Issue 47

J. P. Manaia et alii, Frattura ed Integrità Strutturale, 47 (2019) 82-103; DOI: 10.3221/IGF-ESIS.47.08 97 outwards breaking through the crazed surface on both sides and extremities (resulting in tearing of the crazed region) at approximately the same position along the length of the section. Also, near surface inward growth of crazes from all the sides are observed. SEM images were also taken at a temperature of 50 °C and are shown in Fig. 13. In general mode with increase in temperature, the fracture becomes more homogenous, the extent of craze region decreases and the ductile area/surface increases. In the case of HDPE, at central region, the fracture surface is reduced by neecking, becoming narrower, suggesting that was the last region to fracture. However, the fracture surface is more homogeneous. Also, it is observed, crazing and tearing with microfibrils formation and slope surfaces. High magnification of PP fracture surface shows irregular surface with high voids content; also at fracture extremities large voids surrounded by fibrils are observed. The fracture surface of PP does not undergo with major changes, with increasing the temperature. Even though the brittle failure is dominant, there is some evidence of ductile pulling of microfibrils around the voids at the edges. The “peeling skin layer” is observed in both HDPE and PP in peripheric central region-fracture. At a temperature of 50 °C, PA 6 exhibits a fracture surface completely different from that obtained under room temperature. The fracture surface becomes more ductile with fibril formation at central region and more inhomogeneous at the extremities (the last region to fracture), with massive crazing and tearing formation. HDPE, Room Temperature PP, Room Temperature PA 6, Room Temperature Figure 14 : SEM images of butterfly specimens fractured for combined tensile/shear loading α = 30° 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. SEM images of fracture surfaces of butterfly specimens tested under combined tension/shear (  = 30°, stress triaxiality=0.19), at room temperature and temperature of 50 °C, for HDPE, PP and PA 6, are displayed in Figs. 14 and 15, respectively. At room temperature (Fig. 14), brittle fracture associated with large voids and cavitation, crazing and tearing associated to the combined tension/shear loading, with ductile pulling of microfibrils in the regions away from the centre Elliptically Shaped Voids Crazing and Tearing Cavitation and Voids Microfibrils Peeling Skin Layer Fibrous Morphology Crazing and Tearing Striations Crazing and Tearing