Issue 47

J. P. Manaia et alii, Frattura ed Integrità Strutturale, 47 (2019) 82-103; DOI: 10.3221/IGF-ESIS.47.08 100 (resulting in tearing of the crazed region). PA 6 is the exception; SEM micrographs show a considerable plastic deformation and inhomogeneous morphology with significant localized deformation in the form of crazing tearing at the extremities and at the centre. At high magnification at central region, textured fracture surfaces are observed, with some fibrils formation and crazing tearing formation. At extremity, SEM micrographs shows some amount of microbuckling leading to a corrugated appearance in the regions away from the centre of the fracture surface. At higher temperatures (Fig. 17) the polymer behaves in a much more viscous manner and the crazes widens very rapidly. The fracture surface seems to appear less rough and more homogeneous in the case of PP and PA 6. For HDPE, the regular surface with almost geometric triangular patterns, are elongated along the shear stress direction. HDPE, Temp. of 50 °C PP, Temp. of 50 °C PA 6, Temp. of 50 °C Figure 17 : SEM images of butterfly specimens fractured for shear loading at temperature of 50 °C for HDPE, PP and PA 6. In the first column the geometry of specimen and fracture surface location are indicated by the black square. HDPE fracture surfaces at RT and 50 °C have the same geometric patterns, however at 50 °C and at near surface appears a large number of microfibrils, indicating a continued plastically deformation as decohesion of crazing occurred. The dominant fracture is crazing, as well as for PP. PP fracture surface extremities show large areas covered with striations. The fracture surface is similar between RT and 50 ºC. In the shear deformation of PA 6 at 50 °C three fracture morphologies are identified: brittle with ductile pulling of microfibrils, crazing and shearing. The area fraction of brittle failure decreased with increase in temperature with consequent increase in ductile fracture. Crazing and Tearing Crazing and Tearing Microfibrils Striations Crazing and Tearing Ductile Ductile Brittle Crazing and Tearing