EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The reinforcement of ceramic matrix composites (CMCs) with carbon nanotubes (CNTs) has been widely researched. Nevertheless, the interaction between CNTs and the ceramic has not been sufficiently explored. Thus, fundamental questions such as the influence of the CNT diameter, the relevance of the number of walls of the CNT or the presence of functional groups on the CNT are still under debate. The effect of boron nitride nanotubes (BNNTs) is also lacking research. Therefore, material scientists use to synthesize reinforced CMCs over mainly a phenomenological support.
This work is aimed to clarify some aspects of the interaction between nanotubes with alumina, using Molecular Mechanics, a computational technique that is able to build systems in which mechanical tests can be simulated. The software package Material Studio and Forcite module were employed, with force-fields COMPASS-II for CNTs and Brenner for BNNTs. Pull-out tests were performed considering different configurations: intergranular and intragranular locations, and different relative crystalline orientations. Mechanical parameters such as the nanotube-matrix interaction energy, pull-out force, surface energy or shear stress have been analyzed.
Strong differences between intergranular and intragranular configurations have been revealed. First results have confirmed that intragranular nanotube sliding requires a pull-our force several times higher than the intergranular configuration. The dependence of the mechanical response of the system with the relative crystalline orientation between the nanotube and the grain has been also revealed. Moreover, the deformation of the CNT due to the inclusion within the ceramic matrix has been observed and the morphology of this deformation also depends on the crystalline orientation. However, after pulling-out, the CNTs exhibited almost full recovery while significant permanent deformation was observed in BNNTs. The results of this research are expected to transcend beyond theoretical fields and become significant inputs for the ceramic composite experimental science.