The Experts below are selected from a list of 21264 Experts worldwide ranked by ideXlab platform

M. Hofmann - One of the best experts on this subject based on the ideXlab platform.

  • Effects of finish turning on an austenitic weld investigated using diffraction methods
    The International Journal of Advanced Manufacturing Technology, 2020
    Co-Authors: J. Rebelo Kornmeier, M. Hofmann, W. M. Gan, V. Robin, F. Valiorgue, H. Pascal, J. Gibmeier, J. Saroun
    Abstract:

    Arc welding generally introduces undesired local residual stress states on engineering components hindering high-quality performance in service. Common procedures to reduce the tensile residual stresses are post-heat treatments or mechanical surface treatments like hammering or shot-peening. Assessments of residual stress profiles of post-weld treatments underneath the weld surface are essential, especially in high safety exigency systems like pressure vessels or piping at power plants. In this study, neutron diffraction is used to determine the stress profile after finish milling of an austenitic steel weld in order to verify a chained finite element simulation predicting the final residual stress fields including milling and welding contributions. Non-destructive measurements with spatial resolutions of less than 0.2 mm within the first 1 mm from the surface were mandatory to confirm the finite element simulations of the coarse-grained austenitic material. In the data analysis procedure, the obtained near-surface data have been corrected for spurious strain effects whenever the Gauge Volume was partially immersed in the sample. Moreover, constraining the surface data to values obtained by x-ray diffraction and data deconvolution within the Gauge Volume enabled access of the steep residual stress profile within the first 1 mm.

  • homogeneity of lithium distribution in cylinder type li ion batteries
    Scientific Reports, 2016
    Co-Authors: Anatoliy Senyshyn, M. Hofmann, M J Muhlbauer, Oleksandr Dolotko, Helmut Ehrenberg
    Abstract:

    Spatially-resolved neutron powder diffraction with a Gauge Volume of 2 × 2 × 20 mm3 has been applied as an in situ method to probe the lithium concentration in the graphite anode of different Li-ion cells of 18650-type in charged state. Structural studies performed in combination with electrochemical measurements and X-ray computed tomography under real cell operating conditions unambiguously revealed non-homogeneity of the lithium distribution in the graphite anode. Deviations from a homogeneous behaviour have been found in both radial and axial directions of 18650-type cells and were discussed in the frame of cell geometry and electrical connection of electrodes, which might play a crucial role in the homogeneity of the lithium distribution in the active materials within each electrode.

  • homogeneity of lithium distribution in cylinder type li ion batteries
    arXiv: Materials Science, 2015
    Co-Authors: Anatoliy Senyshyn, M. Hofmann, M J Muhlbauer, Oleksandr Dolotko, Helmut Ehrenberg
    Abstract:

    Spatially-resolved neutron powder diffraction with Gauge Volume 2x2x20 mm3 has been applied to probe the lithium concentration in the graphite anode of different Li-ion cells of 18650-type in situ in charged state. Structural studies performed in combination with electrochemical measurements and X-ray computed tomography under real cell operating conditions unambiguously revealed non-homogeneity of lithium distribution in the graphite anode. Deviations from a homogeneous behaviour have been found in both radial and axial directions of 18650-type cells and were discussed in the frame of cell geometry and electrical connection of electrodes, which might play a crucial role in the homogeneity of the lithium distribution in the active materials within each electrode.

  • analytical model for neutron diffraction peak shifts due to the surface effect
    Journal of Applied Crystallography, 2013
    Co-Authors: J. Saroun, M. Hofmann, Joana Rebelo Kornmeier, P Mikula, M Vrana
    Abstract:

    Residual strains measured by neutron diffraction near sample boundaries can be biased by the surface effect as a result of incomplete filling of the instrumental Gauge Volume. This effect is manifested as anomalous shifts of diffraction lines, which can be falsely interpreted as a lattice strain unless appropriate data corrections are made. A new analytical model for the surface effect has been developed, which covers a broad variety of instrumental arrangements, including flat mosaic and bent perfect crystal monochromators, narrow slits, and Soller and radial collimators. This model permits the spurious peak shifts to be predicted quantitatively, and also allows the optimum configuration parameters, such as curvature of a focusing monochromator, which lead to suppression of the surface effect, to be calculated. The model has been thoroughly validated by comparisons with Monte Carlo simulations and experiments on a stress-free calibration sample. Predictions of the model proved to be very accurate, often within the interval of experimental errors, which makes it suitable for use in data analysis.

  • neutron surface residual stress scanning using optimisation of a si bent perfect crystal monochromator for minimising spurious strains
    Materials Science Forum, 2011
    Co-Authors: Joana Rebelokornmeier, M. Hofmann, Jens Gibmeier, Robert C Wimpory
    Abstract:

    For non destructive stress analysis of surface treated steel samples the application of laboratory X rays or high energy synchrotron radiation in reflection mode covers the region from some micrometers up to a depth of about 150 - 200 µm. To access depth regions deeper than 200 µm the incremental layer removal technique in combination with the repeated application of X‑ray stress analysis for the newly generated surfaces can be used. However, this procedure is destructive, laborious and furthermore, it has to be checked whether corrections have to be applied due to stress relaxation. By using neutron radiation penetration depths generally up to several millimetres can be achieved non destructively [1]. However neutron measurements are critical at the surface. When scanning a sample surface, aberration peak shifts caused by so called spurious strains arise due to the fact that the Gauge Volume defined by the primary and secondary optics is partially outside of the sample. These aberration peak shifts can be of the same order of magnitude as the peak shifts related to residual strains [2-6]. In this exemplary study it will be demonstrated that, by optimising the bending radius of a Si (400) monochromator, the spurious surface strains can be strongly reduced when compared to the values obtained with a traditional Ge (311) mosaic monochromator, even when the Gauge Volume is mainly out of the surface. The objective of the experiments is to find the optimal monochromator settings for the Si (400) monochromator at the STRESS-SPEC instrument at the research reactor FRM II, Munich, Germany. For the parametric studies a stress free steel sample of the fine grained construction steel, S690QL was used. The optimised conditions for the Si (400) monochromator that resulted from the systematic studies were applied to a shot peened plate of steel SAE 4140. The residual stress distribution is analysed by means of through surface strain scanning. The residual stress gradient obtained is in very good agreement with the well characterised residual stress depth profile obtained within a round robin test in the scope of the BRITE-EURAM-project ENSPED (European Network of Surface and Prestress Engineering and Design) [7]. The results indicated that surface residual stress profiles can be measured with neutrons up to 200 µm underneath the surface without time consuming and laborious surface effect corrections.

Helmut Ehrenberg - One of the best experts on this subject based on the ideXlab platform.

  • homogeneity of lithium distribution in cylinder type li ion batteries
    Scientific Reports, 2016
    Co-Authors: Anatoliy Senyshyn, M. Hofmann, M J Muhlbauer, Oleksandr Dolotko, Helmut Ehrenberg
    Abstract:

    Spatially-resolved neutron powder diffraction with a Gauge Volume of 2 × 2 × 20 mm3 has been applied as an in situ method to probe the lithium concentration in the graphite anode of different Li-ion cells of 18650-type in charged state. Structural studies performed in combination with electrochemical measurements and X-ray computed tomography under real cell operating conditions unambiguously revealed non-homogeneity of the lithium distribution in the graphite anode. Deviations from a homogeneous behaviour have been found in both radial and axial directions of 18650-type cells and were discussed in the frame of cell geometry and electrical connection of electrodes, which might play a crucial role in the homogeneity of the lithium distribution in the active materials within each electrode.

  • homogeneity of lithium distribution in cylinder type li ion batteries
    arXiv: Materials Science, 2015
    Co-Authors: Anatoliy Senyshyn, M. Hofmann, M J Muhlbauer, Oleksandr Dolotko, Helmut Ehrenberg
    Abstract:

    Spatially-resolved neutron powder diffraction with Gauge Volume 2x2x20 mm3 has been applied to probe the lithium concentration in the graphite anode of different Li-ion cells of 18650-type in situ in charged state. Structural studies performed in combination with electrochemical measurements and X-ray computed tomography under real cell operating conditions unambiguously revealed non-homogeneity of lithium distribution in the graphite anode. Deviations from a homogeneous behaviour have been found in both radial and axial directions of 18650-type cells and were discussed in the frame of cell geometry and electrical connection of electrodes, which might play a crucial role in the homogeneity of the lithium distribution in the active materials within each electrode.

M J Muhlbauer - One of the best experts on this subject based on the ideXlab platform.

  • homogeneity of lithium distribution in cylinder type li ion batteries
    Scientific Reports, 2016
    Co-Authors: Anatoliy Senyshyn, M. Hofmann, M J Muhlbauer, Oleksandr Dolotko, Helmut Ehrenberg
    Abstract:

    Spatially-resolved neutron powder diffraction with a Gauge Volume of 2 × 2 × 20 mm3 has been applied as an in situ method to probe the lithium concentration in the graphite anode of different Li-ion cells of 18650-type in charged state. Structural studies performed in combination with electrochemical measurements and X-ray computed tomography under real cell operating conditions unambiguously revealed non-homogeneity of the lithium distribution in the graphite anode. Deviations from a homogeneous behaviour have been found in both radial and axial directions of 18650-type cells and were discussed in the frame of cell geometry and electrical connection of electrodes, which might play a crucial role in the homogeneity of the lithium distribution in the active materials within each electrode.

  • homogeneity of lithium distribution in cylinder type li ion batteries
    arXiv: Materials Science, 2015
    Co-Authors: Anatoliy Senyshyn, M. Hofmann, M J Muhlbauer, Oleksandr Dolotko, Helmut Ehrenberg
    Abstract:

    Spatially-resolved neutron powder diffraction with Gauge Volume 2x2x20 mm3 has been applied to probe the lithium concentration in the graphite anode of different Li-ion cells of 18650-type in situ in charged state. Structural studies performed in combination with electrochemical measurements and X-ray computed tomography under real cell operating conditions unambiguously revealed non-homogeneity of lithium distribution in the graphite anode. Deviations from a homogeneous behaviour have been found in both radial and axial directions of 18650-type cells and were discussed in the frame of cell geometry and electrical connection of electrodes, which might play a crucial role in the homogeneity of the lithium distribution in the active materials within each electrode.

Anatoliy Senyshyn - One of the best experts on this subject based on the ideXlab platform.

  • homogeneity of lithium distribution in cylinder type li ion batteries
    Scientific Reports, 2016
    Co-Authors: Anatoliy Senyshyn, M. Hofmann, M J Muhlbauer, Oleksandr Dolotko, Helmut Ehrenberg
    Abstract:

    Spatially-resolved neutron powder diffraction with a Gauge Volume of 2 × 2 × 20 mm3 has been applied as an in situ method to probe the lithium concentration in the graphite anode of different Li-ion cells of 18650-type in charged state. Structural studies performed in combination with electrochemical measurements and X-ray computed tomography under real cell operating conditions unambiguously revealed non-homogeneity of the lithium distribution in the graphite anode. Deviations from a homogeneous behaviour have been found in both radial and axial directions of 18650-type cells and were discussed in the frame of cell geometry and electrical connection of electrodes, which might play a crucial role in the homogeneity of the lithium distribution in the active materials within each electrode.

  • homogeneity of lithium distribution in cylinder type li ion batteries
    arXiv: Materials Science, 2015
    Co-Authors: Anatoliy Senyshyn, M. Hofmann, M J Muhlbauer, Oleksandr Dolotko, Helmut Ehrenberg
    Abstract:

    Spatially-resolved neutron powder diffraction with Gauge Volume 2x2x20 mm3 has been applied to probe the lithium concentration in the graphite anode of different Li-ion cells of 18650-type in situ in charged state. Structural studies performed in combination with electrochemical measurements and X-ray computed tomography under real cell operating conditions unambiguously revealed non-homogeneity of lithium distribution in the graphite anode. Deviations from a homogeneous behaviour have been found in both radial and axial directions of 18650-type cells and were discussed in the frame of cell geometry and electrical connection of electrodes, which might play a crucial role in the homogeneity of the lithium distribution in the active materials within each electrode.

M Vrana - One of the best experts on this subject based on the ideXlab platform.

  • analytical model for neutron diffraction peak shifts due to the surface effect
    Journal of Applied Crystallography, 2013
    Co-Authors: J. Saroun, M. Hofmann, Joana Rebelo Kornmeier, P Mikula, M Vrana
    Abstract:

    Residual strains measured by neutron diffraction near sample boundaries can be biased by the surface effect as a result of incomplete filling of the instrumental Gauge Volume. This effect is manifested as anomalous shifts of diffraction lines, which can be falsely interpreted as a lattice strain unless appropriate data corrections are made. A new analytical model for the surface effect has been developed, which covers a broad variety of instrumental arrangements, including flat mosaic and bent perfect crystal monochromators, narrow slits, and Soller and radial collimators. This model permits the spurious peak shifts to be predicted quantitatively, and also allows the optimum configuration parameters, such as curvature of a focusing monochromator, which lead to suppression of the surface effect, to be calculated. The model has been thoroughly validated by comparisons with Monte Carlo simulations and experiments on a stress-free calibration sample. Predictions of the model proved to be very accurate, often within the interval of experimental errors, which makes it suitable for use in data analysis.

  • suppression of surface effect by using bent perfect crystal monochromator in residual strain scanning
    Materials Science Forum, 2005
    Co-Authors: M Vrana, P Mikula
    Abstract:

    Using our long experience in Bragg diffraction optics we successfully used focusing principles for substantial increasing both luminosity and resolution of the strain scanners with respect to the conventional devices. Monochromatic neutrons are selected by the cylindrically bent monochromator from the reactor spectrum. There is a strong correlation between divergences of incoming and outgoing beams with respect to the polycrystalline sample, which can be easily manipulated by changing the monochromator bending radius. By setting a proper value of the radius, a narrow, quasiparallel and highly luminous output beam can by adjusted. The strong correlation between wavelength and direction of incoming and outgoing beams depending on the monochromator bending radius can be as well used for suppression of surface effect in residual strain scanning. In scanning near a sample surface aberration peak shifts arise due to the fact that the Gauge Volume defined by input and output slits is partially out of the sample and its value can be of the same order as the residual strain effects. In this work we demonstrate that by changing of the bending radius of monochromator, this surface effect can be suppressed to values smaller then experimental errors in residual strain scanning.