High-Cycle, Low-Cycle, Extremely Low-Cycle Fatigue and Monotonic Fracture Behaviors of Low-Carbon Steel and Its Welded Joint

Low-carbon steels are commonly used in welded steel structures and are exposed to various fatigue conditions, depending on the application. We demonstrate that the various transitions in the fracture mode during fatigue testing can be distinguished by their different cyclic response curves and microstructural features after fracture. Fractography, surface damage micrographs, and microstructural evolution clearly indicated the transition of the fracture modes from high-cycle to low-cycle, extremely low-cycle fatigue, and monotonic behavior. The high-cycle fatigue mode showed initial cyclic softening, followed by cyclic stabilization, and showed inclusion-induced crack initiation at fish-eyes, while the low-cycle fatigue mode showed initial cyclic hardening followed by cyclic stabilization, where fractography images showed obvious striations. In addition, the extremely low-cycle fatigue mode showed no cyclic stabilization after initial cyclic hardening, which was characterized by quasi-cleavage fractures with a few micro-dimples and transgranular cracking, while the monotonic fracture mode predominantly showed micro-dimples

Theoretical study of micro/nano roughness effect on water-solid triboelectrification with experimental approach

The application of micro and nano surface roughness in solid-solid contact electrification based triboelectric nanogenerators (TENGs) has been a widely accepted method for pursuing higher energy output. However, the roughness enhancement needs to be reconsidered in the case of TENGs based on water-solid contact electrification because water-solid contact has clearly different interfacial behavior from solid-solid contact. This study reports a theory for investigating the effect of micro/nano roughness on water-solid contact electrification. The relation between micro/nano roughened surface and water-solid contact electrification is developed and specified by utilizing wetting and rheological properties such as fraction of the area in contact and thickness of the air gap layer. For the fabrication of water-driven TENG (WTENG), aluminum plates are anodized and fluorinated to form the dielectric layer and triboelectric layer, respectively. Three types of surface roughness were fabricated by adjusting the fabrication conditions. The WTENG with the lowest roughness shows approximately 14 times higher current and 9 times higher voltage than the WTENGs with higher roughness. The theoretical equations for water-solid contact electrification correspond well with the experimental results with high accuracy. The theory derived in this work is the first insightful perspective on roughness related liquid-solid electrification.114sciescopu

INTEGRATION OF COMPOSITE STRUCTURAL DESIGN WITH THE INTELLIGENT SYSTEM CONCEPT

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Sequential liquid separation using meshes with hierarchical microcube-nanohole structure and controlled surface wettability

In actual industrial processes, in addition to separation of just water and oil, separation of multiphase liquids and separation of organic solvents are also required. Here, we demonstrate successful multiphase liquid separation by simply applying different coating materials to aluminum meshes with a hierarchical microcubic and nanohole structure. A gravity-driven multiphase separation system was designed using these meshes as the separation media, and it showed high collection rate (99%) and high content ratio (95%). The fabricated separation system could sequentially separate liquids with surface tension of 32.0 mN/m by choosing a filter with the proper surface energy. Given the small differences in the surface tension of the liquids used in this study, the separation system with a surface-energy-controlled filter can be an impressive tool to separate numerous liquid mixtures.110sciescopu