When does deformation become flow? Exploring the mechanics of yield-stress materials

Abstract: Can a yield-stress material deform without flowing, and can yielding occur without spreading? Yield-stress materials, such as gels, emulsions and pastes, exhibit a fascinating combination of solid-like and fluid-like behaviour. Despite their widespread use in industrial processes, the physical mechanisms governing their transition from reversible deformation to irreversible flow remain incompletely understood. This talk will explore some of these questions through recent experimental and numerical investigations of elastoviscoplastic fluids. I will first discuss how parallel superposition rheometry can be used to probe the mechanical response of these materials below the yield point, including the challenges associated with distinguishing true bulk deformation from interfacial motion. I will then turn to numerical simulations of gravity-driven drop spreading, examining how the complex interplay between elasticity and plasticity influences the macroscopic response. Together, these studies provide an opportunity to revisit some fundamental assumptions about yield-stress materials and discuss the challenges that remain in understanding and predicting their behaviour.

Bio: Claudio Fonte is Senior Lecturer in Chemical Engineering at the University of Manchester. His research focuses on the fluid dynamics and rheology of complex fluids, with particular emphasis on mixing, viscoelastic and yield-stress materials, and multiphase flows. His work combines experimental, numerical and theoretical approaches to investigate fundamental flow phenomena and their implications for industrial processes.