The fracture of amorphous polymers and their toughness are governed by the competition between the plasticity of the bulk material in the form of shear bands and crazing [1]. The latter also involves the localization of the plastic deformation, but on a smaller scale. The failure is called ductile when it is preceded by plasticity in the solid material, brittle when crazing only appears. We investigate [2] the influence plasticity and its competition with crazing by conducting a detailed 3D study. Polycarbonate is chosen, representative of ductile amorphous polymers. We show that a 2D analysis under the assumption of plane strain is an important simplification of the crack tip fields as the shape of the shear bands is constrained in the thickness. This is also a restriction to the analysis of failure as its initiation is generally governed by a critical hydrostatic stress state. The 3D analysis (Abaqus) accounts for realistic behaviour for the bulk. Crazing is described using a cohesive model whose characteristics in terms of maximum tension and critical opening are borrowed from the literature. We propose to characterize the geometry effects with the thickness/notch radius ratio. Although, qualitatively, the plastic zone is comparable between 2D and 3D as soon as this ratio is larger than 8, we observe that the stress fields estimated in 2D overestimate those obtained from a 3D analysis, even for samples as thick as 15mm. However, the 3D calculations show a stress estimate that varies little with thickness when the ratio thickness/notch radius is larger than 32. A 3D study is necessary to estimate local failure criteria such as a critical local stress state for the appearance of failure. This has implication in the analysis on fracture, that will be discussed.