Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203, USA.
School of Materials Science and Engineering, Fujian University of Technology, Fuzhou 350108, China.
Department of Chemistry, University of North Texas, Denton, TX 76203, USA.
Abstract:
Crack deflection and penetration at the interface of multi-wall carbon nanotube/amorphous carbon composites were studied via molecular dynamics simulations. In-situ strength of double-wall nanotubes bridging a matrix crack was calculated under various interfacial conditions. The structure of the nanotube reinforcement -ideal multi-wall vs. multi-wall with interwall sp3 bonding - influences the interfacial sliding and crack penetration. When the nanotube/matrix interface is strong, matrix crack penetrates the outermost layer of nanotubes but it deflects within the nanotubes with certain sp3 interwall bond density, resulting in inner wall pullout. With increasing the sp3 interwall bond density, the fracture mode becomes brittle; the fracture energy decrease while the bridging strength increases and then decreases. Our results suggest that the outermost nanotube wall can serve as a sacrificial layer such that the interface may be designed by effectively putting it inside the nanotubes. Controlling the density of sp3 interwall bond within the multiwall carbon nanotube makes the transition from brittle to tough failure modes in the composites even when the matrix/nanotube interface is strong.
