The characterization and modeling of failure of metallic materials under extreme conditions, such as the high loads and strain rates found under shock loading, are extremely important for Stockpile Stewardship. In particular, spall failure is a complicated physical process where microstructure plays an important role, due to the presence of both intrinsic (grain boundaries, triple points) and extrinsic (precipitates, inclusions) defects. Furthermore, nucleation of damage is a statistical process where the distribution of sizes and strengths of these defects plays a fundamental role. Studying incipient spall in pure materials to determine the nature of the intrinsic defects that lead to damage nucleation is of paramount importance to develop models that account for the statistical nature of this phenomenon. Work performed so far indicates that grain boundaries and triple points are preferred sites for damage nucleation. However, many studies have been performed under conditions that make it hard to identify and characterize the particular nucleation site. Furthermore, the characterization has been performed mostly in 2-D, which cannot provide a complete picture of the crystallographic and geometric variables that influence damage nucleation and localization in a particular microstructural site. This work focuses on gathering statistics on the main crystallographic and geometric features of microstructural sites that lead to damage localization during incipient spall in 3-D. This will be achieved using a combination of sample preparation and testing techniques recently developed by the PI and his collaborators at LANL, whereby incipient damage can be induced in metallic materials with pores that are smaller than the grain size, so that a clear identification of the nucleation site can be achieved. Serial sectioning via mechanical polishing as well as ion beam techniques will be combined with electron backscattered diffraction (EBSD) to characterize the damage, making emphasis on locations where damage is localizing, e.g., when pores are locally larger than average, and the full geometric and crystallographic characteristics of the damage site will be obtained in 3-D, including orientation of all grains surrounding the site, inclination of grain boundaries with respect to the shock front and the 3-D geometry of the site (facet, ledge, etc.). Statistics will then be gathered on these parameters to obtain fundamental information on the range of these variables that favor damage nucleation during incipient spall conditions. This, in turn, will allow full identification of the weak links in the microstructure and provide data for model formulation and validation of spall damage during shock loading. Characterization experiments will be conducted in samples provided by collaborators at LANL, and additional shock loading experiments will be performed using facilities to be built at ASU and by collaborating with staff members at LANL and LLNL to obtain time at gas gun and laser facilities (TRIDENT, JANUS). Work will be performed in model FCC and HCP materials such as copper and titanium, and other materials such as nickel and zirconium will be explored as time permits. Furthermore, contacts have been initiated with scientists in the Advanced Photon Source at Argonne National Laboratory to perform 3-D characterization using X-Ray tomography and micro-diffraction at higher resolutions than those possible with serial sectioning.TR>
|Effective start/end date||1/11/10 → 1/10/14|
- US Department of Energy (DOE): $435,000.00
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