13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- The ductile-brittle transition temperature was estimated by comparing the percentage of ductile fracture area following the specifications of ASTM E-23[4]. Specimens with L-T orientation showed range lower values of transitions temperature between -38°C to -57°C, while the specimens with T-L orientation exhibited a greater range of the transition temperature values between -8 ° C up to -38 ° C. 3.3. Aspects of delamination phenomenon Fig. 5) shows fractured surface samples with delaminations from the Charpy impact test. In Fig. 5a) is possible to observe crack arrester-type delamination from the specimen tested at -5°C and 265J of absorbed energy. Fig. 5b) also shows a set of crack divider- type delamination from the specimen tested at -36°C and 100J of absorbed energy. It can be seen in Fig. 4a) the crack arrester-type delamination is formed perpendicular to the propagation fracture direction and parallel to the notch, while the crack divider-type delamination (Fig. 4b)) occurs parallel to the propagation fracture direction and perpendicular at notch. Cracks arrester-type delaminations are known by their beneficial effect to increase upper shelf energy [5], this suggests a higher tendency of the L-T orientation specimens present crack arrester-type delamination, which may contribute to increase of energy values for L-T orientation independent on the temperature used, as can be seen in Fig 3a). 3.4. Microtexture Fig. 5 shows an image obtained by scanning electron microscopy in the regions in front of propagated crack by crack divider-type delamination, the distribution map of orientations, the inverse pole figure, the orientation distribution function (ODF) for Bunge angle Φ2 = 45°, and the pole figures of the (100) and (110) planes. Quantification of microtexture was made by EBSD technique, with the following parameters: Fig. 5b) was used step size of 1 micron and 1000 X magnification and Fig. 5c) was used step size of 3 microns and a magnification of 3000X. From Fig. 5b) is possible to notice the presence of dark regions, where shows a crack produced by the formation of delamination. The remaining points may be regions of perlite, which have very a) b) Figure 4. Fractured surface by impact test showing the phenomenon of delamination. a) Crack arrester-type delamination, b) Crack divider-type delamination Propagation fracture direction Propagation fracture direction Notch Notch
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