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

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Based on defined above forces, four independent load cases were defined in numerical stress analysis. The first load case (LC_1, Tab. 3) consist of loads no. 1, 5, 6, 7. These loads act on rotated crankshaft after ignition of the fuel mixture in cylinder 1. Next load cases represent the sum of forces acting on the crankshaft after ignition in cylinder 2, 3 and 4 (for crankshaft position 7 O after TDC).

Table 3. Definition of load cases used in numerical stress analysis Load case number

Load numbers

LC_1 LC_2 LC_3 LC_4

1, 5, 6, 7 2, 5, 6, 7 3, 5, 6, 7 4, 5, 6, 7

5. Results of stress analysis The nonlinear stress analysis of the crankshaft was made with the use of Abaqus program. As a result the stress distributions for crankshaft subjected to the operational loads were obtained. In analysis the maximum principal stress ( σ 1 ) and the equivalent stress were considered. The maximum principal stress is interesting from the fatigue point of view because the tensile stress contribute the most to initiation of the fatigue cracks. Result of the static analysis performed for the load case no. 4 (Fig. 7), showed that the maximum principal ( σ 1 ) stress zone (44.38 MPa) is located on the fillet of the bearing journal no 4. The maximum stress area not covers the crack origin zone where the σ 1 stress has a much smaller value (26.6 MPa, Fig. 7, Tab. 4).

Fig. 7. Maximum principal (  1 ) stress distribution in crankshaft segment (for LC_4), [MPa].

Results presented in Tab. 4 showed that the highest stress values in crack initiation zone are observed for the load case no 4. The σ 1 stress values in critical (crack origin) zone for LC_1, LC_2 and LC_3 equal adequately: 8.1, 8.3 and 16.4 MPa. The higher equivalent stresses (according to Huber-Mises criterion, Table 4) occur for the load case no 4 and have the value of 21.2 MPa. Presented above results showed that relatively low stress value (in comparison to the yield stress of the material (480 MPa)) is observed in crack initiation zone.

Table 4. Values of maximum principal (  1 ) and equivalent stress in the crack initiation zone of the crankshaft. Load case number Maximum principal stress [MPa] Equivalent stress [MPa] LC_1 8.1 8.9 LC_2 8.3 9.3 LC_3 16.4 15.6 LC_4 26.6 21.2