Investigation of deformation mechanisms involved in the plasticity of AZ31 Mg alloy: in situ neutron diffraction and EPSC modelling

In situ neutron diffraction and Elasto-Plastic Self-Consistent (EPSC) polycrystal modelling have been employed to investigate which deformation mechanisms are involved in the plasticity of extruded AZ31 Mg alloy during the tensile loading along the extrusion direction. On the basis of this study we were able to determine the relative activity of the slip and twinning deformation modes. By tuning the parameters of the EPSC model (i.e. the critical resolved shear strengths and hardening parameters), excellent agreement with the experimental data has been achieved. It is shown that the strain in the crystallographic ⟨c ⟩direction is accommodated mainly by ⟨c + a ⟩ dislocation slip on second-order pyramidal planes. The results further indicate that either slip of ⟨a ⟩dislocations occurs on {10.1} pyramidal planes or cross-slip from basal and prismatic planes takes place.

Identification and rationalization of secondary twin variants in a magnesium alloy

The present work combines electron backscatter diffraction, transmission electron microscopy and Schmid analysis to investigate secondary twinning in the magnesium alloy Mg-3AI-1Zn. Inspection of the misorientations between the parent matrix and {1011} - {1012} doubly twinned volumes reveals that there are four possible variants. One of these variants characterized by 38°< 1210 > misorientation with the matrix is favoured much more than the others. This variant involves activation of the secondary twinning systems that are quite inconsistent with the Schmid-type behaviour. For the secondary twin to grow significantly it must take on a shape enforced by the primary twin, however, this is not optimal for strain compatibility. It is argued that the 38° < 1210 > variant occurs most frequently because it provides the closest match between the primary and secondaty twinning planes, thus minimizing the compatibility strain. This conjecture is confirmed by the simulations of twin activity m ellipsoidal grains performed using the visco-plastic self-consistent crystal plasticity model.

Transport properties in ionic liquids and ionic liquid mixtures : the challenges of NMR pulsed field gradient diffusion measurements

Pulsed field gradient NMR is a powerful method for the measurement of diffusion coefficients in liquids and solids and has begun to attract much attention in the ionic liquids field. However, aspects of the methodology as traditionally applied to solutions may not be uniformly applicable in these more viscous and chemically complex systems. In this paper we present data which shows that the Pulsed Gradient Spin Echo (PGSE) method in particular suffers from intrinsic internal gradients and can produce apparent diffusion coefficients which vary by as much as 20% for different ¹H nuclei within a given moleculean obvious anomaly. In contrast, we show that the Pulsed Gradient Stimulated Echo method does not suffer from this problem to the same extent and produces self-consistent data to a high degree of accuracy (better than 1%). This level of significance has allowed the detection, in this work, of subtle mixing effects in [C₃mpyr][NTf₂] and [C₄mpyr][NTf₂] mixtures.

Chemisorbed and physisorbed Structures for 1,10-Phenanthroline and Dipyrido[3,2-a:2',3'-c]phenazine on Au(111)

Scanning tunneling microscopy (STM) images of 1,10-phenanthroline (PHEN) and dipyrido[3,2-a:2‘,3‘-c]phenazine (DPPZ) on Au(111) are recorded using both in situ and ex situ techniques. The images of PHEN depict regimes of physisorption and chemisorption, whereas DPPZ is only physisorbed. All physisorbed structures are not pitted and fluctuate dynamically, involving aligned (4 × 4) surface domains with short-range (ca. 20 molecules) order for PHEN but unaligned chains with medium-range (ca. 100 molecules) order for DPPZ. In contrast, the chemisorbed PHEN monolayers remain stable for days, are associated with surface pitting, and form a (4 × √13)R46° lattice with long-range order. The density of pitted atoms on large gold terraces is shown to match the density of chemisorbed molecules, suggesting that gold adatoms link PHEN to the surface. For PHEN, chemisorbed and physisorbed adsorbate structures are optimized using plane-wave density-functional theory (DFT) calculations for the surface structure. Realistic binding energies are then obtained adding dispersive corrections determined using complete-active-space self-consistent field calculations using second-order perturbation theory (CASPT2) applied to cluster-interaction models. A fine balance between the large adsorbate−adsorbate dispersive forces, adsorbate−surface dispersive forces, gold ligation energy, and surface mining energy is shown to dictate the observed phenomena, leading to high surface mobility and substrate/surface lattice incommensurability. Increasing the magnitude of the dispersive forces through use of DPPZ, rather than PHEN, to disturb this balance produced physisorbed monolayers without pits and/or surface registration but with much longer-range order. Analogies are drawn with similar but poorly understood processes involved in the binding of thiols to Au(111).

Asymmetric rolling of interstitial-free steel using differential roll diameters. Part II : microstructure and annealing effects

The effects of annealing on the microstructure, texture, tensile properties, and R value evolution of an IF steel sheet after room-temperature symmetric and asymmetric rolling were examined. Simulations were carried out to obtain R values from the experimental textures using the viscoplastic self-consistent polycrystal plasticity model. The investigation revealed the variations in the textures due to annealing and symmetric/asymmetric rolling and showed that the R values correlate strongly with the evolution of the texture. An optimum heat treatment for the balance of strength, ductility, and deep drawability was found to be at 873 K (600 _C) for 30 minutes.

A double inclusion homogenization scheme for polycrystals with hierarchal topologies: Application to twinning in Mg alloys

The present work introduces a double inclusion elasto-plastic self-consistent (DI-EPSC) scheme for topologies in which crystals can contain subdomains (i.e. twins, etc.). The approach yields a direct coupling between the mechanical response of grains and their subdomains via a concentration relationship on mean fields derived from both the Eshelby and the Tanaka-Mori properties. The latent effect caused by twinning on the mechanical response is observed on both initially extruded and non-textured Mg alloys. For twinned grains, it is shown that deformation system activities and plastic strain distributions within twins drastically depend on the interaction with parent domains. Moreover, a quantitative study on the coupled influence of secondary slip activities on the material response is proposed. © 2014 Published by Elsevier Ltd.

Evaluating the effect of yttrium as a solute strengthener in magnesium using in situ neutron diffraction

In situ neutron diffraction of two binary Mg alloys, Mg-0.5 wt.% Y and Mg-2.2 wt.% Y have been carried out in compression. The experimental data has been modelled using the elastoplastic self-consistent methodology in order to determine the critical resolved shear stress for basal slip, second-order 〈c + 〉 pyramidal slip and {101̄2} twinning. It was found that the addition of Y strengthens all three of the deformation modes examined. However, increasing the Y concentration from 0.5% to 2.2% showed no additional hardening in the basal slip and {101̄2} twinning modes, indicating that solute strengthening of these deformation modes is already exhausted by a concentration of 0.5% Y. Second-order pyramidal slip showed additional solute hardening at the higher concentration. © 2014 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.

The role of back stress caused by precipitates on {101-2} twinning in a Mg-6Zn alloy

In the present study, the effect of precipitate characteristics on {101-2} extension twinning have been studied in a Z6 magnesium alloy. A strongly textured Z6 alloy plate was mechanically tested in twinning dominated orientation in solution treated and aged states. Optical microscopy, transmission electron microscopy (TEM) and visco-plastic self consistent (VPSC) modelling are used to examine the effect of precipitate characteristics on twinning. The yield stress was observed to increase by ~80. MPa during ageing and it was estimated that CRSS for twinning increased by ~29. MPa based on VPSC simulations. The increment of twin system strengthening can be attributed to back stress generated by elastically deforming particles.

Modeling the effect of asymmetric rolling on mechanical properties of Al-Mg alloys

The mechanical behavior under uniaxial tension of Al-Mg alloy 5182 pre-deformed in conventional rolling (CR), asymmetric rolling-continuous (ASRC), and asymmetric rolling-reversed (ASRR) was investigated and modeled with a rate dependent crystal plasticity finite element method and VPSC (Visco-Plastic Self Consistent) model. M-K theory combined with Yld2000 model by Barlat et al. (Int. J. Plasticity 2003, 19, 1297) was used to predict the strain-based and stress-based formability for AA 5182 material. It was concluded that the new ASRR process has very compatible formability with improved strength compared to CR process. These merits can be directly applied for clam-shell resistant design in rigid-packaging industry.

Texture evolution and grain refinement of ultrafine-grained copper during micro-extrusion

Samples of oxygen-free high conductivity (OFHC) coarse-grained (CG) and ultrafine-grained (UFG) copper were micro-extruded to an equivalent strain of 2.8 in one pass at room temperature. Samples of the OFHC copper were annealed at 650C for 2 h to produce CG copper. Some samples were subsequently processed by equal channel angular pressing of eight passes, route Bc, at room temperature to produce the UFG material. Crystallographic texture and misorientation distributions were obtained locally from EBSD mappings at different radial positions after micro-extrusion. To model the strain path during micro-extrusion, the analytic flow line model of Altan etal. [J Mater. Process. Tech. 33 (1992) p.263] was used and also validated by finite element calculations. Modelling was carried out using the viscoplastic self-consistent (VPSC) model and a recently developed grain refinement model. The results showed large texture variations along the cross-section of the extruded sample for both UFG and CG copper. These cyclic drawing textures in UFG copper were simulated in good agreement with experiments using the presented modelling framework.

Extent of heart failure self-care as an endpoint to patient education: a literature review

Background: In western countries the number of chronic heart failure (CHF) management programs has escalated in recent times. One key component of them is to teach self-care behaviours that enable affected individuals to monitor themselves and engage in lifestyles that improve their health status.
Aim: The aim of this article is to describe CHF self-care management and to review the literature which examines the effectiveness of patient education on patients’ performance of self-care behaviours.
Design/method: bibliographical databases were searched for papers published in English between 1982 to 2006. The search used the key words: heart failure, education, self-care and measures. Only randomized controlled trials (RCTs) were selected.
Results: Ten randomized controlled trials were selected that used education as an intervention and, in total, 1064 patients with CHF participated in these studies. The studies were heterogenous as to the sample population, the health outcomes measured, the education interventions, the expertise of the educator, and the length of time that was spent on teaching patients. No consistent patterns of implementation and specific evaluation of its impact were found, although three respective groups of investigators reported signifi cant differences in recurrent hospitalisation rates and mortality rates which were relative to usual care.
Conclusions: Teaching patients appropriate CHF self-care behaviours can significantly improve their health outcomes. Improvements in self-care were demonstrated in seven studies but only three had used validated instruments to measure such changes. This suggests that no firm conclusions can be drawn about changes in self-care practices.

Interrelationship between anxiety, lifestyle self-reports and fitness in a sample of Hong Kong University students

Although anxiety in university students has been well documented, the influence of lifestyle and fitness status in relation to anxiety has not been investigated from a cultural perspective previously. To make recommendations regarding the avoidance or management of anxiety in this anxiety-prone cohort that are rationally based, this preliminary investigation examined the interrelationship between anxiety, lifestyle self-reports and aerobic fitness in Hong Kong Chinese University students. The State Trait Anxiety Inventory (Form Y-2) and a lifestyle questionnaire were completed by 213 students. Female students were more anxious than male students. Subjects with high anxiety reported more deleterious lifestyle behaviours including higher salt consumption and lower levels of exercise; in addition to more frequent symptoms of anxiety such as headaches and daytime somnolence. The extremes of this sample were stratified into a low anxiety group ( n =17) and a high anxiety group ( n =14) to compare their fitness status. Although both groups had below normal aerobic capacity, the higher systolic blood pressure observed for the high anxiety group is consistent with signs of anxiety, or greater deconditioning in this group or both. The results of this study have highlighted anxiety as a concern in Hong Kong University students and identified some lifestyle and fitness correlates. Understanding lifestyle and pathophysiological correlates of anxiety in Hong Kong University students that may have a cultural basis, is a crucial step toward averting or managing anxiety when these students are studying either in Hong Kong or abroad.

Volunteering and well-being : do self-esteem, optimism, and perceived control mediate the relationship?

Volunteers play a vital role in modern societies by boosting the labor force within both the public and private sectors. While the factors that may lead people to volunteer have been investigated in a number of studies, the means by which volunteering contributes to the well-being of such volunteers is poorly understood. It has been suggested through studies that focus on the absence of depression in volunteers that self-esteem and sense of control may be major determinants of the increased well-being reported by volunteers. This is consistent with the homeostatic model of subjective well-being, which proposes that self-esteem, optimism, and perceived control act as buffers that mediate the relationship between environmental experience and subjective well-being (SWB). Using personal well-being as a more positive measure of well-being than absence of depression, this study further explored the possible mediating role of self-esteem, optimism, and perceived control in the relationship between volunteer status and well-being. Participants (N = 1,219) completed a 97-item survey as part of the Australian Unity Wellbeing project. Variables measured included personal well-being, self-esteem, optimism, and a number of personality and psychological adjustment factors. Analyses revealed that perceived control and optimism, but not self-esteem, mediated the relationship between volunteer status and personal well-being.

The self concepts and possible selves of problem gamblers : a qualitative exploration

The study investigated the self-concepts and possible selves of pathological gamblers. Six female egm users were recruited from a Victorian problem gambling counselling service. Three participants were currently gambling and three were not gambling. They were interviewed in-depth and using thematic analysis four dominant themes were identified. (1) Self-concepts tended to be consistent across all participants, (2) having a past self as being the dominant characteristics of possible selves coincided with greater possible selves clarity, (3) non-gambler’s had more elaborate and specific plans for how to create change than did gambler’s, and (4) non-gambler’s had more plans to become possible selves which address goals of intrinsic meaning, rather then having a general goal to ‘not gamble’. The findings are discussed in terms of implications for the cognitive theory of possible selves and suggestions for further research to investigate the utility of the constructs as a basis for a treatment modality.

When the whole 'bloke' thing starts to crumble : men's access to chronic illness (arthritis) self management programs

This thesis explores the issue of men's access to chronic illness self management programs from a social constructionist perspective. A combination of research methodologies was used; a quantitative analysis to confirm gender differences in levels and patterns of service use; a qualitative analysis to gain an increased understanding of the factors affecting men's access; and a trial to test the application of the research findings. The clients and services of Arthritis Victoria were chosen as the setting for this research. The quantitative analyses were conducted on contingency tables and odds ratios and confirmed that men were under-represented as service users. The analyses also identified gender differences in patterns of service use. The qualitative analysis was based on a series of in-depth, semi-structured interviews. It was undertaken from a grounded theory approach to allow for the development of theoretical explanations grounded in the data. It was found that men's decisions to access chronic illness self management programs were strongly influenced by dominant social constructions of masculinity which constrained help-seeking and health management behaviour. However, the restrictive influence of hegemonic masculinity was progressively undermined by the increasing severity of the chronic condition until a crisis point was reached in terms of the severity of the condition or its impact on lifestyle. This resulted in a reformulation or rejection of hegemonic masculinity. The described conceptual framework was consistent for men from diverse social groupings, although it appeared less prominent in both younger and older men, suggesting that dominant social constructions of masculinity have the greatest influence on health decisions during the middle stage of adulthood when work and family obligations are greatest. The thesis findings informed the development of some guiding principles for reviewing the structure and delivery of chronic illness self management services for men. The guiding principles will have direct application in the planning of Arthritis Victoria programs, and implications for other chronic illness self management programs in Australia, and also in Western countries with a similar health and sociocultural setting to Australia.