A study of residual stresses and their effect on thermo mechanical fatigue in complex geometries

It is known that residual stresses within engine components, such as turbine housings, can combine with service generated stresses and cause unexpected failures during operation, therefore it is important that all the stresses (residual and induced, compressive and tensile) are fully characterised and understood. The use of neutrons as a tool to measure the strains within a material is well established; however, applying this technique to complex engineering components can prove challenging. This research investigates the measurement of residual stresses in complex geometries found within the turbine housing component of a turbocharger using neutron diffraction. The effect of various production methods on residual stress distributions is also explored. Successful strain measurements were taken using the Engin-X instrument at the ISIS spallation source from three turbine housings selected from various stages in the manufacturing process, allowing a study of the effect of heat treatment and machining on stress magnitudes and direction. The turbine housing consists of various sections greater than the maximum 60mm path length of the neutrons, therefore path lengths must be carefully chosen to achieve acceptable neutron count rates. Engin-X benefits from an automated experimental setup to make the selection of this limited path length easier on complex shapes. The turbine housings were mounted on to a positioning table allowing translation in X, Y, Z directions and also rotation in , . Each of the housings were scanned using laser scanners and this in conjunction with the virtual path length measurement software SScanSS allowed automated measurements of acceptable path lengths to be made. On this occasion measurements in one principal direction were measured and the correct measurement methodology established. Continuation of this work was then carried out on SALSA at the ILL reactor source. Measurements were made on turbine housings, one as cast and one heat treated. The internal divider wall of each turbine housing was examined as this is an area where crack initiation can occur. The results showed that, heat treatment can reduce compressive residual stresses. However, compressive stresses are thought to slow the onset of crack initiation and could be beneficial in the material, this will be investigated further in future work. It is hoped that this information will be used to improve production methods and result in improved simulation methodologies to allow accurate predictions of thermal fatigue and fracture locations to be established. The authors wish to thank Dr Jon James (Open University) for his help in setting up the experiment and for the use of the SScanSS software

Three Dimensional Mapping of Texture in Dental Enamel

We have used synchrotron x-ray diffraction to study the crystal orientation in human dental enamel as a function of position within intact tooth sections. Keeping tooth sections intact has allowed us to construct 2D and 3D spatial distribution maps of the magnitude and orientation of texture in dental enamel. We have found that the enamel crystallites are most highly aligned at the expected occlusal points for a maxillary first premolar, and that the texture direction varies spatially in a three dimensional curling arrangement. Our results provide a model for texture in enamel which can aid researchers in developing dental composite materials for fillings and crowns with optimal characteristics for longevity, and will guide clinicians to the best method for drilling into enamel, in order to minimize weakening of remaining tooth structure, during dental restoration procedure

Neutron diffraction studies of magnetostrictive Fe–Ga alloy ribbons

Melt-spun Fe–Ga ribbons were prepared and some ribbons were annealed at 1000 °C for 1 h then slowly cooled to room temperature. X-ray diffraction patterns revealed no evidence of texture and only bcc phase in the as-quenched ribbons. However, high-resolution neutron diffraction patterns gave more information on the structure of these ribbons. Only diffractions from the disordered bcc A2 phase were found in as-quenched ribbons with 15, 17.5, and 19.5 at. % Ga content, without any trace of satellite peaks or splitting peaks from the proposed Ga–Ga pairing superlattice structure. The broadening of the base of the �110� peaks for all samples except the as-quenched 15 at. % Ga ribbon might indicate the existence of some kind of short range ordering. Ribbons developed L12 phase after annealing especially in the Fe 19.5 at. % Ga ribbon where the formation of L12 phase reduced the Ga content in the remaining A2 phase and decreased its lattice parameter dramatically. D03 phase formed in the as-quenched 22.5 at. % Ga ribbon and the following annealing treatment transformed more A2 phase into D03 phase

Secondary ion mass spectrometry and x-ray absorption near-edge structure spectroscopy of isotopically anomalous organic matter from CR1 chondrites GRO 95577

We located interstellar organics from a CR1 chondrite with NanoSIMS and analyzed FIB-extracted sections with XANES. D-rich material appears not associated with a functional group, whereas 15N-rich matter shows some affinity to nitrile functionality

Fossil biomass preserved as graphitic carbon in a late paleoproterozoic banded iron formation metamorphosed at more than 550°C

Metamorphism is thought to destroy microfossils, partly through devolatilization and graphitization of biogenic organic matter. However, the extent to which there is a loss of molecular, elemental and isotope signatures from biomass during high-temperature metamorphism is not clearly established. We report on graphitic structures inside and coating apatite grains from the c. 1850 Ma Michigamme silicate banded iron formation from Michigan, metamorphosed above 550°C. Traces of N, S, O, H, Ca and Fe are preserved in this graphitic carbon and X-ray spectra show traces of aliphatic groups. Graphitic carbon has an expanded lattice around 3.6 Å, forms microscopic concentrically-layered and radiating polygonal flakes and has homogeneous δ13C values around −22‰, identical to bulk analyses. Graphitic carbon inside apatite is associated with nanometre-size ammoniated phyllosilicate. Precursors of these metamorphic minerals and graphitic carbon originated from ferruginous clayrich sediments with biomass. We conclude that graphite coatings and inclusions in apatite grains indicate fluid remobilization during amphibolite-facies metamorphism of precursor biomass. This new evidence fills in observational gaps of metamorphosed biomass into graphite and supports the existence of biosignatures in the highly metamorphosed iron formation from the Eoarchean Akilia Association, which dates from the beginning of the sedimentary rock record

A critical analysis of articles using a Gadamerian based research method

It is over 20 years since Michael Crotty's groundbreaking critique of phenomenological research in nursing. However, rather than entering into the acrimonious discussions that followed, we developed a research method that we believed translated Gadamer's philosophy into the world of empirical research. Fundamental to that work was our differentiation of hermeneutics from phenomenology. The aim of the present paper was to provide a critical analysis of the citations from publication in 2003 until the end of 2017. We identified 402 citations of which 362 were included. One hundred and sixty‐three articles mentioned the article in passing, usually in a list of authors who had discussed hermeneutics. Sixteen citations misrepresented the method mainly claiming that we discussed a method for hermeneutic phenomenology (or phenomenological hermeneutics). Of the 117 citations that partially used the method, the main focus was the four steps of data analysis. Sixty studies used our method in totality although they derive from varying philosophical standpoints. Disappointingly, there has been little critique of our Gadamerian research method. For health disciplines to truly make progress in the academic stage, it is vital that we engage in with critique, some of which will come through open and honest reflexive engagement with our topics

Signatures of Spin Glass Freezing in NiO Nanoparticles

We present a detailed study of the magnetic properties of sol-gel prepared nickel oxide nanoparticles of different sizes. We report various measurements such as frequency, field and temperature dependence of ac susceptibility, temperature and field dependence of dc magnetization and time decay of thermoremanent magnetization. Our results and analysis show that the system behaves as a spin glass.Comment: 8 pages, 9 figure

Crystallographic and magnetic identification of secondary phase in orientated Bi5Fe0.5Co0.5Ti3O15 ceramics

Oxide materials which exhibit both ferroelectricity and ferromagnetism are of great interest for sensors and memory applications. Layered bismuth titanates with an Aurivillius structure, (BiFeO3)nBi4Ti3O12, can possess ferroelectric and ferromagnetic order parameters simultaneously. It has recently been demonstrated that one such example, Bi5Fe0.5Co0.5Ti3O15,where n = 1 with half the Fe3+ sites substituted by Co3+ ions, exhibits both ferroelectric and ferromagnetic properties at room temperature. Here we report the fabrication of highly-oriented polycrystalline ceramics of this material, prepared via molten salt synthesis and uniaxial pressing of high aspect ratio platelets. Electron backscatter images showed that there is a secondary phase within the ceramic matrix which is rich in cobalt and iron, hence this secondary phase could contribute in the main phase ferromagnetic property. The concentration of the secondary phase obtained from secondary electron microscopy is estimated at less than 2.5 %, below the detection limit of XRD. TEM was used to identify the crystallographic structure of the secondary phase, which was shown to be cobalt ferrite, CoFe2O4. It is inferred from the data that the resultant ferromagnetic response identified using VSM measurements was due to the presence of the minor secondary phase. The Remanent magnetization at room temperature was Mr ≈ 76 memu/g which dropped down to almost zero (Mr ≈ 0.8 memu/g) at 460 oC, far lower than the anticipated for CoFe2O4

High-resolution C 1s photoelectron spectra of methane

The C 1s partial photoionization cross section and photoelectron angular distribution of methane (CH4) have been measured with high-energy resolution between threshold and 385 eV photon energy. From the analysis of the vibrational fine structure on the C 1s−1 photoelectron line a vibrational energy of 396±2 meV and an equilibrium bond length of 1.039(±0.001) Å for the CH+4 ion have been determined. The lifetime broadening was found to be 83(±10) meV. The weak feature in the photoabsorption cross section just above threshold does not influence the vibrational fine structure in a way typical for a shape resonance. We therefore suggest that it is due to doubly excited states of the type C (1s)−1(Val)−1(Ryd)1a(Ryd)1b, an assignment which is supported by recent Auger decay studies. Measurements of the shakeup structure revealed six satellite lines, one of which increases strongly in intensity at threshold, thus pointing to the existence of a conjugate shakeup process