Naslov
Fatigue life assessment of engine lateral supports

Autori
Domazet, Željko ; Barlé, Jani ; Đukić, Predrag

Izvornik
Materialove inžinerstvo : materials engineering (1335-0803) 6 (1999), 17; 45-50

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, stručni

Ključne riječi
Fatigue cracks; engine lateral support; hot-spot stresses

Sažetak
Fatigue failures of the main engine lateral supports (top engine bracing) of several bulk carrier vessels have been analyzed. Failures occurred after a few months of service. In order to solve the problem and avoid future time and money losses, it was necessary to establish main causes of failures. The strain gage measurements were performed in large scale during the sea trial. Possible reasons for these fatigue failures are: - loads are higher than one used for design of supports, - weldments are not correctly manufactured, - design of supports is inadequate. To obtain operational loads (axial force and the bending moments) strain gages were installed on each beam (1÷5 on Fig. 1.). The significant difference of measured axial forces between supports was discovered. One of the beams was loaded with approx. 50% lower load than the others. However, maximal axial force (20kN) was within a range of design load values. Measurements gave no significant bending moments. Stresses at the crack initiation points were measured to describe the quality of design. Strain gages 6÷8 were used for extrapolation of maximal stresses. Typical time record of measured local stresses is shown in Fig.2. The values of maximal stresses at the end of the weld are extrapolated, Fig. 3. According to [1], and to the determined maximal stresses it is possible to predict the fatigue life of approx. 5ˇ106 cycles, or a few weeks of service. This service life is too short, compared with expected 20 years. This prediction is in good agreement with the time to failure observed on former failures. Failures are mainly caused by inadequate design, of the joint of support and ship (hull) structure from one side, and insufficient weld quality.

Izvorni jezik
Engleski

Znanstvena područja
Strojarstvo

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