13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- 2. Experiments Commercially pure magnesium was hot rolled to a thickness of 125 µm. Tensile specimens were machined using electrical-discharge wire cutting. The tensile specimens had a reduced gage section with a length of 2 mm and a width of 1 mm. The samples were polished with 0.05 µm colloidal silica to ensure a smooth surface for laser machining. Holes with a diameter of approximately 13 µm, were laser drilled into the gage section of the tensile samples using a Ti:sapphire laser system. For one set of experiments, samples with a single row of holes perpendicular to the tensile axis were tested with different center to center hole distances to examine the effects of void fraction on the failure strain. The distances used were 40, 55 and 70 µm. In another set of experiments, samples with a single row of holes oriented at various angles with respect to the tensile direction were tested to analyze the effects of void orientation on failure strain. The angles were 45, 60 and 75˚. After laser drilling, the samples were annealed in a tube furnace purged with argon, at 450 ˚C for 1 hour, to remove the heat affected zone in the vicinity of the holes. The average grain size was approximately 50 µm with a standard deviation of 25 µm, after the final annealing process. EBSD patterns were obtained to determine the initial texture in the vicinity of the holes. Tensile tests coupled with electron microscopy have been used to visualize void growth and linkage in-situ. Samples were pulled in uniaxial tension at room temperature under the SEM. The tensile stage utilizes a 220 N load cell and experiments were carried out at a constant test speed of 10 µm/s. Images were obtained in increments during deformation. Tests were stopped when microstructural features or damage was observed. EBSD was carried out on the deformed samples and micro computed tomography scans were employed to observe the bulk of the deformed samples. The Skyscan 1172 micro computed tomography unit was used in the analysis. 3. Results The EBSD patterns obtained on the deformed samples allowed for characterization of the microstructural features which led to failure. Figure 1 shows the SEM image series of a row of holes perpendicular to the tensile axis with a center to center hole distance of 40 µm. The EBSD patterns have been overlaid on the SEM images where necessary. Figure 1: SEM image series at various far field strains and misorientation profile across the twin circled.
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