Mechanical characterization of aerogel materials with digital image correlation

Silica aerogels are ultralow density materials with nano-sized skeleton network of pores. Their high brittle nature presents a major challenge for mechanical testing and a need exists for novel testing methods. Two new mechanical setups and testing techniques are proposed for measuring the aerogel elastic mechanical properties. Both techniques employ full-field Digital Image Correlation (DIC) for surface deformation measurements. The first setup uses disk compression experiment, known as diametral compression test (Brazilian disk). However, the elastic properties of the material cannot be obtained directly. Instead, an inverse mechanics computational scheme, using both a finite element (FE) model and analytical solution, is proposed. The second direct testing setup is uniaxial compression of rectangular-shaped blocks. The Young's modulus and Poisson's ratio are extracted directly from the experimental stress-strain curves. Our results of tested samples show the relation between the density and the Young's modulus to coincide with previously published trends. The direct and iterative inverse-mechanics solution methods agree well with each other. The Poisson's ratio is found to be independent of the material apparent density. Comparisons between the two methods and recommendations for expanding the disk testing approach to fracture toughness are discussed.