Evaluation of environmentally assisted fracture of austempered ductile iron (ADI) under cyclic load bearing

This paper aims to characterize the behaviour of austempered ductile iron (ADI) under cyclic load bearing and its surface in contact with water. The first part is devoted to verifying the drop in Ultimate tensile strength and the elongation that takes place when ADI tensile samples are tested submerged in water as compared to values obtained in dry condition. Focus of this work is placed on crack initiation and propagation when submerged SEN(B) samples are tested applying cyclic loads. Different test stages of fissure nucleation and propagation on the lateral face of the sample were documented by microscopic imaging during the test, thereby allowing to characterize the manner in which failure occurred. The resulting fracture surfaces were analysed by scanning electron microscopy (SEM), and possible fracture mechanisms are discussed. The main contributions of this work include characteristic values of the time of crack initiation, crack growth rate and a methodology to study some particularities of the operating fracture mechanisms based on lateral observations and fracture surface images.