NANOTUBE/FIBER MULTI-SCALE HYBRID COMPOSITES USING ELECTROPHORETIC DEPOSITION: PROCESSING, CHARACTERIZATION, AND SMART SENSING APPLICATIONS

Carbon nanotubes are widely known to have unique physical and mechanical properties at the nanoscale. Because carbon nanotubes have diameters three orders of magnitude smaller than traditional advanced fibers used in structural composites there is unique opportunity to create multi-scale hybrid composite systems where reinforcement scales are combined. Our recent research has developed a highly efficient and industrially scalable electrophoretic deposition technique for nanoscale hybridization. The resulting composites show a hierarchical structure, where the structural fibers, which have diameters in micrometer range, are coated with carbon nanotubes having diameters around 10–20 nm. Microscopic characterization shows the integration of carbon nanotubes throughout the thickness of the fabric, where individual fibers are coated with carbon nanotubes. Within the composite, networks of carbon nanotubes span between adjacent fibers, and the resulting composites exhibit good electrical conductivity and considerable increases in the interlaminar shear strength, relative to fiber composites without integrated carbon nanotubes. We have demonstrated that conducting carbon nanotube networks formed in a polymer matrix can be utilized as highly-sensitive sensors for detecting the onset, nature and evolution of damage in advanced polymer-based fiber composites. The potential of carbon nanotubes for in situ monitoring of damage accumulation in fiber composites will be discussed and recent research on utilizing carbon nanotubes in monitoring of large-scale structures highlighted. Please click Additional Files below to see the full abstract

Sensor Formed from Conductive Nanoparticles and a Porous Non-conductive substrate

In various aspects, the sensors include a substrate that is porous and non-conductive with nanoparticles deposited onto the substrate within pores of the substrate by an electrophoretic process to form a sensor element. The nanoparticles are electrically conductive. The sensor includes a detector in communication with the sensor element to measure a change in an electrical property of the sensor element. The change in the electrical property may result from alterations in quantum tunneling between nanoparticles within the sensor element, in various aspects

Processes for Depositing Functionalized Nanoparticles upon a substrate

Processes for depositing functionalized nanoparticles upon a non-conductive substrate are disclosed herein. The processes may include the step of aerosolizing one or more particles into suspension within a gas, each of the one or more particles comprising functionalized nanoparticles having an electric charge. The processes may include the step the step of attracting the one or more particles onto a non-conductive substrate by a static electric charge opposite of the electric charge, wherein at least portions of the non-conductive substrate are having the static electric charge. The processes may include the step of depositing the functionalized nanoparticles onto the non-conductive substrate

Development of Self-Sensing Carbon Nanotube-Based Composites for Civil Infrastructure Applications

Presented at the 5th International Symposium on Sensor Science (I3S 2017), Barcelona, Spain, 27–29 September 2017. Worldwide, civil infrastructure systems are aging and deteriorating due to maintenance neglect, increasing traffic, and an environment that is becoming increasingly more severe. In particular, bridges play a critical role in the transportation network. With limited monies available for maintenance and repair, a need exists for effective yet inexpensive solutions to strengthen and monitor bridges. This presentation provides an overview of the development of carbon nanotube (CNT)-based composites, which offer a means to strengthen and monitor a deteriorated bridge member simultaneously. CNT sensors are created by infusing a fabric, which can be structural or non-structural, with carbon nanotubes to form a piezo-resistive network. Changes in the measured resistance between electrodes, which are attached to the composite layer, have been found to directly correlate to deformations and the formation and accumulation of internal damage. The resulting novel self-sensing composites are sensitive, inexpensive, and able to adhere to almost any shape. Two particular civil infrastructure applications will be presented and discussed in detail. First, two largescale reinforced concrete beams were strengthened with a composite layer that had an embedded sensing layer and then loaded to failure using load cycles of increasing amplitude. The objective of the second application was to increase the remaining fatigue-life of a cracked steel bridge member. For this application, ASTM E647 test specimens were rehabilitated with self-sensing composites and loaded cyclically to failure. Both applications highlight the potential of CNT-based composites in bridge rehabilitation and monitoring

Development of Self-Sensing Carbon Nanotube-Based Composites for Civil Infrastructure Applications

Worldwide, civil infrastructure systems are aging and deteriorating due to maintenance neglect, increasing traffic, and an environment that is becoming increasingly more severe. [...

Comparative Study of the Thermoresistive Behavior of Carbon Nanotube-Based Nanocomposites and Multiscale Hybrid Composites

Advances in carbon nanotube (CNT) based composites over the past decade have demonstrated broad potential of utilizing them as multifunctional sensors because of their unique electrical properties. This article studies the thermoresistive behavior of two-component (CNT-epoxy) nanocomposites and hierarchical (CNT-fiber-epoxy) multiscale composites using in situ electrical resistance measurements during thermal cycling from 25 to 145 °C. A series of CNT-based composites with controlled nanotube morphologies were created via three-roll-milling, dip-coating and electrophoretic deposition methods. The results show that the thermoresistive behavior of CNT-based composites is influenced by the CNT concentration, thermal expansion, fiber/polymer properties, and interfacial interactions. CNT-epoxy nanocomposites with randomly dispersed CNTs show a positive temperature correlation. In comparison, multiscale composites with fibers show a double-crossover-shaped temperature dependence of their electrical resistance influenced by the changes of the CNT network that are induced by the polymer thermal motions and the residual thermal stresses. The thermal expansion behavior of the composites was characterized using a thermomechanical analyzer and a simplified finite element model was used to qualitatively examine the fiber-matrix interfacial residual stresses. While the thermoresistive behavior of nanocomposites has been investigated more broadly, this research is a first step in understanding the processing-structure-thermoresistive response relationship of multiscale CNT/fiber composites

Processing and Characterization of a Novel Distributed Strain Sensor Using Carbon Nanotube-Based Nonwoven Composites

This paper describes the development of an innovative carbon nanotube-based non-woven composite sensor that can be tailored for strain sensing properties and potentially offers a reliable and cost-effective sensing option for structural health monitoring (SHM). This novel strain sensor is fabricated using a readily scalable process of coating Carbon nanotubes (CNT) onto a nonwoven carrier fabric to form an electrically-isotropic conductive network. Epoxy is then infused into the CNT-modified fabric to form a free-standing nanocomposite strain sensor. By measuring the changes in the electrical properties of the sensing composite the deformation can be measured in real-time. The sensors are repeatable and linear up to 0.4% strain. Highest elastic strain gage factors of 1.9 and 4.0 have been achieved in the longitudinal and transverse direction, respectively. Although the longitudinal gage factor of the newly formed nanocomposite sensor is close to some metallic foil strain gages, the proposed sensing methodology offers spatial coverage, manufacturing customizability, distributed sensing capability as well as transverse sensitivity

Integration of Carbon Nanotube Sensing Skins and Carbon Fiber Composites for Monitoring and Structural Repair of Fatigue Cracked Metal Structures

Advanced composite materials have been investigated for repair of fatigue-damaged metal structures, but one of the challenges is the repair often covers-up underlying damage, preventing visual inspection. A novel approach where a carbon nanotube-based sensing layer integrated in a steel/composite adhesive bond has been investigated as an approach for repair while adding capability to detect the adhesive bond integrity and monitor propagation of cracks in the underlying substrate. The sensing layer, composed of a random mat of aramid fibers coated with carbon nanotubes, offers tremendous application flexibility for integration of sensing capabilities in structures. Experiments examining fatigue crack propagation in structural steel with a composite repair and integrated bondline sensing increased the fatigue life by 380% to over 500%, depending on configuration. The sensing layer was able to monitor deformation and crack propagation in real-time and shows potential for use in periodic inspection-based monitoring of cracks using electrical property changes

Experimental and Numerical Investigation on the Bond Strength of Self-sensing Composite Joints

Laboratory experiments demonstrate that a novel carbon nanotube (CNT)-based sensing layer embedded in the bondline of an adhesively bonded structural joint can detect and monitor deformation and damage progression of the adhesive layer. In this study, experimental and numerical investigations were performed to identify any effect of an embedded CNT-based sensing layer on the bond strength of that joint. To evaluate the mechanical behavior of such a bondline configuration, two sets of single-lap specimens, with and without sensing layer, were prepared and tested to determine the bond strengths of the respective types. Two-dimensional digital image correlation (2D DIC) was utilized to estimate the load-displacement response of the test specimens. Three-dimensional cohesive surface finite element models of the test specimens, with and without the sensing layer, were created and validated using the experimental measurements. It is shown that the embedded CNT-based sensing layer does not influence the bond strength of the single-lap joint

Experimental and Numerical Investigation on the Bond Strength of Self-sensing Composite Joints

Laboratory experiments demonstrate that a novel carbon nanotube (CNT)-based sensing layer embedded in the bondline of an adhesively bonded structural joint can detect and monitor deformation and damage progression of the adhesive layer. In this study, experimental and numerical investigations were performed to identify any effect of an embedded CNT-based sensing layer on the bond strength of that joint. To evaluate the mechanical behavior of such a bondline configuration, two sets of single-lap specimens, with and without sensing layer, were prepared and tested to determine the bond strengths of the respective types. Two-dimensional digital image correlation (2D DIC) was utilized to estimate the load-displacement response of the test specimens. Three-dimensional cohesive surface finite element models of the test specimens, with and without the sensing layer, were created and validated using the experimental measurements. It is shown that the embedded CNT-based sensing layer does not influence the bond strength of the single-lap joint