Mechanical characterisation and modelling of flexible silica aerogels using DIC

Abstract

Aerogels are open-porous nanostructured materials with a distinctive combination of low density, high specific surface area, and low thermal conductivity [Hüsing and Schubert, 1998]. In order to accelerate the practical implementation of aerogel applications, flexible silica aerogels were developed, allowing for high flexibility [Hayase et.al., 2011]. However, the mechanical characterisation of these materials is challenging due to their flexible, porous nature, which makes it difficult to ascertain their structure-property relationships. Previous research on flexible carbon aerogels [Rege et.al., 2020] has employed in-situ methods during compression, such as scanning electron microscopy (SEM) and digital image correlation (DIC), a method already established for porous materials [Marter et.al., 2018]. However, in this previous study, DIC was limited to small finite strains. To investigate the high deformations of the flexible silica aerogels, it is necessary to develop a characterisation method that allows for the evaluation of the material's flexibility and the global tracking of stress distribution.

This work aims to provide insights on enhanced methods for the mechanical characterisation of flexible silica aerogels using DIC and finite element analysis (FEA). Following the aerogel synthesis and the measurement of the final specimens using 3D scanning, quasi-static tensile and cyclic compression tests were conducted, using DIC. Two different specimen geometries, namely rectangular bars and dogbone-shaped specimens were compared under tension. Cyclic compression tests enabled the evaluation of their inelastic properties. Furthermore, a comprehensive sensitivity analysis comparing two DIC methods and the impact of DIC correlation parameters was studied. Subsequently, the experimental data was employed to construct a digital twin of the flexible silica material using FEA. In this model, the impact of friction between the pressure plate and the aerogel during compression was investigated to enhance understanding of non-ideal testing conditions. These findings can facilitate the advancement of aerogel development and their practical applications.