Papers by Author: Jong Won Lee

Abstract: This study introduces a nano smart material to develop a novel sensor for Structural Health Monitoring (SHM) of mechanical and civil systems. Mechanical, civil, and environmental systems need to become self-sensing and intelligent to preserve their integrity, optimize their performance, and provide continuous safety for the users and operators. Present smart materials and structures have fundamental limitations in their sensitivity, size, cost, ruggedness, and weight. Smart materials developed using nanotechnology have the potential to improve the way we generate and measure motion in devices from the nano to the macro scale in size. Among several possible smart nanoscale materials, Carbon Nanotubes (CNT) have aroused great interest in the research community because of their remarkable mechanical, electrochemical, piezoresistive, and other physical properties. To address the need for new intelligent sensing based on CNT, this study presents piezoresistivity and electrochemical properties and preliminary experiments that can be applied for SHM. This study is anticipated to develop a new multifunctional sensor which can simultaneously monitor strain, stress and corrosion on a structure with a simple electric circuit.

Abstract: To address the need for new smart materials, this paper explores the use of carbon nanotubes to develop a nanocomposite smart material having electrochemical impedance properties for sensing and actuation. Fabrication and characterization of the carbon nanocomposite material are discussed in the paper. The issues related to hurdles in the practical manufacturing of commodity level macro size nanocomposite smart materials with prescribed electrical and electrochemical properties are also discussed.

Abstract: This paper introduces a new sensor design based on a carbon nanotube structural neuron for structural health monitoring applications. The carbon nanotube neuron is a thin and narrow polymer film sensor that is bonded or deposited onto a structure. The electrochemical impedance (resistance and capacitance) of the neuron changes due to deterioration of the structure where the neuron is located. A network of the long carbon nanotube neurons can form a structural neural system to provide large area coverage and an assurance of the operational health of a structure without the need for actuators and complex wave propagation analyses that are used with other SHM methods. The neural system can also reduce the cost of health monitoring by using biomimetic signal processing to minimize the number of channels of data acquisition needed to detect damage. The carbon nanotube neuron is lightweight and easily applied to the structural surface, and there is no stress concentration, no piezoelectrics, no amplifier, and no storage of high frequency waveforms. The carbon nanotube neuron is expected to find applications in detecting damage and corrosion in large complex structures including composite and metallic aircraft and rotorcraft, bridges, and almost any type of structure with almost no penalty to the structure.

Abstract: This paper presents an experimental finding in the Split Hopkinson Pressure Bar (SHPB) technique to obtain a better compressive stress strain data for rubber materials. An experimental technique which modifies the conventional SHPB has been developed for measuring the compressive stress strain responses of materials with low mechanical impedance and low compressive strengths such as rubber. This paper uses an all-polymeric pressure bar to achieves a closer impedance match between the pressure bar and the specimen materials. In addition, a pulse shaper is utilized to lengthen the rising time of the incident pulse to ensure stress equilibrium and homogeneous deformation of rubber materials. It is found that the modified technique can determine the dynamic deformation behavior of a rubber more accurately.

Abstract: This paper presents a modified Split Hopkinson Pressure Bar (SHPB) technique to obtain compressive stress-strain data for rubber materials. An experimental technique that modifies the conventional SHPB has been developed for measuring the dynamic compressive stress-strain responses of rubber materials with low mechanical impedance and low compressive strengths. This paper introduces an all-polymeric pressure bar set-up which achieves a closer impedance match between the pressure bar and the specimen materials. In addition, a pulse shaper is utilized to lengthen the rising time of the incident wave which helps the stress equilibrium and homogeneous deformation of rubber materials. It is found that the modified technique can determine the dynamic deformation behavior of NR and NBR rubber more accurately than those from the conventional SHPB technique.