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- Olofsson, Jakob, 1980-, et al.
(author)
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Characterisation and investigation of local variations in mechanical behaviour in cast aluminium using gradient solidification, Digital Image Correlation and finite element simulation
- 2014
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In: Materials & Design. - : Elsevier. - 0261-3069. ; 56, s. 755-762
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Journal article (peer-reviewed)abstract
- Due to design and process-related factors, there are local variations in the microstructure and mechanical behaviour of cast components. This work establishes a Digital Image Correlation (DIC) based method for characterisation and investigation of the effects of such local variations on the behaviour of a high pressure, die cast (HPDC) aluminium alloy. Plastic behaviour is studied using gradient solidified samples and characterisation models for the parameters of the Hollomon equation are developed, based on microstructural refinement. Samples with controlled microstructural variations are produced and the observed DIC strain field is compared with Finite Element Method (FEM) simulation results. The results show that the DIC based method can be applied to characterise local mechanical behaviour with high accuracy. The microstructural variations are observed to cause a redistribution of strain during tensile loading. This redistribution of strain can be predicted in the FEM simulation by incorporating local mechanical behaviour using the developed characterization model. A homogeneous FEM simulation is unable to predict the observed behaviour. The results motivate the application of a previously proposed simulation strategy, which is able to predict and incorporate local variations in mechanical behaviour into FEM simulations already in the design process for cast components.
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- Olofsson, Jakob, 1980-, et al.
(author)
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Closed chain simulations of a cast aluminium component - Incorporating casting process simulation and local material characterization into stress-strain simulations
- 2014
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In: ISIJ International. - Tokyo, Japan : The Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:2, s. 259-265
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Journal article (peer-reviewed)abstract
- The coupling between simulations of solidification, microstructure and local mechanical behaviour and simulation of stress-strain behaviour is studied by applying a recently developed simulation strategy to a high pressure die cast aluminium component. In the simulation strategy, named a closed chain of simulations for cast components, the mechanical behaviour throughout the component is determined locally by a casting process simulation. The entire casting process, including mould filling and solidification, is simulated to predict the formation of microstructure and residual stresses throughout the component, and material characterization models are applied to relate microstructural features to local elastic and plastic mechanical material behaviour. The local material behaviour is incorporated into a finite element method (FEM) stress-strain simulation of a realistic load case of the component in service.In the current contribution the influences of local variations in mechanical behaviour and residual stresses on the component behaviour are investigated. The simulation results for local microstructure and mechanical behaviour are compared to experimental results, and the predicted local mechanical behaviour is incorporated on an element level into the FEM simulation. The numerical effect of the variations in mechanical behaviour is quantified by comparing the results achieved using local behaviour and homogeneous behaviour. The influence of residual stresses predicted by the casting process simulation on the component behaviour is also studied.The casting process simulation is found to accurately predict the local variations in microstructure throughout the component, and the local variations in mechanical behaviour are well described. The numerical results show that casting process simulation and modelling of microstructure formation, material behaviour and residual stresses are important contributions to correctly predict the behaviour of a cast aluminium component in service. This motivates the use of the proposed simulation strategy, and show the importance of incorporating materials science and casting process simulations into structural analyses of cast components. It is discussed that integration of these areas, e.g. using the closed chain of simulations, is important in order to increase the accuracy of FEM simulations and the product development efficiency in the future.
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- Svensson, Ingvar L., et al.
(author)
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Mathematical characterization of the tensile deformation curve of cast iron materials
- 2018
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In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. - 9783035710557 ; 925, s. 444-450
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Journal article (peer-reviewed)abstract
- The manufacturing process gives cast iron castings properties which are dependent on component design, metallurgy and casting method. Factors such as local wall thickness influences the coarseness and type of microstructure and the castings will have local properties depending on the local metallurgical and thermal history. The stress/strain behaviour of cast materials is typically determined by performing a tensile test in a tensile test machine. The deformation behaviour will normally be determined by two mechanisms, namely, elastic and plastic phenomena. The plastic behaviour is based on dislocation movements in the lattice. Commonly, the deformation history of cast iron involves elastic, plastic and crack phases. The cast iron material has a complex microstructure and first order equations cannot be used to predict the deformation during loading. Until methods have been developed, the characterization of complex microstructure materials such as cast iron has to be determined by use of empirical methods. The empirical methods have to couple the internal microstructure and composition of the material with deformation phenomena during loading. The paper will show a method to characterize tensile test curves of cast iron materials which can be used to couple deformation phenomena with for example microstructure. The equations are aimed to make the tensile test curve ready for curve fitting and optimization in two steps. Each stress/strain curve is like a finger print of the material and requires well performed tests and some advices are given. The paper also wants to encourage researchers and people working with tensile testing to get out more of their effort to measure strength of cast iron materials and connect the result to the microstructure of the specimens.
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- Bäckman, Jonas, et al.
(author)
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Influence of ingate system design on mechanical properties for a cast A1-10Si-0.38Mg alloy
- 1999
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Reports (other academic/artistic)abstract
- In this work the influence of the ingate system design on the as-cast mechanical properties of an Al-10Si-0.38Mg alloy have been clarified. The Weibull distribution has been seen to describe the spread in mechanical properties very well. The Weibull modulus has therefore been used as a measure of the soundness of an ingate system. Different ingate systems were investigated, including: expanding systems, pressurised systems, systems with and without filter, systems with different designs of the connection between the downsprue and the runner, and systems with and without an additional pocket at the end of the runner. The modification index of the microstructure was also measured in order to investigate if the spread in data is more dependent on the modification index than on the ingate system design. The results showed that a high Weibull modulus is more dependent on the ingate system design than on the modification index of the microstructure. The ultimate tensile strength was not significantly affected by the ingate system design, while the fracture elongation seemed to be more dependent on the melt quality than on the ingate system design. The Weibull modulus indicates that expanding systems are better than pressurised systems, and that the use of a filter in the runner is very beneficial. An additional pocket at the end of the runner has no beneficial effect when using a filter. The connection between the downsprue and the runner should have a rounded bend and the change in cross-section between the downsprue and the runner should be chamfered and not sharp.
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- Dugic, Izudin, 1962-, et al.
(author)
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An investigation of the effect of inoculants on the metal expansion penetration in grey iron
- 1999
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In: International Journal of Cast Metals Research. - 1364-0461 .- 1743-1336. ; 11:5, s. 333-338
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Journal article (peer-reviewed)abstract
- The production of quality castings requires the casting surface to be clean and free fromdefects. In some grey cast iron components which are cast in sand moulds, the metalsometimes penetrates into the mould, producing difficulties in cleaning the components. Thedefect causes very high costs due to component rejection and increased fettling in the castingindustry. Most of the grey iron foundries around the world have problems with metalpenetration on applicable components.In this work the problem of metal penetration has been studied using a commercial castingcomponent. Eight castings were mounted on the pattern plate and five different inoculantswere investigated. The experiments show that the inoculation of grey cast iron will influencethe metal penetration in areas with late solidification times and where the melt is in contactwith the sand mould. In all experiments 0.14 % inoculant was added in the pouring ladle.The experiments show that the best results to reduce metal penetration have been obtainedwhen using the inoculant which contained silicon, aluminium and zirconium. Using thisinoculant, the average penetration area was only about 20 % of what was found using theworst inoculant. However, this inoculant also gave rise to a large tendency to formation sinks.The experiments also show two main classes of eutectic cell size. One class nucleated at thebeginning of the eutectic solidification and one at the end of the solidification.Two other inoculants, both containing Al and Si have about the same base composition. Fromthe measurements of penetration areas, one can draw the conclusion that the inoculant withthe smallest grain size gives nuclei with the shortest lifetime. The coarser grains give a longerdissolution time and this promotes the survival of the nuclei. At the end of solidification, a larger amount of graphite will precipitate at higher temperatures if new nuclei can beactivated. If the hot spot is located close to the metal surface, the metal will expand into themould; resulting in metal expansion penetration.The worst cases of metal penetration have been obtained using an inoculant containingtitanium. A large number of small eutectic cells and high volume of the small cells wereobserved, which leads to severe penetration.
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