Failure of a large diesel engine crankshaft due to inadequate material properties

	cases Techno Fysica BV is a Dutch-based engineering company, highly specialised in solving all kinds of problems related to the dynamic loading of machinery and installations. For this, several measuring and analysis techniques are used. In a series of articles, we will give examples of what can go wrong in the engineering and operating of vessels, and what errors lie at the root of the damages observed.
	Inadequate material properties due to wrong composition, structure or production
	A general cargo ship, equipped with a 2400 kW, 8 cylinder engine suffered from a fractured crankshaft in the first crank pin on the non-drive side within 2700 hours after commissioning. The fracture mechanism was fatigue due to cyclic bending. However, measurements after repair showed that no excessive cyclic stresses were present in the free end of the crankshaft that is also the most lightly loaded part of the shaft. Electron microscopy showed that the crack initiation had taken place near an inclusion in the shaft material and that crack arrest marks (striations) were clearly visible.
	$Fracture fae of a large diesel engine which fractured as a result of bending fatigue$	However, this inclusion was too small to be the single cause of the crack initiation in such a lightly loaded area. Further inquiries revealed that the crankshaft was cold straightened after production, which causes internal residual stresses in the crankshaft. These stresses, in combination with the inclusions caused crack initiation.
	Fractured crankshaft of the main engine of a general cargo ship due to cyclic bending. Inclusions and residual stresses due to production contributed to the fracture.

	$REM image of fracture detail$
	Electron microscopy photograph of the inclusion (left) and the crack arrest marks (right) in the vicinity of the crack initiation.
	For more information, please contact us at: Techno Fysica BV p.o. box 351 2990 AJ Barendrecht The Netherlands Tel. +31 180 620211 Fax. +31 180 620705 info@technofysica.nl www.technofysica.nl

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