When a biaxially oriented polystyrene film was stretched along one direction and subsequently stretched along the perpendicular direction, the film showed enhanced ductility with pronounced yield softening and extended strain hardening. In the forward deformation, at least two types of shear bands were observed. The bands at the early stages of yielding did not seem to contribute to the reduction of thickness. They were approximately 200 mum thick and had an intersection angle of approximately 120degrees. The bands developed in the later stages contributed to the thickness reduction. These bands were smaller and possessed an intersection of approximately 90degrees. In the cross deformation, new shear bands developed that were likely related to the reverse shearing of the existing bands. Stress relaxation showed a power-law relationship between the stress rate and relaxation time. The internal stress of the cross deformation was significantly (ca. 3 times) lower than that of the forward deformation at the same strain. The enhancement in ductility may be attributed to the lowering of internal stress during the cross deformation. The internal stress increased with the applied stress and strain. Fracture occurred when the internal stress reached a certain level, about 57-68 MPa for deformation along both directions and approximately 44-47% of the final applied stress. (C) 2003 Wiley Periodicals, Inc.