Papers by Author: Brent L. Adams

Abstract: An extension to a previously published, novel stereological method is reported which infers experimentally inaccessible components of the Nye GND tensor. Limitations imposed by electron-opacity of metals prevent direct measurement of four components of the Nye tensor, but it is possible to use additional experimentally-obtainable information in connection with underlying field equilibrium equations to estimate these additional components. This approach uses derivatives to the infinitesimal elastic distortion tensor to reduce error imposed by pattern center inaccuracy.

Abstract: As EBSD techniques improve, researchers are rapidly gaining access to quantities of high-caliber information previously unavailable. However, these benefits bring their own drawbacks. Engineers must either learn to cope with large amounts of data, or they must be more selective about which data is captured. In either case, machine learning techniques may play an important role. Data mining techniques can be used to extract knowledge from large databases, while other machine learning methods enable the identification of critical features, and the efficient search for such features at the data acquisition phase. One particular application of these techniques involves the investigation of fracture and fatigue mechanisms. Methods are required for finding and recording critical event inception. The development of in-situ test equipment, and high-resolution microscopy techniques (such as high-resolution EBSD: HREBSD) have placed invaluable tools into the hands of researchers. Nevertheless, practical considerations limit the volume of material that can be carefully monitored during a given testing regime. Machine learning techniques offer a promising framework for enhancing efficiency in the search for critical events. This paper presents initial efforts to develop an intelligent microscopy environment for EBSD users based upon machine learning methods. The test bed for the study will include ductility studies in magnesium, exploiting recent advances by the authors in the area of HREBSD.

Abstract: Recent advances in high-resolution electron backscatter diffraction (EBSD)-based microscopy are applied to the characterization of incompatibility structures near the grain boundaries (GBs) in polycrystals. The principal interest described here is recovery of geometrically-necessary dislocation (density) tensors, of the 2- and 3-D type, described by Nye and Kröner. These developments are presented in the context of the continuum dislocation theory. High resolution data obtained near a single grain boundary in well-annealed, low content steel suggests that it may be possible to measure the intrinsic elastic properties of GBs.