Papers by Author: René V. Martins

Abstract: A conical slit cell for depth-resolved diffraction of high-energy X-rays was tested at the high-energy materials science beamline HEMS at PETRA III and used for the analysis of residual stresses in a laser beam welded steel overlap joint. With a conical slit width of 20 µm and beam cross-sections below 100 µm, depth resolutions well below 1 mm were achieved. The residual stress distributions obtained from the steel joint were in very good agreement with previous results from neutron diffraction measurements, although they were still noisier because of inferior grain statistics.

Abstract: Two autogenously edge welded beams made from SA508 ferritic steel were investigated with the purpose of validating residual stress modelling tools which are relevant for integrity assessment of structural power plant components. The two specimens were welded with two different torch travel speeds. The residual strain and phase distributions were non-destructively determined by high-energy synchrotron X-ray diffraction. Good agreement between numerical and experimental data was found for the specimen welded at fast speed. Furthermore, the texture changes in the specimen welded at slow speed were analysed by the same experimental technique.

Abstract: An 18 mm thick three-pass slot weld specimen in austenitic stainless steel, manufactured for the purpose of benchmarking Finite Element weld residual stress simulation codes, is currently undergoing extensive non-destructive characterization within a research network. First results from the non-destructive full three dimensional spatially resolved macro-strain mapping in this specimen are presented here. Focussed high-energy synchrotron radiation together with the spiral slit technique was used to obtain depth-resolved information about the variation of lattice parameters. The results show a strong concentration of tensile strain, transverse to the weld at mid-depth of the weld. The maximum longitudinal strains were observed beneath the weld. Furthermore significant weld start- and stop-effects were observed.

Abstract: Grain tracking is a term used to describe experiments that investigate polycrystalline materials in terms of the crystallites or grains from which they are composed, non-destructively and in three dimensions. The new German high brilliance synchrotron radiation source, Petra III, will become available to users in 2010 [1]. The GKSS research centre will operate two beamlines, including the high energy materials science beamline (HEMS) [2]. HEMS will feature an instrument dedicated to grain tracking, able to support a range of experiments of this kind. This paper describes the design and specification of this instrument, and gives examples of the types of experiments that will be possible.

Abstract: The future High Energy Materials Science Beamline HEMS at the new German high brilliance synchrotron radiation storage ring PETRA III [1] will have a main energy of 120 keV, will be fully tunable in the range of 50 to 300 keV, and will be optimized for sub-micrometer focusing with Compound Refractive Lenses and Kirkpatrick-Baez Multilayer mirrors. Design and construction is the responsibility of the Research Center Geesthacht, GKSS, with approximately 70 % of the beamtime being dedicated to Materials Research, the rest reserved for “general physics” experiments covered by DESY, Hamburg. Fundamental research will encompass metallurgy, physics and chemistry. For first experiments in investigating grain-grain-interactions a dedicated 3D-microstructure-mapper will be designed. Applied research for manufacturing process optimization will benefit from the high flux in combination with ultra-fast detector systems allowing complex and highly dynamic in-situ studies of microstructural transformations. The beamline infrastructure will allow easy accommodation of large user provided equipment. Experiments targeting the industrial user community will be based on well established techniques with standardised evaluation, allowing "full service" measurements. Environments for strain mapping [2] on large structural components up to 1 t will be provided as well as automated investigations of large numbers of samples, e.g. for tomography and texture determination. The current design for the beamline (P07 in sector 5 of the future experimental hall) consists of a nearly five meter in-vacuum undulator source (U19-5) optimized for high energies, a general optics hutch, an in-house test facility and three independent experimental hutches working alternately, plus additional set-up and storage space for long-term experiments. HEMS should be operational in spring 2009 as one of the first beamlines running at PETRA III.

Abstract: The strain and phase distributions in friction stir welds (FSW) of AA2024-T3 to AA2024-T3 and AA2024-T3 to AA6082-T6 are investigated non-destructively. The measurements are performed using a novel depth resolved strain and phase mapping technique. The technique is based on the use of a focussed high energy synchrotron beam, a novel spiral slit system, and an area detector system. The strain scans across the dissimilar FSW exhibit a strong asymmetry in particular for the longitudinal strain component. A depth resolved strain mapping across the weld shows for the dominant longitudinal strain component variations in depth, especially on the AA6082 side of the dissimilar weld. The variations are significantlty weaker in the AA2024 / AA2024 weld. Results from the strain measurements are related to the depth resolved map of the material distribution in the weld zone.