Browsing by Author "Sun, Y"

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    Biogeochemical mobility of contaminants from a replica radioactive waste trench in response to rainfall-induced redox oscillations
    (American Chemical Society, 2021-06-10) Kinsela, AS; Bligh, MW; Vázquez-Campos, X; Sun, Y; Wilkins, MR; Comarmond, MJ; Rowling, B; Payne, TE; Waite, TD
    Results of investigations into factors influencing contaminant mobility in a replica trench located adjacent to a legacy radioactive waste site are presented in this study. The trench was filled with nonhazardous iron- and organic matter (OM)-rich components, as well as three contaminant analogues strontium, cesium, and neodymium to examine contaminant behavior. Imposed redox/water-level oscillations, where oxygen-laden rainwater was added to the anoxic trench, resulted in marked biogeochemical changes including the removal of aqueous Fe(II) and circulation of dissolved carbon, along with shifts to microbial communities involved in cycling iron (Gallionella,Sideroxydans) and methane generation (Methylomonas,Methylococcaceae). Contaminant mobility depended upon element speciation and rainfall event intensity. Strontium remained mobile, being readily translocated under hydrological perturbations. Strong ion-exchange reactions and structural incorporation into double-layer clay minerals were likely responsible for greater retention of Cs, which, along with Sr, was unaffected by redox oscillations. Neodymium was initially immobilized within the anoxic trenches, due to either secondary mineral (phosphate) precipitation or via the chemisorption of organic- and carbonate-Nd complexes onto variably charged solid phases. Oxic rainwater intrusions altered Nd mobility via competing effects. Oxidation of Fe(II) led to partial retention of Nd within highly sorbing Fe(III)/OM phases, whereas pH decreases associated with rainwater influxes resulted in a release of adsorbed Nd to solution with both pH and OM presumed to be the key factors controlling Nd attenuation. Collectively, the behavior of simulated contaminants within this replica trench provided unique insights into trench water biogeochemistry and contaminant cycling in a redox oscillatory environment. © 2024 American Chemical Society.
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    Numerical investigation of residual stresses in chain-die formed AHSS u-channels
    (Materials Research Forum LLC, 2016-07-03) Sun, Y; Qian, Z; Luzin, V; Daniel, WJT; Zhang, M; Ding, S
    Advanced high-strength steel is increasingly being used in automotive structural components due to its excellent strength-to-weight ratios. However, the variations of residual stresses magnitude in AHSS products are usually very complex and unpredictable due to the fabrication process and the material’s high strength. Consequently, unbalanced residual stresses are responsible for a series of product defects. Chain-die forming is a novel AHSS fabrication method which has the characteristics of preserving the material’s ductility maximally and also reducing the residual stresses in the product. In this study, the finite element method is employed to investigate the equivalent residual stresses (Von Mises) in Chain-die formed AHSS U-channels. Finite element simulation of roll forming of the same type as AHSS U-channel forming is performed to make a comparison of the residual stresses distribution characterizations in AHSS U-channels which are fabricated by roll forming and by Chain-die forming. The results indicate that the residual stresses in Chain-die formed U-channels stay at a very low level and are almost negligible. In the meanwhile, due to the bending, reverse bending and other unpredictable redundant deformation types in the roll forming process, the residual stresses are more significant than those of Chain-die formed AHSS channels. The comparison of the longitudinal strain developments of flange edges of roll formed and Chain-die formed U-channels is given to explain the differences between the residual stress distributions in the roll formed and Chain-die formed U-channels. This paper gives a comprehensive understanding of the characteristics of the residual stress distribution in Chain-die formed AHSS U-channels. It provides a clear evidence to illustrate the superiority of Chain-die forming in reducing the residual stresses in AHSS products. © The Authors
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    Predicting an optimal inter-pass temperature to mitigate residual stress and distortion in ferritic steel weldments
    (ASME International, 2016-12-01) Sun, Y; Hamelin, CJ; Smith, MC; Edwards, L
    The residual stress and distortion found in multi-pass welds are often influenced by the prescribed inter-pass temperature. In ferritic steel components, the severity of this influence is affected by solid-state phase transformation (SSPT) kinetics, which will depend on the overall heat input and cooling conditions. The development of an optimised welding procedure to mitigate weld residual stress (WRS) and distortion in these components can therefore necessitate an extensive test matrix, varying both preheat and inter-pass temperatures as well as the transient weld heat input. Computational parametric studies provide an opportunity to dramatically reduce the cost and time associated with the development of welding procedure specifications. Welding procedures can be simulated using validated modelling approaches to examine parametric sensitivity and gain insights into optimal conditions for a given welding task. In the present study, a three-pass tungsten inert gas (TIG) groove weld in SA508 Gr.3 Cl.1 ferritic steel is numerically investigated using the ABAQUS finite element code with a user defined subroutine to incorporate the effect of SSPT kinetics. Parametric sensitivity is assessed whereby a representative heat input is applied to simulate weld deposition for each pass, and the inter-pass temperature is varied to examine its effect on WRS and distortion in the weldment. The implications of the overall heat input on cross-weld microstructure are also presented using this approach. © 2016 by ASME