13th International Conference on Fracture June 16-21, 2013, Beijing, China -4- Figure 2. Display a) SE-picture with red dots marking the area of EBSD-analysis, b) EBSD-map showing band slope and the distribution of LAGB and grain boundaries (GB) and c) the grain boundary legend shows the colour of corresponding angle [°] and the frequency distribution of LAGB and GB. Zero solution is marked white. The pure linear elastic part of a typical stress-strain curve for a flake graphite iron can related to the small tensile load that the graphite can withstand without microscopic yielding [16, 17] and the atomic forces. In this region the SE images did not revile any changes in the microstructure in neither the matrix nor the graphite. Also the EBSD mapping looks the same as in the un-stressed case, no statistical significant changes were found. Figure 3. Obtained stress-strain curve from the experiment. What then can be seen in SE-images, see Figure 2, when the applied load is slightly more than the critical value PL; (were the stress-strain curve starts to deviate from its linear path) the flaky graphite tends to open in the middle and a void appears inside. This phenomenon can be seen and detected in graphite orientated both perpendicular and parallel to the loading axis at loading levels above PL , 0 50 100 150 200 250 300 0 0,1 0,2 0,3 0,4 Stress [MPa] Strain [%] Sample 1 Sample 2 PL a) b c)
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