Use of carbon nano-fiber foams as strain gauges to detect crack propagation

Abstract

This thesis focuses on testing the feasibility of using carbon nanofiber foams as strain gauge material to detect crack propagation in aluminum structures. We produced the tridimensional carbon nanofiber foams using a process that exposed palladium catalyst particles to a fuel rich oxygen/ethylene mixture at moderate temperatures in a tubular furnace. The microstructure of the foam generated was characterized using a scanning electron microscope to determine diameter and distribution of the fibers within the foam. Sections of the foam, electrically isolated, were attached to aluminum tensile specimens. Simultaneous mechanical and electrical measurements were conducted on the aluminum-foam fixtures. The mechanism responsible for the conductivity values seems to be related to the number of contacts established between all fibers as the foam was compressed or stretched during tensile tests, as opposed to the electrical properties of the individual fibers. The design of the foam sensor and the way it is attached to the aluminum plates presented challenges that will need to be further addressed. The data showed a correlation between strain levels in the aluminum probes and the resistivity detected in the foam, confirming that the later can be employed as a sensor to monitor the structural integrity of the former.