ues, which were used in the lifetime analysis program. T e consideration of local S–N curves
leads to double the number of cycles until failure compared to using the con- ventional method. T is explains why no castings failed on the test stand.
Durability Prediction of Gray Iron Bearing Support
A durability strength value of 190
MPa was measured for a gray iron bearing support. Conventional methods, which are based on established stan- dards, showed only a value of 140 MPa for this material. Results of fatigue tests for the bearing support are shown in Figure 8 for two diff erent melts. Besides showing these quantitative
diff erences in values, it clearly defi nes potentially weak areas. Figure 9 com- pares the conventional (microstructure independent) and improved prediction of crack initiation areas in the bear- ing support. Only the microstructure distribution-based durability calcula- tion predicts the correct location of weak spots in the casting.
Outlook T e results of this research project
are the fi rst steps toward integrating process and application simulation to predict correct and robust fatigue/ lifetime values. One essential goal of the work presented here was to realize
Fig. 10. The predicted locally varying durability values are compared to measured values in a windmill base frame.
a new methodology and show its po- tential. T e local material behavior of many cast alloys is not only defi ned by their microstructure distribution, but also by local defects. T is is especially important for ductile iron materials. T eir performance can be signifi cantly reduced by inclusions and dross. T e calculation of these eff ects, so they can be considered in predictive tools, is currently being worked on. The proposed concept of local
durability values offers great poten- tial in the design of safety critical
components, like wind energy parts. Figure 10 shows the local durability values for a ductile iron (GJS-400) windmill base frame. T e red dots in Figure 11 on
the left side show the local fatigue strengths (351–455 MPa) based on conventional standards. T at approach leads to a very conservative design compared to when locally predicted durability values would be used. T e conventional approach puts ductile iron to a disadvantage. Casting buyers and designers
have learned over the years that early information regarding expect- ed property distributions in castings is contributing to quality assurance and risk minimization. They are also increasingly utilizing this informa- tion as a chance to reduce weight and optimize the performance of castings. A casting design where the application load and weight are optimized is only achievable if the designer can fully unlock the poten- tial of the material. The integration of process and application simula- tion offers the development of more realistic design rules for castings.
Fig. 11. Calculated (blue) tension-compression durability for ductile iron is compared to predicted standard values (red) in the same locations.
T is research presented in this article was originally published online in the Interna- tional Journal of Metalcasting in 2016. It can be found in the Volume 11 April 2017 Issue 2.
https://link.springer.com/journal/ volumesAndIssues/40962
Mar/Apr 2017 | METAL CASTING DESIGN & PURCHASING | 27
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