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Fig. 3. Shown are the measured and simulated nodularities for the step casting and selected locations of the engine block. I-bars depict the range of the measurements.


ignition. Tey are led through the pistons and connection rods into the crankshaft, bearings and bearing bridges, into the screws and finally into the crankcase. Te durability of an engine is


3


proven through extensive durability runs on engine test stands. Crankcase durability is evaluated on a simplified two-axis impulse test stand (Fig. 4). Te two-axis impulse test derives


two inscribing force ellipses from the simulation results, which are scaled to consider statistical deviations due to machining, assembly and applica- tion loads. To fine-tune the models, calculated elongation profiles are compared to locally measured elon- gation signals (Fig. 5). Te strength calculation is derived


from the local stresses and elonga- tions based on the vectors of the inscribing bearing load ellipses. Local concepts then are used to evaluate the damaging effect and estimate the lifetime (durability). Acceptable


38 | MODERN CASTING July 2013


Results and Conclusions Te essential mechani-


cal application loads of a crankcase are caused by the pressures apparent during


limits for the application loads are derived from cyclical sample runs. Highly loaded areas in the 3.01 V6 engine block were found using this method (Fig. 6). The calculated lifetime esti-


mate included evaluations of the microstructure in critical areas. The predicted nodularity was 20%


and the pearlite fraction was more than 90% (Fig. 7). Due to the high pearlite fraction, the upper S-N (Whoelher) curve can be used for lifetime prediction. Tis shows an approximate 20 MPa higher durability than usually is used when designing for CGI. Tis leads to double the number of cycles until


Fig. 4. Researches used a two-axis impulse test stand on the crankcase casting.


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