Large scale axial fatigue testing of ductile cast iron for heavy section wind turbine components

Abstract

The present paper deals with axial fatigue testing of heavy section EN-GJS-400-18-LT ductile cast iron specimens with 120 mm × 140 mm cross section and also smaller cylindrical specimens with 21 mm diameter at room temperature and load ratio R = −1. The load levels for heavy section specimens were adjusted to cover endurances from 10,000 to 14 million cycles. Each heavy section specimen weights 380 kg. The specimens were cut from castings with 150 mm thickness. The heavy section specimens thickness is close to the common thicknesses of heavy section wind turbine ductile cast iron components. Fatigue strength of large 120 mm × 140 mm specimens were compared with fatigue strength of smaller 21 mm diameter specimens and geometrical size effect was evaluated. To evaluate the wall thickness effect on fatigue strength (technological size effect), the obtained fatigue test results for 21 mm specimens from billets with 150 mm thickness were compared with the published fatigue test results of the same specimens but from billets with 95 mm thickness. Metallography analysis of 21 mm specimens from billets with 95 mm and 150 mm thicknesses were performed and important microstructural parameters were measured and compared. Finally the effect of casting thickness and microstructure on fatigue strength of this material was evaluated.