Ultrathin, uniform single-walled carbon nanotube networks of varying densities have been fabricated at room temperature by a vacuum filtration method. Measurements of the sheet conductance as a function of nanotube network density show 2D percolation behavior. In addition, the network transparency in the visible spectral range was examined and the results are in agreement with a standard thin-film model: fits to the standard theory indicate U ac ) Udc for transmission measurements at 550 nm. Transmission measurements also indicate the usefulness of nanotube network films as a transparent, conductive coating. Avenues for improvement of the network conductance are discussed.

/pdf/percolation-in-transparent-and-conducting-carbon-nanotube-2ips8cug7q.pdf

Percolation in transparent and conducting carbon nanotube networks

A carbon nanotube polymer material was used to form a piezoresistive strain sensor for structural health monitoring applications. The polymer improves the interfacial bonding between the nanotubes. Previous single walled carbon nanotube buckypaper sensors produced distorted strain measurements because the van der Waals attraction force allowed axial slipping of the smooth surfaces of the nanotubes. The polymer sensor uses larger multi-walled carbon nanotubes which improve the strain transfer, repeatability and linearity of the sensor. An electrical model of the nanotube strain sensor was derived based on electrochemical impedance spectroscopy and strain testing. The model is useful for designing nanotube sensor systems. A biomimetic artificial neuron was developed by extending the length of the sensor. The neuron is a long continuous strain sensor that has a low cost, is simple to install and is lightweight. The neuron has a low bandwidth and adequate strain sensitivity. The neuron sensor is particularly useful for detecting large strains and cracking, and can reduce the number of channels of data acquisition needed for the health monitoring of large structures.

https://iopscience.iop.org/article/10.1088/0964-1726/15/3/009/pdf

A carbon nanotube strain sensor for structural health monitoring

Sensors and actuators based on carbon nanotubes and their composites: A review

https://eprints.qut.edu.au/18477/1/c18477.pdf

Tunneling effect in a polymer/carbon nanotube nanocomposite strain sensor

Graphene in its pristine form is one of the strongest materials tested, but defects influence its strength. Using atomistic calculations, we find that, counter to standard reasoning, graphene sheets with large-angle tilt boundaries that have a high density of defects are as strong as the pristine material and, unexpectedly, are much stronger than those with low-angle boundaries having fewer defects. We show that this trend is not explained by continuum fracture models but can be understood by considering the critical bonds in the strained seven-membered carbon rings that lead to failure; the large-angle boundaries are stronger because they are able to better accommodate these strained rings. Our results provide guidelines for designing growth methods to obtain sheets with strengths close to that of pristine graphene.

Anomalous Strength Characteristics of Tilt Grain Boundaries in Graphene

Carbon nanotubes change their electronic properties when subjected to strains. In this study, the strain sensing characteristic of carbon nanotubes is used to develop a carbon nanotube film sensor that can be used for strain sensing on the macro scale. The carbon nanotube film is isotropic due to randomly oriented bundles of single-wall carbon nanotubes (SWCNTs). Using experimental results it is shown that there is a nearly linear change in voltage across the film when it is subjected to tensile and compressive stresses. The change in voltage is measured by a movable four-point probe in contact with the film. Multidirectional and multiple location strains can be measured by the isotropic carbon nanotube film.

https://iopscience.iop.org/article/10.1088/0957-4484/15/3/026/pdf

Nanotube film based on single-wall carbon nanotubes for strain sensing

Carbon Nanotube Film Sensors

The present invention is directed toward devices comprising carbon nanotubes that are capable of detecting displacement, impact, stress, and/or strain in materials, methods of making such devices, methods for sensing/detecting/monitoring displacement, impact, stress, and/or strain via carbon nanotubes, and various applications for such methods and devices. The devices and methods of the present invention all rely on mechanically-induced electronic perturbations within the carbon nanotubes to detect and quantify such stress/strain. Such detection and quantification can rely on techniques which include, but are not limited to, electrical conductivity/conductance and/or resistivity/resistance detection/measurements, thermal conductivity detection/measurements, electroluminescence detection/measurements, photoluminescence detection/measurements, and combinations thereof. All such techniques rely on an understanding of how such properties change in response to mechanical stress and/or strain.

/pdf/smart-materials-strain-sensing-and-stress-determination-by-2z9j0zuev9.pdf

Smart materials: strain sensing and stress determination by means of nanotube sensing systems, composites, and devices

An ovel technique is introduced to detect and isolate the failures of multiple actuators connected to a system. The failure of actuator considered in this study could be any type of erroneous input that is different from the commanded one. The interaction matrix technique allows the development of input-output equations that are only influenced by one target input. These input-output equations serve as an effective tool to monitor the integrity of each actuator regardless of the status of the other actuators. Although the procedure requires the knowledge of analytical model of the system being tested, the analytical redundancy can be experimentally predetermined through standard input-output-based system identification algorithms such as observer/Kalman-filter identification (OKID) and eigensystem realization algorithm (ERA). This method is capable of real-time actuator failure detection and isolation under any type of input excitation. Both numerical simulations of a spring-mass-damper system and a laboratory experiment using eight-bay NASA truss structure verify the feasibility of the proposed method.

/pdf/actuator-failure-detection-through-interaction-matrix-g13dxxhhh6.pdf

Actuator Failure Detection Through Interaction Matrix Formulation

A newly developed structural damage monitoring technique is presented. The study focuses on capturing the initiation of multiple damages as they occur in a structure, which is similar to the concept of the fault detection filter. Previously, it has been shown that modified interaction matrix formulation provides a series of input error functions that generate a nonzero residual signal when the system experiences erroneous inputs. Error functions for each individual structural member are developed from the analogy between actuator failure and damageinduced residual force. When each individual error function is monitored, multiple damages as they occur in a structure can be simultaneously detected and isolated. Because the technique does not require frequency-domain measurements, it is readily applicable to online monitoring systems. This real-time technique also accommodates nonlinear breathing cracks and works for any type of excitation. A numerical simulation using a spring‐mass system and truss structure successfully demonstrates the proposed method.

/pdf/real-time-structural-damage-monitoring-by-input-error-58g3nbit1b.pdf

Prasad Dharap

Papers

Nanotube film based on single-wall carbon nanotubes for strain sensing

Carbon Nanotube Film Sensors

Smart materials: strain sensing and stress determination by means of nanotube sensing systems, composites, and devices

Actuator Failure Detection Through Interaction Matrix Formulation

Real-Time Structural Damage Monitoring by Input Error Function