STATISTICAL INVESTIGATION OF THE BEHAVIOUR OF MICROCRACKS IN CARBON STEELS

Abstract— In order to clarify the statistical behaviour of microcracks, rotating bending fatigue tests of plain specimens were carried out using two kinds of carbon steel with different microstructures, normalized 0.21% C steel and heat-treated 0.45% C steel. The emphasis is to investigate separately the statistical properties of the initiation and propagation of microcracks through successive observations of the specimen surface. Results show that the microcrack initiation life distributions of normalized and heat-treated steels are expressed by a two-parameter Weibull distribution and a Weibull distribution of the mixed type, respectively. On the other hand, the microcrack propagation life distributions of these steels are represented by three-and two-parameter Weibull distributions, respectively. The three-parameter Weibull distribution is well fitted to the crack length distribution for both the steels.