Sensing skin could reveal cracks in bridges

A new sensing skin for bridges, buildings and aeroplanes developed by engineers at the University of Michigan could prevent disasters similar to the recent bridge collapse in Minneapolis.

Bridges undergo regular testing for cracks, corrosion and other damage, but even rigorous visual inspection might not catch all potential problems. The ideal would be for materials with built-in sensors that alert testers to structural changes well before they become a problem.

Sensing skin could reveal cracks in bridges

Tsung-Chin Hou, Kenneth Loh and research leader Jerome Lynch have taken a step toward this ideal by developing a sensing skin made from thin polymer films embedded with carbon nanotubes. Each layer can be configured to measure a single parameter such as acidity or pressure, and by measuring changes in electrical resistance when a current is passed through the skin, one can generate a two-dimensional structural map of the underlying material.

The films are assembled using a layer-by-layer (LBL) process and mounted with electrodes along the boundaries. Coatings could in theory be sprayed or painted onto surfaces, but with LBL the electrodes can be included in the skin design.

‘The sensors are fairly durable mechanically, but they still need to be tested in the field where they will be exposed to harsh weather conditions,’ says Lynch. ‘We are in the process of planning for the first field deployment in Korea on multiple bridges, and it is anticipated that the sensors will be installed by the end of 2008.’

While reluctant to predict the future, Lynch has great hopes for the technology: ‘With major funded research programs in multifunctional materials, I am certain we will see more of these types of self-sensing materials in the future, and perhaps in industrial applications within three to five years.’

‘These sensors work on critical bridge components just like skin on our bodies’ says civil engineering expert Victor Li. ‘They tell you where it hurts, all by themselves. The potential to better manage infrastructure, in relation to improved maintenance and enhanced safety, is enormous.’

Further reading: Spatial conductivity mapping of carbon nanotube composite thin films by electrical impedance tomography for sensing applications, Hou et al., Nanotechnology 18, 315501 (2007).

Figure: Multifunction carbon nanotube composite sensing skin for structures (© University of Michigan).

Article first published in Nanomaterials News.