  Magnetic field evolution in neutron-star crusts is driven by the Hall effect
and Ohmic dissipation, for as long as the crust is sufficiently strong to
absorb Maxwell stresses exerted by the field and thus make the momentum
equation redundant. For the strongest neutron-star fields, however, stresses
build to the point of crustal failure, at which point the standard evolution
equations are no longer valid. Here, we study the evolution of the magnetic
field of the crust up to and beyond crustal failure, whence the crust begins to
flow plastically. We perform global axisymmetric evolutions, exploring
different types of failure affecting a limited region of the crust. We find
that a plastic flow does not simply suppress the Hall effect even in the regime
of a low plastic viscosity, but it rather leads to non-trivial evolution -- in
some cases even overreacting and enhancing the impact of the Hall effect. Its
impact is more pronouced in the toroidal field, with the differences on the
poloidal field being less substantial. We argue that both the nature of
magnetar bursts and their spindown evolution will be affected by plastic flow,
so that observations of these phenomena may help to constrain the way the crust
fails.
