Synthesis, mechanical characterisation and modeling of super flexible silica aerogels and their joining techniques

Abstract

Silica aerogels are open-porous nanostructured materials with a wide range of practical applications. While they are often recognized for their exceptional insulating capabilities, they offer a wide range of promising characteristics such as low density, high porosity, and high specific surface area. The advancement of flexible aerogels and composites has been especially advantageous in addressing their inherent mechanical brittleness and fragility, which had previously limited their potential application in the aerospace industry. While there have been recent advances, there remain several challenges that need to be addressed for the practical application of super flexible silica aerogels. Mechanical characterization is of great importance in defining material behaviour and ensuring durability and reliability. While researchers have explored various approaches to improve the mechanical properties of silica aerogels, the methods used to characterize these properties vary depending on the specific field of application. Specific properties such as compressive and tensile strength are often derived; however, there is a lack of standardization in testing methods and reporting. This makes comparison between different studies challenging. Likewise, there is a scarcity of data and experiments about the practical application of aerogels in sandwich layers for aerospace applications, e.g., adhesively joined aerogel composites with lightweight materials and how to characterize them. To overcome these challenges, this work aims to present comprehensive mechanical characterization methods. It covers the complete stress-strain analysis and lateral deformation through uniaxial tensile and compression tests on flexible silica aerogels using a two-camera DIC setup based on from the methodology from Marter et. al. Samples of flexible silica aerogels were prepared in specific shapes (dogbone, cubic, or rectangular) using 3D printed moulds, reducing induced pre-stress resulting from cutting, based on the recipe used in previous study. The gathered mechanical data is then used to create a digital twin of the material using finite element simulations. Using the model, detailed investigations of buckling phenomena and flexibility properties are performed to predict material behaviour and derive correction factors to account for the non-ideal test conditions of flexible silica aerogels. Additionally, this study explores epoxy-resin bonded aluminium-aerogel joints and their mechanical characterization through tensile, shear, and peel tests. The methods are also used to investigate fibre-reinforced flexible silica aerogels and their potential benefits on adhesion bond strength. The methods presented in this study provide helpful standardized ways to mechanically characterize flexible aerogel performance and coherent joints for various applications including aerospace.