  We study breaking stress of deformed Coulomb crystals in a neutron star
crust, taking into account electron plasma screening of ion-ion interaction;
calculated breaking stress is fitted as a function of electron screening
parameter. We apply the results for analyzing torsional oscillation modes in
the crust of a non-magnetic star. We present exact analytic expression for the
fundamental frequencies of such oscillations and show that the frequencies of
all torsional oscillations are insensitive to the presence of the outer neutron
star crust. The results can be useful in theoretical modeling of processes
involving deformed Coulomb crystals in the crust of neutron stars, such as
magnetic field evolution, torsional crustal or thermo-elastic quasi-periodic
oscillations of flaring soft gamma-ray repeaters, pulsar glitches. The
applicability of the results to soft gamma-ray repeaters is discussed.
