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Investigations into carbon nanotube fibers as not only structural reinforcement materials but also standalone or embedded strain/damage, thermal, atmospheric and biochemical sensors are driven by their high specific strength, stiffness, electrical and thermal conductivity, and extreme flexibility. With future applications in view, we have studied their load transfer mechanisms, coupled electrical and mechanical response, high strain rate behavior and adaptability to resin infusion. This article is intended to cover our research over the past couple years and to highlight relevant and interesting work performed by others in the area of carbon nanotube fiber mechanics and experimental characterization. [Copyright &y& Elsevier]

Abstract: The efficiency of damage sensing in fiber composites with uniformly and non-uniformly dispersed carbon nanotubes has been compared in this study. A highly uniform dispersion of carbon nanotube in fiber composites was achieved through the three-roll-mill technique while a non-uniform dispersion of carbon nanotubes was obtained using a nanotube-containing fiber sizing agent. Both techniques are effective in creating electrically conductive network for damage sensing in fiber composites. The sizing agent/glass fiber composite shows much lower resistance change than that of the composites fabricated by three-roll-mill technique. Advantages of the sizing agent approach in composites fabrication have also been examined. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the modeling of damage sensing in [0°/90°]s cross-ply glass fiber composites using embedded carbon nanotube network. The wavy nanotubes are distributed in the polymer matrix between fibers and their contact resistances are modeled considering the electrical tunneling effect. The effective electrical resistance of the percolating nanotube network is calculated by considering nanotube matrix resistors and employing the finite element method for electrical circuits. The entire deformation process of the composite, from initial loading to final failure, is simulated by using the finite element method for two-dimensional stress analyses. The deformation and damage induced resistance change is identified in each loading step. The results demonstrate that the current simulation model captures the essential parameters affecting the electrical resistance of nanotube networks, which can serve as an efficient tool for structural health monitoring of fiber composites. [Copyright &y& Elsevier]

In the fabric shaping process during resin transfer molding, fabrics are deformed due to inter-fiber sliding and buckling of yarns. We have observed inter-fiber sliding and yarn buckling in the deep drawing of fabrics by a cylindrical punch. The amount of punch traveling and the molding die radius affect the occurrence of inter-fiber sliding and yarn buckling. Comparing simulation results and actual deformation of fabrics, we should take account of inter-fiber-sliding and buckling of yarns. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports an innovative approach to enhance electrical conductivity of fiber composites based on non-conductive fiber and polymer matrix. The dispersion of carbon nanotubes (CNTs) is carried out using a fiber sizing agent which contains uniformly distributed CNTs. The infusion of the sizing agent into the fiber preform prior to resin infusion gives rise to high agglomeration of CNTs on the fiber surface and results in electrical conductivities of 2–3 orders of magnitude higher than those of specimens prepared by a calendering approach. [Copyright &y& Elsevier]

Abstract: This paper provides an overview of recent advances in nanocomposites research. The key research opportunities and challenges in the development of structural and functional nanocomposites are addressed in the context of traditional fiber composites. The state of knowledge in processing, characterization, and analysis/modeling of nanocomposites is presented with a particular emphasis on identifying fundamental structure/property relationships. Critical issues in nanocomposites research as well as promising techniques for processing precursors for macroscopic nanocomposites are discussed. [Copyright &y& Elsevier]

Facile and scalable fabrication of high energy density wire-shaped asymmetric supercapacitor via wet-spinning assembly coupled with in situ electrosynthesis. Wire-shaped supercapacitors (WSC) have attracted tremendous attention for powering portable electronic devices. However, previously reported WSC suffered from a complicated fabrication process and high cost. The objective of this study is to develop a facile and scalable process for the fabrication of high energy density WSC. We coupled the wet-spinning assembly with an in situ electrodeposition technique to prepare carbon nanotube (CNT)-based composite fibers. The charge balance between the electrodes was realized by controlling the deposition time of the pseudocapacitive materials. A wire-shaped asymmetric supercapacitor (WASC) was fabricated by twisting MnO 2 /CNT fiber cathode and PPy/CNT fiber anode with LiCl/PVA electrolyte. The flexible MnO 2 /CNT//PPy/CNT WASC operated in a broadened voltage range of 0–1.8 V exhibited a high capacitance of 17.5F cm−3 (10.7F g−1). In addition, it delivered a maximum energy and power densities of 7.88 mWh cm−3 (4.82 Wh kg−1) and 2.26 W cm−3 (1382 W kg−1), respectively. The WASC device demonstrated satisfactory cycling stability with 86% capacitance retention, and its Coulombic efficiency remained at 96% after 5000 charge–discharge cycles. The contributions of the diffusion-controlled insertion and the surface capacitive effect were theoretically quantified to investigate the energy storage mechanism. The fabrication approaches hold potential for the construction of cost-effective and high-performance WSC. [ABSTRACT FROM AUTHOR]

Stretchable conductive fibers have attracted significant attention due to their ability to be directly woven into or stitched onto fabrics, making them ideal for use in the design of integrated wearable strain sensors. Here, we report on a highly stretchable multi-walled carbon nanotube (MWCNT)/Thermoplastic Polyurethane (TPU) fiber produced via a wet spinning process. The effects of MWCNT content and alignment on the structural, mechanical, electrical and strain-sensing properties of the composite fibers were investigated. The highest conductivity (6.77 S cm−1), tensile strength (28 MPa) and maximum elongation at break (565%) were obtained by controlling the MWCNT content. Gauge factor (GF) values were also affected by the content and MWCNT alignment in the composite fibers, as these parameters determine the change in the effective contact area and number of conductive paths available during stretching. The well-aligned MWCNT/TPU fiber showed a high GF value of 5200. Wearable strain sensors capable of obtaining real-time mechanical feedback for various human motion detections with different GFs and working strain ranges could be realized by controlling the MWCNT concentrations in the TPU matrix. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotube networks have been used previously for in situ sensing of matrix damage in fiber-reinforced composites. In this research, the ability of carbon nanotube networks to sense and distinguish different types of damage in adhesively-bonded hybrid composite-to-metal joints is evaluated. Toward this end, conductive networks of carbon nanotubes are introduced to the composite substrate as well as the epoxy adhesive. By altering the geometry and chemically treating the steel substrate surface, different failure mechanisms of the single-lap shear joints are achieved. It is demonstrated that these failure mechanisms each possess a distinct resistance response, therefore proving the ability to not only sense failure in situ, but also to distinguish the extent and nature of damage which occurs. [Copyright &y& Elsevier]

Abstract: Material and structural reliability is crucial for the potential use of composite materials in a variety of structural applications. As a result, damage detection and health monitoring of fiber-reinforced composites are attracting progressively more attention in the field of materials research. In this work, small amounts of carbon nanotubes are added into traditional fiber composites to form electrically conductive networks throughout the polymer matrix. The electrical response of the carbon nanotube network to accumulated damage combined with the acoustic emission (AE) technique is utilized to sense damage initiation and evolution in laminated composites. The parameters which correspond to the resistance change of the specimen due to damage in quasi-static and cyclic tests are used to evaluate the damage state in the material. There exists a bi-linear relationship between the resistance change and AE signal cumulative counts which gives insight toward the damage state of the material during quasi-static and cyclic tests. [Copyright &y& Elsevier]

The concept of multifunctional hybrid composites has generated considerable research interest in the past two decades. A very significant advancement in this area has been the development of truly multifunctional components, which can simultaneously handle structural and nonstructural functionality in composites. Success in the development of stiff, strong and lightweight continuous fiber structural composites with the capability of energy storage has led to the evolution of "structural power composites." Among the many structural power composites studied, significant progress has been made in recent years in structural supercapacitor (SSC) composites. The ability of SSCs to carry mechanical loads while simultaneously storing/releasing electrical energy has enabled their potential applications in many fields, such as portable electronics, electric vehicles and aerospace vehicles. In this review, we assess state-of-the-art advances in SSC composites in terms of the development of carbon fiber-based electrodes, solid polymer electrolytes and separators. The fabrication process and performance characterization of SSCs are discussed. Finally, the challenges and future opportunities in SSC composites research are presented. Image 1 [ABSTRACT FROM AUTHOR]

Many stretchable conductive composite fibers exhibit high elongation at break, but most of them do not have a large workable strain range towing to the low conductivity when used as strain sensors. In this paper, we fabricated a highly conductive silver nanowire (Ag NW)/multi-walled carbon nanotube (MWCNT)/thermoplastic polyurethane (TPU) fiber via a wet-spinning process to improve the workable strain range of composite fibers. TPU was used as a matrix material to introduce superior stretchability. MWCNTs act as sensing elements and Ag NWs were used to increase conductivity. We investigated the effect of Ag NW content on the mechanical, electrical, and strain-sensing performance of the fiber-type strain sensors. The optimal content of Ag NWs extended the workable strain range as higher as 254% with an electrical conductivity of 0.803 S/cm. A weight-to-strain cloth sensor was assembled by writing Ag NW/MWCNT/TPU fibers in the coagulation solution. Furthermore, such composite fiber can be free-written into any designed pattern, which can be used to prepare fiber-based devices. [ABSTRACT FROM AUTHOR]