In this study, the effects of the ring diameter of a ring-shaped beam on keyhole behavior and spatter generation mechanisms during bead-on welding of stainless steel（SUS304） were investigated. First, the relationship between penetration depth, penetration ratio, keyhole diameter and spatter generation was investigated using a single beam and ring-shaped beams with ring diameters of ϕ 440, ϕ 800 and ϕ 1000 μm formed by a beam-splitting diffractive optical element （DOE）. The single beam had the deepest penetration depth. Among the ring beams, the ϕ 440 μm ring-shaped beam had a better penetration ratio than the other ring-shaped beams. The number of spatters was several hundred for a single beam at any welding speed. On the other hand, with the ring-shaped beam, the spatter suppression effect was confirmed for all ring diameters. In particular, when a ϕ 440 μm ring-shaped beam was used, the number of spatters was the lowest and the keyhole diameter reached a maximum of 620 μm. The keyhole welding phenomenon on the stainless steel edge surface was observed through quartz glass. In a single beam, spatter was observed when a protrusion formed on the keyhole rear wall ascended toward the keyhole aperture at a high speed of 1100 mm/sec. At the ϕ 1000 μm ring-shaped beam, the protrusion rise rate reached 735 mm/sec, and no spatter occurred. At this time, the molten pool formed around the keyhole by the ring-shaped beam was thought to act as a relaxation layer, contributing to a decrease in the rise rate of the protrusion within the keyhole and to the relaxation of shear stresses on the keyhole wall. With a ϕ 440 μm ring-shaped beam, no protrusions formed on the keyhole inner wall, and the internal shape of the keyhole was maintained. This is thought to be due to an increase in the power density of the ring part, which led to a greater amount of metal vapor generated inside the keyhole. Consequently, the keyhole diameter expanded and the shape inside the keyhole stabilized.

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 Thermal energy storage (TES) systems are increasingly recognized for their potential to support additional power generation and reduce reliance on fossil fuels. By storing excess energy during off-peak periods and releasing it during peak demand, these systems help stabilize energy supply and improve overall efficiency. In this study, a new type of solid biofuel, Japanese cedar (JC) bio-coke with enhanced heat storage capacity was developed through the incorporation of calcium carbonate (CaCO₃) and calcium sulfate (CaSO₄) at specific blending ratios of 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 g/g. Key thermal properties including thermal conductivity, thermal diffusivity, and volumetric heat capacity were evaluated. The addition of CaCO₃ resulted in decreased thermal conductivity and volumetric heat capacity, while enhancing thermal diffusivity. Conversely, the incorporation of CaSO₄ led to a reduction in volumetric heat capacity, accompanied by increases in both thermal conductivity and diffusivity. These results indicate that the choice and proportion of additives have a significant impact on the thermal performance of bio-coke, highlighting its potential as an efficient solid-state thermal energy storage material.

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 In this research, the stereolithography method was used to process photosensitive pastes that were prepared by dispersing metal particles within a liquid resin. The metal particles were deposited onto aluminium and titanium substrates by UV curing and thermal post-processing to form hard surface phases. Finite Element Analysis was used to assess mechanical strengthening of substrates by complex surface modifications such as Hilbert curve geometries of various fractal order. Results of computational simulations, experimental processing, and tensile testing of samples demonstrated that this method could be used for mechanical strengthening of lightweight metal materials widely used in transportation, energy, and construction applications with sustainable development in mind.

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 Amid growing concerns over energy consumption and environmental sustainability, power semiconductor devices have emerged as a highly efficient technology for electrical energy conversion. Operating in high-temperature environments （typically between 200 and 300℃）, these devices experience significant thermal stress due to frequent switching operations. To overcome these challenges, we developed a Cu-SnAgCu （SAC） molded sheet using a high-pressure powder compression method that leverages the plastic flow of SAC particles. This die attach material is engineered to withstand demanding thermal conditions. This Cu-SAC molded sheets can be fabricated to a thickness of 40μm without voids. Additionally, the bonded layer maintained its strength after a 1000-hour heat resistance test at 300℃, and no cracks were observed in the SiC die following a －40/+175℃ thermal cycle test for 1000 cycles. Moreover, our results indicate that incorporating a high Cu content in the bonded layer enhances both the coefficient of thermal expansion and the elastic modulus of conventional Cu₃Sn, aligning these properties more closely with those of pure Cu. Moreover, our results indicate that incorporating a high Cu content in the bonded layer enhances the elastic modulus of conventional Cu₃Sn, aligning these properties more closely with those of pure Cu. These effects and fewer voids are considered that the bonded layer contributed to the reliability of the joint.

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