Capillary control of failure in soft composite materials

A solid subjected to an in-plane compression buckles when the compressing load reaches a critical value and an infinitesimal deformation leads to a large amplitude out-of-plane deflection. Since Euler’s original study on the elastic instability of a column subjected to longitudinal compressing forces at its ends, buckling has been extensively studied in homogeneous, isotropic, linear-elastic solids. Here, we examine the nature of the buckling in inhomogeneous soft composite materials. In particular, we consider a soft host with liquid inclusions both large and small relative to the elastocapillarity length, which lead to softening and stiffening of a homogeneous composite respectively. By imposing a gradient of the liquid volume fraction or varying the inclusion size we tailor the elastic behavior spatially, and hence we can deliberately manipulate the failure properties of the elastic composite. We have applied this setup to the study of the buckling of compressed columns as well as thin sheets floating on a liquid.