Zhiling Li

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

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.

Actuator Failure Detection Through Interaction Matrix Formulation

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.

Continuum field model of defect formation in carbon nanotubes

While considerable efforts in the form of (numerical) atomistic simulations have been expended to understand the mechanics of defect formation under applied strain, analogous analytical efforts have been rather few. In this work, based on the physics at the nanoscale, defect nucleation in single-walled carbon nanotubes is studied using both classical continuum field theory as well as gauge field theory of defects. Despite the inherent continuum assumption in our models, reasonably close qualitative and quantitative agreement with existing atomistic simulations is obtained. The latter lends credence to the belief that continuum formulations, with correct incorporation of the relevant physics, can be a powerful and yet simple tool for exploring nanoscale phenomena in carbon nanotubes. The results are more sensitive to chirality than to the size of the nanotubes.

Flexural strain sensing using carbon nanotube film

Strain sensing characteristic of carbon nanotubes has been established in the past at nanoscale. In this study, it is shown that the carbon nanotube film sensors, made up of randomly oriented carbon nanotubes, can be used as strain sensors at macro level. A nearly linear trend between the change in voltage, measured using a movable four point probe, and strains, measured using conventional electrical strain gage, indicates the potential of such carbon nanotube films for measuring flexural strains at macro level. Isotropic strain sensing capability of the carbon nanotube film sensors, due to randomly oriented carbon nanotubes, allows multidirectional and multi‐location measurements.

Online Actuator Failure Detection using Direct Approach

A novel actuator failure detection algorithm is developed in this paper. An actuator failure is considered to occur when it produces an input to the structure that is dierent from the commanded input. In this paper, an error function, one for each actuator, is developed to monitor the working status of the examined actuator in real-time, regardless the status of other actuators. Non-zero signal profile in the error function indicates the time instant of failure of the examined actuator (for measurement noise free case). The coecients of the error function are calculated directly from the healthy input data (from the examined actuator) and all outputs without having to identify the state-space model of the system. Thus the need to know the state-space model of the plant is bypassed in the presented direct approach. Experimental results from a NASA eight bay truss show that the direct method can successfully isolate and identify the failure of the examined actuator in real-time.