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

Making the cut for the contour method

The contour method is becoming an increasingly popular measurement technique for mapping residual stress in engineering components. The accuracy of the technique is critically dependent on the quality of the cut performed. This paper presents results from blind cutting trials on austenitic stainless steel using electro-discharge machines made by three manufacturers. The suitability of the machines is assessed based on the surface finish achieved, risk of wire breakages and the nature of cutting artefacts introduced

An Investigation into Creep Cavity Development in 316H Stainless Steel

Creep-induced cavitation is an important failure mechanism in steel components operating at high temperature. Robust techniques are required to observe and quantify creep cavitation. In this paper, the use of two complementary analysis techniques: small-angle neutron scattering (SANS), and quantitative metallography, using scanning electron microscopy (SEM), is reported. The development of creep cavities that is accumulated under uniaxial load has been studied as a function of creep strain and life fraction, by carrying out interrupted tests on two sets of creep test specimens that are prepared from a Type-316H austenitic stainless steel reactor component. In order to examine the effects of pre-strain on creep damage formation, one set of specimens was subjected to a plastic pre-strain of 8%, and the other set had no pre-strain. Each set of specimens was subjected to different loading and temperature conditions, representative of those of current and future power plant operation. Cavities of up to 300 nm in size are quantified by using SANS, and their size distribution, as a function of determined creep strain. Cavitation increases significantly as creep strain increases throughout creep life. These results are confirmed by quantitative metallography analysis

Determination and mitigation of the uncertainty of neutron diffraction measurements of residual strain in large-grained polycrystalline material

For large-grained samples it is advantageous to perform pairs of neutron diffraction measurements at the same spatial location but rotated 180° around the geometric centre of the gauge volume as a means of minimizing the scatter coming from the random positioning of grains within the gauge volume

Advancing the Contour Method for the Measurement of Residual Stress in Unbalanced Asymmetric CFRP Laminate

Residual stresses are inevitably generated in composites during the curing phase of manufacture, where cooling from high cure temperature to room temperature is accompanied by constrained shrinkage. The high cure temperature represents a stress free state owing to the viscous nature of the matrix. Due to their inherent anisotropic and heterogeneous nature, both fibre and matrix constituents contract and expand differently leading to constraint induced differences in strains between fibre and matrix at the micro-scale and between plies having different fibre orientations at the macro-scale. The resulting residual stresses are directly associated with dimensional stability such as warpage, shape distortion and the structural integrity of composite structures (e.g matrix cracking, reduced fibre-matrix bondage and delamination). Therefore, knowledge and accurate characterisation of residual stress is imperative for optimising the design and structural integrity of polymer composites. Up until now, numerous analytical, computational and experimental methods have been developed to characterise residual stresses in polymer composites. However for analytical models, knowledge of anisotropic viscoelastic behaviour of materials involves extensive characterisation in order to capture complex thermo-chemo-rheological properties [1]. Numerical models get computationally expensive when internal state variables such as cure and temperature dependent viscoelasticity, mechanical properties and chemical shrinkage of resin are considered to simulate the entire complicated curing cycle. Furthermore, composites may also undergo temperature and moisture changes during and after the manufacturing process inducing hygrothermal residual stress; but these parameters cannot be readily predicted in numerical or analytical models. In addition, the reliability of the numerical and analytical solutions are highly dependent on the quality of input data. Experimental measurements offer an alternative solution for developing a quantitative understanding of the sign, magnitude and distribution of residual stresses. But there is no consensus regarding what experimental method to use for measuring bulk (through-thickness) residual stress in polymer composites. The present PhD research will investigate the viability of using the Contour Method for measuring residual stress in polymer composites. The contour method is a powerful measurement technique that provides two-dimensional (2D) map of residual stress in engineering components [2]. It involves sectioning the component in two halves along the plane of interest, measuring the deformation of the created cut surfaces and use the measured deformations to back calculate residual stresses by an elastic stress analysis. Traditionally, the contour method has been solely applied to metallic structures. The challenge to address in this research is to expand its applications to non-metallic materials such as composites

Aerobic capacity, activity levels and daily energy expenditure in male and female adolescents of the kenyan nandi sub-group

The relative importance of genetic and socio-cultural influences contributing to the success of east Africans in endurance athletics remains unknown in part because the pre-training phenotype of this population remains incompletely assessed. Here cardiopulmonary fitness, physical activity levels, distance travelled to school and daily energy expenditure in 15 habitually active male (13.9±1.6 years) and 15 habitually active female (13.9±1.2) adolescents from a rural Nandi primary school are assessed. Aerobic capacity ([Formula: see text]) was evaluated during two maximal discontinuous incremental exercise tests; physical activity using accelerometry combined with a global positioning system; and energy expenditure using the doubly labelled water method. The [Formula: see text] of the male and female adolescents were 73.9±5.7 ml(.) kg(-1.) min(-1) and 61.5±6.3 ml(.) kg(-1.) min(-1), respectively. Total time spent in sedentary, light, moderate and vigorous physical activities per day was 406±63 min (50% of total monitored time), 244±56 min (30%), 75±18 min (9%) and 82±30 min (10%). Average total daily distance travelled to and from school was 7.5±3.0 km (0.8-13.4 km). Mean daily energy expenditure, activity-induced energy expenditure and physical activity level was 12.2±3.4 MJ(.) day(-1), 5.4±3.0 MJ(.) day(-1) and 2.2±0.6. 70.6% of the variation in [Formula: see text] was explained by sex (partial R(2) = 54.7%) and body mass index (partial R(2) = 15.9%). Energy expenditure and physical activity variables did not predict variation in [Formula: see text] once sex had been accounted for. The highly active and energy-demanding lifestyle of rural Kenyan adolescents may account for their exceptional aerobic fitness and collectively prime them for later training and athletic success

phot1 inhibition of ABCB19 primes lateral auxin fluxes in the shoot apex required for phototropism

It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperm

Rats selectively bred for low aerobic capacity have reduced hepatic mitochondrial oxidative capacity and susceptibility to hepatic steatosis and injury

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65411/1/jphysiol.2009.169060.pd

Positional identification of variants of Adamts16 linked to inherited hypertension

A previously reported blood pressure (BP) quantitative trait locus on rat Chromosome 1 was isolated in a short congenic segment spanning 804.6 kb. The 804.6 kb region contained only two genes, LOC306664 and LOC306665. LOC306664 is predicted to translate into A Disintegrin-like and Metalloproteinase with Thrombospondin Motifs-16 (Adamts16). LOC306665 is a novel gene. All predicted exons of both LOC306664 and LOC306665 were sequenced. Non-synonymous variants were identified in only one of these genes, LOC306664. These variants were naturally existing polymorphisms among inbred, outbred and wild rats. The full-length rat transcript of Adamts16 was detected in multiple tissues. Similar to ADAMTS16 in humans, expression of Adamts16 was prominent in the kidney. Renal transcriptome analysis suggested that a network of genes related to BP was differential between congenic and S rats. These genes were also differentially expressed between kidney cell lines with or without knock-down of Adamts16. Adamts16 is conserved between rats and humans. It is a candidate gene within the homologous region on human Chromosome 5, which is linked to systolic and diastolic BP in the Quebec Family Study. Multiple variants, including an Ala to Pro variant in codon 90 (rs2086310) of human ADAMTS16, were associated with human resting systolic BP (SBP). Replication study in GenNet confirmed the association of two variants of ADAMTS16 with SBP, including rs2086310. Overall, our report represents a high resolution positional cloning and translational study for Adamts16 as a candidate gene controlling B