Plasticity of Neutron Star Crusts

We use first-principles molecular dynamics simulations to study the deformation and breaking of neutron star crusts. When simulating with strain rates several orders of magnitude slower than prior work, we find a new regime of steady plastic flow beyond the breaking point that is independent of the initial crystal structure. Polycrystals exhibit a robust transition from linear elasticity to perfect plastic flow at shear strains of $\epsilon = 0.05$, while monocrystals break at $\epsilon = 0.11$ and then flow plastically. The universal post-break plasticity may arise because the crystal self-consistently assumes a defect density to accommodate the imposed strain rate. If broken crusts can re-anneal to large crystal sizes, crust breaking may repeat with implications for magnetar bursts and flares.