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The change in hydrogen thermal desorption characteristic of low‐alloy steel due to fatigue was investigated to examine the possibility of hydrogen as a tracer for detecting and evaluating lattice defects caused by cyclic loading. Specimens were subjected to the uniaxial fully push–pull fatigue test at 288°C, and some tests were interrupted at various stages of the fatigue life. After measurement of surface crack, hydrogen‐charging into the fatigue‐damaged specimens was conducted by means of cathodic electrolysis, and thermal desorption analysis (TDA) was applied to those specimens for measuring hydrogen evolution curve. The experimental results showed that the amount of desorbed hydrogen, CH, increased with increasing number of cycles, especially at an early stage of fatigue life. The CH was well correlated with a newly proposed Coffin–Manson‐type parameter Δεp·N0.4, irrespective of the strain range and number of cycles. [ABSTRACT FROM AUTHOR]

A new fatigue testing technique, the small bulge fatigue (SBF) test using a small disk‐type specimen with flat and concave surfaces, was developed in this study. In the technique, a cyclic oil pressure could be alternatively applied to both specimen surfaces at the frequency of 10 Hz. After some verification tests for the displacement and strain measurements, type 316 austenitic stainless steel specimens were subjected to a preliminary test using this newly developed testing technique. As a result, the SBF test results (S‐N curve) were in good agreement with those of conventional fatigue tests by defining fatigue life as the number of cycles to the sudden drop in oil pressure because of fracture. [ABSTRACT FROM AUTHOR]