PSI - Issue 5

Lucjan Witek et al. / Procedia Structural Integrity 5 (2017) 369–376 Lucjan Witek et al. / Structural Integrity Procedia 00 (2017) 000 – 000

376

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7. Conclusions In this study the failure, stress and modal analysis of the crankshaft of natural aspirated diesel engine was performed. In order to explain the fracture reasons both the visual examination and the investigation of the shaft material were made. In next part of the work the nonlinear finite element analysis was performed in order to determine the stress state in the crankshaft during work of the engine at maximum power. In numerical analysis the complex boundary conditions were defined in order to simulate the interaction of the connecting rods and the crankshaft. In final part of the work the numerical modal analysis of the crankshaft was performed. As a result the modes and frequencies of free vibration for the shaft were determined. Based on the results of presented investigations the following conclusions were formulated: 1. The beach marks detected on the fracture indicate that the crankshaft failure was related to the fatigue of material. The crack origin was not covered by the corrosion products. 4. The maximum principal stress value (44.38 MPa, results of nonlinear static analysis for LC_4) is located on the fillet of the bearing journal no. 4. This zone not overlaps the crack origin (fillet of the crank pin no 4) where the σ 1 stress is equal to 26.6 MPa. The stress value in fillet of the crank pin no. 4 (crack origin zone) achieves only 6 % of the yield stress of the crankshaft material (445 MPa). 5. Results of numerical modal analysis showed that during second mode of free vibrations the high stress area (306 MPa at amplitude of 0.1 mm) is located in critical zone of crankshaft where the crack was initiated. 6. The crankshaft failure was probably caused by the resonant vibrations excited by an unbalanced shaft. The high cycle fatigue conditions related to resonant vibrations caused decrease the fatigue life of crankshaft. Recommendations: 1. Introduce the larger fillet radius on the crank pins in order to decrease the notch effect. 2. Extend the material investigations in order to check the genesis of micro-cracks presented in Fig. 3b. 3. Introduce the fillet rolling process on crank pins fillets. The negative preliminary stress obtained after rolling process causes increase the number of load cycles to crack initiation. 2. The micro cracks was detected on crankshaft fracture, in the crack initiation zone. 3. The mechanical properties of crankshaft material cover the standard values.

Acknowledgements

The research leading to these results has received funding from the People Programme (Marie Curie International Research Staff Exchange) of the European Union's Seventh Framework Programme FP7/2007-2013/ under REA grant: PIRSES-GA-2013-610547.

References

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