The fracture of notched elements under mode I loading (tension) is still an inexhaustible research topic, especially when it comes to the fracture of thermoplastic materials such as Polymethylmethacrylate (PMMA), which experience large plastic strains. The paper points out that traditional brittle fracture criteria such as Mean stress (MS) or Maximum tangential stress (MTS) criteria used to predict this phenomenon do not accurately indicate the value of the critical load. They work much better when combined with the Equivalent material concept (EMC) and Fictious material concept (FMC). While pointing out that the effectiveness of both concepts depends on the size of the notch root radius and thus the size of the yield zone.