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Publication
Failure analysis of cylinder head studs of a four stroke marine diesel engine
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Authors
Advisor(s)
Abstract(s)
After about seven years in service, four cylinder head studs, which tight the block and cylinder
heads of a marine main engine, have fractured. Meantime, they were changed for new ones
without to determine the root cause of failure. The aim of this research work is to carry out a
failure analysis in order to avoid recurrent damages in that engine. The fracture morphology and
thread roots of fractured studs were carefully observed by optical devices. Thread material defects
and corrosion were not found. However, the thread roots, where the stress concentration are
higher, can be pointed as the local of fatigue crack initiation. As is well-known, all cylinder head
stud bolts are pre-tensioned in order to increase the mean stress σm and reduce the stress amplitude
σa. The steel alloy quality and design are of primordial importance for improving the
lifetime of studs, and this is supervised by the Classification Societies (CS), as is indicated by an
engraved stamp on each stud end, that certifies each one of them. The pre-tightening of the studs
was calculated, and results point as root cause of failure a significant high stress concentration
mainly at the second thread root of the studs, close to the bottom side of the nut, which are
critical stress zones.
Description
Keywords
Marine diesel engine failures Cylinder head studs Pre-tightening of stud bolts Fatigue failure
Pedagogical Context
Citation
Fonte, M., Reis, L., Infante, V., & Freitas, M. (2019). Failure analysis of cylinder head studs of a four stroke marine diesel engine. Engineering Failure Analysis, 101, 298-308
Publisher
Elsivier