Research Projects

Amorphous materials—ranging from metallic glasses and polymers to foams—are ubiquitous and exhibit similar mechanical behaviour despite their compositional diversity. These systems respond elastically under small strains but yield plastically beyond a critical threshold. Predicting the onset of such failure remains a key challenge across materials science, engineering, and geophysics. Unlike crystals, amorphous solids lack a reference lattice or defects; plastic deformation arises from local, irreversible rearrangements, but their structural precursors remain poorly understood. Recent work involving one of the current investigators developed a novel structural order parameter (SOP) to quantify local structure, demonstrating that it predicts dynamics in simulations. Further, collaborative work involving two investigators validated this SOP experimentally in dense colloidal suspensions, showing excellent agreement with rearrangements in both quiescent and sheared conditions. This project will aim to establish a comprehensive understanding of the structural origins of elasto-plastic deformation in amorphous materials. We will combine theory, simulations, and experiments to explore new directions in driven and active disordered systems. We will first study the relationship between ductility, brittleness, and structural change. Poorly annealed glasses are ductile, while well-annealed ones are brittle. Cyclic shear can drive systems from high-energy (ductile) to low-energy (brittle) states. Although the energies evolve under shear, the structural metrics that track this change are unclear. We will use SOP to investigate how structural softness and rearrangement propensity evolve during and after cyclic deformation, providing a structural basis for annealing and fatigue. We will also explore how SOP correlates with deformation mechanisms across brittle and ductile regimes. Brittle materials fail catastrophically with stress overshoot and shear bands, while ductile systems flow gradually. Using SOP, we will study how shear-induced structural changes accompany such deformation. Simulations will vary material properties using different quenching protocols, and experiments will use oscillatory shear to control mechanical properties and assess resulting structural changes. To capture anisotropy under shear, we will extend SOP to include directional dependence. Sheared materials stretch along one axis and compress along another, making their local structure anisotropic. We will compute directionally resolved SOPs to assess whether rearrangements preferentially occur along soft directions. These ideas will be tested using both simulations and experiments, with oscillatory shear used to control the system’s anisotropy and effective ductility. Finally, we will investigate how active forcing influences structure and mechanical response in systems with partial pinning. Preliminary work showed that soft pinning—using heavier or larger particles—alters the structural landscape in predictable ways. We will extend this analysis to include activity, applying persistent random forces to a subset of particles. We will explore whether activity can mobilise otherwise frozen regions, how SOP evolves under such nonequilibrium conditions, and whether a structural signature predicts activity-induced rearrangements. These results will have implications for understanding confined active matter and biological tissues. In summary, this project will develop a unifying structural framework using SOP to understand plasticity and failure in amorphous systems. We will apply this across passive and active, brittle and ductile, isotropic and anisotropic systems—using simulations and experiments. By bridging structure and dynamics at the particle level, this work will advance our ability to control mechanical responses in soft and disordered materials.