Influence of load ratio on fatigue crack growth behavior of SS316L(N) using a two parameter model

In this paper, an investigation was carried out to study the load ratio effects on the Fatigue crack growth (FCG) behaviour of nitrogen added (0.078-0.22 wt%) SS316L (N). Primarily, the fatigue crack growth rate (da/dN) is analysed in terms of two crack tip driving forces (OK and Kmax) and load ratio (R). Fractographic observation explains the FCG mechanism associated with load ratio. An attempt was made to explain the R ratio effect with the help of a master curve at ambient temperature, which includes the crack closure approach and two-parameter Kujawski models, and it was compared with the RCC MR Code equation. A new approach incorporated to get better correlation using a curve shape correction factor named this approach as the 'iterative method' was found to be more appropriate than other models. This method is tested with the literature room and high-temperature FCG data, showing a reasonably good correlation. This two-parameter driving force equation is also used to predict the threshold behaviour.