Failure analysis of crankshafts used in maritime V12 diesel engines

Maintenance of equipment requires constant monitoring of the components that constitute a mechanical system, as well as the monitoring of the conditions of service, among others. One first indication of failure in a crankshaft is given by the low-pressure value of the lubrication circuit. This is mainly due to the accumulation of debris in the lubrication channels, which causes the oil filters to be clogged. As such, this will cause poor lubrication of the crankshaft, which can consequently cause its catastrophic failure, and frequently originates damage propagation to other components of the engine, namely crankcase, bearing shells, connecting rods, pistons and other mechanical parts. In the 4-stroke internal combustion maritime V12 diesel engine herein studied, there has been a frequent failure of crankshafts. The seven cases of failure of the crankshafts reported in the last 25 years are presented in the paper and several causes of failure were listed. From those, the influence of initial imperfections in the material was discussed in the article, as well as the influence of the loadings applied to the crankshaft. Hence, the theoretical dimensioning of the crankshaft was firstly assessed assuming the conservative Soderberg criterion and the crankshaft model was then analysed using the Finite Element Method, during a complete combustion cycle, at several stress concentration regions. The Rainflow cycle counting method was applied to determine the stress cycles induced during functioning and a stress-life equation was then used to estimate the fatigue lifespan of the crankshaft. Additionally, a modification to the crankshaft's geometry was suggested and a significant reduction of the induced stresses was obtained.