Experimental and theoretical developments in understanding yielding

Gels exhibit yielding behavior are used in many applications, from spreadable foods and cosmetics to direct write three-dimensional printing inks. Their key design feature is the ability to transition behaviorally from solid to fluid under sufficient load or deformation. Despite their widespread applications, little is known about the dynamics of yielding in real processes, as the nonequilibrium nature of the transition impedes understanding. We demonstrate an iteratively punctuated rheological protocol that combines strain-controlled oscillatory shear with stress-controlled recovery tests. This technique provides an experimental decomposition of recoverable and unrecoverable strains, allowing for solidlike and fluid-like contributions to a yield stress material’s behavior to be separated in a time-resolved manner. Using this protocol, we investigate the overshoot in loss modulus seen in materials that yield. We show that this phenomenon is caused by the transition from primarily solid-like, viscoelastic dissipation in the linear regime to primarily fluid-like, plastic flow at larger amplitudes. We further show the development of a simple model based on these measurements that shows yielding is a smooth and continuous transition that may be viscoelastic in nature.