Direct observation of dynamic shear jamming in dense suspensions

Abstract

Liquid-like at rest, dense suspensions of hard particles can undergo striking transformations in behaviour when agitated or sheared¹. These phenomena include solidification during rapid impact^2,3, as well as strong shear thickening characterized by discontinuous, orders-of-magnitude increases in suspension viscosity^4,5,6,7,8. Much of this highly non-Newtonian behaviour has recently been interpreted within the framework of a jamming transition. However, although jamming indeed induces solid-like rigidity^9,10,11, even a strongly shear-thickened state still flows and thus cannot be fully jammed^12,13. Furthermore, although suspensions are incompressible, the onset of rigidity in the standard jamming scenario requires an increase in particle density^9,10,14. Finally, whereas shear thickening occurs in the steady state, impact-induced solidification is transient^2,15,16,17. As a result, it has remained unclear how these dense suspension phenomena are related and how they are connected to jamming. Here we resolve this by systematically exploring both the steady-state and transient regimes with the same experimental system. We demonstrate that a fully jammed, solid-like state can be reached without compression and instead purely with shear, as recently proposed for dry granular systems^18,19. This state is created by transient shear-jamming fronts, which we track directly. We also show that shear stress, rather than shear rate, is the key control parameter. From these findings we map out a state diagram with particle density and shear stress as variables. We identify discontinuous shear thickening with a marginally jammed regime just below the onset of full, solid-like jamming²⁰. This state diagram provides a unifying framework, compatible with prior experimental and simulation results on dense suspensions, that connects steady-state and transient behaviour in terms of a dynamic shear-jamming process.