The demand for enhanced materials in the Polymer Science field requires the development of new strategies for the creation high-performance plastics. A well-known procedure consists in the creation of rubber-toughened polymeric blends}, where the combination of two or more thermoplastics with the addition of small dispersed rubber particles improves the mechanical behaviour of its neat constituents. A case of interest is the ternary amorphous PC/ABS blends - although neat polycarbonate has high ductility, thermal stability and durability, it lacks notch-sensitivity and fracture toughness, properties that are highly improved by the addition of ABS, a rubber-toughened polymer [1]. The deformation mechanisms of rubber-toughened polymers are known to be governed by matrix shear yielding and crazing, interconnected with cavitation of the rubber particles, depending on the applied stress state. In compression, these polymers usually show plastic deformation by shear-yielding; in tension, a competition between shear-yielding and crazing takes place. Crazing often appears in sharp notches and is associated internal cavitation. This work presents a new detailed three-dimensional constitutive framework for the analysis of amorphous polymers, based on the achievements made by the work of Anand's research group [2]. Considering an implicit integration scheme, the PC/ABS rubber-toughened polymer is characterised under different stress states and volume-fraction compositions, analysing the deformation mechanism paths taken during the mechanical response and defining specific failure criteria for this field of materials. The benchmark experimental results allow the attainment of the material properties through a specialised parameter identification procedure. A comprehensive set of numerical examples is presented taking into account a wide range of mechanical conditions and is appraised against the experimental set of results obtained by our group. [1] J. Hund, J. Naumann and T. Seelig, An experimental and constitutive modeling study on the large strain deformation and fracture behavior of PC/ABS blends. \textit{Mech. Mater.}, Vol. \textbf{124}, 132--142, 2018. [2] L. Anand and N.M. Ames, On modelling the micro-indentation response of an amorphous polymer. \textit{Int. J. Plasticity}, Vol. \textbf{22}, 1123--1170, 2