There is a good correlation between the S-N curve and crack growth law in carbon steel. Also, the fatigue limit of that can be evaluated from the param-eters of hardness and crack initiation conditions. The crack initiation behavior is related to the distribution of microstructures and the sizes of inclu-sions. Therefore, when the fatigue limit and life of carbon steel are predicted, it is better to consider the initial crack length and crack growth behavior. In this study, one such case was investigated by push-pull with constant stress amplitude by using 0.45% carbon steel. The initial crack lengths were varied with the specimen used and testing conditions. The prediction method of the S-N curve from a corrected crack growth law in such case was pro-posed. Also, a method of prediction of fatigue limit and life from the point of safety was discussed in this study.
The amount of trapped hydrogen was determined with the aid of Gaussian distribution function, to study the state of hydrogen. In CCT (cyclic corrosion test), hydrogen absorption is cyclically interrupted, and this causes the delay of hydrogen saturation. The V alloyed steel, which contains strong hydrogen trap sites, desorbs hydrogen limitedly: It attains the equilibrium state to the environment in rather short-term exposure to CCT environment. Com-bining the amount of the strongly trapped hydrogen with Fermi-Dirac statis-tics, the hydrogen occupation at lattice site (the occupancy, in short) was successfully determined as 4×10-7. This value is not affected by the kind of steel or the amount of pre-straining; it only depends to the environment. In the case of immersion in ammonium thiocyanate aqueous solution, the occu-pancy has a power law relationship with the concentration of the solution and this allows to determine the concentration of ammonium thiocyanate, which is equivalent to CCT exposure, as 0.5%. The experimental methods with this hydrogen charging solution were additionally explored for evaluat-ing the hydrogen embrittlement. (170 words)
Carbon Fiber Reinforced Plastic (CFRP) pressure vessels are widely used for high pressure hydrogen container such as fuel tank of fuel cell vehi-cle (FCV) and accumulators at the hydrogen fueling stations. To commer-cialize FCV and hydrogen station, the cost of the CFRP pressure vessels have to be reduced with safety. The sufficient safety of the CFRP pres-sure vessels have been mostly examined by the performance and production tests so far since the Finite Element (FE) modeling of CFRP layers has not been sophisticated enough so as to yield reliable failure analysis result. In-stead of conventional continuum-based modeling method, we have proposed meso-scale modeling, where carbon fiber bundle and resin are exactly sepa-rated. Strength models of carbon fiber and resin are directly introduced for adequate strength prediction of CFRP layer. We exemplify the merit of the proposed methodology in a problem of manufacturing error caused by winding path variation in this study. We also reveal the limitation of conven-tional methodology based of macro-scale axisymmetric modeling of CFRP pressure vessel.
The author has reported incidents of storage facilities for energy products at the EST-1 Committee of High Pressure Institute of Japan. The information was obtained from the internet when the incidents occurred. In this paper, 42 in-cidents of storage facilities for energy products which occurred overseas in the first half of 2020 are reported.