2,686 research outputs found
Generation of internal stress and its effects
Internal stresses may be generated continually in many polycrystalline materials. Their existence is manifested by changes in crystal defect concentration and arrangement, by surface observations, by macroscopic shape changes and particularly by alteration of mechanical properties when external stresses are simultaneously imposed
Internal stresses in steel plate generated by shape memory alloy inserts
Neutron strain scanning was employed to investigate the internal stress fields in steel plate coupons with embedded prestrained superelastic NiTi shape memory alloy inserts. Strain fields in steel were evaluated at T = 21 °C and 130 °C on virgin coupons as well as on mechanically and thermally fatigued coupons. Internal stress fields were evaluated by direct calculation of principal stress components from the experimentally measured lattice strains as well as by employing an inverse finite element modeling approach. It is shown that if the NiTi inserts are embedded into the elastic steel matrix following a carefully designed technological procedure, the internal stress fields vary with temperature in a reproducible and predictable way. It is estimated that this mechanism of internal stress generation can be safely applied in the temperature range from −20 °C to 150 °C and is relatively resistant to thermal and mechanical fatigue. The predictability and fatigue endurance of the mechanism are of essential importance for the development of future smart metal matrix composites or smart structures with embedded shape memory alloy components
Study of the stress intensity factors in the bulk of the material with synchrotron diffraction
Artículo de Proceedings de Congreso Internacional Fatigue2017In this work we present the results of a hybrid experimental and
analytical approach for estimating the stress intensity factor. It uses the
elastic strains within the bulk obtained by synchrotron X-ray diffraction
data. The stress intensity factor is calculated using a multi-point overdeterministic
method where the number of experimental data points is
higher than the number of unknowns describing the elastic field
surrounding the crack-tip. The tool is tested on X-ray strain
measurements collected on a bainitic steel. In contrast to surface
techniques the approach provides insights into the crack tip mechanics
deep within the sample.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. The authors are grateful to the ESRF for ID15 beamtime awarded under MA-1483. Financial
support of Universidad de Malaga through Plan Propio, Junta de Andalucía through Proyectos de
Excelencia grant reference TEP-3244, Campus de Excelencia Internacional del Mar (CEIMAR)
and Ministerio de Economia y Competitividad through grant reference MAT2016-76951-C2-2-P is
also acknowledged. PJW acknowledges an ERC advanced grant
Review of robust measurement of phosphorus in river water: sampling, storage, fractionation and sensitivity
International audienceThis paper reviews current knowledge on sampling, storage and analysis of phosphorus (P) in river waters. Potential sensitivity of rivers with different physical, chemical and biological characteristics (trophic status, turbidity, flow regime, matrix chemistry) is examined in terms of errors associated with sampling, sample preparation, storage, contamination, interference and analytical errors. Key issues identified include: The need to tailor analytical reagents and concentrations to take into account the characteristics of the sample matrix. The effects of matrix interference on the colorimetric analysis. The influence of variable rates of phospho-molybdenum blue colour formation. The differing responses of river waters to physical and chemical conditions of storage. The higher sensitivities of samples with low P concentrations to storage and analytical errors. Given high variability of river water characteristics in space and time, no single standardised methodology for sampling, storage and analysis of P in rivers can be offered. ?Good Practice' guidelines are suggested, which recommend that protocols for sampling, storage and analysis of river water for P is based on thorough site-specific method testing and assessment of P stability on storage. For wider sampling programmes at the regional/national scale where intensive site-specific method and stability testing are not feasible, ?Precautionary Practice' guidelines are suggested. The study highlights key areas requiring further investigation for improving methodological rigour. Keywords: phosphorus, orthophosphate, soluble reactive, particulate, colorimetry, stability, sensitivity, analytical error, storage, sampling, filtration, preservative, fractionation, digestio
Reexamining echidna physiology: The big picture for Tachyglossus aculeatus acanthion
The early divergence of monotremes and therian mammals has resulted in considerable interest in the comparative physiology of the short-beaked echidna (Tachyglossus aculeatus), the most common and widespread living monotreme. However, there are many and varied interpretations of its physiology, reflecting the many and varied studies, limitations and uncertainties of aspects of some previous studies, and potential differences between the various subspecies. Consequently, we thoroughly examine here the standardized physiology of the most widely distributed subspecies of short-beaked echidna (T. aculeatus acanthion) over a wide range of ambient temperatures to definitively assess its physiology in a comparative context. We conclude that the low and variable body temperature of the short-beaked echidna is physiologically “primitive,” but it also reflects adaptation to its myrmecophagous niche. Other aspects of its physiology are more typically mammalian. A low metabolic rate reflects its low body temperature, and ventilatory variables are matched to accommodate a modest gas exchange requirement. Thermal conductance is typical for a mammal of equivalent mass. In contrast to previous studies, we demonstrate that short-beaked echidnas can enhance evaporative water loss above thermoneutrality, like other mammals, with a similar capacity for evaporative heat loss. Cooling of their nasal blood sinus with nasalmucousmay contribute to this enhanced evaporative cooling. Their capacity to evaporatively cool explains how their distribution can include habitats where ambient temperature, even in shelters, exceeds their supposed critical thermal limit
Residual stress of as-deposited and rolled Wire + Arc Additive Manufacturing Ti–6Al–4V components
Wire + arc additive manufacturing components contain significant residual stresses, which manifest in distortion. High-pressure rolling was applied to each layer of a linear Ti–6Al–4V wire + arc additive manufacturing component in between deposition passes. In rolled specimens, out-of-plane distortion was more than halved; a change in the deposits' geometry due to plastic deformation was observed and process repeatability was increased. The Contour method of residual stresses measurements showed that although the specimens still exhibited tensile stresses (up to 500 MPa), their magnitude was reduced by 60%, particularly at the interface between deposit and substrate. The results were validated with neutron diffraction measurements, which were in good agreement away from the baseplate
Settling of cohesive sediment: particle-resolved simulations
We develop a physical and computational model for performing fully coupled,
particle-resolved Direct Numerical Simulations of cohesive sediment, based on
the Immersed Boundary Method. The model distributes the cohesive forces over a
thin shell surrounding each particle, thereby allowing for the spatial and
temporal resolution of the cohesive forces during particle-particle
interactions. The influence of the cohesive forces is captured by a single
dimensionless parameter in the form of a cohesion number, which represents the
ratio of cohesive and gravitational forces acting on a particle. We test and
validate the cohesive force model for binary particle interactions in the
Drafting-Kissing-Tumbling (DKT) configuration. The DKT simulations demonstrate
that cohesive particle pairs settle in a preferred orientation, with particles
of very different sizes preferentially aligning themselves in the vertical
direction, so that the smaller particle is drafted in the wake of the larger
one. To test this mechanism in a system of higher complexity, we perform large
simulations of 1,261 polydisperse settling particles starting from rest. These
simulations reproduce several earlier experimental observations by other
authors, such as the accelerated settling of sand and silt particles due to
particle bonding. The simulations demonstrate that cohesive forces accelerate
the overall settling process primarily because smaller grains attach to larger
ones and settle in their wakes. For the present cohesion number values, we
observe that settling can be accelerated by up to 29%. We propose physically
based parametrization of classical hindered settling functions proposed by
earlier authors, in order to account for cohesive forces. An investigation of
the energy budget shows that the work of the collision forces can substantially
modify the relevant energy conversion processes.Comment: 39 page
Automatic annotation of bioinformatics workflows with biomedical ontologies
Legacy scientific workflows, and the services within them, often present
scarce and unstructured (i.e. textual) descriptions. This makes it difficult to
find, share and reuse them, thus dramatically reducing their value to the
community. This paper presents an approach to annotating workflows and their
subcomponents with ontology terms, in an attempt to describe these artifacts in
a structured way. Despite a dearth of even textual descriptions, we
automatically annotated 530 myExperiment bioinformatics-related workflows,
including more than 2600 workflow-associated services, with relevant
ontological terms. Quantitative evaluation of the Information Content of these
terms suggests that, in cases where annotation was possible at all, the
annotation quality was comparable to manually curated bioinformatics resources.Comment: 6th International Symposium on Leveraging Applications (ISoLA 2014
conference), 15 pages, 4 figure
2D mapping of plane stress crack-tip fields following an overload
The evolution of crack-tip strain fields in a thin (plane stress) compact tension sample following an
overload (OL) event has been studied using two different experimental techniques. Surface behaviour has been
characterised by Digital Image Correlation (DIC), while the bulk behaviour has been characterised by means of
synchrotron X-ray diffraction (XRD). The combination of both surface and bulk information allowed us to
visualise the through-thickness evolution of the strain fields before the OL event, during the overload event,
just after OL and at various stages after it. Unlike previous work, complete 2D maps of strains around the
crack-tip were acquired at 60m spatial resolution by XRD. The DIC shows less crack opening after overload
and the XRD a lower crack-tip peak stress after OL until the crack has grown past the compressive crack-tip
residual stress introduced by the overload after which the behaviour returned to that for the baseline fatigue
response. While the peak crack-tip stress is supressed by the compressive residual stress, the crack-tip stress
field changes over each cycle are nevertheless the same for all Kmax cycles except at OL
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