Calculation of crankshafts for reciprocating internal combustion engines
|Publication Date:||1 July 2019|
This class guideline contains an alternative method to the method given in IACS UR M53 for calculation of safety against fatigue failure in pin and journal fillets and in oil bores.
In principle, any relevant calculation method may be applied, e.g. the fatigue criteria assume that maximum respectively minimum bending stresses occur simultaneously with the maximum respectively minimum torsional stresses.
If properly documented, an evaluation of the fatigue capacity by using multi-axial fatigue methods may replace the criteria applied in this class guideline.
A crankshaft will be approved when the calculation methods, as presented in this class guideline, is fulfilled. Crankshafts that cannot satisfy these rules may be subject to special consideration when detailed calculations and/or measurements are made to demonstrate equivalence to these rules.
Field of application
This method apply to engines for both main propulsion and auxiliary purpose, being designed for continuous operation at the specified (nominal) rating. If frequent use of overload (in excess of nominal) rating is foreseen, i.e. accumulating several millions of stress cycles, this overload should form the basis for the calculation. Further, the methods apply to solid forged or semibuilt crankshafts of forged or cast steel, and with one crank throw between main bearings. Designs with more than one crank throw between main bearings, fillets between offset crankpins, fully built crankshafts, or welded crankshafts will be specially considered on basis of equivalence with the "normal" requirements.
This method is also valid for:
- surface treated fillets
- when fatigue parameter influences are tested
- when working stresses are measured.
Note that surface treated fillets also include crankpin hardening that may influence the fillet fatigue strength.