Influence of nodule count on the fatigue properties of ferritic thin wall ductile iron

M. CALDERA; M. CHIAPETTI; J. MASSONE; J. SIKORA

MATERIALS SCIENCE AND TECHNOLOGY

Maney Publishing

Año: 2007 vol. 23 p. 1000 - 1004

0267-0836

The present work focuses on the study of the fatigue resistance of ductile iron samples with noticeable different nodule count. Specimens  taken from Thin Wall Ductile Iron (TWDI) plates of 2 and 4 mm thickness and standard “Y” Blocks of 12.7mm thickness, having nodule counts ranging between 1800 and 300 nod/mm2 , were used to perform fatigue tests. All samples were ferritised before testing in order to obtain a homogeneous ferritic matrix. The results obtained through S-N curves, considering only sound test samples, show a significant ncrease of fatigue strength as the nodule count increases. Nevertheless, when all the samples were considered, an important dispersion of fatigue strength values was achieved. Casting defects, especially microshrinkage revealed by SEM analysis on the fracture surface, were responsible of the premature failure, due to the reduction of the cracks initiation stage. The influence of defects on the fatigue life was estimated by using the fracture mechanics theory, calculating the fatigue life of some cracks already initiated in such defects and comparing with the fatigue life measured experimentally.