ORCID Profile
0000-0001-9244-7376
Current Organisation
Los Alamos National Laboratory
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Publisher: AIP
Date: 2012
DOI: 10.1063/1.3686525
Publisher: Oxford University Press (OUP)
Date: 03-02-2012
DOI: 10.1017/S1431927611012554
Abstract: Scientific digital imaging in three dimensions such as when using X-ray computed tomography offers a variety of ways to obtain, filter, and quantify data that can produce vastly different results. These opportunities, performed during image acquisition or during the data processing, can include filtering, cropping, and setting thresholds. Quantifying features in these images can be greatly affected by how the above operations are performed. For ex le, during binarization, setting the threshold too low or too high can change the number of objects as well as their measured diameter. Here, two facets of three-dimensional quantification are explored. The first will focus on investigating the question of how many voxels are needed within an object to have accurate geometric statistics that are due to the properties of the object and not an artifact of too few voxels. These statistics include but are not limited to percent of total volume, volume of the in idual object, Feret shape, and surface area. Using simple cylinders as a starting point, various techniques for smoothing, filtering, and other processing steps can be investigated to aid in determining if they are appropriate for a specific desired statistic for a real dataset. The second area of investigation is the influence of post-processing, particularly segmentation, on measuring the damage statistics in high purity Cu. The most important parts of the pathways of processing are highlighted.
Publisher: AIP Publishing
Date: 08-2011
DOI: 10.1063/1.3607294
Abstract: Plate impact experiments have been carried out to examine the influence of grain boundary characteristics on the dynamic tensile response of Cu s les with grain sizes of 30, 60, 100, and 200 μm. The peak compressive stress is ∼1.50 GPa for all experiments, low enough to cause an early stage of incipient spall damage that is correlated to the surrounding microstructure in metallographic analysis. The experimental configuration used in this work permits real-time measurements of the s le free surface velocity histories, soft-recovery, and postimpact examination of the damaged microstructure. The resulting tensile damage in the recovered s les is examined using optical and electron microscopy along with micro x-ray tomography. The free surface velocity measurements are used to calculate spall strength values and show no significant effect of the grain size. However, differences are observed in the free surface velocity behavior after the pull-back minima, when reacceleration occurs. The magnitude of the spall peak and its acceleration rate are dependent upon the grain size. The quantitative, postimpact, metallographic analyses of recovered s les show that for the materials with grain sizes larger than 30 μm, the void volume fraction and the average void size increase with increasing grain size. In the 30 and 200 μm s les, void coalescence is observed to dominate the void growth behavior, whereas in 60 and 100 μm s les, void growth is dominated by the growth of isolated voids. Electron backscatter diffraction (EBSD) observations show that voids preferentially nucleate and grow at grain boundaries with high angle misorientation. However, special boundaries corresponding to Σl (low angle, & 5 °) and Σ3 (∼60 ° & & misorientation) types are more resistant to void formation. Finally, micro x-ray tomography results show three dimensional (3D) views of the damage fields consistent with the two dimensional (2D) surface observations. Based on these findings, mechanisms for the void growth and coalescence are proposed.
Publisher: AIP Publishing
Date: 28-05-2014
DOI: 10.1063/1.4880435
Abstract: For ductile metals, dynamic fracture occurs through void nucleation, growth, and coalescence. Previous experimental works in high purity metals have shown that microstructural features such as grain boundaries, inclusions, vacancies, and heterogeneities can act as initial void nucleation sites. However, for materials of engineering significance, those with, second phase particles it is less clear what the role of a soft second phase will be on damage nucleation and evolution. To approach this problem in a systematic manner, two materials have been investigated: high purity copper and copper with 1% lead. These materials have been shock loaded at ∼1.5 GPa and soft recovered. In-situ free surface velocity information and post mortem metallography reveals the presence of a high number of small voids in CuPb in comparison to a lower number of large voids in Cu. This suggests that damage evolution is nucleation dominated in the CuPb and growth dominated in the pure Cu.
Publisher: EDP Sciences
Date: 2012
Publisher: IOP Publishing
Date: 07-05-2014
Publisher: EDP Sciences
Date: 2012
No related grants have been discovered for Brian Patterson.