·Table of Contents ·Materials Characterization and testing | Statistical Void analysis from CT Imagery with Applications to Damage Evolution in an AM60B Magnesium AlloyAmy M. Waters, Harry E. Martz, Kenneth W. Dolan. ,Lawrence Livermore National Laboratory Livermore, CA 94550 USA Mark F. Horstemeyer Lawrence Livermore National Laboratory Livermore, CA 94550 USA Permanent address Sandia National Laboratory, Livermore, CA 94550 Robert E. Green, Jr Lawrence Livermore National Laboratory Livermore, CA 94550 USA Permanent address Center for Nondestructive Evaluation, 102 Maryland Hall, The Johns Hopkins University, Baltimore MD 21218 Contact |
^{1} This work is supported by and is performed under the auspices of the U.S. Department of Energy by the LLNL under contract W-7405-ENG-48
Fig 1: Representative CT slices from sample H24 at 60% of failure load. The image to the left is a CT slice through the y-axis (note that it consists of 6 separate CT scans stacked together), and the image on the right is a CT slice through the z-axis. |
The 3-D CT volumes were segmented using a simple threshold, and then inverted and masked, resulting in a 3-D binary volume, with voids equal to 1, and material equal to 0. We performed a 3-D cluster analysis routine on the segmented volume which labeled connected voxels [4]. We then selected only those clusters containing more than 100 connected voxels for further statistical analysis. This corresponds to a minimum void volume of 1.33 x 10^{-5} mm^{3}, equivalent to a cube of dimension 0.110-mm (4.64 pixels) on a side. These voids were then selected and moved to a clean volume of identical size containing only the voids larger than 1.33 x 10^{-5} mm^{3}, where further analysis was performed. The centroid of each of these voids was calculated, and the 3-D nearest neighbor distance for each void was determined. Void size distributions and nearest neighbor distance distributions are shown in Figure 2 for one tensile bar after each loading.
Fig 2: Nearest neighbor distance distribution, and void size probability plots for one tensile bar (H24) after each loading. Note the shape of the distributions does not appear to change significantly with load. |
Several additional statistical parameters were determined for each of the three tensile bars. Table 1 shows some void statistics calculated for one tensile bar at 4 loading conditions and failure.
Sample Number | Number of voids/mm^{3} | Avg. void vol (mm^{3}) | Median void vol (mm^{3}) | Avg. Near. Neighbor Dist (mm) | Max Void vol (mm^{3}) |
H24-1 (60%) | 0.394 | 0.00522 ± 0.00685 | 0.00244 | 0.687± 0.3978 | 0.04614 |
H24-2 (87%) | 0.432 | 0.00602 ± 0.00985 | 0.00278 | 0.6593 ± 0.3525 | 0.09361 |
H24-3 (93%) | 0.353 | 0.00632 ± 0.01218 | 0.00295 | 0.6754 ± 0.3778 | 0.13840 |
H24-4 (95%) | 0.372 | 0.00664 ± 0.01473 | 0.00272 | 0.6795 ± 0.3976 | 0.13909 |
H24-5*(failure) | N/A | 0.00597 ± 0.01652 | 0.00253 | 0.7097 ± 0.4215 | 0.19868 |
Table 1: Void statistics for sample H24 loaded and scanned 5 times. The minimum void volume used in this analysis was 1.33 x 10^{-5} mm^{3}. |
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