A critical issue that needs to be addressed for wider utilization of hydrogen as fuel is protection against hydrogen embrittlement during cryogenic storage as it weakens the microstructure bonding force of metals through hydrogen penetration. Austenitic stainless steel, which is usually used in cryogenic vessels and is well known for its high hydrogen resistance at room temperature, has also been reported to be vulnerable to hydrogen embrittlement under cryogenic temperatures. In addition, because large storage vessels are operated over a wide range of temperatures, material behavior at various temperature conditions should also be considered. Therefore, in the present study, hydrogen charging of austenitic stainless steel was performed under various temperature conditions for carrying out prestrain and tensile tests. A decrease in the tensile strength and elongation and an increase in the yield strength were observed in all cases. In particular, the case of 20% prestrain at cryogenic temperature followed by tensile test at room temperature after hydrogen charging showed fracture in the elastic region. The hydrogen index was evaluated from the perspective of elongation and reduction in area, which are factors that indicate the degree of ductility. The aforementioned case showed the most severe results, while non-prestraining followed by tensile tests at room temperature was the least effected by hydrogen. In addition, the effect of strain-induced martensite on hydrogen embrittlement was analyzed using electron backscattered diffraction (EBSD). It was observed that the higher is the prestrain at cryogenic temperatures, the greater is the volume fraction of α’ martensite, which leads to hydrogen embrittlement. The edges and center of the fracture surface were analyzed using scanning electron microscopy (SEM). The hydrogen-charged specimens exhibited brittle fractures at the edges and ductile fractures at the center. The more severe the embrittlement, the more were the number of intergranular fractures and microdimples observed at the edges.

Hydrogen has emerged as a promising carbon-neutral fuel source, spurring research and development efforts to facilitate its widespread adoption. However, the safe handling of hydrogen requires precise leak detection sensors due to its low activation energy and explosive potential. Various detection methods exist, with thermal conductivity measurement being a prominent technique for quantifying hydrogen concentrations. However, challenges remain in achieving high measurement sensitivity at low hydrogen concentrations below 1% for thermal-conductivity-based hydrogen sensors. Recent research explores the 3ω method’s application for measuring hydrogen concentrations in ambient air, offering high spatial and temporal resolutions. This study aims to enhance hydrogen leak detection sensitivity using the 3ω method by conducting thermal analyses on sensor design variables. Factors including substrate material, type, and sensor geometry significantly impact the measurement sensitivity. Comparative evaluations consider the minimum detectable hydrogen concentration while accounting for the uncertainty of the 3ω signal. The proposed suspended-type 3ω sensor is capable of detecting hydrogen leaks in ambient air and provides real-time measurements that are ideal for monitoring hydrogen diffusion. This research serves to bridge the gap between precision and real-time monitoring of hydrogen leak detection, promising significant advancements in the related safety applications.

Movable object type wave power generators produce energy through the process of primary energy conversion, which converts the potential and kinetic energy of the waves into mechanical energy, secondary energy conversion that converts it into energy for generator operation using a mechanical system or hydraulic system, and final energy conversion, the last step in power generation. The secondary energy conversion system that transmits and amplifies energy according to the primary energy conversion needs to secure durability while power generation performance varies greatly depending on how the secondary energy conversion system is built. As a result, reliability assessment of systems based on system engineering are a very important issue. Therefore, in this study, for the conceptual design based on reliability assessment of the secondary energy conversion system, the system concept was established using the integrated computer-aided manufacturing (ICAM) definition for function modeling (IDEF0), a system analysis method, while necessary equipment and process flow diagrams (PFD) were derived. In addition, the database (DB) and formula of the secondary energy conversion system were constructed, and reliability assessment algorithms and programs were developed. Finally, the PFD and reliability assessment program were verified by applying them to a representative movable object type wave power generator.

서 론 최근 산업계에서 사용하고 있는 밸브는 운전조건과 운전환경에 따라 성능이 변화 되고 저하됨에 따라

Syntactic foams combine low density and thermal-insulation capability, but their dynamic flexural properties at subzero temperatures remain insufficiently characterized. This study applied an Euler–Bernoulli beam-based inverse framework to natural frequencies and damping ratios of four epoxy syntactic-foam specimens representing four formulations at 0, −20, and −40 °C. Apparent storage, loss, and complex flexural moduli and equivalent modal loss factors were identified for the first two bending modes, with intermodal consistency and analytical sensitivity evaluated. The storage flexural modulus increased with decreasing temperature for every specimen and mode, with first-mode increases of approximately 5.8–11.0% from 0 to −40 °C. At equal nominal weight fractions, the S38HS-based specimens exhibited higher storage flexural moduli than the corresponding S28HS-based specimens. First- and second-mode estimates agreed within 5% for most conditions, while S4 showed a 10.93% discrepancy at −40 °C. Equivalent modal loss factors were non-monotonic and more variable in the second mode; the maximum values, ${\eta }_2$ = 0.1040 and $E_2^{\prime \prime }$ = 0.298 GPa, occurred for S3 at −40 °C. Effective free length showed the greatest normalized influence on the inverse estimate. The identified properties provide temperature- and mode-specific, coupon-level effective inputs for preliminary vibration analyses of moderately low-temperature marine insulation components under comparable conditions.