The far-field high-energy diffraction microscopy technique is presented in the context of high-energy synchrotron x-ray diffraction. For each grain in an illuminated polycrystalline volume, the volume-averaged lattice orientations, lattice strain tensors, and centre-of-mass (COM) coordinates may be determined to a high degree of precision: better than 0.05°, 1 × 10−4, and 0.1 pixel, respectively. Because the full lattice strain tensors are available, corresponding mean stress tensors may be calculated unambiguously using single-crystal elastic moduli. A novel formulation for orientation indexing and cell refinement is introduced and demonstrated using two examples: first, sequential indexing and lattice refinement of a single-crystal ruby standard with known COM coordinates; and second, indexing and refinement of simulated diffraction data from an aggregate of 819 individual grains using several sample rotation ranges and including the influence of experimental uncertainties. The speed of acquisition and penetration depth achievable with high-energy (that is, >50 keV) x-rays make this technique ideal for studies of strain/stress evolution in situ, as well as for residual stress analysis.

This article presents a quantitative strain analysis (QSA) study aimed at determining the distribution of stress states within a loaded Ti-6Al-4V specimen. Synchrotron X-rays were used to test a sample that was loaded to a uniaxial stress of 540 MPa in situ in the A2 experimental station at the Cornell High Energy Synchrotron Source (CHESS). Lattice-strain pole figures (SPFs) were measured and used to construct a lattice strain distribution function (LSDF) over the fundamental region of orientation space for each phase. A high-fidelity geometric model of the experiment was used to drastically improve the signal-to-noise ratio in the data. The threedimensional stress states at every possible orientation of each a (hcp) and b (bcc) crystal within the aggregate were calculated using the LSDF and the single-crystal moduli. The stress components varied by 300 to 500 MPa over the orientation space; it was also found that, in general, the crystal stress states were not uniaxial. The maximum shear stress resolved on the basal and prismatic slip systems of all orientations within the a phase,ŝ rss ; was calculated to illustrate the utility of this approach for better identifying ''hard'' and ''soft'' orientations within the loaded aggregate. Orientations with low values ofŝ rss ; which are potential microcrack initiation sites during dwell fatigue conditions, are considered hard and were subsequently illustrated on an electron backscatter diffraction (EBSD) map.

No abstract

No abstract

No abstract

A salient manifestation of anisotropy in the mechanical response of polycrystalline materials is the inhomogeneous partitioning of elastic strains over the aggregate. For bulk samples, the distributions of these intergranular strains are expected to have a strong functional dependence on grain orientations. It is then useful to formulate a mean lattice strain distribution function (LSDF) over the orientation space, which serves to characterize the micromechanical state of the aggregate. Orientation-dependent intergranular stresses may be recovered from the LSDF via a constitutive assumption, such as anisotropic linear elasticity. While the LSDF may be determined directly from simulation data, its experimental determination relies on solving an inverse problem that is similar in character to the fundamental problem of texture analysis. In this paper, a versatile and robust direct method for determining an LSDF from strain pole figures is presented. The effectiveness of this method is demonstrated using synthetic strain pole figures from a model LSDF obtained from the simulated uniaxial deformation of a 1000-crystal aggregate.research papers

Object Hospital readmission after discharge is a commonly used quality measure. In a previous study, the authors had documented the rate of readmission and reoperation after pediatric CSF shunt surgery. This study documents the rate of readmission and reoperation after pediatric neurosurgical procedures excluding those related to CSF shunts. Methods Between May 1, 2009, and April 30, 2013, 3098 non-shunt surgeries during 2924 index admissions were performed at a single institution. Demographic, socioeconomic, and clinical characteristics were prospectively collected in the administrative, business, and clinical databases. Clinical events within the 30 days following discharge were reviewed and analyzed. The following events of interest were analyzed for risk factor associations using multivariate logistic regression: return to the emergency department (ED), all-cause readmission, readmission to the neurosurgical service, and reoperation. Results The number of all-cause readmissions within 30 days of discharge was 304 (10.4%, 304/2924). Admission sources consisted of the ED (n = 173), hospital transfers (n = 47), and others (n = 84). One hundred eighty of the 304 readmissions were associated with an operation, but only 153 were performed by the neurosurgical service (reoperation rate = 5.2%). These procedures included wound revisions (n = 30) and first-time shunt insertions (n = 35). The remaining 124 readmissions were nonsurgical, and only 54 were admitted to the neurosurgical service for issues related to the index non-shunt surgery. Thus, the rate of related readmission was 7.1% ([153 + 54]/2924). A longer length of stay and admission to the neonatal intensive care unit during the index admission were associated with an increased likelihood of return to the ED and readmission. Certain procedures, such as baclofen pump insertion and intracranial pressure monitor placement, were also found to be associated with adverse clinical events in the 30-day period. Lastly, patients were more likely to a undergo reoperation if the index procedure had started after 3 p.m. Conclusions The all-cause readmission rate within 30 days of discharge after a pediatric neurosurgical procedure was 10.4%, and the rate of related readmission was 7.1%. Whether these readmissions are preventable and to what extent they are preventable requires further study.

The basic equations are derived for the calculation of the angle settings of a five-circle diffractometer used for surface X-ray diffraction. This is done for a specified angle of incidence. An additional constraint that may be imposed is the horizontal alignment of the diffraction rods to match the divergence of the synchrotron X-ray source or the horizontal setting of the physical surface normal. Alignment procedures and the derivation of the orientation matrix are discussed.