Direction‐sensitive stress measurements with carbon nanotube sensors

Single‐wall nanotubes (SWNTs) embedded in polymer can be used as mechanical sensors because the position of the D* Raman band of SWNTs is strongly dependent on the strain transferred from the matrix to the nanotubes. In order to detect the stress (or strain) information in specific directions, polarized Raman spectroscopy is used to select out the signal from the nanotubes that are parallel to the polarization direction. This method is demonstrated by measuring the stress distribution around a circular hole in the SWNT/polymer composites under uniaxial tension. Then the stress field in a polymer matrix in the vicinity of a single glass fiber is mapped on the micrometer scale. A stress concentration zone is observed around the fiber end. The importance of this technique and the measurements for composite design and micro‐mechanical models is discussed briefly.