Nano-fillers (nanotubes, nanosheets): do they toughen brittle matrices?

摘要

The aim of the contribution is to provide a view inside the current state of the art on the real effect of nanoscale fillers incorporated into glass and/or ceramic matrix on fracture resistance of the composite. The investigated materials included model composites based on silica and borosilicate glass matrices, and, in addition, also exploiting common ceramic matrices like alumina or zirconia. The nano-fillers, i.e. carbon and boron nitride nanotubes, graphen and boron nitride nanosheets have been explored in different volume fractions in order to analyse experimentally their quantitative effect on toughening mechanisms. The fracture toughness, K_(IC), was evaluated applying mainly chevron notch technique. Fracture surfaces were also analysed to get exact imagination about fracture micromechanisms acting during crack propagation. Almost positive effect of the nano-fillers has been confirmed for carbon nanotube, graphen, boron-nitride nanotubes and nanosheets. It has been effective thanks to elastic deformation energy dissipation thanks to several toughening mechanisms like crack deflection and bridging, pull-out being conditioned by good bonding of the filler to ceramic/glass matrix. Two toughening mechanisms specific for the applied nano-reinforcements have been recognised: telescopic pull-out (sword-in-sheath) and nanosheet shear delamination (interlayer sliding).