, and energy is accomplished, allowing the industrial production of vertically aligned carbon nanotubes.National Science Foundation (U.S.) (Nanomanufacturing Program (CMMI-0800213))Massachusetts Institute of Technology (Nano-Engineered Composite aerospace STructures (NECST) Consortium

New architecture and processes for hierarchical composites of aligned carbon nanotubes and continuous carbon fibers

A new laminate nanoengineered composite laminate architecture employing aligned carbon nanotubes (CNTs) is designed, fabricated, and characterized. This multi-fiber architecture targets mass-efficient inter- and intra-laminar enforcement of aerospace-grade carbon fiber reinforced plastics (CFRPs). Aligned CNTs are integrated between the advanced fibers and tows at room temperature after CNT growth, yielding a tailorable distributed CNT network throughout the structure. Unlike existing approaches, such as weaving, stitching, and z-pinning that result in in-plane mechanical property reduction, we demonstrate that in-plane mechanical properties can be maintained. In addition to expected toughness and strength enhancement from such architectures, modest enhancement of electrical conductivities was observed in both in-plane and through-thickness directions. Future work includes refinements of the mechanical assembly method and processing to expand and improve multi-functional properties