STP1372

    Endurance Limit Design of Spheroidal Graphite Cast Iron Components Based on Natural Defects

    Published: Jan 2000


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    Abstract

    Cast irons are used extensively in the production of large diesel engines for power generation or oceangoing ships. One current trend is to replace grey iron with spheroidal graphite (SG) iron for fatigue critical components. In order to take advantage of the higher fatigue strength of SG iron and ensure the reliability of a design, better understanding of the typical defects for these large castings and the relationship between these defects and the endurance limit fatigue strength have been studied. Testing included uniaxial constant amplitude, constant amplitude torsion, and simple variable amplitude loading sequences in the long-life regime. Defects in several thick wall castings have been statistically evaluated. A fracture mechanics based model involving matrix hardness and √area successfully related the defect size to the experimentally observed fatigue limit. For ferritic-pearlitic SG iron, the hardness of the tougher pearlite phase was used in the model. The model also correlated the torsion and tension endurance limits. Endurance limit as a function of mean stress is presented in the form of Haigh diagrams.

    Keywords:

    fatigue, nodular cast iron, spheroidal graphite cast iron, GRP 500, endurance limit, nonpropagating cracks, fatigue threshold, casting defects, shrinkage pores


    Author Information:

    Marquis, G
    Researcher, VTT Manufacturing Technology, VTT,

    Rabb, R
    Section Manager, Wärtsilä NSD Corp., Vaasa,

    Siivonen, L
    Researcher, VTT Manufacturing Technology, VTT,


    Paper ID: STP13446S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP13446S


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