Silica aerogels are highly porous 3D nanostructures and have exhibited excellent physio-chemical properties. Although silica aerogels have broad potential in many fields, the poor mechanical properties greatly limit further applications. In this study, we have applied the finite volume method (FVM) method to calculate the mechanical properties of silica aerogels with different geometric properties such as particle size, pore size, ligament diameter, etc. The FVM simulation results show that a power law correlation existing between relative density and mechanical properties (elastic modulus and yield stress) of silica aerogels, which are consistent with experimental and literature studies. In addition, depending on the relative densities, different strategies are proposed in order to synthesize silica aerogels with better mechanical performance by adjusting the distribution of pore size and ligament diameter of aerogels. Finally, the results suggest that it is possible to synthesize silica aerogels with ultra-low density as well as high strength and stiffness as long as the textural features are well controlled. It is believed that the FVM simulation methodology could be a valuable tool to study mechanical performance of silica aerogel based materials in the future.

A reasonable constitutive model is the prerequisite to accurately estimate the mechanical behaviours of the composite propellant and the structural analysis of solid rocket motor grain. Through coaxial tensile tests, the viscoelastic properties of the solid propellant, especially dewetting, under actual loading is studied. The concept of dewetting point is proposed to describe the behaviour of dewetting. Based on the experimental results, a nonlinear viscoelastic constitutive model considering strain rate was applied to composite propellant and modified by the dewetting factor to extend the original one to a wide strain variation. Based on the updated Lagrangian approach, the incremented form of the constitutive model is deduced using the updated Kirchhoff stress tensors and strain tensors. By the numerical method and user defined material subroutine, the model is implemented to the 3D structural analysis of the grain during the ignition pressurization procedure. The model is validated by one set of experiments and further grain structural integrity analysis is carried out to study the influence of the pressurization rate and dewetting elongation.

No abstract

No abstract