An investigation of the fatigue crack growth behavior of INCONEL 690

This paper describes the use of a crack growth rate superposition model. In this model, the total crack growth rate is taken to be the sum of the crack growth rate in air plus the local corrosion rate. For purpose of statistical data analysis, the fatigue threshold was incorporated into the model. The fatigue threshold for the chosen material (INCONEL 690) is defined and taken to be the crack length per unit cycle of 1.0 × 10−10 m/cycle. To account for threshold values in fatigue crack growth, Klesnil and Lukas developed a modified equation to the Paris Law. By incorporating the modified equation into the model developed and put forth by Argonne National Laboratory, the test data in the threshold region became statistically significant. A comparison of the model developed both with and without the threshold term in the environments of ambient temperature laboratory air and pressurized water reactor (PWR), or low dissolved oxygen (DO) (<10 ppb) water, is made. Results reveal that by incorporating threshold terms into the model, a better correlation between model projection and the actual experimental test data obtained on the material in the ambient temperature laboratory air environment are obtained. The results obtained from using the superposition model are presented and discussed.