Papers by Keyword: Synchrotron

Abstract: Synchrotron X-rays have the advantage of being a micro beam, allowing us to create detailed stress maps. However, due to a dendritic structure, measuring the residual stresses of a welded part is difficult. This challenge is caused by the difference in the positions of the diffracted crystal grains. To address this problem, we proposed a double exposure method. In this presentation, the double exposure method was applied to measure the residual stress of the plate that was cut from the welded pipe. Detailed strain maps under a plane stress state were obtained. Conversely, the residual stress distributions of the welded pipe under a triaxial stress state were measured using neutrons. From these results, the detailed stress maps of the root part of the butt-welded pipe were made up by the complimentary use of the synchrotron X-rays and neutrons. The results can significantly explain theinitiation and propagation of stress-corrosion cracking. We name this analysis method the quantum beam hybrid stress analysis.

Abstract: Shallow cracks are often observed in dental enamel, however do not normally lead to deep fractures. Previous work has highlighted the toughening mechanisms that operate in enamel during crack propagation, but very little is known about the deformation and stress fields arising around the propagating cracks during realistic loading conditions. This work aims to elucidate how the stresses are distributed within human dental enamel when a pre-existing crack is subjected to opening and surface contact with in situ indentation. We present a synchrotron-based in situ analysis coupled with a linear elastic finite element method simulation. The experimental reconstructed stress fields identified a prominent residual stress within the enamel, accompanied by a visible pattern that appeared clearly associated with its underlying microstructure. The numerical modelling of the stress field and discerning of surface contact and crack opening caused by the indentation was subsequently possible, even if in this study the influence of the anisotropy induced by the presence of features at a smaller scale was neglected. The implications of these findings and directions for future research are discussed.

Abstract: Aging increases the yield strength of aged Mg-Zn alloys. The effect of aging on the stress required for twinning is examined using in-situ transmission based synchrotron X-ray diffraction. The as extruded material was aged at variety of temperatures for different times. It is found that increasing sample diameter (thickness) results in peak broadening. The data are analysed to establish the evolution of twin volume fraction with stress. Results indicated an increase in twinning stress at 10% twin volume fraction in aged samples in comparison with non-aged condition. The investigation showed a strong relation between the macroscopic yield stress and the twinning stress (at 10% twin volume fraction).

Abstract: Among the severe plastic deformation techniques, the equal channel angular pressing (ECAP) has drastically improved the mechanical properties of the processed alloys. However, information regarding friction phenomenon, which modifies the deformation at the surface and the heterogeneity microstrain state produced by the process itself, is still scarce. In the present work, the deformation heterogeneity and the friction effect, at the surface in the bulk material of the 6061-T6 aluminum alloy processed by ECAP, is presented and discussed. The residual stress (RS) measurements were performed by means of X-Ray diffraction. By means of synchrotron diffraction, volumetric sections of the ECAPed samples were characterized. Finite element analysis showed a good agreement with the experimentally obtained residual stress and microhardness mapping results. The study also showed that the highest deformation zones were located at the outer parts of the deformed samples (top and bottom), while the inner zone showed strain oscillations of up to 49±2 MPa.

Abstract: With respect to residual stress analysis the inner gearing of an automotive sliding collar is a component with a challenging, complex geometry. The accessibility of the tooth root does not exist for conventional measuring approaches. However, the process steps like e.g. broaching and case hardening induce characteristic residual stress distributions, which must be known for the valuation of the mechanical integrity of the parts. For lab X-ray stress analysis approaches according to the sin2ψ-method [1] the ring like structure must be sectioned, which affects the process induced residual stress state. The tooth root is rather small, which further leads to shadowing effects during tilting of the sample. Standard mechanical approaches like incremental hole drilling can be excluded due to the narrow tooth root. Local neutron diffraction residual stress analysis in the tooth root by means of neutron through surface strain scanning at the STRESS-SPEC instrument at the research reactor FRM II, Garching (Germany) was successfully carried out for the inner gearing. A measuring and evaluation strategy is proposed, where special attention is paid to the compensation of the surface effect due to the incomplete immersion of the nominal gauge volume during through surface scanning and to the local variation of the D₀-value as a consequence of the case hardening process.

Abstract: This paper investigates the effect of 1 wt% TiO₂ on the formation of primary and interfacial Cu₆Sn₅ in Sn-0.7wt%Cu and Sn-0.7wt%Cu-0.05wt%Ni solder pastes soldered on a Cu substrate using a real-time synchrotron imaging technique. It was found that TiO₂ had altered the nucleation time of the primary Cu₆Sn₅ intermetallics and increased the number of particles observed. In addition, a more planar Cu₆Sn₅ interfacial layer had formed in joints made with TiO₂ reinforced solders. This indicated that TiO₂ promotes nucleation of primary Cu₆Sn₅ intermetallics in the early stages of soldering while being a barrier for further growth of interfacial Cu₆Sn₅ intermetallics. The synchrotron imaging technique provides direct evidence of the sequence of events in the soldering reaction and how these are influenced by TiO₂ reinforcement.

Abstract: The solidification of Sn-3Ag-0.5Cu and Sn-0.7Cu-0.05Ni are overviewed and compared. In joints on Cu substrates, both solders begin solidification with primary Cu₆Sn₅ growing in the bulk liquid prior to tin nucleation. In freestanding balls and joints, SAC305 generally solidifies with a single tin nucleation event and exhibits a mutually-twinned tin grain structure. In contrast, SN100C BGA balls and joints exhibit multiple independent tin grains that grow as a columnar array in joints.

Abstract: Underwater attachment is a significant challenge, for which we have no good general solutions in our technology. Yet, a number of biological organisms have evolved solutions to this problem. One intriguing approach to underwater attachment is that of the marine bivalve mussel Anomia simplex that uses a biomineralized byssus to permanently anchor itself to substrates. The byssus has a highly complex hierarchical structure and contains over 90 wt% CaCO₃. The byssus features a complex set of porosities, presumed to be highly important for the function of the attachment system. The pore space is the main focus of the present work. We characterize the three dimensional distribution of pore spaces in the byssus using micro-computed tomography (µCT) through a combination of in house mCT and high resolution synchrotron µCT. The pore structures are observed to fall into distinct categories in various parts of the byssus. We discuss the branching of one set of pores that reach the byssus substrate interface in particular. They form a network reaching the byssus surface that we now visualize in three dimensions.

Abstract: This paper demonstrates the development of an experimental technique of in-situ observation for soldering of Sn-0.7wt%Cu lead-free solder on a Cu substrate which was achieved for the first time by synchrotron X-ray imaging. Reactions between liquid solder and Cu substrate during a soldering process were able to be recorded in real-time. Individual stages of the soldering process consisted of flux activation in removal of Cu oxide, solder melting and contact with the Cu substrate (wetting) and intermetallic compound (IMC) and void formation between the solder and Cu substrate. The technique development which includes experimental setup with calculated optimum beam energy in the range of 20 – 30 keV appears to result in a clear observation of real-time X-ray imaging of the soldering process. This technique provides a key method to understand the mechanism of formation of micro-electronic inter-connects for future electronic packaging applications.

Abstract: In an experiment conducted at the Tomsk synchrotron "Sirius", the photon yield of parametric X-ray radiation generated by 500 MeV electrons in a tungsten monocrystal in Bragg geometry has been studied. The (111) tungsten monocrystal, having a thickness of 1.7 mm and a surface mosaicity of not more than 80^², was oriented at the Bragg angle θ_B = 45^° to the direction of the electron beam. The photons were detected at the angle 2θ_B = 90° relative to the electron beam. A comparison of PXR angular distributions with calculations has been carried out with taking into account the actual conditions of the experiment.