| 1. |
- Andersson, Björn, 1989, et al.
(författare)
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Computationally efficient simulation methodology for railway repair welding: cyclic plasticity, phase transformations and multi-phase homogenization
- 2024
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Ingår i: Journal of Thermal Stresses. - 0149-5739 .- 1521-074X. ; 47:2, s. 164-188
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Tidskriftsartikel (refereegranskat)abstract
- The in-situ railway repair welding process consists of multiple weld passes, which makes it significantly different from other rail welding processes. In this study, finite element simulations of repair welding are performed to predict the resulting microstructure and residual stresses. To accurately simulate the material behaviour, the modelling includes phase transformation kinetics, cyclic hardening plasticity, transformation induced plasticity, and multi-phase homogenization. More specifically, four different homogenization methods are investigated: isostrain, isostress, self-consistent and linear mixture rule. The performance of the material modelling is demonstrated by simulating multiple weld passes using a classical three-bar welding experiment. Based on the results, the self-consistent method and linear mixture rule are used in a 3D full-scale railhead repair weld simulation, in which the former generates a more realistic mechanical response. The immense computational cost associated with 3D full-scale, full-detail multi-pass welding simulations is addressed by exploring different model reduction schemes. From this study, a 2D generalized plane strain model, extended with out-of-plane axial and bending stiffness, is found to replicate the full-scale model at a mere fraction of the computational cost. Finally, the longitudinal residual stress distribution obtained from the reduced model is shown to correlate well with experimental measurements.
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| 2. |
- Andersson, Björn, 1989, et al.
(författare)
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Homogenization based macroscopic model of phase transformations and cyclic plasticity in pearlitic steel
- 2022
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Ingår i: Journal of Thermal Stresses. - : Informa UK Limited. - 0149-5739 .- 1521-074X. ; 45:6, s. 470-492
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution macroscopic modeling of phase transformations and mechanical behavior of low alloy steels are developed and investigated. Such modeling is of importance in simulations of transient thermo-mechanical processes which can cause phase transformations, examples from the railway industry include train braking induced frictional heating as well as rail grinding and welding operations. We adopt a modeling approach which includes phase transformation kinetics and individual constitutive models for the phases in combination with different homogenization methods. Algorithmic implementations of the isostrain, isostress and self-consistent homogenization methods are presented and demonstrated in finite element simulations of a laser heating experiment. Stress field results from the different homogenization methods are compared against each other and also against experimental data. The importance of including transformation induced plasticity in the modeling is highlighted, as well as the multi-phase stages of the heating and cooling.
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| 3. |
- Bhatti, Ayjwat Awais, 1983-
(författare)
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Computational weld mechanics : Towards simplified and cost effective FE simulations
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is the demand of the world’s ever increasing energy crisis to reduce fuel consumption wherever possible. One way of meeting this demand is by reducing the weight of a structure by replacing thick plates of low strength steel with thin plates of high strength steel in the structure. Fusion welding process is extensively used in the manufacturing industry, however, despite many advantages different problems such as weld defects, residual stresses and permanent distortions are associated with this process.Finite element (FE) method has proved itself as an alternative and acceptable tool for prediction of welding residual stresses and distortions. However, the highly nonlinear and transient nature of the welding process makes the FE simulation computationally intensive and complex. Thus, simplified and efficient welding simulations are required so that they can be applied to industrial scale problems.In this research work an alternative FE simulation approach for the assessment of welding residual stresses, called rapid dumping is developed. This approach proved to be efficient and predicted the residual stress with acceptable accuracy for different small scale welded joints. This approach was further implemented on a large scale welded structures along with other available approaches. It was found that the computational time involved in the welding simulations for large structures using rapid dumping approach can be reduced but at the cost of accuracy of the results.Furthermore, influence of thermo-mechanical material properties of different steel grades (S355-S960) on welding residual stresses and angular distortion in T-fillet joints is investigated. It is observed that for assessment of residual stresses, except yield stress, all of the thermo-mechanical properties can be considered as constant. For the prediction of angular distortions with acceptable accuracy, heat capacity, yield stress and thermal expansion should be employed as temperature dependent in the welding simulations.Finally, the influence of two different LTT (Low Transformation Temperature) weld filler material on residual stress state and fatigue strength was investigated. It was observed that a reduction in tensile residual stresses at the weld toe of the joint was observed. Furthermore, at higher R-ratio no significant increase in the fatigue strength was observed . However, at low R-ratio significant increase in fatigue strength was observed.
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| 4. |
- Brouzoulis, Jim, 1984, et al.
(författare)
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Orbital friction welding of steel bars – heat generation and process modelling
- 2023
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications. - : SAGE Publications. - 1464-4207 .- 2041-3076. ; 237:8, s. 1715-1724
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Tidskriftsartikel (refereegranskat)abstract
- Welding of rails in the field is usually associated with a large heat input, which results in a large heat-affected zone (HAZ), which in turn may impair the welded rail head and decrease its service life. An innovative orbital friction welding (OFW) process with an intermediate eccentrically oscillating disk is proposed, and a demonstrator has been constructed. This enables welding of rails, which have a non-symmetric cross-sectional area and must be stationary during welding. The process is characterized by low heat input, creating a narrow HAZ, and low welding deformations. A thermo-mechanical finite element model is developed to determine suitable process parameters to create a narrow HAZ. A phenomenological model for heat generation during friction welding is developed for pearlitic rail steel with parameters calibrated from rotary friction welding experiments on pipes. The temperature dependence of the friction coefficient in the interface is established. Pilot tests with the demonstrator OFW machine on bars with a quadratic cross section showed that preheating will be required to guarantee a fully pearlitic weld zone. This was verified by the simulations of the thermo-mechanical finite element model.
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| 6. |
- Gaiotti, Marco, et al.
(författare)
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A numerical sensitivity analysis on the cohesive parameters of a carbon-steel single lap joint
- 2020
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 198
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Tidskriftsartikel (refereegranskat)abstract
- One of the key issues concerning the use of composite materials in the construction of steel ships, or vice versa, the use of steel in the construction of composite ships, is related to the ways of joining composite parts to the adjacent steel structure. Carbon-steel joints are of increasing interest for the maritime industry, but knowledge is scarce. Applications of adhesive joints as an alternative method to welding or riveting has numerous advantages. Still, gathering more information about the behaviour of such joints through numerical sensitivity analysis and simulation are necessary to speed up applications on ships and marine structures. The present investigation aims at assessing the sensitivity of the parameters that define the traction separation law on the numerical simulation of the de-bonding of a steel to composite single lap joint, following a previous experimental campaign. The test is intended to induce a mode II separation, although the slight bending moment caused by the misalignment of the two ends leads to mixed mode effects, as well. Two finite element software were compared, ADINA and LS-DYNA. The influence of peak traction, penalty stiffness and energy release rate were investigated, along with the effect of a mixed mode opening behaviour.
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