| 1. |
- Hedström, Peter, et al.
(författare)
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Load partitioning and strain-induced martensite formation during tensile loading of a metastable austenitic stainless steel
- 2009
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Ingår i: Metallurgical and Materials Transactions A - Physical Metallurgy and Materials Science. - Springer New York LLC. - 1073-5623. ; 40:5
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- In-situ high-energy X-ray diffraction and material modeling are used to investigate the strain-rate dependence of the strain-induced martensitic transformation and the stress partitioning between austenite and α′ martensite in a metastable austenitic stainless steel during tensile loading. Moderate changes of the strain rate alter the strain-induced martensitic transformation, with a significantly lower α′ martensite fraction observed at fracture for a strain rate of 10-2 s-1, as compared to 10-3 s-1. This strain-rate sensitivity is attributed to the adiabatic heating of the samples and is found to be well predicted by the combination of an extended Olson-Cohen strain-induced martensite model and finite-element simulations for the evolving temperature distribution in the samples. In addition, the strain-rate sensitivity affects the deformation behavior of the steel. The α′ martensite transformation at high strains provides local strengthening and extends the time to neck formation. This reinforcement is witnessed by a load transfer from austenite to α′ martensite during loading.
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| 2. |
- Larsson, C., et al.
(författare)
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Measurement and modeling of residual stress in a welded Haynes® 25 cylinder
- 2005
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Ingår i: Materials Science and Engineering A: Structural Materials: Properties, Microstructures and Processing. - Elsevier S.A.. - 0921-5093. ; 399:1-2
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld, used to join a hemispherical end cap to a cylinder. The capped cylinder is used in a satellite application and was fabricated from a Co-based Haynes® 25 alloy. The cylinder was 34.7 mm in outer diameter and 3.3 mm in thickness. The experimental measurements were made by neutron diffraction and the simulation used the implicit Marc finite element code. The experimental resolution was limited to approximately 3 mm parallel to the axis of the cylinder (the weld was 6 mm in the same direction) and comparison over the same volume of the finite element prediction showed general agreement. Subject to the limited spatial resolution, the largest experimentally measured tensile residual stress was 180 MPa, located at the middle of the weld. However, the predictions suggest that there are regions in the weld where average tensile residual stresses as much as 400 MPa exist. One qualitative disparity between the model and the experiments was that the measurement included a larger degree of asymmetry on either side of the weld than predicted by the model.
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| 3. |
- Liu, J., et al.
(författare)
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Finite element modelling of superplastic-like forming using a dislocation density-based model for AA5083
- 2013
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Ingår i: Modelling and Simulation in Materials Science and Engineering. - Institute of Physics Publishing. - 0965-0393. ; 21:2
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- Superplastic-like forming is a newly improved sheet forming process that combines the mechanical pre-forming (also called hot drawing) with gas-driven blow forming (gas forming). Non-superplastic grade aluminium alloy 5083 (AA5083) was successfully formed using this process. In this paper, a physical-based material model with dislocation density and vacancy concentration as intrinsic foundations was employed. The model describes the overall flow stress evolution of AA5083 from ambient temperature up to 550 °C and strain rates from 10−4 up to 10−1 s−1. Experimental data in the form of stress–strain curves were used for the calibration of the model. The calibrated material model was implemented into simulation to model the macroscopic forming process. Hereby, finite element modelling (FEM) was used to estimate the optimum strain-rate forming path, and experiments were used to validate the model. In addition, the strain-rate controlled forming was conducted for the purpose of maintaining the gas forming with an average strain rate of 2 × 10−3 s−1. The predicted necking areas closely approximate the localized thinning observed in the part. Strain rate gradients as a result of geometric effects were considered to be the main reason accounting for thinning and plastic straining, which were demonstrated during hot drawing and gas forming by simulations.
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| 4. |
- Tam, S.C., et al.
(författare)
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Computer simulation of temperature fields in mechanised plasma-arc welding
- 1989
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Ingår i: Journal of Mechanical Working Technology. - Elsevier. - 0378-3804. ; 19:1
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- The process of the mechanised plasma-arc butt-welding of thin-gauge mild-steel sheets has been studied, both theoretically and experimentally. The transient temperature distribution has been computed using an analytical model due to Rosenthal. The results have then been compared with those generated by finite-element analysis using the commercial package PAFEC. The two sets of results were found to be in reasonably good agreement; moreover, the theoretical values were found to correlate fairly well with the results of experiments performed on a Messer Griesheim Uniwig G-200P plasma-arc welding machine. The extent of the heat-affected zone (HAZ) in the butt-welded specimens has been computed by analysing the temperature history at points lying transverse to the weldment: the theoretical values match fairly closely with those obtained from the welding experiments. The efficiency of the plasma-arc welding process has been estimated to be around 32% to 35%.
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| 5. |
- Toda-Caraballo, I., et al.
(författare)
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Effect of residual stress on recrystallization behavior of mechanically alloyed steels
- 2010
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Ingår i: Scripta Materialia. - Pergamon. - 1359-6462. ; 62:1
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- This paper presents a finite element modeling analysis of deformation on iron-base mechanically alloyed oxide dispersion strengthened alloy by spherical indentations (Brinell test). Results of the model are used to interpret the role of residual shear stresses on the development of recrystallized grain structure and the temperature at which recrystallization occurs.
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| 6. |
- Lindgren, Lars-Erik, et al.
(författare)
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Automatic remeshing for three-dimensional finite element simulation of welding
- 1997
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - Elsevier BV. - 0045-7825. ; 147:3-4
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- Three-dimensional finite element simulation of electron beam welding of a large copper canister has been performed. The use of an automatic remeshing algorithm, based on a graded hexahedral element was found to be effective. With this algorithm the strongly nonlinear thermomechanical effects locally close to the moving heat source can accurately be modelled using a dense element mesh that follows the heat source.
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| 7. |
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