Abstract
The effects of hydrogen on plastic zone formation in near-threshold fatigue crack propagation have been investigated in niobium at room temperature. Fatigue tests were performed on a hydrogen-free specimen as well as specimens containing hydrogen in solid solution and in the form of hydride. The specimens were tested using tension-tension loading cycle at a frequency of 4 Hz and two load ratios of 0.05 and 0.4. Microhardness was measured on the fatigued specimens in order to determine the plastic zone size. Analysis of the data indicates that the plastic zone size is controlled by extensive cyclic plasticity, and that the cyclic flow stress is similar to static flow stress which weakly depends on hydrogen concentration. Analysis also shows that a decohesion fracture theory cannot be used to explain experimental results.
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