Analysis of a diesel generator crankshaft failure F. Jiménez Espadafor * , J. Becerra Villanueva, M. Torres García Departamento Ingeniería Energética, Escuela Superior de Ingenieros, Universidad de Sevilla, Camino de los Descubrimientos S/N, 41092 Sevilla, Spain article info Article history: Received 3 March 2009 Accepted 11 March 2009 Available online 20 March 2009 Keywords: Crankshaft Engine failure Fatigue crack initiation abstract This paper analyses a catastrophic crankshaft failure of a four-stroke 18 V diesel engine of a power plant for electrical generation when running at a nominal speed of 1500 rpm. The rated power of the engine was 1.5 MW, and before failure it had accumulated 20,000 h in service operating mainly at full load. The fracture occurred in the web between the 2nd journal and the 2nd crankpin. The mechanical properties of the crankshaft including tensile properties and surface hardness (HV 1 ) were evaluated. Fractographic studies show that fatigue is the dominant mechanism of crankshaft failure, where the beach marks can be clearly identified. A thin and very hard zone was discovered in the template surface close to the fracture initiation point, which suggests that this was the origin of the fatigue fracture. A finite element model of the crankshaft has predicted that the most heavily loaded areas match the fractured zone. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Diesel plants for electrical power generation are especially sensible to outage events. In case of a crankshaft failure, the cost of the reparation includes not only that of the crankshaft itself, but also the cost of other parts of the engine affected by crankshaft failure (connecting rod, piston, cylinder, and bearings) and the lengthy time period required for repair, mainly because of the crankshaft location inside the engine. Smith and Donovan conducted a study [1] for US Army Engineering and Housing Support Centre (EHSC) which showed results of up to 2 MW from diesel engines. This study includes a detailed classification of the parts involved in the failure in this power range and reveals that even though failures per year related to the engine crankshaft were low, these resulted in a higher mean time to perform corrective maintenance. Similar conclusions are shown in [2,3]. The most common cause of crankshaft failure is fatigue. In order for fatigue to take place, a cyclic tensile stress and a crack initiation site are necessary. Diesel engines crankshafts in power plants run with harmonic torsion combined with cyclic bending stress due to the radial loads of combustion chamber pressure transmitted from the pistons and connecting rods, to which inertia loads from pistons and connecting rods have to be added. Although crankshafts are generally designed with a high safety margin in order to not exceed the fatigue strength of the material, the high cyclic loading and local stress con- centrations allow cracks to grow even when fatigue strength does not exceed in average values. Pandey [4] analysed failures in the crankshafts of 35 hp two-cylinder engines used in tractors, where the break plane was located between the main bear- ing and the journal. The crack started in the crankpin web region in a plane of about 45° with respect to the rotational axis, showing a typical fatigue failure with beach marks. The stress related to the fatigue initiation was estimated at 175 MPa, far below the tensile stress of the nodular cast iron of these crankshafts which is close to 680 MPa. Taylor et al. [5] developed two fatigue experiments in a crankshaft of a four-cylinder engine made of spheroidal graphite cast iron, with a tensile strength of 440 MPa: one torsional and the other flexural. The crankshafts underwent torsional and flexural cyclic loading 1350-6307/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2009.03.019 * Corresponding author. Tel.: +34 95 448 72 45; fax: +34 95 448 72 43. E-mail addresses: fcojjea@esi.us.es, fcojjea@us.es (F.J. Espadafor). Engineering Failure Analysis 16 (2009) 2333–2341 Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal