Search

Three-dimensional X-ray diffraction (3DXRD) is shown to be feasible at the I12 Joint Engineering, Environmental and Processing (JEEP) beamline of Diamond Light Source. As a demonstration, a microstructually simple low-carbon ferritic steel was studied in a highly textured and annealed state. A processing pipeline suited to this beamline was created, using software already established in the 3DXRD user community, enabling grain centre-of-mass positions, orientations and strain tensor elements to be determined. Orientations, with texture measurements independently validated from electron backscatter diffraction (EBSD) data, possessed a $\sim 0.1^\circ$ uncertainty, comparable with other 3DXRD instruments. The spatial resolution was limited by the far-field detector pixel size; the average of the grain centre of mass position errors was determined as $\pm \sim 80 \mu$m. An average per-grain error of $\sim 1 \times 10^{-3}$ for the elastic strains was also measured; this could be reduced in future experiments by improving sample preparation, data collection and analysis techniques. Application of 3DXRD onto I12 shows great potential, where its implementation is highly desirable due the flexible, open architecture of the beamline. User-owned or designed sample environments can be used, thus 3DXRD could be applied to previously unexplored scientific areas., Comment: 13 pages, 10 figures. Published in Journal of Synchrotron Radiation

The effect of Strain Path Changes (SPCs) on the mechanical properties and crystal-level features of deformation for a single phase, ferritic steel has been investigated. SPCs were applied via a two-step deformation process, which included pre-straining via cold rolling, followed by uniaxial tension. The pre-strain magnitude and direction, as well as the tensile direction, varied between the specimens. The role of texture and micromechanics were examined in-situ, via Synchrotron X-Ray Diffraction (SXRD), and ex-situ, via Electron Backscatter Diffraction (EBSD). Abrupt strain paths (i.e. strain paths where the pre-strain and the subsequent loading directions differ; here they are orthogonal) result in a significant ductility reduction, becoming more prevalent for high pre-strain magnitudes. The macroscopic response, as well as the texture configuration were greatly dependent on the pre-strain direction but were insensitive to the direction of uniaxial tension. Increasing pre-strain magnitudes resulted in a stagnation of lattice strain hardening rates in all macroscopic directions and in a significant increase in the Geometrically Necessary Dislocation (GND) densities. This was vastly increased for specimens rolled perpendicular to the as-received prior rolling direction. No correlation was found between the GND density and the grain orientation, eliminating this as a controlling ductility factor for BCC ferrite. Instead, the initial texture, the texture developed in a subsequent pre-strain influences the density of dislocations accumulated in all grains, and ultimately determines ductility.

Background: Postconditioning with multiple very short coronary occlusions immediately after prolonged ischemia is a new endogenous mechanism for protection of the ischemic heart. We tested whether postconditioning is effective in limiting infarct size in hypercholesterolemic rabbits. Methods: Male rabbits were fed a cholesterol-enriched diet for 6 weeks. Animals were subjected to 30 min of regional ischemia of the heart and 3 h of reperfusion with the following additional interventions: Control group no additional intervention, ischemic preconditioning (IPC) group to two cycles of 5 min ischemia separated by 10 min reperfusion before the index ischemia, 6110 IPostC group to six cycles of 10 s ischemia separated by 10 s reperfusion and 4130 IPostC group to four cycles of 30 s ischemia separated by 30 s reperfusion immediately after the end of the index ischemia. In a second series of experiments the same interventions were applied to animals fed with a normal diet. Infarct size (I) was determined by triphenyltetrazolium chloride staining. Results: The I/R in hypercholesterolemic rabbits was 55.2 +/- 5.9% in Control, 17.9 +/- 4.2% in IPC (P < 0.01 versus Control), 63.4 +/- 4.8% in 6110 IPostC and 55.6 +/- 8.2% in 4130 IPostC (P = NS between them and the Control group). In the normal diet rabbits, the I/R was 48.2 +/- 4.3% in Control, 15.1 +/- 2.1% in IPC, 20.4 +/- 2.9% in 6110 IPostC (P < 0.01 versus Control) and 45.1 +/- 8.9% in 4130 IPostC (P = NS versus Control). Blood cholesterol levels were increased and atheromatic lesions were present in the first series. Conclusion: Postconditioning is ineffective in limiting the infarct size in rabbits with hypercholesterolemia and atherosclerosis while preconditioning continued to be effective under the same conditions. (c) 2005 Elsevier Ireland Ltd. All rights reserved.