When casting complex shapes for structural applications, variation in microstructural features and thus material properties will exist in the final part due to differences in cooling rate and solidification time between different sections of the casting. One such microstructural feature is Dendrite Arm Spacing (DAS), which closely correlates with local solidification time. Variation in the DAS field is associated with differences in local strength, causing different regions of the part to be more or less resistant to failure, depending on location. Structural simulation can be used to predict the expected stresses in a component, but analyzing the effect of these stresses against an accurate set of local material properties that reflect the differences in strength within the part has not been possible. Commercially available software packages for casting simulation are capable of predicting local solidification time throughout a casting. Predicted local solidification time can be readily converted to DAS via simple empirical relationships between the two that are built into popular codes. In this way, a continuous map of DAS can be established. Mechanical properties can be determined and associated with specific DAS values in regions of the casting where the properties pertain. This results in establishment of a relationship between DAS and strength for discrete DAS values. This paper details a study substantiating this approach, herein called 'property mapping' in developing fields of tensile strength and fatigue strength used in Goodman analysis for safety factor calculations. It could be shown that predicted DAS from solidification modeling correlates well with measured DAS. Predicted DAS also correlates well with other microstructural features such as porosity and maximum pore section size, and with mechanical properties such as UTS and HCF. Solidification modeling can be extended beyond its normal scope of use, and be combined with mechanical testing, to develop a map of mechanical properties in a casting based on a microstructural feature such as DAS. Use of node-by-node properties that reflect local solidification conditions can lead to more accurate safety factor calculations for FEA simulations.
Integration of process and structural simulation in castings
Integration von Prozess- und Struktursimulationen bei Gussteilen
2007
22 Seiten, 17 Bilder, 4 Quellen
Aufsatz (Konferenz)
Englisch
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