To achieve the integrity of the honeycomb structure without interlocking or bonding, a 3D braided honeycomb structure was designed and developed using natural fiber (jute) reinforced epoxy resin. To optimize the in-plane compressive performance of 3D braided composite honeycombs, the effects of resin, unit cell opening angle, and joint wall length on the in-plane compressive strength, deformability, stiffness and energy absorption were investigated. Furthermore, a theoretical model was established between braiding parameters, geometric parameters of honeycomb cell structure, and in-plane compressive modulus. It is found that if 3D braided composite honeycombs are designed for high load-bearing capacity, it is necessary to reduce the resin strain to failure, increase free wall columns, align the angle between the free wall with the main loading direction, or load along the braiding direction. If the design objective is to maximize the energy absorption, the number of cell rows must be maximized. This study establishes the relationship between braiding parameters, honeycomb geometric parameters, and the in-plane compression performance of the 3D braided composite honeycomb, providing a reference for its structural design and performance optimization.@en

Insulated Gate Bipolar Transistor (IGBT) is the core component of current converter equipment in application scenarios such as flexible DC transmission and flexible AC transmission, and its junction temperature increases significantly with the increase of current level. Therefore, the junction temperature control of IGBT devices has become one of the bottlenecks to further increase the transmission capacity. Al/Diamond material has a much higher thermal conductivity than traditional packaging materials and a smaller coefficient of thermal expansion, so applying Al/Diamond material to IGBT packaging may improve the heat dissipation ability of IGBT and thus reduce the junction temperature. This paper constructs the IGBT model based on Al/Diamond material and the IGBT model based on traditional copper material through COMSOL simulation software, and compares the internal electro-thermal-stress distribution of the two models. In addition, this paper calculates the maximum and average values of temperature, maximum and average values of thermal stress and other parameters of each component inside the model according to the simulation data set. After comparison, it can comprehensively reflect the greater enhancement of heat dissipation capability of IGBT after applying Al/Diamond material to its encapsulation, which provides guidance for the subsequent research on the encapsulation optimization mechanism of high-power IGBT devices based on Al/Diamond material and the actual device fabrication.

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Both CH₄ hydrate accumulation and hydrate-based CO₂ sequestration involve hydrate formation in mixed clay sediments. The development of realistic clay models and a nanoscale understanding of hydrate formation in mixed clay sediments are crucial for energy recovery and carbon sequestration. Here, we propose a novel molecular model of pseudo-hexagonal montmorillonite nanoparticles. The stress-strain curves of tension, compression, and shear of pseudo-hexagonal montmorillonite nanoparticles exhibit linear characteristics, with tension, compression, and shear moduli of ∼435, 410, and 137 GPa, respectively. We perform microsecond molecular dynamics simulations to study CH₄ and CH₄/CO₂ hydrate formation in montmorillonite-illite mixed clay sediments with surface defects. The results indicate that hydrate formation in mixed clay sediments is significantly influenced by the presence of clay defects. CH₄ and CH₄/CO₂ mixed hydrates are challenging to form at the junction between the inside and outside clay defects. CH₄ and CH₄/CO₂ mixed hydrates exhibit a preference for forming outside the clay defects rather than inside the clay defects. Some CH₄ and CO₂ molecules from the inside clay defect migrate to the outside clay defect, thereby promoting CH₄ and CH₄/CO₂ mixed hydrate formation outside the clay defects. This molecular insight advances the development of clay particle models and expands an understanding of natural gas hydrate accumulation and hydrate-based CO₂ sequestration.

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Knowledge on the kinetics of gas hydrate dissociation in clay pores at static and dynamic fluid conditions is a fundamental scientific issue for improving gas production efficiency from hydrate deposits using thermal stimulation and depressurization respectively. Here, molecular dynamics simulations were used to investigate poly- and mono-crystalline methane hydrates in Na-montmorillonite clay nanopores. Simulation results show that hydrate dissociation is highly sensitive to temperature and pressure gradients, but their effects differ. Temperature changes increase thermal instability of water and gas molecules, leading to layer-by-layer dissociation from the outer surface. Under flow conditions, laminar flow predominates in nano-pores, and non-Darcy flow occurs due to clay-fluid interactions. Viscous flow disrupts hydrogen bonding at the hydrate surface, enhancing kinetic instability of water. Grain boundaries of polycrystalline hydrates are less stable compared to bulk phases and preferentially decompose, forming new dissociation fronts. This accelerates dissociation compared to monocrystalline hydrates. Fracture occurs at the grain boundaries of polycrystalline hydrate in the fluid, resulting in separate hydrate crystal grains. This fracture process further accelerates hydrate dissociation. In flow systems, methane nanobubbles form in fluid and readily transport with fluid flow. Unlike surface nanobubbles at static conditions, these liquid nanobubbles exhibit mobility. The findings of this study can contribute to a better understanding of the complex phase transition behavior of hydrate in confined environment, and provide theoretical support for improving production control technology.

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This paper presents the design and development of three-dimensional braided honeycomb structures. The basic principles and braiding process are described. The relationship between braiding parameters and honeycomb geometric parameters is established and several three-dimensional (3D) braided honeycomb fabrics are introduced. Based on the principle of the 3D braiding ‘four-step’ method, the interlaced state of yarns can be changed by controlling the movement of yarn carriers, so the separation and combination of the braid can be controlled, then 3D braided honeycomb fabric can be formed. As the number of braiding cycles of wall length increases, the relative density will gradually decrease, but the number of braiding cycles of free wall length has a greater effect on the relative density. When the number of columns of yarns participating in wall thickness increases, the relative density will gradually increase. The relative density also showed a positive correlation with the braiding angle. With the increase of the opening angle, the relative density gradually decreases, although there is a minimum point after which a little increase is observed. This paper provides significant guidance for designing various 3D braided honeycomb structures and evaluating their relative density, and can be a reference for the design and development of new honeycombs structures.

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This paper presents experimental investigations into the effects of ultrafine blast furnace slag on microstructure improvements against chloride penetration in saturated and unsaturated cementitious systems exposed to cyclic drying–wetting conditions. The hydration kinetics of ultrafine slag powders and pore solution chemistry in slag-blended cementitious systems at different ages, together with the main hydration products and pore structure characteristics, were determined. The chloride profiles accounting for different slag contents and drying–wetting cycles were measured. The results reveal that the reactivity of ultrafine slag can be well described with Avrami’s equation. The dilution effect of the slag predominated the pore solution chemistry, and the pH value decreased with a higher inclusion of slag. An optimal inclusion of 65% slag by mass of the binder corresponding to the finest pore structure and highest hydrotalcite content was found, which provides a reasonable basis for the slow chloride diffusion and high chloride binding. Under drying–wetting exposure, the specimen with a lower saturation exhibited a higher chloride transport caused by capillary absorption in the skin layer. The chloride transport tended to be diffusion controlled after sufficient drying–wetting cycles@en