Low Cycle Fatigue Crack Growth Behavior at Elevated Temperature Under the Combined Strain-Wave-Shape Cycling in Type 304 Stainless Steel

Abstract

The low-cycle fatigue crack growth behavior of Type 304 stainless steel, when the slow-fast type strain cycles were introduced into the repeat of fast-fast type strain cycle either in a periodical type (denoted as Type-I sequence) or in a block type (denoted as Type-II sequence), was investigated at the temperature of 873 K. It was found that an inertia accelerating phenomenon of crack growth rate occurred during the repeat of fast-fast type strain cycle, which followed the slow-fast type strain cycles introduced. It was also found that the above inertia accelerating phenomenon led to the significantly shorter fatigue crack propagation life than that evaluated from the linear damage summation rule, especially in the Type-I sequence. The observations of the longitudinal section through the specimen and the distribution of Vickers hardness suggested that a creep affected zone would be produced at the crack tip by the introduction of slow-fast type strain cycles, and it would cause the inertia acceleration of crack growth rate. In this work, the creep affected zone size, Rc was defined by the size of the region where the inertia acceleration of crack growth rate occurred. There was a linear relationship between Rc thus defined and the range of creep J-integral, which was produced just when the introduction of slow-fast type strain cycles was finished. Furthermore, based on the results thus obtained, the predicting method of crack growth rates both in the Type-I sequence and in the Type-II sequence was discussed.