Mechanical and impact properties of carbon-nanotube-reinforced amorphous silicon carbide composites via atomistic simulation studies

The rapidly growing interest in ceramic and ceramic-matrix composite (CMC) materials stems from their proposed use in various structural, thermal-protection, abrasive, integral armor, and high temperature electronic materials operating under extreme conditions. Using large-scale molecular dynamics (MD) simulations we have studied the mechanical properties, hypersonic velocity impact induced damage, shock propagation, and shielding characteristics of pristine amorphous silicon carbide (a-SiC) and carbon nanotube reinforced a-SiC composites. A comparative study of mechanical properties of pristine a-SiC, and CNT-reinforced a-SiC-based composites have shown that presence of CNTs leads to a considerable increase in elastic constants, with the effect being CNT orientation dependent. The micro-structural changes taken place in the shock-loaded samples have been investigated and will be reported on in this talk. The velocity and shock-wave-front structure of the impact-induced shock waves were studied and compared in the cases of pristine a-SiC and composite samples with different orientations of CNTs. For the spherical diamond nanometer-size projectile impact, the penetration depth is investigated as a function of the impact velocity. It is found that the penetration depth does not depend appreciably on the nature of the CNT alignment on the target material. A theoretical framework was developed to describe the penetration depth in case of spherical diamond nanoparticle impact on pristine a-SiC target. The scaling relations and analytical forms are derived to describe the penetration depth as a function of projectile velocity and radius. For the diamond nano-particle impact on the composite with parallel alignment of CNTs, fast energy transfer and channeling of the materials damage, similar to the one observed for the shock wave propagation, is also observed. The details of the results obtained and strategies of materials design in nanophase composites for impact protection in aerospace thermal tiles and integrated ballistic armor will be described in this manuscript.