Diffusion and evolution of the atomic structure during the compression process.

No abstract

Silicon carbide has excellent properties such as high hardness and decomposition temperature, but its applications are limited by its poor toughness. Here, we investigate the enhancement of SiC’s toughness by compositing silicon carbide–aluminum (SiC–Al) interpenetrating phase composites (IPCs) via molecular dynamics simulations. IPCs are a class of composites consisting of two or more phases that are topologically continuous and three-dimensionally interconnected through the microstructure. The Young’s modulus and ultimate strength gradually increases with an increment of the volume fraction of SiC, opposite to the fracture strain. The interface between SiC and Al affects the mechanical properties of SiC–Al IPCs. When the volume fraction of SiC is less than 0.784, the attenuation rate of ultimate strength and fracture strain decreases. The attenuation rate increases when the volume fraction of SiC is more than 0.784. There are a minimum of ultimate strength and fracture strain at the 0.784, 0.7382 and 2.8610, respectively. The hardness of SiC–Al IPCs is about 48% of SiC. The change of SiC–Al IPCs hardness is more stable than that of SiC in the later stage of the nanoindentation test.

To accurately predict the aerodynamic forces and heating of hypersonic vehicles, an elaborate gas–surface interaction (GSI) model is essential to describe the rarefied gas effect at the interface. By far, the Cercignani–Lampis (CL) model is the most sophisticated GSI model, but it has not been systematically examined under hypersonic conditions where the gas flow possesses large velocity and temperature differences relative to the boundary surface. In this work, the accuracy of the CL model is first assessed by comparing with molecular dynamics simulation results under a variety of conditions of temperature and velocity differences, surface temperature, and surface roughness. It is found that the tangential scattering kernel of CL model is perfect only when the surface is smooth and the gas kinetic energy is close to the surface kinetic energy. To accurately capture the momentum and temperature of the reflected gas molecules, a modified CL model with independent momentum and thermal accommodation coefficients is developed. A hybrid diffusive and modified CL model is further proposed to account for the adsorption phenomenon. With these modifications, the new GSI model can accurately describe the scattering of gas molecules in a wider range of hypersonic rarefied gas flows.