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

Raman mapping microspectroscopy was then used to investigate the interfacial stress distributions of the films during different cryogenic-room temperature cycles (-198-25 °C, 0-300 cycles). It was found that the micro stress of CNT-PI films (around 175 MPa) had no significant changes even after 300 cycles. The cryogenic cycling had very little effect on the internal stress, indicating that PI had a good low temperature resistance. For the CF/CNT-PI films, the micro stress distributions of CFs, interface, and matrix regions were successfully obtained. It was found that the CFs bear a greater stress than the matrix, showing that CFs had always been the major stress bearer, confirming the strengthening effect of CFs. When the CF/CNT-PI films were cycled fewer than 250 times, the effect of cryogenic cycling on the micro stress was insignificant. But once the number of cycles reached 300, the compressive stresses on the fiber and interface increased by 21% and 12.9%, respectively, implying a deterioration of the mechanical properties. By Raman mapping, the micro-mechanical distributions of the reinforced material, matrix and interface of the composites under cyclic temperature changes were effectively quantified. This is therefore an effective method for evaluating the safety of composite materials.