Carbon-nanotube Reinforced Composite Materials and Structural Health Monitoring

By reinforcing composite parts with carbon nanotubes (CNTs), researchers from Rey Juan Carlos University in Madrid structural health monitoring can be achieved.

Carbon nanotubes provide electrical conductivity in the reinforced materials that they are applied to. In that way, a specified point with structural damage can be located by identifying the weakest electrical connection.

Initially, the researchers 3D printed, via DLP 3D printing technology, a set of six composite samples with CNT composition varying from 0.03% to 0.15% by weight. Then they tried to evaluate the impact of the carbon nanotubes on the electrical conductivity, something that could allow the creation of self-sensing composite parts. Nanotubes create a UV shielding effect, which leads to inadequate curing, therefore the specimens with higher composition of carbon nanotubes needed to be UV exposed for longer time. The researchers explained: “Their addition in low contents into an insulator resin allows the formation of electrical percolating networks inside the material, leading to an increase in electrical conductivity of the material of several orders of magnitude.”

Subsequently, tensile and three-point bending tests were conducted on each printed sample. During all tests, currents running though the composite parts were recorded. Copper wires with silver conductive paste, for the abatement of inter-material resistance at the connections, were used for the electrical connections.

Experimental formation of test specimens (Credits: RJCU)

Based on the experiments, it was concluded that electrical resistance is strongly correlated to applied strain and that the sensitivity increased as CNT content decreased. The last remark is explained because of the higher interparticle distance, which allows easier electrical charge transport.

 Micrographs showing CNTs (0.1 wt % CNT specimen) distribution at (a) low magnifications and (b) high magnifications. (Credits: RJCU)

The results of this study make the research team believe that DLP-fabricated CNT reinforced composites could monitor precisely their structural damage. The study was recently published in Polymers.