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characteristics were evaluated, specifically the number, shape, and size of the graphite particles, as well as the ferrite/pearlite ratio. The chemical composition was considered as well. Te microstructure characteristics


found also were used to validate the accuracy of prediction of the casting process simulation tool used in this project (Fig. 3). Comprehensive variance and


regression analysis were used by the project partners to derive S–N curves (Woehler curves) from the correlation between the microstructure distribu-


Fig. 7. The calculated distribution of nodularity (left) and pearlite fraction (right) in the most stressed areas of the CGI crankcase are shown.


tions found in the samples and castings and the durability test runs (Fig. 4). The predicted and measured


durability values for samples in tension–compression runs had an 87% correlation. These findings were implemented into the simula- tion program. Now it is possible to consider process conditions at any location in a casting when predict- ing durability values (Fig. 5). Te durability values distributions


developed in this project provide a significant qualitative and quantitative improvement compared to the conven- tional method. Tis integrated virtual process chain was validated on one ductile iron and one CGI alloy.


Local Durability Prediction in a Crankcase


Two major microstructure char-


Fig. 8. Shown are the fatigue test results for bearing support made with two different melts (charges).


acteristics drive the strength of CGI: the shape and size of the graphite particles and the ferrite/pearlite ratio (assuming no defects or gray/ white microstructure is present). Predicted nodularity and pearlite content of test castings and an Audi 3,0l V6 TDI CGI crankcase were used for the coupling of local micro- structures with durability values and validated by measurements. The most stressed areas of the crankcase are shown in Figure 6. The simulation tool was used to


Fig. 9. Weak spots in a bearing support are compared. The new method shows the correct crack initiation locations.


38 | MODERN CASTING April 2017


predict the nodularity and pearlite content in the critical areas. The program predicted a nodularity of about 20% and a pearlite fraction of more than 90% in the critical areas (Fig. 7). Based on these values, the tool calculated local durability val- ues, which were used in the lifetime analysis program. Te consideration of local S–N curves


leads to double the number of cycles until failure compared to using the con-


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