CLASSIFICATION NOTES - Indian Register of Shipping

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Page 24 of 41Calculation of Crankshafts for Internal Combustion EnginesSection 5Calculation of Equivalent Alternating Stress5.1 GeneralIn the fillets, bending and torsion lead to two different biaxial stress fields which can berepresented by a Von Mises equivalent stress with the additional assumptions thatbending and torsional stresses are time phased and the corresponding peak values occurat the same location (See Appendix I). As a result the equivalent alternating stress is to becalculated for the crankpin fillet as well as for the journal fillet by using the Von Misescriterion.At the oil hole outlet, bending and torsion lead to two different stress fields which can berepresented by an equivalent principal stress equal to the maximum of principal stressresulting from combination of these two stress fields with the assumption that bendingand torsion are time phased (See Appendix II).The above two different ways of equivalent stress evaluation lead to stresses which maybe compared to the same fatigue strength value of crankshaft assessed according to VonMises criterion.5.2 Equivalent alternating stressThe equivalent alternating stress is calculated in accordance with the formulae given.For the crankpin fillet:σv 2 2σ σ 3.τBHaddHFor the journal fillet:σv 2 2σ σ 3.τBGaddGFor the outlet of crankpin oil bore:where,σv1 σ3BO. 1 29 σ14 σroBO2 v [N/mm 2 ] equivalent alternating stressfor other parameters see items 2.1.3, 2.2.3 and 3.4.Indian Register of Shipping
Classification NotesPage 25 of 41Section 6Calculation of Fatigue StrengthThe fatigue strength is to be understood as that value of equivalent alternating stress (VonMises) which a crankshaft can permanently withstand at the most highly stressed points.The fatigue strength may be evaluated by means of the following formulae:Related to the crankpin diameter:σDW K.0.2785 B 196 10.42.σ 39.3.0.264 1.073.D . B4900σBRxwith:R x = R Hin the fillet areaR x = D o / 2 in the oil bore areaRelated to the journal diameter:σDW K.0.2785 B 196 10.42.σ 39.3.0.264 1.073.DG . B4900σBRGwhere, DW [N/mm 2 ]K [-]allowable fatigue strength of crankshaftfactor for different types of crankshafts without surface treatment.Values greater than 1 are only applicable to fatigue strength infillet area.= 1.05 for continuous grain flow forged or drop-forged crankshafts= 1.0 for free from forged crankshafts (without continuous grainflow)factor for cast steel crankshafts with cold rolling treatment in filletarea= 0.93 for cast steel crankshafts manufactured by companies usingan approved cold rolling process B [N/mm 2 ]minimum tensile strength of crankshaft materialIndian Register of Shipping
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CLASSIFICATION NOTES - Indian Register of Shipping

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