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Pittel, C. Bleicher, H. Kaufmann. Fraunhofer Institute for Structural Durability and System Reliability LBF, Germany.
ASSESSMENT OF LOCAL COMPONENT STRENGTH BASED ON THE VIRTUAL LIMITING SAMPLE CONSIDERING THE FATIGUE STRENGTH INFLUENCED BY CASTING IMPERFECTIONS.
Abstract
Cast components made of nodular cast iron (GJS) are widely used in the wind energy sector due to their high freedom in design and cost-effectiveness. The occurrence of material imperfections such as shrinkages, dross, or chunky graphite is crucial in terms of fatigue life and can result in rework or component rejection. The fatigue life assessment of large castings with material imperfections requires knowledge of the material strength and additional information taken from casting process simulations and from non-destructive testing (NDT). Investigations on specimens with shrinkages, dross,or chunky graphite made of EN GJS 400 18 LT, EN GJS 450-18, EN GJS 700 2, and ADI 1050 are based on strain-controlled fatigue tests. The results are correlated with the results of computer tomography (CT) images to provide information on the influence of imperfections on fatigue strength. In addition, metallographic and fractographic investigations on failed fatigue specimens are correlated with the results of the fatigue tests. The results of all these investigations are included in the virtual limiting sample to derive the influence of the respective imperfection sizes on the fatigue strength of the cast component. To reduce the component rejection, the information on locally-detected imperfections and the resulting local stress can be compared with the local material strength. Furthermore, it helps to assign an acceptable size of imperfections for each component area, depending on the local stress and the required fatigue life. For example, in areas of high stresses, either none or only small imperfections are allowable, while in areas subject to low stresses larger imperfections are also allowable without risking a premature failure of the component.
Keywords: nodular cast iron, local fatigue strength, casting imperfections, local microstructure, virtual limiting sample.
2.
Zovko Brodarac, A. Mahmutovic, S. Zeljko, L. Zeljko. University of Zagreb, Faculty of Metallurgy, Sisak, Croatia, Livarstvo d.o.o., Slovenia, Plamen d.o.o., Pozega, Croatia.
EFFICIENCY OF NUMERICAL SIMULATION IN OPTIMIZATION OF CASTING PRODUCTION.
Abstract
Grey cast iron is frequently used in industry, due to its good thermal conductivity, low price, and good mechanical properties. Chemical properties and solidification conditions have a significant influence on microstructure and mechanical properties development. The most common use of grey cast iron is in the automotive industry and heating elements. The application in the casting of thin-walled castings requires careful elaboration of the technological casting process parameters due to the curving tendency and the appearance of the burn. The advantage of numerical simulations is ineffective and fast calculation of pouring and solidification of castings. Economic advantage lies in the fast change of more different product variations in a short time. The experimental part of this paper has several versions of the numerical simulation of the casting process. The first one is the original geometry, which has been used in the regular casting process of thin-walled castings framework for fireplace doors. Other versions with optimizing the geometry of the castings have been elaborated. The pouring process of all casting versions of EN GJL-200 quality was performed followed by an investigation of casting quality and process parameters interaction. The influence of clamp position, ingates size, and temperature distribution during casting solidification on microstructure development, hardness, and tensile strength of grey cast iron EN GJL-200 casting samples was determined and compared with the results obtained by numerical simulation.
Keywords: grey cast iron, numerical simulation, microstructure, mechanical properties, optimization.
3.
Voncina, T. Balasko, K. Rudolf, J. Medved. Livarski vestnik. Faculty of Natural Sciences and Engineering, University of Ljubljana, Slovenia.
INFLUENCE OF SPECIFIC SURFACE AND RECYCLING ALUMINIUM CONTENT ON QUALITY OF AlSi10Mg(Fe) ALLOY.
Abstract
Recycling is of great importance for the conservation of raw material resources and the reduction of environmental pollution. The amount of used secondary material in the production of aluminium alloys is increasing every year. If new and old scrap is pre-treated and sorted, recycled aluminium can be used for almost any purpose. The quality of the material depends on several factors: scrap purity, coatings, specific surfaces, etc.
The objective of the study was to analyse the effects of different proportions of recycled alloy and specific surface area on the quality of the alloy produced. Seven samples were produced and analysed. The first sample, which served as the basis, consisted of 100% of the input alloy ingot, and the other six were made from different proportions of recycled alloy with different specific surfaces. All samples were analysed in the as-cast state.
It was confirmed that the melting efficiency decreases with an increasing proportion of recycled alloy used and with the increasing specific surface area of the recycled alloy. The chemical analysis changes significantly with the addition of different proportions of the recycled alloy used with different specific surface areas. Iron accumulates in the alloy, causing an increase in the amount of β-Al5FeSi needle phase and a decrease in the tensile strength and elongation at break compared to the sample prepared from the ingot only.
Keywords: aluminium recycling, the proportion of recycled material, specific surface area, solidification, microstructure, mechanical properties.