Dense suspensions of small solid particles in a simple liquid exhibit a range of intriguing non-Newtonian flow behaviors . One of the most striking and counter-intuitive of these is the transformation from overall liquid-like to solid-like behavior under rapid impact, shear or extension. This talk discusses some of the mechanisms driving such behavior, emphasizing the differences between steady-state responses to applied forcing, such as shear thickening, and dynamic responses, such as impact-activated solidification. We recently showed that impact-activated solidification involves rapidly moving fronts that emanate from the impact point and convert fluid-like, unjammed suspension into rigidly jammed material in their wake . Measuring the speed of sound, we find that such fronts do not involve any significant increase in local packing fraction, while imaging of the flow field with high-speed ultrasound directly links the evolving front position to regions of high shear intensity. Taken together, this provides evidence for a solidification process we call dynamic shear jamming. We discuss the relationship to shear jamming in frictional granular systems, and we introduce a state diagram that delineates dynamic shear jamming from discontinuous shear thickening (DST) on the one hand and traditional jamming by densification on the other .
 E. Brown and H. M. Jaeger, Shear thickening in concentrated suspensions: phenomenology, mechanisms, and relations to jamming, Reports On Progress In Physics 77, 046602 (2014).
 S. R. Waitukaitis and H. M. Jaeger, Impact-activated solidification of dense suspensions via dynamic jamming fronts, Nature 487, 205-209 (2012).
 I. R. Peters, S. Majumdar, and H. M. Jaeger, Direct observation of dynamic shear jamming in dense suspensions, Nature 532, 214â??217 (2016).