Temperature-variable Raman scattering study on micromechanical properties of the carbon fiber reinforced polyimide composite film

Temperature-variable Raman spectroscopy equipped with a mapping function was used to investigate the micro-mechanical properties of a carbon fiber (CF)-reinforced polyimide (PI) composite film using carbon nanotubes (3 wt%) dispersed in PI as the stress sensor. The stress distributions in the CFs and the interface region during heating from 25 to 300 °C were mapped based on the stress sensitive Raman G` band (around 2679 cm−1) shifts of the CNTs. Results indicated that thermal motion of PI chains affects the mechanical properties when the CF/CNT-PI film was heated up to 300°C. Both CFs and the interface region were compressively stressed below 200°C, and the stress decreased with increasing temperature and was eliminated at around 200°C. A tensile stress developed above 200 °C which was distributed mainly on the CFs, and increased with temperature. Furthermore, stress transfer between the CFs and the matrix was less than 100% due to the thermal stress hysteresis in the PI matrix.