Abstract

Due to their unique properties, carbon fiber reinforced polymers (CFRP) are becoming ever more prevalent in today's society. Unfortunately, CFRP suffer from a wide range of failure modes and structural health monitoring methods are currently insufficient to predict these failures. It is apparent that self-sensing structural health monitoring could be advantageous to protect consumers from catastrophic failure in CFRP structures. Previous research has shown that embedded nickel nanostrand nanocomposites can be used to instantaneously measure strain in carbon fiber composites, but these methods have been severely limited and can induce high stress concentrations that compromise the structural integrity of the carbon fiber structure. In this research the strain sensor material and the connective circuitry to the sensor are analyzed to improve the practicality of in situ strain sensing of carbon fiber structures. It has been found that the use of nickel nanostrands embedded directly onto carbon fiber as a strain sensor material has no advantages over a carbon fiber strain sensor alone. Additionally, it has been shown that the circuitry to the strain sensor plays a critical role in obtaining a strong, consistent piezoresistive signal that can be related to strain. The use of nickel coated carbon fiber in the circuitry has been evaluated and shown to reduce the noise in a piezoresistive signal while allowing for remote strain sensing from greater distances away from the strain location. The piezoresistive strain sensing utilized in the tested sensor designs relies on electrons tunneling through an insulting barrier between two conductors. This phenomenon is known as quantum tunneling. Two factors - tunneling barrier height and gap distance - affect the probability of quantum tunneling occurring. Thus, to accurately model and predict the piezoresistivity of nanocomposites these two parameters must be known. Through the use of dielectric spectroscopy the gap distance can be determined. Using nanoindenting, the barrier height for various polymers was also determined. The measured values can be used, in future work, to improve the modeling of nickel nanostrand nanocomposite.

Degree

MS

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2012-06-08

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd5290

Keywords

carbon fiber, nanocomposite, nickel nanostrands, strain sensing, barrier height

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