Shota Hasunuma

Initiation and Growth of Small Fatigue Cracks of Steels Used for Nuclear Power Plants Under Low Cycle Regime

Low cycle fatigue tests were conducted for carbon steel, STS410, low alloy steel, SFVQ1A, and austenitic stainless steel, SUS316NG, which were used for nuclear power plants, in order to investigate the mechanism of fatigue damage when the plants were subjected to huge seismic loads. In these tests, the surface behavior of fatigue crack initiation and growth was observed in detail using cellulose acetate replicas, while the interior behavior was detected in terms of fracture surface morphology developed by multiple two-step strain amplitude variations with periodical surface removals. Fatigue crack growth rates were evaluated by elasto-plastic fracture mechanics approach. For SFVQ1A and SUS316NG, the fracture mechanics approach is available in order to predict the crack growth life from the metallurgical crack initiation size to the final crack length of the specimens. For STS410, numerous small cracks initiated, grew and coalesced each other on the specimen surface under low cycle fatigue regime.Copyright

Effect of Specimen Size on Elastic-Plastic Fatigue Crack Growth and Resistance Curve of Carbon Steel

In order to investigate the ultimate strength of structures and components under an unexpected huge earthquake, it is necessary to understand the final fracture condition under static and cyclic loadings. This study compared the crack growth behavior under monotonic and cyclic loading conditions for carbon steel SGV410 used for pressure vessels in nuclear power plants. Fatigue tests were carried out for CT specimens 50 mm wide (1CT), 75 mm wide (1.5CT) and 100 mm wide (2CT) using three kinds of test methods, namely monotonic loading (ML), load line displacement amplitude increasing (V-inc.) and fatigue crack growth (FCG) tests. For the FCG tests, the maximum load was kept constant under cyclic loading with full unloading (R = 0), fully reversed loading (R = −1) and fully reversing the load line displacement (R = −1.5) and the crack growth characteristics were evaluated by the fracture mechanics approach.© 2014 ASME

Characteristics of Fatigue Crack Growth and Stress Corrosion Cracking in Aggressive Environments of Aluminum Alloys for Hydrogen Gas Containers

Hydrogen gas container is one of the critical components for fuel cell electric vehicle (FCEV), which is expected for CO2-free personal transportation. In order to choose an appropriate material for its metal boss and liner, crack growth resistance should be evaluated for various aspects such as fatigue crack growth (FCG) and stress corrosion cracking (SCC) in salt water or humid air environments for the purpose of commercial vehicle use. In the present study, FCG tests were carried out for A6061 and A6066 alloys in laboratory air and in 3.5% NaCl solution for compact (CT) and single edge notched (SEN) specimens. Some SEN specimens were cut from machined hydrogen container made of A6066 at the neck and the shoulder locations. SCC tests were carried out for A6061, A6066 and A6351 (fine and coarse grains) alloys in 3.5% NaCl solution and in humid air for CT specimen.Copyright