SEDL / STP / STP770-EB / STP32437S

Prediction of Fatigue Life of Smooth Specimens of SG Iron by Using a Fracture Mechanics Approach

Starkey, MS
Metallurgist and Section Head, GKN Technology Ltd., Wolverhampton,

Irving, PE
Metallurgist and Section Head, GKN Technology Ltd., Wolverhampton,

Pages: 17    Published: Jan 1982

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Abstract

Studies have been made of factors influencing fatigue life of smooth specimens of SG iron. It is shown that nodule size does not influence fatigue life, whereas pore size exerts a strong influence. Microcrack growth commenced from the pores within a few percent of the life of the specimen, for lives up to 10⁵ reversals. Using an experimentally determined expression for microcrack growth, and approximating the defects to small cracks, fatigue lives for a variety of starting defect shapes and sizes have been calculated. Calculated lives agree with the experimentally determined lives within a factor of four. It is shown that fatigue life is predominantly controlled by pores (owing to their larger size and more rapid crack initiation) rather than by nodules. The variation in observed fatigue lives can be related to the variation in pore size within the iron.