Raman mapping microspectroscopy to reveal the effects of cryogenic-room temperature cycling on the interfacial micromechanics of carbon fiber reinforced polyimide composites

Raman spectroscopy has unique advantages in studying the micro-mechanical behavior of interface. First, we used carbon nanotubes (CNTs) as a stress sensor to prepare carbon fiber reinforced polyimide composite films (CF/CNT-PI). Then we applied Raman mapping microspectroscopy to investigate the interfacial stress distribution of the films under different cryogenic-room temperature cycle times (-198~25℃，0~300 cycles). It was found that the micro stress of CNT-PI films (being around 175MPa) had no significant changes even after 300 cycle time. The cryogenic-room cycling had very little effects on the internal stress, indicating that PI had good low temperature resistance. In the case of CF/CNT-PI, the micro stress distributions of CF, interface, and matrix regions were successfully obtained. It was found that CF bears greater stress than the matrix, showing that CF had always been the major bearing body of stress, thus confirming the reinforcement effect of CF. When the CF/CNT-PI films were cycled less than 250 times, the effect of cryogenic-room cycling on the micro stress was not apparent. But once up to 300 cycle times, the compressive stress in the CF and interface area increased by 21% and 12.9%, respectively, implying the decrease of the mechanical properties. By means of Raman mapping, the micro-mechanical distributions of the reinforced material, matrix and interface of the composites under cryogenic-room temperature cycling were effectively quantified, which provided an effective evaluation method and theoretical basis for the detection of the safety of composite materials.