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Ruiz-Hervias J.,Technical University of Madrid | Steuwer A.,ESS Scandinavia | Steuwer A.,Nelson Mandela Metropolitan University | Gurauskis J.,CSIC - Institute of Materials Science | And 2 more authors.
Materials Science Forum | Year: 2010

Residual strain profiles were measured by synchrotron X-ray radiation in Al2O3/Ystabilized ZrO2 (YSZ) ceramic laminates. Different stacking sequences were employed, including alternating layers containing 5 and 40 vol.% YSZ. Residual strains were found to be fairly constant within each layer; although they change at the interface between layers with different compositions. Different behaviour is observed for the strains along the in-plane and normal directions. © (2010) Trans Tech Publications.


Tremsin A.S.,University of California at Berkeley | McPhate J.B.,University of California at Berkeley | Steuwer A.,ESS Scandinavia | Steuwer A.,Nelson Mandela Metropolitan University | And 6 more authors.
Strain | Year: 2012

Conventional neutron radiography can be strongly enhanced by obtaining Bragg-edge information spatially correlated with the attenuation coefficient. This can now be achieved through time-of-flight techniques at pulsed neutron sources, utilising a neutron counting detector with high-spatial and high-temporal resolution. In these measurements, the positions of Bragg edges can in principle be obtained for each 55 × 55 μm 2 pixel of the radiographic image. The combination of both Bragg-edge and attenuation information enables high spatial resolution studies to be carried out on material composition, phase transitions, texture variations, as well as residual strain mapping. In this article, we present the results of high-resolution strain maps of a ferritic steel cantilever sample measured at different loads by both transmission and conventional diffraction modes, as well as strains in an austenitic steel compact-tension (CT) crack sample. The proof of principle experiments performed on the ENGIN-X beamline on a bent cantilever arrangement resulting in a uni-axial stress field verified that the strain values measured in diffraction and transmission mode are in good agreement. The characteristics of the transmission mode detector as well as the measured strain maps and future possibilities of this technology are discussed. © 2011 Blackwell Publishing Ltd.


Tremsin A.S.,University of California at Berkeley | McPhate J.B.,University of California at Berkeley | Vallerga J.V.,University of California at Berkeley | Siegmund O.H.W.,University of California at Berkeley | And 7 more authors.
Materials Science Forum | Year: 2014

The spatial resolution of time of flight neutron transmission diffraction was recently improved by the extension of photon/electron counting technology to imaging of thermal and cold neutrons. The development of novel neutron sensitive microchannel plates enables neutron counting with spatial resolution of ~55 μ and time-of-flight accuracy of ~1 μs, with efficiency as high as 70% for cold and ~40% for thermal neutrons. The combination of such a high resolution detector with a pulsed collimated neuron beam provides the opportunity to obtain a 2-dimensional map of neutron transmission spectra in one measurement. The results of our neutron transmission measurements demonstrate that maps of strains averaged along the beam propagation direction can be obtained with ~100 microstrain accuracy and spatial resolution of ~100 μ providing there are sufficient neutron events collected. In this paper we describe the capabilities of the MCP neutron counting detectors and present the experimental results of 2-dimensional strain maps within austenitic steel compact tension (CT) crack samples measured at the ENGIN-X beamline of the ISIS pulsed neutron source. © (2014) Trans Tech Publications, Switzerland.


Tremsin A.S.,University of California at Berkeley | McPhate J.B.,University of California at Berkeley | Vallerga J.V.,University of California at Berkeley | Siegmund O.H.W.,University of California at Berkeley | And 3 more authors.
Proceedings of IEEE Sensors | Year: 2010

High resolution neutron counting sensors with microchannel plates coupled to a Timepix readout enable high spatial (∼55 μm) and temporal (∼1 μs) accuracy for each detected thermal and cold neutron. One of the attractive applications for those sensors is the high resolution strain mapping in engineering samples through transmission Bragg edge diffraction. The unique combination of high detection efficiency (up to 70%), high spatial and temporal resolution of MCP detectors enable ∼100 μm strain mapping with ∼100 μstrain accuracy. We present the results of proof of principle measurements performed at ROTAX beamline at ISIS spallation neutron source. Strain map of a bent steel sample is measured with very high spatial resolution. The same sensors enable high resolution non-destructive studies in such diverse areas as neutron microtomography, dynamics of fuel injection, material composition, archaeology, water propagation and many others. ©2010 IEEE.


Tremsin A.S.,University of California at Berkeley | McPhate J.B.,University of California at Berkeley | Vallerga J.V.,University of California at Berkeley | Siegmund O.H.W.,University of California at Berkeley | And 3 more authors.
IEEE Sensors Journal | Year: 2011

High-resolution neutron counting sensors with microchannel plates coupled to a Timepix readout enable high spatial (∼55 μm) and temporal (∼1 μs) accuracy for each detected thermal and cold neutron. One of the attractive applications for those sensors is the high-resolution strain mapping in engineering samples through transmission Bragg edge diffraction. The unique combination of high detection efficiency (up to 70%), high spatial and temporal resolution of , detectors enable ∼100μ m strain mapping with ∼100μstrain accuracy. We present the results of proof of principle measurements performed at ROTAX beamline at ISIS spallation neutron source. Strain map of a bent steel sample is measured with very high spatial resolution. The same sensors enable high-resolution nondestructive studies in such diverse areas as neutron microtomography, dynamics of fuel injection, material composition, archaeology, water propagation and many others. © 2011 IEEE.


Josic L.,Paul Scherrer Institute | Steuwer A.,Paul Scherrer Institute | Lehmann E.,ESS Scandinavia
Applied Physics A: Materials Science and Processing | Year: 2010

Energy selective neutron radiography was performed to describe a complex structure in polycrystalline materials. Experiments were performed with currently the highest energy and spatial resolutions achieved simultaneously, by employing a double crystal monochromator for selecting narrow energy bands from the initially polychromatic neutron beam and the neutron absorbing scintillator screen coupled with the cooled CCD camera as a detection system. It was shown that the detailed structure of the welded steel sample can be visualized and quantified by performing energy selective neutron imaging in the cold energy range, where elastic coherent scattering dominates the total cross section of the sample, showing characteristic Bragg edges. With the maps of crystallographic orientations over the sample area of 2 × 2 cm2 and thickness 11.2 mm, obtained directly from radiographs, the complex structure was energy resolved with a spatial resolution of 50 μm. © Springer-Verlag 2010.


Chahardehi A.,Cranfield University | Brennan F.P.,Cranfield University | Steuwer A.,ESS Scandinavia
Engineering Fracture Mechanics | Year: 2010

Residual stresses have in the past been introduced to manipulate growth rates and shapes of cracks under cyclic loads. Previously, the effectiveness of shot peening in retarding the rate of fatigue crack growth was experimentally studied. It was shown that the compressive residual stresses arising from the shot peening process can affect the rate of crack growth. Laser shock peening can produce a deeper compressive stress field near the surface than shot peening. This advantage makes this technique desirable for the manipulation of crack growth rates. This paper describes an experimental program that was carried out to establish this effect in which steel specimens were partially laser peened and subsequently subjected to cyclic loading to grow fatigue cracks. The residual stress fields generated by the laser shock peening process were measured using the neutron diffraction technique. A state of compressive stress was found near the surface and tensile stresses were measured in the mid-thickness of the specimens. Growth rates of the cracks were observed to be more affected by the tensile core than by the compressive surface stresses. © 2010 Elsevier Ltd.


Klopper J.J.,University of Johannesburg | Laubscher R.F.,University of Johannesburg | Steuwer A.,ESS Scandinavia | James M.N.,University of Plymouth
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications | Year: 2011

This article presents an experimental investigation of thermally induced residual stresses in fabricated 3CR12 (DIN 1.4003) T-sections. 3CR12 is a weldable utility stainless steel developed to provide a superior alternative to coated carbon steels and other alloys which have a poor corrosion/abrasion resistance. Because of the difficulty and costs involved in hot-rolling stainless steel structural sections, they are usually fabricated by welding. In this investigation, full-penetration laser- and manual metal arc (MMA) joints were considered along with partialpenetrated MMA- and metal inert gas (MIG) welded joints. The residual stresses induced during welding were measured by neutron diffraction. All the sections displayed a largely tensile residual stress field around the weld that subsequently implied a compressive residual stress field in the flange regions. This was most pronounced for the MMA and MIG welds. The laser-welded sections displayed a more localized tensile residual stress field in the heat-affected zone that translated to lower average stresses in the flanges. In the latter part of this article, the effect of the weld-induced residual stress fields on the structural performance of appropriate T-section-based columns are assessed and compared. A significant difference in structural performance between the different weld techniques is predicted with the laser-welded sections displaying the highest predicted strength. © University of Johannesburg 2011.

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