Load history effects in ductile cast iron for wind turbine components

Fracture-mechanics experiments were carried out on samples of ductile cast iron to investigate the fracture behaviour under cyclic and random loading. Under cyclic loading, the crack growth rate was described well by the ESACRACK model. Fatigue crack growth behaviour depends on the graphite particle size. Increasing particle size leads to higher threshold-values ΔKth, lower da/dN values and higher transition to static fracture Kfc. The investigation of load history effects with low–high and high–low transitions shows that crack growth acceleration is independent of the transition type. The computation of the a–N curves based on different load history models yields non-conservative results.