International Journal of Fatigue, Volume 54:Evaluating surface deformation and near surface strain hardening resulting from shot peening a tempered martensitic steel and application to low cycle fatigue

The plastic deformation resulting from shot peening treatments applied to the ferritic heat resistant steelFV448 has been investigated. Two important effects have been quantified: surface roughness and strainhardening. 2D and 3D tactile and optical techniques for determining surface roughness amplitude parametershave been investigated; it was found that whilst Ra and Sa were consistent, Sz was generally higherthan Rz due to the increased probability of finding the worst case surface feature. Three different methodsfor evaluating the plastic strain profile have been evaluated with a view to establishing the variation inyield strength near the surface of a shot peened component. Microhardness, X-ray diffraction (XRD) linebroadening and electron backscatter diffraction (EBSD) local misorientation techniques were applied toboth uniaxially deformed calibration samples of known plastic strain and samples shot peened at intensitiesvarying from 4A to 18A to establish the variation in plastic strain and hence the variation in yieldstrength. The results from the three methods were compared; XRD and EBSD profiles were found to bethe most similar with microhardness profiles extending much deeper into the sample. Changes in themeasured plastic strain profile after exposure to low cycle fatigue and the correlation of these changeswith the cyclic stress–strain behaviour of the material are also discussed with a view to assessing theimportance of the dislocation profile in component life assessment procedures. 2013 Elsevier Ltd. All rights reserved

Modelling of Nb influence on phase transformation behaviours from austenite to ferrite in low carbon steels

In this paper, a new model has been developed to predict the phase transformation behaviours from austenite to ferrite in Nb-containing low carbon steels. The new model is based on some previous work and incorporates the effects of Nb on phase transformation behaviours, in order to make it applicable for Nb-containing steels. Dissolved Nb atoms segregated at prior austenite grain boundaries increase the critical energy for ferrite nucleation, and thus the ferrite nucleation rate is decreased. Dissolved Nb atoms also apply a solute drag effect to the moving transformation interface, and the ferrite grain growth rate is also decreased. The overall transformation kinetics is then calculated according to the classic Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. The new model predictions are quite consistent with experimental results for various steels during isothermal transformations or continuous cooling

Microstructural characterization of the heat-affected zones in grade 92 steel welds: Double-pass and multipass welds

The microstructure in the heat affected zone (HAZ) of multipass welds typical of those used in power plant made from 9 wt.% chromium martensitic Grade 92 steel is complex. There is therefore a need for systematic microstructural investigations to define the different regions of the microstructure across the HAZ of Grade 92 steel welds manufactured using traditional arc welding processes in order to understand possible failure mechanisms after long term service. In this study, the microstructure in the HAZ of an as-fabricated two-pass bead-on-plate weld on a parent metal of Grade 92 steel has been systematically investigated and compared to a complex, multi-pass thick section weldment using an extensive range of electron and ion-microscopy based techniques. A dilatometer has been used to apply controlled thermal cycles to simulate the microstructures in distinctly different regions in a multi-pass HAZ using sequential thermal cycles. A wide range of microstructural properties in the simulated materials were characterised and compared with the experimental observations from the weld HAZ. It has been found that the microstructure in the HAZ can be categorized by a combination of sequential thermal cycles experienced by the different zones within the complex weld metal, using the terminology developed for these regions based on a simpler, single pass bead on plate weld, which have been systematically categorised as Complete Transformation (CT), Partial Transformation (PT) and Over Tempered (OT)

Cadmium chloride assisted re-crystallisation of CdTe: The effect on the CdS window layer

© 2015 Materials Research Society. The cadmium chloride annealing treatment is an essential step in the manufacture of efficient thin film CdTe solar cells. In previous work we have shown that the primary effect of the treatment is to remove high densities of stacking faults from the as-deposited material. Use of density functional theory has shown that some of the higher energy stacking faults are hole traps. Removal of these defects dramatically improves cell efficiency. In this study we focus on the effect of the activation treatment on the underlying n-type cadmium sulphide layer. A range of techniques has been used to observe the changes to the microstructure as well as the chemical and crystallographic changes as a function of treatment parameters. Electrical tests that link the device performance with the micro-structural properties of the cells have also been undertaken. Techniques used include High Resolution Transmission Electron Microscopy (HRTEM) for subgrain analysis, EDX for chemical analysis and XPS and SIMS for composition-depth profiling. By studying the effect of increasing the treatment time and temperature, we will show that the cadmium sulphide layer depletes to the point of complete dissolution into the absorber layer. We will also show that chlorine penetrates and decorates the grain boundaries in the cadmium sulphide. In addition we will show that chlorine builds up at the heterojunction and concentrates in voids at the cadmium telluride/cadmium sulphide interface. A combination of these effects damages the electrical performance of the solar cell

Color image registration under illumination changes

The estimation of parametric global motion has had a significant attention during the last two decades, but despite the great efforts invested, there are still open issues. One of the most important ones is related to the ability to recover large deformation between images in the presence of illumination changes while kipping accurate estimates. Illumination changes in color images are another important open issue. In this paper, a Generalized least squared-based motion estimator is used in combination with color image model to allow accurate estimates of global motion between two color images under the presence of large geometric transformation and illumination changes. Experiments using challenging images have been performed showing that the presented technique is feasible and provides accurate estimates of the motion and illumination parameter

The effect of a post-activation annealing treatment on thin film CdTe device performance

The cadmium chloride activation treatment of cadmium telluride solar cells is essential for producing high efficiency devices. The treatment has many effects but the most significant is the complete removal of stacking faults in the cadmium telluride grains and the diffusion of Chlorine along the grain boundaries of the device. Chlorine decorates all cadmium telluride and cadmium sulphide grain boundaries and also builds up along the CdTe/CdS junction. . This paper reveals that by annealing devices to temperatures of 400ºC to 480 ºC for times ranging from 30 to 600 seconds in moderate vacuum results in the re-appearance of stacking faults and the removal of Choline from the grain boundaries. STEM analysis confirms the re-appearance of the stacking faults and SIMS and EDX confirm the removal of chlorine from the grain boundaries. This directly corresponds to a lowering in cell efficiency. The study provides further evidence that CdCl2 diffusion and certain microstructural defects directly affect the performance of cadmium telluride photovoltaic devices

Patient ethnicity and three psychiatric intensive care units compared: the Tompkins Acute Ward Study

Background: Psychiatric Care Units provide care to disturbed patients in a context of higher security and staffing levels. Although such units are numerous, few systematic comparisons have been made, and there are indications that ethnic minority groups may be over-represented. Aim: To compare the rates of adverse incidents and patterns of usage of three Psychiatric Intensive Care Units. Method: The study used a triangulation or multi-method design, bringing together data from official statistics, local audit and interviews conducted with staff. Results: Intensive care patients were more likely to be young, male, and suffering a psychotic disorder, as compared to general acute ward patients. Caribbean patients were twice as likely, and Asian patients half as likely, to receive intensive care (age, gender and diagnosis controlled). There were large differences in service levels, staffing, team functioning and adverse incidents between the three units. Various aspects of physical security were important in preventing absconds. Conclusions: More evaluative research is required in order to define effective service levels, and to explore the nature of the interaction between ethnicity and inpatient care provision during acute illness

Search for Doubly-Charged Higgs Boson Production at HERA

A search for the single production of doubly-charged Higgs bosons H^{\pm \pm} in ep collisions is presented. The signal is searched for via the Higgs decays into a high mass pair of same charge leptons, one of them being an electron. The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment at HERA. No evidence for doubly-charged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only decays into an electron and a muon via a coupling of electromagnetic strength h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3, masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl

Time-integrated luminosity recorded by the BABAR detector at the PEP-II e+e- collider

This article is the Preprint version of the final published artcile which can be accessed at the link below.We describe a measurement of the time-integrated luminosity of the data collected by the BABAR experiment at the PEP-II asymmetric-energy e+e- collider at the ϒ(4S), ϒ(3S), and ϒ(2S) resonances and in a continuum region below each resonance. We measure the time-integrated luminosity by counting e+e-→e+e- and (for the ϒ(4S) only) e+e-→μ+μ- candidate events, allowing additional photons in the final state. We use data-corrected simulation to determine the cross-sections and reconstruction efficiencies for these processes, as well as the major backgrounds. Due to the large cross-sections of e+e-→e+e- and e+e-→μ+μ-, the statistical uncertainties of the measurement are substantially smaller than the systematic uncertainties. The dominant systematic uncertainties are due to observed differences between data and simulation, as well as uncertainties on the cross-sections. For data collected on the ϒ(3S) and ϒ(2S) resonances, an additional uncertainty arises due to ϒ→e+e-X background. For data collected off the ϒ resonances, we estimate an additional uncertainty due to time dependent efficiency variations, which can affect the short off-resonance runs. The relative uncertainties on the luminosities of the on-resonance (off-resonance) samples are 0.43% (0.43%) for the ϒ(4S), 0.58% (0.72%) for the ϒ(3S), and 0.68% (0.88%) for the ϒ(2S).This work is supported by the US Department of Energy and National Science Foundation, the Natural Sciences and Engineering Research Council (Canada), the Commissariat à l’Energie Atomique and Institut National de Physique Nucléaire et de Physiquedes Particules (France), the Bundesministerium für Bildung und Forschung and Deutsche Forschungsgemeinschaft (Germany), the Istituto Nazionale di Fisica Nucleare (Italy), the Foundation for Fundamental Research on Matter (The Netherlands), the Research Council of Norway, the Ministry of Education and Science of the Russian Federation, Ministerio de Ciencia e Innovación (Spain), and the Science and Technology Facilities Council (United Kingdom). Individuals have received support from the Marie-Curie IEF program (European Union) and the A.P. Sloan Foundation (USA)

Low Q^2 Jet Production at HERA and Virtual Photon Structure

The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure