Influence of Porosity on Fracture Toughness of Hydroxyapatite/Multi-Walled Carbon Nanotubes Biocomposite Materials

The paper analyzes the influence of porosity of hydroxyapatite (HA)/multi-wall carbon nanotubes (MWCNTs) composites on their fracture toughness. It is found that two competing factors affect the resulting fracture toughness. On the one hand, MWCNTs, which are stronger than the surrounding HA matrix, promote the increase in the fracture toughness owing to the possible crack path deflection from the planar geometry, that leads to a decrease in the crack driving force. On the other hand, the higher MWCNT concentration leads to the reduction in the composite porosity. The computer simulation of the crack formation in HA composite with different porosity shows that the lower porosity provided by the sintering activation due to the MWCNT addition, leads to a reduction in the fracture toughness of ceramics. It is shown that the MWCNT addition in the amount of less than 0.5 wt.% does not lead to a significant growth in the fracture toughness due to these two competing factors.