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The composite bolted joints are the weak points of overall structure, lacking an effective and accurate monitoring method. In this paper, a novel MXene/CNTs film sensor with high sensitivity and stability was synthesized for the damage evolution monitoring of composite bolted joints. The correlation between the response signals of the sensors and the mechanical behaviors of the composite structures is established. Based on this research, the damage evolution monitoring and failure level evaluation of composite bolted joints were studied. The damage properties of the composite bolted joints can be reflected in real‐time by the resistance change rates of the sensors. The experimental results show that the failure level of composite bolted joints can be divided into four levels (I‐II‐III‐IV) according to the resistance change rates of sensors. Especially when the damage extended to the III stage, the ∆R/R0 surged from 0.3 to 0.75. The time point of this step signal occurred about 1 min earlier than the time point of max bearing strength, which can effectively warn the occurrence of structural failure. Highlights: Research used high‐sensitivity MXene/CNTs sensor to monitor bolt structureSensor array can be integrated with the composite bolted structureStructural damage of composite bolted joints was accurately monitoredFailure level evaluation of composite bolted structure was achieved [ABSTRACT FROM AUTHOR]

Composite laminates are susceptible to impact damage during service, and some damage is invisible. So it is necessary to monitor the impact location on the surface of composite laminates. Novel carbon nanomaterials represented by carbon nanotubes and MXene films have unique nanoscale structures and excellent physical properties. Applying the carbon nanotubes (CNT) and MXene films to monitoring the damage area of composite laminates under impact. Laying sensor arrays within the monitoring range, a localization algorithm suitable for sensor arrays is proposed, which can accurately calculate and locate the impact position to the monitoring area. Then check the impact location area, detect damage in time, and avoid structural damage or even failure caused by accumulated damage. After the impact test, the sum of the resistance change rate of the sensor in the M5 area is 0.6030, which is higher than the sum of the resistance change rate of other areas, and the impact point is determined to be in the M5 area. The calculation results are completely consistent with the real impact area, which greatly improves the efficiency of detection and maintenance, and has certain engineering significance. [ABSTRACT FROM AUTHOR]

High‐performance electrode materials are the key to advances in the energy storage area. 2D transition metal carbide Ti3C2TX is the most widely studied MXene with a unique two‐dimensional structure, exhibiting excellent electrochemical properties and becoming a new choice electrode material for supercapacitors in many studies However, the poor mechanical properties of pure the Ti3C2TX film has become the bottlenecks for the application. Ti3C2TX with less Li+ was prepared by proton acid colloid treatment, and then the single‐walled carbon nanotubes (SWCNTs) were used as interlayer barriers in the films to prevent Ti3C2TX layers from restacking to prepare Ti3C2TX and SWCNTs composite films. The composite films were tested and analyzed by different electrochemical techniques. The results showed that the film formed by MXene colloidal filtration after proton acid treatment was denser and the electrical conductivity reached 608700 S/m, which was 3.2 times higher than that of the original Ti3C2TX film. The composite film was prepared by mixing MXene colloidal proton acid treatment and SWCNTs, followed by filtration showd good capacitive capacity, reaching 270.5 F/g by testing in the 1 m H2SO4 electrolyte with the CV cycle of 5 mV/s. And the specific capacitance retention reaches 97.6 % under 5000 CV cycles. The tensile test of composite film shows that the ultimate strength up to 50.3 MPa, which is about 2.3 times compared to original Ti3C2TX film. [ABSTRACT FROM AUTHOR]

In this paper, a method with highly sensitive multi-wall carbon nanotubes (MWCNTs) film sensors was put forward to evaluate the health condition of glass fiber-reinforced composite single lap joints in real time. With this method, the single lap joint fracture can be predicted when the resistance change rate reached 1.11% to 5.89% approximately. Meanwhile, for the single lap joints, the reality can be found that the farther distance was from the interface to different layers, the more easily defect might emerge under the force introduced in the interface plane. And the stress in the middle area of the interface for the joint was greater than that in the edge when it was stretched. The results of experiments indicated that the effectiveness of MWCNTs sensors to monitor the health condition of the single lap joints was confirmed. [ABSTRACT FROM AUTHOR]

This paper prepares a flexible MXene/CNT film by layer‐by‐layer (LbL) self‐assembly process. Based on excellent conductivity and good compatibility with resin, MXene/CNT can be used for on‐line monitoring of large and complex liquid composite molding (LCM). In this paper, the MXene/CNT will be used as a novel micro‐nano sensor. The MXene/CNT sensor is embedded between the sandwich layers of the sandwich composite structure. The resistance information of the MXene/CNT sensor was collected by online monitoring system during LCM. The tube cross‐linked network's conductive model will be established to reveal the resistance response sensing mechanisms of MXene/CNT sensors and the response rules of resin flow states and resistance signals. Using the real‐time monitoring information collected by the MXene/CNT sensor, combined with Darcy's law, the comparison results of different permeability are obtained. The monitoring results show that polyvinyl chloride (PVC) interlayer significantly influences the resin flow trend and penetration of the core layer. Simultaneously, the interlayer's presence will also affect the resin flow trend and penetration of the lower layer of the PVC sandwich layer. The research results will provide theoretical guidance and technical support for designing process parameters and in situ real‐time monitoring of LCM in the engineering industry. [ABSTRACT FROM AUTHOR]

This study develops a facile approach to fabricate adhesives consists of epoxy and cost-effective graphene platelets (GnPs). Morphology, mechanical properties, electrical and thermal conductivity, and adhesive toughness of epoxy/GnP nanocomposite were investigated. Significant improvements in mechanical properties of epoxy/GnP nanocomposites were achieved at low GnP loading of merely 0.5 vol%; for example, Young's modulus, fracture toughness (K1C) and energy release rate (G1C) increased by 71%, 133% and 190%, respectively compared to neat epoxy. Percolation threshold of electrical conductivity is recorded at 0.58 vol% and thermal conductivity of 2.13 W m−1 K−1 at 6 vol% showing 4 folds enhancements. The lap shear strength of epoxy/GnP nanocomposite adhesive improved from 10.7 MPa for neat epoxy to 13.57 MPa at 0.375 vol% GnPs. The concluded results are superior to other composites or adhesives at similar fractions of fillers such as single-walled carbon nanotubes, multi-walled carbon nanotubes or graphene oxide. The study promises that GnPs are ideal candidate to achieve multifunctional epoxy adhesives. [ABSTRACT FROM AUTHOR]

A novel, omnidirectional, nanomaterial-based sensor technology which can provide wide area damage detection of composite structures was proposed in this work. The behaviors of the buckypaper sensors subjected to both tensile and low-velocity impact were investigated. The experimental results showed that the rectangle buckypaper sensor has a large range of sensing coefficients from 21.40 to 35.83 at different directions under tensile. However, the circular buckypaper sensor has a steady sensing coefficient of about 155.63. Thus, the circular buckypaper sensor as a kind of omnidirectional sensor was chosen to monitor the impact damage. The low-velocity impact damage of composite structures is characterized by the gauge factor of omnidirectional buckypaper sensors and the results of C-scanning. Omnidirectional buckypaper sensors' electrical resistance increases with repeated impact loading; composite structure elastic deformation and damage evolution can be identified from resistance change. Experiment results show that structure monitoring based on the omnidirectional buckypaper sensor not only can detect small barely visible impact damage flaws and the damage evaluation of composite structures subjected to impact but also can determine the location of low-velocity impact damage through the analysis of results. Through comparison with C-scan, the results have preliminarily demonstrated that the omnidirectional carbon nanotubes' buckypaper sensor can serve as an efficient tool for sensing the evolution of impact damage as well as serve structural health monitoring of composite structures. [ABSTRACT FROM AUTHOR]

Electromagnetic interference (EMI) originated from radio stations to various electronic appliances and devices is an increasingly serious problem, and there are significant interests in the development of light-weight, high-efficiency materials for EMI shielding. Herein we report novel carbon nanotube (CNT) composite films synthesized by a simple spray and vacuum-filtration method. The film containing 30 wt% single-walled CNTs demonstrates high electrical conductivity up to 20,000 S/m and excellent EMI shielding effectiveness 65 dB, with ∼130 μm in thicknesses and 0.011 g/cm 2 in areal density. The composite films are stiffer, stronger and more ductile than neat MWCNT film, i.e. 17.4 versus 3.3 MPa in tensile strength. Our films are sufficiently smooth, tough and flexible, which allow themselves to attach onto any complex curved surface. SWCNTs play an essential role in achieving such exceptional functional and mechanical performance; both SWCNTS and MWCNTS need to be well disentangled prior to the filtration. The composite films would have a wide range of engineering applications, i.e. production of conventional composite laminates due to their porous structure. [ABSTRACT FROM AUTHOR]

In this study, we developed a buckypaper (BP) composed of a mono-dispersion of multi-walled carbon nanotubes (MWCNTs) via a spray-vacuum filtration method. This highly flexible and sensitive carbon nanotube buckypaper (MWNCTs-BP) sensor can be integrated into complex curved surfaces and at critical stress areas to monitor the dynamic manufacturing process of fibre-reinforced composites in real time. A dynamic heating cure cycle and two revised cure cycles were designed to study the response of the resistance of the buckypaper to resin phase changes during the composite manufacturing process. Dynamic mechanical analysis (DMA) was performed to obtain the cure behaviour of a glass fibre/epoxy composite as a baseline to compare with the MWCNTs-BP sensor output. The experimental results show that the cure behaviour of epoxy/glass composites can be effectively monitored by the relative resistance change of the BP sensor embedded in the composite laminate. The MWCNTs-BP shows that the lowest viscosity point and gelation point of the composite resin were at 78 °C and 125 °C during the dynamic heating cure cycle, which is consistent with the DMA results. The lowest viscosity and gelation point can also be accurately obtained during the revised cure cycles. The MWCNTs-BP system has great potential as a sensor to establish and optimize manufacturing processes and to improve the cure quality of fibre-based resin composites. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) Buckypapers can be infused with resin and easily incorporated into conventional fiber reinforced composites. In this paper, we propose to use Buckypaper (BP) as a new measuring method to determine the glass transition temperature of polymeric composites. The CNT-only BP was fabricated by spray-vacuum filtration method with monodispersion of multi-wall carbon nanotubes, and then co-cured with polymeric composites. After manufacturing, the glass transition temperature of polymeric composites could be obtained from the relationship between resistance and temperature of BP during the dynamic heating process. Experimental results show that the glass transition temperature of composite samples A and B monitored by BP sensors were 127 °C and 180 °C, while such temperatures obtained from a dynamical mechanical analyzer (DMA) were 128 °C and 184 °C respectively. This paper not only reveals the ability of BP as a sensor for monitoring the glass transition temperature of composite but also provides a new way to understand the glass transition phenomenon of composite. [ABSTRACT FROM AUTHOR]

In this paper, we report the fabrication of a high-sensitivity strain sensor fabricated using graphene platelets (GnPs) and multi-walled carbon nanotubes (MWCNTs) for monitoring joint-bending movement. The optimized ultrasonic time and the ball mill-mixing process make the GnPs disperse evenly in the MWCNTs. The strain sensor made up of the GnP/MWCNT mixture (30 wt% GnPs loading) is fabricated by a spray-method and its conductivity is up to 104 S/m. The as-prepared GnP/MWCNT sensor exhibits relatively high tensile strength of 5.4 MPa, sensing range of 7.5%, gauge factor of 181.36, linearity of 99.545%, and great bending reproducibility over 5000 cycles. These remarkable features endow our sensing devices to monitor joint bending in human health monitoring, e.g., elbow, finger and wrist bending. The results demonstrate that our flexible GnP/MWCNT sensor shows promising applications prospects in smart wearable device monitoring human health. [ABSTRACT FROM AUTHOR]

In this paper, the health monitoring of Al 7075 friction stir welded structure was carried out, including elastic and plastic deformation during stretching and bending. A thin film sensor composed of MXene and single-walled carbon nanotubes was developed by simple mixing and vacuum filtration. This flexible MXene/SWCNT thin film sensor combining the sensitivity of MXene with the stability of carbon nanotubes and can be pasted on the surface of Al 7075 FSW joints through polyimide encapsulation to achieve structural health monitoring. The experimental results show that the MXene/SWCNT sensors encapsulated in polyimide can effectively capture the micro strain of different areas during stretching and bending. When the strain of the welded structure is less than 3000, only elastic deformation occurs in different regions of the welded structure, and the sensors located in different regions show the same resistance change rate. When the strain is greater than 3000, the resistance change rate of the sensors in the thermal-mechanical affected zone and heat affected zone obviously, and when the external force is released, there is residual resistance, which proves that the plastic deformation occurs in the welded structure at this time. By comparing the resistance change rate of the sensors in different regions, it can be inferred whether plastic deformation occurs. As the strain further increases, the resistance change rate of the sensor further increases and make a stable response until the structure breaks. This sensor can be used to track the whole process monitoring of welded structure before fracture. [Display omitted] • Thin film sensors composed of SWCNT and MXene were prepared by vacuum filtration. • The MXene/SWCNT sensor can monitor different strain with different aera of welding structure in real-time. • The MXene/SWCNT sensor adopted by polyimide package has good sensitivity and synchronization to cyclic load. • The MXene/SWCNT sensor can be used to follow the entire strain of welding structure till end-of-life. [ABSTRACT FROM AUTHOR]

Composite overwrapped pressure vessel (COPV) with their excellent specific properties and fatigue resistance are used for high-pressure storage in aerospace industries. To predict the life of COPV and avoid disasters, carbon nanotubes have been used as buckypaper (BP) sensors embedded in COPV for permanently monitoring damage in hydrostatic pressure tests and hydraulic fatigue tests. The changes in resistance measured by BP sensors are compared with the strain changes measured by strain gages. The experimental results show BP sensors are more sensitive and reliable to the initiation and propagation of microcrack and slight stiffness degradation in COPV than strain gauges. Embedding the BP sensors into COPV is effective for real-time structural health monitoring. [ABSTRACT FROM AUTHOR]

In this paper, lifetime health monitoring of composites was conducted, included manufactured monitoring and structural health monitoring. A thin film sensor composed of multi-walled carbon nanotubes (MWCNTs) and MXene was developed through simple mixing and spray vacuum filtration. This highly flexible and susceptible MXene/CNT film sensor can be embedded in polymer composites to monitor the phase change of the resin and the determination of the gel point during the preparation of the composite in real-time. The MXene/CNT film sensors were embedded and arrayed in fiber-reinforced composites, which can be used for resin curing monitoring, then continued structural health monitoring. Experimental results show that the MXene/CNT film sensor embedded in the composite laminates can effectively capture the change of the resin phase, that characterized by resistance. MXene/CNT films have a good ability to respond to changes in the resin state. The gel point of resin obtained from the MXene/CNT film sensor is 134 °C, which is consistent with 137 °C from the DMA results. The accurate gel point can optimize the curing system and improve the quality of composite products. Then the tensile, bending, and fatigue tests of fiber-reinforced composite laminates embedded with MXene/CNT film sensors were carried out. MXene/CNT film sensor can keep good response and response consistency for a long time. As a novel sensor, the MXene/CNT film sensor has the advantages of high response sensitivity, solid real-time performance, and long service time. The MXene/CNT film sensor has great potential to establish and optimize manufacturing processes and to improve the cure quality of fiber-based resin composites. This sensor can be used to follow the entire life cycle of a composite from fabrication till end-of-life. The 3D structure of the MXene/CNT film sensor can be used for life-long health monitoring of fiber-reinforced composite materials [Display omitted] • Thin film sensors composed of MWCNTs and MXene were prepared by mixing and spray vacuum filtration. • The MXene / CNT film sensor, which has good compatibility with resin, can monitor the phase change of resin during curing. • The MXene/CNT film sensor can monitor gel spots with different positions and thickness in real-time. • The MXene/CNT film sensor embedded in fiber reinforced composites has good sensitivity and synchronization to bending. • The MXene/CNT film sensor can be used to follow the entire life cycle of a composite from fabrication till end-of-life. [ABSTRACT FROM AUTHOR]

The properties of polymer nanocomposites depend greatly on the dispersion of nanoparticles in the polymer matrix. To improve the dispersion of single-walled carbon nanotubes (SWCNTs) in bismaleimide (BMI) resin, this paper developed a feasible method for non-covalent modification of SWCNTs by using polyvinylpyrrolidone (PVP). Moreover, the effect of functionalized SWCNTs on the properties of BMI composites was systematically investigated. The results showed that it was very effective for PVP as a surface modifier for the dispersion of SWCNTs in BMI resin. As a consequence, the electrical conductivity and mechanical properties of the SWCNT/BMI composites were all improved by the incorporation of SWCNTs at a low content. The study also presented that the heat resistance and thermal stability of SWCNT/BMI composites were simultaneously enhanced. [Display omitted] • A simple and feasible dispersion method for SWCNTs in BMI resin was developed. • The threshold percolation of SWCNTs/BMI composites was less than 0.01 wt%. • The mechanical properties of the composites increased substantially with a very low SWCNTs content. [ABSTRACT FROM AUTHOR]

The traditional wearable sensor has the problem of insufficient sensing coefficient and sensing range. In order to solve these problems, this paper innovatively prepared CNTs and MXene monodisperse waterborne slurry mixed with waterborne thermoplastic polyurethane and nanocellulose to prepare composite ink. The monodisperse CNTs and MXene have good conductive network construction ability, so that when the content of CNTs and MXene in the ink is as low as 0.08%, a stable sensing conductive network can still be formed (conductivity 127s/cm). The low addition of nanomaterials are cost saving along with the influence in conductivity which made the experiment to implement the bonding strength and viscous attributes of the inkjet in printing. The mechanical properties of the composite ink film sensor assembled by ink and medical fabric can be carried out by digital spraying printing technology. The results show that the sensitivity of the MXene/CNTs/WPU/CNFs ink sensor in the tensile test is up to 43.61, and the sensor resistance still shows a linear change under the strain of 0–89%. At the same time, after 2100 fatigue tests, the sensor resistance change remains stable. Finally, the MXene/CNTs/WPU/CNFs ink sensor has also been successful in human monitoring. From monitoring small changes such as finger bending and cervical spine bending to monitoring large movements such as arm flexion and knee bending, the corresponding electrical response can be obtained in time respectively. Therefore, the MXene/CNTs/WPU/CNFs ink sensor has the characteristics of high sensitivity, real-time monitoring and recording, which shows that the research has broad application prospects in the future development. [ABSTRACT FROM AUTHOR]