Direction-sensitive strain-mapping with carbon nanotube sensors

Single-wall carbon nanotubes (SWNTs) embedded in a polymer can be used as mechanical sensors because the position of the D* Raman band is strongly dependent on the strain transferred from the matrix to the nanotubes. The unpolarized Raman spectrum of the nanotubes has high strain sensitivity if the nanotubes are oriented along the principal strain axis in the polymer, whereas with polarized Raman, even unoriented nanotubes exhibit a strong wavenumber shift in the Raman spectrum with strain. These methods are demonstrated here by measuring the stress distribution around a circular hole in SWNT/polymer composites under uniaxial tension. In both cases the results fit the classical linear elasticity solution.