Comparison of the mechanical deterioration behavior of C/BMI composite under hygro-thermal or vacuum-thermal cycling

The effects of vacuum-thermal cycling and hygro-thermal cycling on the fiber/matrix interface characteristics of a carbon fiber reinforced bismaleimide (C/BMI) composite were investigated to assess the degradation behavior of the mechanical property of C/BMI composite in low earth orbit (LEO) and atmosphere environment. The feasibility of using one comprehensive accelerated test procedure capable of representing the LEO and atmosphere environmental effects simultaneously for the aerospace plane was explored for the first time. A simplified mathematical approach and the corresponding model was supplied firstly to prove the reliability and effectiveness of the widely-used SEM observation method in the assessment of fiber matrix interface properties. The dominating degradation mechanism of the C/BMI composites caused by vacuum-thermal cycling in LEO environment is the interfacial sliding induced by thermal stress, whereas the thermal oxidation and decomposition of the matrix is the main degradation mechanism after hygro-thermal cycling in atmosphere environment. Candidate composite materials for aerospace plane must be tested in atmosphere and LEO environments separately in the environmental simulation experiments before their application.