A microcracking-based model for the dynamic failure of carbon/carbon composites

The ‘pseudoplastic’ deformation and failure of the carbon/carbon composites (C/Cs) are strain-rate-sensitive while the mechanism has not yet been properly elaborated. To delve into the design and fabrication strategy of the C/Cs towards anti-impact applications, the influences of preform architectures and carbon nanotubes (CNT) doping on the dynamic mechanical behaviors of the C/Cs were studied, showing that the CNT-doped plain weave preform exhibits better anti-impact performances than the other structures. The experimental results indicate that the fragmentation of the C/Cs at high strain rate is due to the activation of all the possible cracking paths with excessive kinetic energy being deposited, which is significantly different with the growth of a main crack under the quasi-static loading. A two-scale modeling is established to backtrack from the macroscale mechanical response to the microscale cracking behavior, where the quasi-static and dynamic failure of the composite were elaborated within a unified framework of linear elastic fracture mechanism. The coupling of the experiments and modeling revealed that the CNT-doped layer would constrain the microcracking behavior at elevated strain rates. Further nanomechanical tests and molecular dynamics simulations verify that the buffering function and the enhanced energy absorption of the CNT-doped interphase are responsible for the improved anti-impact performances of the C/Cs.