## 1 Introduction  
The presence of discontinuities such as cracks and notches in structures leads to stress concentrations that increase the risk of failure under different kinds of loading condition, and significantly reducing the corresponding structural strength. Sometimes, the presence of these defects is unavoidable due, for example, to the manufacturing process of the material or the need for certain structural details (e.g., welds). Therefore, great attention has been paid by many researchers to studying the fracture behavior of components containing defects. Most of the research dealing with the fracture of cracked or notched components has been performed under mode I and mixed mode I/II loading conditions, where fracture is caused by local tensile stresses. Under such conditions, physical aspects of failure are analogous between cracked and notched components, beyond the evident relaxation of the stress field when moving from cracked to notched conditions. However, under compressive stresses, defects experience closing mode loading, also known as negative mode I loading, and there is a greater difference between the behavior of components in cracked and notched conditions. In fact, when the cracked component is subjected to negative mode I loading, the crack faces contact each other and the crack mouth does not open. Consequently, crack growth is not expected. Conversely, in the case of notched components, the probability of contact between the notch faces is related to the distance between them, and a fracture may be expected because of damage nucleation and propagation from the notch tip. Many researchers have investigated the fracture of notched components with different notch geometries. However, U- and V-shaped notches have been studied much more than the others due to their extensive engineering applications. Several papers have been published in the literature dealing with brittle fracture of U- and V-notched components under pure mode I and pure mode II loadings (e.g., [1; 2; 3; 4; 5; 6; 7; 8; 9]), as well as under mixed mode I/II loading (e.g., [10; 11; 12; 13; 14; 15; 16]). Different stress-based and energy-based failure criteria have been applied in these works for estimating the brittle fracture conditions in a wide variety of materials containing notches, generating estimations of their corresponding load-carrying capacity (LCC). Nowadays, polymers are used increasingly in different engineering and industrial applications. These applications for polymeric materials are possible because of their satisfactory physical, mechanical, thermal, and chemical properties [17]. In engineering structures, polymeric components are usually subjected to mechanical and/or thermal loadings, and the prediction of their LCC requires their mechanical properties to be known. One of the main mechanical properties that is used for evaluating the fracture of polymeric components is the fracture toughness, which must be accurately specified. Since polymeric components in engineering structures may contain notches of various shapes, the resulting stress concentrations may cause their ultimate fracture. Therefore, it is important to evaluate the strength of notched polymeric components against fracture. This subject is studied nowadays by means of notch fracture mechanics (NFM). The mechanical behavior of brittle polymeric components has been studied in various research works in the presence of cracks and notches (e.g., [18; 19; 20; 21]). Polymethyl-methacrylate (PMMA) and general-purpose polystyrene (GPPS) are two commercial polymers whose fracture behaviors in the presence of different notches have already been investigated under various loading conditions [5; 6; 22; 23]. Regarding a literature survey of the brittle fracture of notched components under compression, it should be mentioned that the first research works were conducted before 2000 (e.g., [24; 25; 26; 27; 28; 29; 30]). Afterwards, [PERSON] et al.