Issue 47

J. P. Manaia et alii, Frattura ed Integrità Strutturale, 47 (2019) 82-103; DOI: 10.3221/IGF-ESIS.47.08 95 modifies the fracture surface and influences the void growth and size. Contrasting with the fracture surface of HDPE and PP, PA 6 features a “smooth surface” with radial striations and also some disperse cavitation/voids are detected in both notched radii, R=5 and R=30. The absence of fibrils formation is an indication of brittle fracture. The voids distribution density is higher at the specimen centre and decreases toward the specimen border. By comparing the two radii, the voids amount and size decrease with notch radius increasing (lower stress triaxiality ratio). Similar features on the mechanisms of void growth on cylindrical notched specimens were observed by Laiarinandrasana et al. [12]. In specimens with notch radius R=5 the dominant mode of deformation near surface was crazing. An impression from comparing the fracture surfaces and the two notch radii of HDPE and PP specimens is that a higher radius causes a rougher fracture surface with higher fibrils formation. Therefore, the presence of notches (triaxial state of stress) change the fracture mechanism of the tested material from ductile (low stress triaxiality) to brittle (high stress triaxiality). HDPE, Room Temperature PP, Room Temperature PA 6, Room Temperature Figure 12 : SEM images of butterfly specimens fractured for tensile loading at room temperature for HDPE, PP and PA 6. In the first column the geometry of specimen and fracture surface location are indicated by the black square. Analysis of Combined Tensile/Shear Loading Fracture Morphologies at Stress Triaxialities between 0 and 0.58 Fracture morphologies of butterfly specimens subjected to different loading angles of HDPE, PP and PA 6 materials were investigated with SEM. Due to the three loading angles (  = 90°, 30°, and 0°) applied to the butterfly specimens at crosshead speed of 200 mm/min and at two temperatures, RT and temperature of 50 °C, distinct fracture morphologies are generated for each material. To explore the underlying fracture mechanisms under  = 90° (stress triaxiality=0.58) at room temperature and at temperature of 50 °C, for HDPE, PP and PA 6 SEM images were taken from the fracture surfaces and presented in Figs. 12 and 13, respectively. The fracture morphologies exhibit different modes of deformation for  = 90° at Room Crazing with Microfibrils Crazin Fibrillation/Crazing Cavitation and Voids Crazing and Tearing Crazing and Tearing Brittl Crazing and Tearing Peeling Skin Layer