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Fig. 3. Calculated and measured nodularity are compared for the step casting and crankcase. All values provided by the simulation are within the measurement tolerance of the measured samples.


packaging). With this, it is possible to predict the static local mechanical properties over the entire casting.


Experimental Research to Locally Couple Microstructure and Expected Lifetime


Te framework of this research


project included the evaluation of major microstructure characteristics of a ductile iron (GJS-400) and a com- pacted graphite iron (GJV-450) and their impact on component lifetime. For GJS-400, the impact of its ferrite/ pearlite ratio was evaluated. For GJV- 450, its nodularity and pearlite content were evaluated. Both characteristics can be predicted locally with casting process simulation. Te consideration of inclusions and oxides was excluded on purpose in this research project.


Fig. 4. Shown is an example of measured S-N curves for ductile iron with two different pearlite contents.


To realize a complete chain of


information, both materials under- went comprehensive cyclic load testing using tension–compression and cyclical bending tests for various microstructures. In order to develop a represen-


tative correlation between micro- structure and component lifetime, typical microstructures found in the relevant castings were used in the test pieces. Due to the required sizes of the test pieces, only a limited amount of pieces could be derived from the castings (windmill bed- plate/frame, bearing support, and crankcase). Therefore, additional test castings were poured (Figure 2). Te different melts were dialed in


by the research partners in a manner to achieve typical variations in nodular-


ity for compacted graphite iron (CGI) found in crankcases. Te different wall thicknesses in castings and test castings led to sufficient variation in ferrite/pearlite ratios for the gray iron. Te samples were machined and polished to exclusively evaluate the influ- ence of the microstructure on the lifetime performance. Te impact of the casting surface was not part of this research. Te fatigue test runs were per-


formed under tension-compression and cyclical bending conditions. Ten- sion and elongation monitored test runs were performed, as the lifetime prediction analysis uses both concepts. After failure, the fracture sur-


faces of the samples and the local microstructure were evaluated using automatic image analysis according to DIN EN ISO 945. Twenty-two


Fig. 5. Calculated durability values shown here as a function of the local microstructure prediction can be transferred into lifetime analysis programs.


Fig. 6. The most stressed areas of the crankcase are in color.


April 2017 MODERN CASTING | 37


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