On the use of the weight function approach to study fatigue crack growth in cast iron components

Large mechanical components subjected to cyclic loading quite often spend a considerable part of their life in the propagation of one or more fatigue cracks. Therefore the knowledge of materials crack propagation behaviour under cyclic loading appears of considerable interest. During tests conducted for the determination of the classical S-N fatigue curves, useful information on crack growth can usually he collected and a reliable evaluation of the stress intensity factor can be realised. In this paper the results of fatigue tests performed on large cast irons specimens are discussed. During each test the crack initiation was detected and several crack propagation measurements were collected. On the basis of the weight function approach, using a solution proposed for the evaluation of the stress intensity factor (K) in case of corner cracks with elliptical front, delta K values were calculated and correlated with the corresponding da/dN values, with the intent of determining the Paris laws for the studied material.