The development of shear bands at the stretched surface of a bent plate is analysed numerically, based on an approximate continuum model of a ductile porous material. This material model accounts for the nucleation and growth of voids as well as the effect of the yield surface curvature, which is represented by a combination of kinematic hardening and isotropic hardening. An imperfection in the form of an initial surface waviness is assumed, which triggers shear bands at the wave bottoms. The corresponding periodic pattern of shear bands is considered, and the growth of the bands is followed, until shear cracks develop from the void-sheets inside the bands. The delay of localization due to the nonuniform strain field is studied for different versions of the material model. Furthermore, the stability of the uniform growth of several adjacent shear bands is investigated.