Browsing by Author "Hamelin, CJ"

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    Electron beam weld modelling of ferritic steel: effect of prior-austenite grain size on transformation kinetics
    (Elsevier B. V., 2020-11-19) Vasileiou, AN; Hamelin, CJ; Smith, MC; Francis, JA; Sun, YL; Flint, TF; Xiong, Q; Akrivos, V
    Ferritic steels experience solid-state phase transformation (SSPT), which causes volumetric changes due to differences in the atomic packing density of different phases in the steel. The importance of the prior austenite grain size (PAGS) as an input physical variable is assessed, for adequately modelling the anisothermal SSPT during welding of ferritic steels. The knowledge of the PAGS value pre-requires a thorough microstructural study of each particular weld, information that might be difficult to acquire. A relationship between hardness, PAGS and phase fractions is proposed to be used to feed in weld models. The case of a single-pass, autogenous, reduced-pressure electron beam weld is used for this study. The adequacy of the finite-element weld model in predicting the micro-constituents, the hardness and the residual stress is demonstrated via comparing the predicted results of the thermo-metallurgical and stress analyses with the set of corresponding experimental data. This work aims at providing a better understanding of the impact of PAGS on transformation kinetics and best practice guidelines for modelling, using an extensively validated electron beam weld model as baseline. © 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
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    The impact of axi-symmetric boundary conditions on predicted residual stress and shrinkage in a PWR nozzle dissimilar metal weld
    (American Society of Mechanical Engineers (ASME), 2012-07-15) Bendeich, PJ; Muránsky, O; Hamelin, CJ; Smith, MC; Edwards, L
    Simulation of a dissimilar metal weld (DMW) in a pressurised water reactor (PWR) nozzle was performed to predict both axial distortion and hoop residual stresses in the weld. For this work a computationally efficient axi-symmetric finite element (FE) simulation was carried out rather than a full 3D analysis. Due to the 2-dimensional nature of the analysis it was necessary to examine the effect of structural restraint during welding of the main dissimilar metal weld (DMW). Traditionally this type of analysis is set up to allow one end of the structure, in this case the safe-end forging, to be unrestrained in the axial direction during welding. In reality axial expansion and subsequent contraction of deposited weld metal at the current torch position is restrained by solidified material both ahead and behind the torch. Thus the conventional axi-symmetric analysis is under-restrained in the axial direction at least during the early weld passes. The significance of this was examined by repeating the current simulation with the safe-end forging fixed to limit expansion during the heat up cycle. Contraction was however, allowed during cooling cycle. This modified boundary control method provided a significantly improved prediction of the axial distortion across the weld as well as improved prediction of through wall axial and hoop residual stresses. Copyright © 2012 The American Society of Mechanical Engineers
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    The influence of austenite grain size during welding simulations of ferritic steels
    (Trans Tech Publications, 2014-08) Hamelin, CJ; Muránsky, O; Edwards, L
    In recent years, considerable progress has been made in the simulation of ferritic steel welding processes. The successful validation of a single-pass autogenous TIG beam weld in SA508 Gr.3 Cl.1 steel has identified key simulation variables required for the accurate prediction of post-weld residual stress in ferritic weldments. The present work outlines a sensitivity study performed to examine the influence of austenite grain growth on predicted solid-state phase transformation kinetics and consequently, residual stress predictions.© 2014, Trans Tech Publications.
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    The influence of constitutive material models on accumulated plastic strain in finite element weld analyses
    (Elsevier, 2015-09-01) Muránsky, O; Hamelin, CJ; Patel, VI; Braham, C
    Recent studies in computational weld mechanics have revealed the importance of the material plasticity model when predicting weld residual stresses. The present work seeks to extend this level of understanding to include the effects of the assumed material annealing behaviour, particularly when modelling multi-pass welds that comprise several thermo-mechanical loading cycles. A series of numerical analyses are performed to examine the variability in predicted residual stress profiles for different material models, using a validated finite element model for a three-pass slot weld in AISI 316LN austenitic steel. The material models consider both the work hardening and annealing assumptions for the chosen material. Model sensitivity is established not only from a weld residual stress perspective, but also from an assessment of the post-weld plastic strain accumulated in the weldment. Predictions are compared with indirect measurements acquired using cross-weld micro-hardness maps taken from benchmark specimens. Sensitivity studies reveal that the choice of annealing behaviour will have a significant impact on plastic flow predictions, which is dependent on the annealing temperature specified. Annealing assumptions will have a varying impact on the weld residual stress predictions, such that the extent of sensitivity is dependent on the plasticity model chosen. In contrast, the choice of plasticity model will have a significant effect on the predicted weld residual stresses, but relatively little effect on predictions of equivalent plastic strain. © 2015 Elsevier Ltd.
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    Investigating optimal cutting configurations for the contour method of weld residual stress measurement
    (Elsevier, 2018-07) Muránsky, O; Hosseinzadeh, F; Hamelin, CJ; Traore, Y; Bendeich, PJ
    The present work examines optimal cutting configurations for the measurement of weld residual stresses (WRS) using the contour method. The accuracy of a conventional, single-cut configuration that employs rigid clamping is compared with novel, double-embedded cutting configurations that rely on specimen self-constraint during cutting. Numerical analyses examine the redistribution of WRS and the development of cutting-induced plasticity (CIP) in a three-pass austenitic slot weld (NeT TG4) during the cutting procedure for each configuration. Stress intensity factor (SIF) analyses are first used as a screening tool; these analyses characterise lower stress intensities near the cutting surface when double-embedded cutting configurations are used, relative to SIF profiles from a single-cut process. The lower stress intensities indicate the development of CIP – which will ultimately affect back-calculated WRS – is less likely to occur when using an embedded configuration. The improvements observed for embedded cutting approaches are confirmed using three-dimensional finite element (FE) cutting simulations. The simulations reveal significant localised plasticity that forms in the material ligaments located between the pilot holes and the outer edges of the specimen. This plasticity is caused by WRS redistribution during the cutting process. The compressive plasticity in these material ligaments is shown to reduce the overall tensile WRS near the weld region before this region is sectioned, thereby significantly reducing the amount of CIP when cutting through the weld region at a later stage of the cutting procedure. Further improvements to the embedded cutting configuration are observed when the equilibrating compressive stresses in material ligaments are removed entirely (via sectioning) prior to sectioning of the high WRS region in the vicinity of the weld. All numerical results are validated against a series of WRS measurements performed using the contour method on a set of NeT TG4 benchmark weld specimens. © 2017 Elsevier Ltd.
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    Mitigating cutting-induced plasticity in the contour method. Part 2: Numerical analysis
    (Elsevier, 2016-09-01) Muránsky, O; Hamelin, CJ; Hosseinzadeh, F; Prime, MB
    Cutting-induced plasticity can have a significant effect on the measurement accuracy of the contour method. The present study examines the benefit of a double-embedded cutting configuration that relies on self-restraint of the specimen, relative to conventional edge-crack cutting configurations. A series of finite element analyses are used to simulate the planar sectioning performed during double-embedded and conventional edge-crack contour cutting configurations. The results of numerical analyses are first compared to measured results to validate the cutting simulations. The simulations are then used to compare the efficacy of different cutting configurations by predicting the deviation of the residual stress profile from an original (pre-cutting) reference stress field, and the extent of cutting-induced plasticity. Comparisons reveal that while the double-embedded cutting configuration produces the most accurate residual stress measurements, the highest levels of plastic flow are generated in this process. This cutting-induced plastic deformation is, however, largely confined to small ligaments formed as a consequence of the sample sectioning process, and as such it does not significantly affect the back-calculated residual stress field. © 2016 Elsevier Ltd.
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    Numerical analysis of the effect of weld-induced residual stress and plastic damage on the ballistic performance of welded steel plate
    (Elsevier, 2012-06-01) Flores-Johnson, EA; Muránsky, O; Hamelin, CJ; Bendeich, PJ; Edwards, L
    The current paper presents numerical analyses that elucidate the effects of post-weld residual stress and associated plastic damage on the ballistic performance of 316L austenitic steel plate. Impact simulations of an 18 mm thick plate with a centreline three-pass slot weld by hemispherical-nosed and flat-nosed projectiles are performed, with initial velocities in the range of 300-800 m/s. The numerical framework consists of three interdependent stages: (i) a weld model was developed in Abaqus/Standard and validated using two independent experimental data sets; (ii) a Johnson-Cook material model is calibrated and validated along with the shear failure fracture criterion available in Abaqus/Explicit for impact models; and (iii) the weld modelling results were transferred to an impact model built in Abaqus/Explicit, which employs the validated material and fracture models to predict the ballistic performance of welded plate. It is shown that the associated plastic strain damage accumulated during the welding process - and its distribution - has an adverse effect on the ballistic performance. It has also been determined that a fracture criterion that accounts for pre-existing damage in the weldment must be used for accurate impact analyses of welded structures. Crown Copyright (C) 2012 Published by Elsevier B.V.
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    Prediction and measurement of weld residual stresses in thermally aged girth-welded austenitic steel pipes
    (American Society of Mechanical Engineers (ASME), 2012-07-15) Muránsky, O; Smith, MC; Bendeich, PJ; Hamelin, CJ; Edwards, L
    The current paper describes finite element simulation of the complete manufacturing and service exposure history of girth-welded austenitic steel pipes fabricated from ESSHETE 1250 material for the STYLE Framework 7 project. The simulation campaign examines the impacts of prior quenching of pipe material, fabrication of closely adjacent welds, variation in mixed isotropic-kinematic hardening material constitutive models, and high temperature (650°C) service exposure (thermal ageing). The predicted residual stresses are validated using measurements made with the deep hole drilling (DHD) and incremental deep hole drilling (iDHD) techniques. Copyright © 2012 The American Society of Mechanical Engineers
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    The role of plasticity theory on the predicted residual stress field of weld structures
    (Materials Science Forum, 2014-11) Muránsky, O; Hamelin, CJ; Smith, MC; Bendeich, PJ; Edwards, L
    Constitutive plasticity theory is commonly applied to the numerical analysis of welds in one of three ways: using an isotropic hardening model, a kinematic hardening model, or a mixed isotropic-kinematic hardening model. The choice of model is not entirely dependent on its numerical accuracy, however, as a lack of empirical data will often necessitate the use of a specific approach. The present paper seeks to identify the accuracy of each formalism through direct comparison of the predicted and actual post-weld residual stress field developed in a three-pass 316LN stainless steel slot weldment. From these comparisons, it is clear that while the isotropic hardening model tends to noticeably over-predict and the kinematic hardening model slightly under-predict the residual post-weld stress field, the results using a mixed hardening model are quantitatively accurate. Even though the kinematic hardening model generally provides more accurate results when compared to an isotropic hardening formalism, the latter might be a more appealing choice to engineers requiring a conservative design regarding weld residual stress. © 2014, Trans Tech Publications.
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    A validated numerical model for residual stress predictions in an eight-pass-welded stainless steel plate
    (Trans Tech Publications, 2014-02-06) Patel, VI; Muránsky, O; Hamelin, CJ; Olson, MD; Hill, MR; Edwards, L
    Welding processes create a complex transient state of temperature that results in post-weld residual stresses. The current work presents a finite element (FE) analysis of the residual stress distribution in an eight-pass slot weld, conducted using a 316L austenitic stainless steel plate with 308L stainless steel filler metal. A thermal FE model is used to calibrate the transient thermal profile applied during the welding process. Time-resolved body heat flux data from this model is then used in a mechanical FE analysis to predict the resultant post-weld residual stress field. The mechanical analysis made use of the Lemaitre-Chaboche mixed isotropic-kinematic work-hardening model to accurately capture the constitutive response of the 316L weldment during the simulated multi-pass weld process, which results in an applied cyclic thermo-mechanical loading. The analysis is validated by contour method measurements performed on a representative weld specimen. Reasonable agreement between the predicted longitudinal residual stress field and contour measurement is observed, giving confidence in the results of measurements and FE weld model presented.
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    Validation of a numerical model used to predict phase distribution and residual stress in ferritic steel weldments
    (Elsevier, 2014-08-15) Hamelin, CJ; Muránsky, O; Smith, MC; Holden, TM; Luzin, V; Bendeich, PJ; Edwards, L
    Numerical finite element analyses were combined with experimental observation of a single-pass autogenous beam weld in SA508 Gr.3 Cl.1 ferritic steel. Two weldment sets were prepared using different weld heat inputs, resulting in different post-weld residual stress and ferritic phase distributions. Neutron diffraction was employed to measure the residual stress distribution while microhardness measurements were used to measure the post-weld phase distribution in each weldment. In both cases, the numerical model accurately predicts the ferritic phase distribution and residual stress field. Model predictions illustrate how the higher cooling rates associated with a faster torch speed result in an increased martensite volume fraction within the weldment. Consideration of both the transformation kinetics and transformation plasticity are proven to significantly improve model accuracy when comparing measured and predicted residual stress profiles. © 2014, Acta Materialia Inc.