  Under an applied traction, highly concentrated suspensions of solid particles
in fluids can turn from a state in which they flow to a state in which they
counteract the traction as an elastic solid: a shear-jammed state. Remarkably,
the suspension can turn back to the flowing state simply by inverting the
traction. A tensorial model is presented and tested in paradigmatic cases. Its
effectiveness in reproducing the phenomenology of shear jamming shows that it
is advantageous to link this effect to the elastic response supported by the
microstructure rather than to a divergence of the viscosity.
