Strain-based modeling of fatigue crack growth – An experimental approach for stainless steel

Abstract

This study aimed at correlation of the crack growth rates to the strain range and assessment of the fatigue life by crack growth prediction. First, the fatigue crack growth rate was investigated using Type 316 stainless steel specimens. Cylindrical specimens were subjected to a fully reversed load in order to apply cyclic plastic strain. The crack growth during the tests was monitored by taking replicas. Then, the crack growth rates were correlated to a parameter derived using the strain range. It was shown that, under the same stress intensity factor range, crack growth rates obtained by the fully reversed fatigue tests were more than ten times those obtained using compact tension specimens under the small scale yielding condition, and the strain intensity factor derived assuming the linear stress–strain relation (strain hardening exponent of n=1) correlated well with the growth rates obtained under various conditions. That the strain intensity factor could represent the fatigue crack growth driving force was reasonably explained by the strain field at the crack tip as examined by finite element analyses. Finally, the relationship between the crack growth rates and the fatigue life was discussed. It was found that the fatigue life could be predicted by integrating the crack growth rates represented by the strain intensity factor without considering the incubation period before the crack initiation. The emergence of a crack with a depth of 0.1mm indicated the remaining fatigue life was less than 0.3Nf regardless of the applied strain range.