Carbon Nanotube Strain Sensors for Structure Health Monitoring in Bridges

Carbon nanotubes (CNTs) are rolled up sheets of graphite that form into a tube with only one layer of carbon atoms (single walled carbon nanotubes) or a tube with many layers of carbon atoms (multi wall carbon nanotubes) with diameters in the nanometer range and only a few microns in length.

The carbon-carbon bond in addition to the unique rolled up structure give carbon nanotubes a rare combination of excellent mechanical, electrical and thermal transport properties.

Due to their excellent mix of properties, small size and high aspect ratios (length to diameter ratio) carbon nanotubes can be incorporated into different materials to form composites with a wide range of functional capabilities.

Polymer-Carbon Nanotube Composite

When incorporated into polymers, for instance, the high conductivity of carbon nanotubes transforms the polymer composites into electrical conductors at very low nanotube contents.

If the polymer-carbon nanotube composite is subjected to mechanical load, a change in the electrical resistance results. This change could arise from the loss of contact between neighboring CNTs or increase in the inter-tube distances which results in a rise of tunneling resistance.

High sensitivity of carbon nanotube composites to mechanical strain means that they can be used as sensors for detection of strain, force and pressure in engineering structures, such as bridge.

Carbon Nanotube as Strain Sensors for Structural Health Monitoring

These carbon nanotubes strain sensors open a new way of developing cheaper multifunctional sensing units for structural health monitoring.

Tiny multiple-point sensors could be used to monitor and feed the state of structural health to a central collection point, making it easier to manage and maintain large structures.

The expected benefits to society include enhanced safety, reduced maintenance cost and improved asset lives.

Our current work involves investigating the effects of operating environment on the mechanical and electrical performance of bulk and thin film carbon nanotube composites as strain sensors.

A fundamental understanding of the effects of environmental temperature, moisture and loading modes on electrical behavior of these sensors is critical for any practical application.

Designs that allow reliable performance, multi-directional sensing and flexible installation are of particular interest for wide acceptance of carbon nanotube strain sensors over conventional ones.