Characterisation of Plastic and Creep Strains From Lattice Orientation Measurements

Electron backscatter diffraction (EBSD) is a powerful technique for measuring crystallographic orientation in polycrystalline materials. This thesis explores the potential of EBSD for characterising localised inelastic strain from lattice orientation measurements. A systematic study under uniaxial isothermal loading conditions was performed to examine the influence of microstructure and deformation conditions on strain-induced lattice orientation changes (misorientation). The study was conducted on both service-aged and un-aged Type 316H stainless steels through a series of monotonic tests in tension, compression and in constant load creep. The study demonstrates that the development of misorientation depends on many factors which need consideration before EBSD can be applied for strain assessment. It is shown that the measured evolution of misorientations is a function of microstructure and grain size. A misorientation-based strain assessment method is proposed which is relatively insensitive to microstructure and grain size. In service-aged steel, the measured evolution of misorientations is shown to be independent of the deformation temperature (between 24°C and 550°C) and deformation mode (tension vs. compression) for strain rates down to about 10-6s-1. Empirical correlations between the accumulated plastic strain and different misorientation metrics are developed for true strains up to 0.23. However, at 550°C the evolution of measured misorientations is shown to be strain rate dependent below 10-6s-1. The potential of EBSD to distinguish plastic strain from creep strain is demonstrated. Misorientation development is shown to occur at a faster rate with increasing strain in plastic than in creep deformation. Similarly, the proportion of twin boundaries in service-aged steel is shown to reduce with increasing strain at a faster rate in creep than in plastic deformation. Two novel methods for creep strain estimation are proposed which utilise the disparities in the misorientation development and twin boundary reduction under the two different deformation regimes. A good correspondence is established between the strain estimates from the proposed methods and those derived from hardness measurements and digital image correlation. The methods are shown to be applicable to real power plant components through successful mapping of plastic and creep strain distributions in weldments after different periods in service

Application of Advanced Techniques for Metals Identification and Characterisation

The appraisal of metallic materials requires application of advanced characterisation techniques. In this paper, the use has been made of Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy techniques to characterise morphological, structural and chemical composition of 316-stainless steel and unknown brass sample. The determined lattice parameter of unknown brass sample was 3.6812A and consisted of 63% Cu and 37% Zn by weight. The XRD analysis indicated a faced-centred-cubic crystal structure and the sample concluded to be an alpha brass. The measured dislocation density in 316-stainless steel increased with increasing plastic strain and the dislocation structures varied from relatively uniform distribution at low strains to cell-like structures at high strains. The spread of X-ray diffraction peak related linearly with the dislocation content of 316-stainless steel. Keywords: Characterisation, Crystal Structure Dislocation Structure, Diffraction Peak, Stainless Steel

Digital Image Analysis for Chemical Phase Identification and Particle Size Determination

A methodology employing digital image analysis for chemical phase identification and particle size determination is presented. The phase of unknown iron-oxide based particulate sample was identified by analyzing its transmission electron microscope diffraction patterns and diffraction contrast images using ImageJ pattern recognition software. A standard diffraction pattern with known crystallographic spacing and a standard diffraction contrast image with known fringe spacing were used to calibrate the sample’s diffraction patterns and diffraction contrast images, respectively. The phase of unknown sample was identified as iron (III) oxide with an average particle size of 8.9 nm computed from digitized binary images through thresholding process. The particles size distribution closely resembled Poisson cumulative distribution function with 61% of the particles having diameters between 1-10 nm. Keywords: Phase identification, ImageJ, Diffraction pattern, Digital image, Particle size determination

Industrial Waste-water Characterisation and Image-Based Assessment of its Color Load

The characteristics of waste-water discharged from a reactive dyeing machine are examined and a simple method of quantifying its color load proposed. The discharged waste-water is typified by a pH value of 10.2, a turbidity value of 230 NTU, a color load of 290 mg/L and total suspended solids of about 970 mg/L. Application of digital image correlation to assess the color load in waste-water is explored through the use of Image Correlator plugin installed in the ImageJ software. The pixel scatter plot from the image correlation exhibit a characteristic spread with increasing concentration of dye solution thus demonstrating its applicability for waste-water color load assessment. The correlation coefficient derived from the image measurement, correlates almost linearly with the dye concentration in water and can thus be used for assessing the efficacy of color removal from the waste-water. With proper calibration, the resultant correlation curve can be applied in the quantification of the colour load in waste-water. Keywords: Digital Image Correlation, Waste-water, ImageJ, Color Load, Image Correlator, pixel scatter plo

Atomic Analogy of Poverty

An analogy between the model of an atom and poverty of an individual in a poverty field is presented to construe that poverty levels are quantized in similar notions as in the models of an atom. This analogy provides a rational explanation of the observed phenomena in society in part as well as it can be used to predict future observations. Concepts proposed in this paper may lead to a framework to quantify poverty, absolute or relative, and suggest enhanced collaboration between moral science and natural science to study poverty dynamic

Electron backscatter diffraction (EBSD) measurement of accumulated strain

Reliable life prediction depends on a sound knowledge of the accumulated strain in components subject to creep. Electron backscatter diffraction (EBSD) is now well-established for estimating/measuring plastic strain and there have been a number of different EBSD metrics proposed for this. Microstructure has a strong effect on the calibration of most of these, limiting their use in critical areas such as around welds where microstructure is inhomogeneous. During the service life of materials such as 316 steel there is extensive precipitation but most published applications of EBSD are on precipitate-free materials. A systematic study has been made on the applicability of different EBSD metrics to both solution-annealed and service-aged 316H stainless steel subject to a range of plastic and creep strains between 0 and 35% to determine the conditions for maximum strain sensitivity of each. A simple new method of assessing cumulative strain, ‘deformed grain fraction’ (DGF) is presented and DGF has been compared with more conventional EBSD strain metrics. In 316H steel with a range of microstructures the effects of plastic and creep strains are additive for all metrics. DGF is relatively insensitive to changes in microstructure and its use is demonstrated in measuring total plastic strain in ex-service welded components

Analysis of Effect of Heat-Setting Temperatures on Crimp Parameters in Polypropylene Single-Fibres via Favimat-Robot

The study on the effects of heat-setting temperature on crimp parameters of Polypropylene (PP) single-fibres was initiated by a non-woven manufacturing industry. The study is therefore important as it is addresses the real need raised by the industry to have a better comprehension of effects of heat-setting temperatures  in order to optimize and develop a superior end-product. The exploratory research was conducted on non-conventional single-fibre tester Favimat-Robot (Technico), Germany at the Textile Physical testing Laboratory of Vakgroep Textielkunde Universiteit Gent (Ghent University), Belgium. Testing of PP single-fibres was limited to the following crimp parameters: Crimp Force, Crimp Length, Crimp Extension, Crimp Amplitude and Number of Crimps per cm. The collected data was statistically analyzed by the Analysis of Variance test ANOVA, using STATGRAPHICS Centurion XVI.II software, while chart was generated using Microsoft excel program. Major findings of this study reviled that all crimp parameters show a high variation. The study also revealed that the Number of Crimps per cm is increasing with increased temperature, while Crimp Length and Crimp Amplitude are decreasing with increased temperature. From the results it can be also concluded that neither of heat-setting temperatures had a clear effect on Crimp Force and on Crimp Extension. Two crimp parameters-Crimp Extension and Number of Crimps per cm-showed statistically significant difference. For more definite conclusions, the study recommends, in further research-experiments, to break the temperature-range into smaller segments, and to increase subject-temperature from two to five, by incorporating 125,130 and 135o C. Keywords: single fibre, Polypropylene, crimp, Favimat, testing

Characterization of Clay Bricks Surface Deformation Behavior through Digital Image Analysis

Handmade compacted clay bricks are an important integral building material especially for the low cost durable and affordable housing segment. Characterisation of physical, mechanical and deformation behavior of handmade clay bricks is essential to ensure material integrity and durability. In this paper, physical and mechanical properties are determined and the Particle Image Velocimetry (PIV) method is used to assess deformation behavior of bricks under uniaxial compressive loading. The bricks exhibit brittle failure with high strain localized along the cracks. The initiation and development of cracks on loading redistribute compressive strain within the brick with some regions experiencing minimum strain at failure. The relatively large displacements between cracks account for relatively large failure strain for the brittle bricks. A good concurrence is established between the strain assessment based on uniaxial compressive test and on image correlation using the PIV method. The average vector magnitude derived from PIV measurements, correlate well with the engineering strain and can thus be used for strain estimation in handmade clay bricks. Keywords: clay brick, Digital Image Correlation, deformation, particle image velocimetry, characterisation

Fragmented health systems in COVID-19: rectifying the misalignment between global health security and universal health coverage

The COVID-19 pandemic has placed enormous strain on countries around the world, exposing long-standing gaps in public health and exacerbating chronic inequities. Although research and analyses have attempted to draw important lessons on how to strengthen pandemic preparedness and response, few have examined the effect that fragmented governance for health has had on effectively mitigating the crisis. By assessing the ability of health systems to manage COVID-19 from the perspective of two key approaches to global health policy—global health security and universal health coverage—important lessons can be drawn for how to align varied priorities and objectives in strengthening health systems. This Health Policy paper compares three types of health systems (ie, with stronger investments in global health security, stronger investments in universal health coverage, and integrated investments in global health security and universal health coverage) in their response to the ongoing COVID-19 pandemic and synthesises four essential recommendations (ie, integration, financing, resilience, and equity) to reimagine governance, policies, and investments for better health towards a more sustainable future

Fabrication, Characterization and Deformation Behavior of a New Acrylate Copolymer-based Nonwoven Structure

A method of fabricating nonwoven structure from dry-laid cotton fibers and atomized acrylate copolymer is presented. The method based on a consolidation pressure of about 2kPa and room temperature curing, is used to produce structures with fiber mass to binder volume ratio (FBR) of 0.7, 0.5, 1, 1.5, 2 and 3. Structurally stable structures are produced and characterized in terms of their bursting strength, areal density, water absorption, and monotonic deformation behavior. At constant FBR, the bursting strength and areal density of the structures increases with the fiber mass. The structures’ water absorption capacity reduces with the increase in the volume of binder applied. At FBR of 1 and area density of 295 grams per square meter, the structure’s load-strain curve is characterized by a linear and non-linear behavior corresponding to elastic and inelastic strain, respectively. At peak loads, the structure’s deformation is relatively uniform but becomes localized as the failure point is approached. A good correspondence is established between the strain assessment based on uniaxial tensile test and on image correlation using Particle Image Velocimetry (PIV) method. The average vector magnitude derived from PIV measurement, correlate well with the engineering strain and can thus be used for strain estimation. Keywords: Nonwoven, Dry-laid, Deformation, Particle Image Velocimetry, acrylate copolyme