Influence of graphite spherical size on fatigue behaviour and fracture toughness of ductile cast iron EN-GJS-400-18LT

Abstract

The employment of ferritic nodular cast iron for components subjected to high stress requires a detailed fracture mechanics evaluation of crack growth under static and cyclic loading. During operation, for instance, in wind power plants, such component parts are subjected to loading of variable amplitude, which influences their lifetime considerably. For the evaluation of crack propagation and the remaining service life in this case, the calculation methods currently well-established in practice cannot be employed for cast iron with nodular graphite, since overloads lead to microstructure-related and material-specific load history effects in terms of crack growth acceleration. In this work, investigations of crack growth under constant and variable amplitude loading as well as static fracture toughness investigations and strain-controlled cyclic deformation experiments are presented.

Micromechanisms of fracture in nodular cast iron: From experimental findings towards modeling strategies – A review

“…Fatigue properties of NCI and the correlation to microstructural parameters were investigated by a number of researchers [26,83,99]. They found a strong relation between graphite particle size and fatigue life.…”

“…Thereby, the Paris regime is mostly independent of the material microstructure. There is only a small influence of the graphite particle distance on the threshold value and the critical cyclic stress intensity factor [83,97]. Furthermore, by applying statistical quantile crack growth curves, a procedure for obtaining conservative safety assessment results was developed [49,97] by using the NASGRO equation.…”

Overload Effects During Fatigue Crack Growth in Nodular Cast Iron - simulation with an Extended Strip-yield Model

“…Calculations of the remaining lifetime using different load interaction models showed, that the mentioned overload effects lead to non-conservative results for nodular cast iron. In recent experiments Mottitschka et al (2012) studied the influence of consecutive single spike overloads interspersed every 1000 load cycles into a constant base load. The corresponding crack propagation curve is depicted in Fig.…”

“…Due to the inhomogeneity of the material, consisting of a ferrite matrix and embedded nodular graphite particles, the probability of fatigue cracks emanating from the embedded particles must be taken into account within the fracture mechanics assessment of structural components. Recent experimental investigations of fatigue crack growth in cast iron materials under variable amplitude loading show, that there are unexpected effects in terms of pure crack growth acceleration after overloads (Hübner et al, 2007;Mottitschka et al, 2012). Optical investigations revealed, that ductile mechanisms are responsible for the acceleration effects.…”

Optimización microestructural de fundiciones grises dúctiles no aleadas, con matriz ferrítica, empleadas en la fabricación de bujes de aerogeneradores

“…The component under study was manufactured to comply with Euronorm EN-GJS-400-18-LT standard, which corresponds to a spheroidal graphite cast iron (Mottitschka et al, 2012). Wind turbine manufacturing specifications for these parts require a tensile strength of over 370 MPa, total elongation greater than 12%, and values above 10 J in the Charpy test at −20 °C (Asensio-Lozano and Álvarez-Antolín, 2007).…”