744 research outputs found
High magnification crack-tip field characterisation under biaxial conditions
This work presents a novel methodology for characterising fatigue cracks under biaxial conditions.The methodology uses high magnification Digital Image Correlation (DIC) technique for measuringdisplacement and strain crack-tip fields. By applying micro-speckle pattern on the metal surface it is possible toachieve high magnification for DIC technique. The speckles were created by electro-spray technique. Thevalidity of this novel technique is demonstrated by direct comparison with standard extensometermeasurements, under tension-compression and torsion conditions. In order to image the correct region, thenotch effect on the fatigue life was also evaluated
Study of the stress intensity factors in the bulk of the material with synchrotron diffraction
ArtĂculo 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 MĂĄlaga. Campus de Excelencia Internacional AndalucĂa 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 AndalucĂa 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
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Direct Observation of the Spontaneous Emission of the Hyperfine Transition F = 4 to F = 3 in Ground State Hydrogenlike 165Ho66+ in an Electron Beam Ion Trap
We report the first direct laboratory measurement of the spontaneous emission due to the hyperfine splitting of the ground state of a highly charged hydrogenlike ion excited by electron collisions. The transition between the F = 4 and F = 3 levels of the 1s2S1/2 configuration of hydrogenlike 165Ho65+ was observed and its wavelength was determined to 5726.4±1.5Ă
. After taking into account relativistic, nuclear charge distribution, Bohr-Weisskopf, and QED corrections, we observe a significant deviation from commonly tabulated values of the nuclear dipole magnetic moment of this nucleu
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Precision measurement of the lifetime of the 1s2s3S1 metastable level in heliumlike O6+
The lifetime of the 1s2s3S1 level of the He-like O6+ ion has been measured using the Electron Beam Ion Trap in the magnetic trapping mode. A value of 956-4+5 ÎŒs is found, which corresponds to a radiative transition rate of 1046-5+4 s-1 for the magnetic dipole transition to the 1s21S0 ground state. This value is in excellent agreement with recent theoretical predictions and distinguishes among different treatments of negative energy states and correlation in multiconfiguration Dirac-Fock calculations
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 60ïm 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
Study of overload effects in bainitic steel by synchrotron X-ray diffraction
This work presents an in-situ characterisation of crack-tip strain fields following an overload bymeans of synchrotron X-ray diffraction. The study is made on very fine grained bainitic steel, thus allowing avery high resolution so that small changes occurring around the crack-tip were captured along the crack plane atthe mid-thickness of the specimen. We have followed the crack as it grew through the overload location. Oncethe crack-tip has progressed past the overload event there is strong evidence that the crack faces contact in theregion of the overload event (though not in the immediate vicinity of the current locations of the crack tip) atKmin even when the crack has travelled 1mm beyond the overload location. It was also found that at Kmax thepeak tensile strain ahead of the crack-tip decreases soon after the overload is applied and then graduallyrecovers as the crack grows past the compressive region created by the overload
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A high-resolution transmission-type x-ray spectrometer designed for observation of the Kα transitions of highly charged high-Z ions
High-resolution reflection-type crystal spectrometers have been used for x-ray energies up to 13 keV, e.g., the K-shell radiation of heliumlike Kr. In order to extend crystal spectrometer measurements to higher energy x rays from higher-Z elements, we employ the crystal in transmission. The geometry we use is known as DuMond geometry. Using such a transmission-type crystal x-ray spectrometer, we have measured the K-shell radiation of various highly charged high-Z ions. In particular, we present a measurement of the 1s2pâ1P1â1s2â1S0 transition in heliumlike xenon, Xe52+. For this transition, we measure a linewidth of 34 eV, which demonstrates that the resolving power we achieved with the new spectrometer is on the order of 100
Some experimental observations of crack-tip mechanics with displacement data
In the past two decades, crack-tip mechanics has been increasingly studied with full-field techniques. Within these techniques, Digital Image Correlation (DIC) has been most widely used due to its many advantages, to extract important crack-tip information, including Stress Intensity Factor (SIF), Crack Opening Displacement, J-integral, T-stress, closure level, plastic zone size, etc. However, little information is given in the literature about the experimental setup that provides best estimations for the different parameters.The current work aims at understanding how the experimental conditions used in DIC influence the crack-tipinformation extracted experimentally. The influence of parameters such as magnification factor, size of theimages, position of the images with respect the crack-tip and size of the subset used in the correlation is studied. The influence is studied in terms of SIF and T-stress by using Williamsâ model. The concept of determination of the K-dominance zone from experimental data has also explored. In this regard, cyclic loading on a fatigue crack in a compact tension (CT) specimen, made of aluminium 2024-T351 alloy, has been applied and the surface deformation ahead of the crack tip has been examined. The comparison between theoretical and experimental values of KI showed that the effect of subset size on the measured KI is negligible compared to the effect of size of the image
An efficient procedure for reducing in-line-inspection datasets for structural integrity assessments
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