  We study experimentally the slow growth of a single crack in polycarbonate
films submitted to uniaxial and constant imposed stress. For this visco-plastic
material, we uncover a dynamical law that describes the dependence of the
instantaneous crack velocity with experimental parameters. The law involves a
Dugdale-Barenblatt static description of crack tip plastic zones associated to
an Eyring's law and an empirical dependence with the crack length that may come
from a residual elastic field.
