Simulation and Mechanical Characterization of Crosslinked Nanostructured Silica Aerogels

Abstract

Crosslinked silica aerogel (x-aerogel) is low density nanostructured porous material with good mechanical properties. The mechanical characterization tests of x-aerogel were performed to establish the feasibility of using this material in different engineering applications as a multi-functional material. Mechanical response of x-aerogel was studied under compression, three-point bending, tension and DMA (dynamic mechanical analysis) tests. A primary glass transition temperature of 130 °C was identified for xaerogel material through DMA. Under uniaxial compression, x-aerogel was found linearly elastic under small strains (<4%), then exhibited yield behavior (until 40% strain), followed by densification and inelastic hardening. At room temperature, the compressive Young’s modulus and Poisson’s ratio were determined to be 129±8 MPa and 0.18, respectively, while the average specific compressive strength was 3.89×10 Nm/kg, which is higher than other conventional materials. Flexural response of x-aerogel material was also studied at room and cryogenic temperature. The specific flexural strength at room temperature was found to be 2.16×10 Nm/kg. The average CTE of x-aerogel was found to be 4.8×10/ C. Numerical simulations were performed to develop a better understanding of structure-property response of highly porous x-aerogel material. The numerical models have attempted to incorporate micro-scale effects, such as particle stiffness, bond strength, particles frictional coefficient, and initial cluster porosity, into macro-scale structure-property relationship for the prediction of Young’s modulus and strength. Compression, tension and bending simulations were performed, and compared with corresponding experiments. Modeling methodology will provide insights for both stiffening and strengthening mechanisms and how these mechanisms can be optimized with minimum weight penalty. Therefore, it is envisioned that numerical modeling will greatly reduce the number of “trial-and-error” experiments necessary to further enhance the properties of this novel material.