2.5D机织复合材料冲击后剩余强度研究

本文主要对2.5D机织复合材料冲击后的剩余拉伸强度进行研究。采用落锤法预制冲击损伤,并进行剩余拉伸试验。用了基于层合板理论的软化夹杂法对冲击后试样进行刚度衰减的模拟,用有限元软件根据点应力破坏准则计算得到剩余强度,并与剩余拉伸试验结果进行比较,验证了模型的有效性。为便于对比,对平面机织斜纹布铺设的层合板进行了同种计算和实验,得到了在相同冲击能量下2.5D机织复合材料剩余拉伸强度衰减比例小于层合材料的结论,证明2.5D机织复合材料由于Z方向经纱的存在因而具有良好的抗冲击性。     

Impact strengthening of 3Y-TZP dental ceramic root posts

3Y-TZP ceramics are commonly used in restorative dentistry for fixed partial dentures, implants, abutments and root posts. The stress-induced transformation-toughening mechanism leads to improved mechanical properties advocating 3Y-TZP to be ground or sandblasted for better clinical performance. Such invasive mechanical treatments facilitate the additional surface strengthening as a result of the residual compressive stresses, but the exact origin is not completely understood. This study evaluated the effect of continuous impacting between 3Y-TZP root posts during 500 -h-long shaking on the extent of (sub)surface microstructural changes affecting the fracture strength. With an increase of the shaking time the surface roughness decreased, where the grains were flattened and partially spalled. The observed 6-micrometre-thick altered subsurface region containing compressive residual stresses contributed to a systematic increase in the forces of fracture within the sample population; however, only for those containing the surface type of critical flaws that were in the form of mould imprints.     

Sintering kinetics and microstructure evolution in α-Al2O3 nanocrystalline ceramics: Insensitive to Fe impurity

Diffusion kinetics, processing, and microstructures of alumina ceramics have been of great scientific and technological interests. Here we reported the sintering kinetics and microstructure evolution in high-purity dispersed ultrafine α-Al₂O₃ nanoparticles with superior sinterability. An extremely fine grain size of 34 nm with 99.6 % theoretical density and a uniform microstructure can be produced by two-step pressureless sintering. Systematic kinetic analysis further points out to a surprising insensitivity of α-Al₂O₃ nanocrystalline ceramics to Fe and other impurities, which contrasts with prior reports in the literature. We propose this insensitivity is originated from extensive grain boundaries in nanocrystalline ceramics, which allows segregation of impurities and lowers their concentrations at grain boundaries.     

Smart Anisotropic Wetting Surfaces with Reversed pH‐Responsive Wetting Directions

Smart pH‐responsive surfaces that could autonomously induce unidirectional wetting of acid and base with reversed directions are fabricated. The smart surfaces, consisting of chemistry‐asymmetric “Janus” silicon cylinder arrays (Si‐CAs), are prepared by precise modification of functional groups on each cylinder unit. Herein, amino and carboxyl groups are chosen as typical pH‐responsive groups, owing to their protonation/deprotonation effect in response to pH of the contacted aqueous solution. One side of the Si‐CAs is modified by poly(2‐(dimethylamino)ethyl methacrylate), while the other side is modified by mixed self‐assembled monolayers of 1‐dodecanethiol and 11‐mercaptoundecanoic acid. On such surfaces, it is observed that acid and base wet in a unidirectional manner toward corresponding directions that are modified by amino or carboxyl groups, which is caused by asynchronous change of wetting property on two sides of the asymmetric structures. The as‐prepared Janus surfaces could regulate the wetting behavior of acid and base and could direct unidirectional wetting of water with reversed directions when the surfaces are treated by strong acid or base. Due to the excellent response capability, the smart surfaces are potential candidates to be applied in sensors, microfluidics, oil/water separation, and smart interfacial design.     

Rheology of simulated radioactive waste slurry and cold cap during vitrification

During the vitrification of radioactive waste in a Joule‐heated melter, aqueous melter feed slurry forms a cold cap, a reacting and melting material, which floats on the surface of the molten glass. The rheological behavior of the feed affects cold cap formation and shape, and is vital for modeling the feed‐to‐melt conversion process. We used slurry feed simulant and fast‐dried slurry solids representing the cold cap to investigate the rheological behavior of the feed as it transforms into glass. Both low‐temperature and high‐temperature rheometry were performed and a new scheme was applied to estimate the feed viscosity. This study shows that the conversion advances in four sequential stages that form distinct regions in the cold cap: (i) a fast‐spreading boiling slurry from which water evaporates, (ii) a porous solid region (viscosity > 10⁸ Pa s) containing reacting solids and molten salts, (iii) a plastic region in which glass‐forming melt connects the refractory solids (~10⁸ to ~10⁶ Pa s), and (iv) a viscous foam layer in which the viscosity drops from ~10⁵ to ~10¹ Pa s. The implications for the mathematical modeling of the cold cap are discussed.     

Service design for intelligent parking based on theory of inventive problem solving and service blueprint

This study refines a structural service design stages based on the Theory of Inventive Problem Solving (TRIZ) and the service blueprint approach. This study uses the case study of intelligent parking services with the mobile application technology and vehicle license plate recognition system in a high-end shopping mall. In the problem definition stage, the research analyzes the enterprise problem. In the service resolution stage, the TRIZ contradiction analysis and the service blueprint of the parking service as it existed is depicted from the principles of problem resolution. In the solution evaluation stage, new intelligent parking mobile applications (apps) are proposed following the principles generated in the second stage. Furthermore, the failure points and waiting points in the prior service blueprint are overcome and the new service performance is significantly improved. It contributes to enriching the service design literature, and extends the range of TRIZ applications for future parking technology.     

Development of refractory ceramics from residual silica derived from rice husk ash

Rice husk has been used as a thermal energy source for electricity generation, resulting in the formation of silica from rice husk as a by-product. This research aims to develop refractory ceramic materials by replacing kaolin clay with rice husk silica at 5%, 10% and 20% volume percentages. The samples were investigated in terms of their density, apparent porosity, tensile strength in three-point bending test, compressive strength, thermal shock and mineralogical composition. The use of 20% silica resulted in an increase in the formation of cristobalite, higher packing of granular mixtures, and consequently, an improvement in the tensile strength and compression strength of the samples. However, the material that was most successful in increasing the mechanical strength without decreasing the thermal shock strength was the sample processed with 10% clay replacement by silica from rice husk.     

Fabrication and thermal stability of NH4HF2-etched Ti3C2 MXene

MXene, a new family of 2D transition metal carbides and carbonitrides, has been proved to possess excellent electrical conductivity and hydrophilicity. In this work, a single-step method to produce the larger interplanar spacing 2D MXene Ti₃C₂ by etching Ti₃AlC₂ with NH₄HF₂ was demonstrated, and the optimal reaction conditions between Ti₃AlC₂ and NH₄HF₂ were systematically researched. The morphology and microstructure of samples were characterized by scanning electron smicroscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD). The thermal stability of Ti₃C₂ was investigated by the thermogravimetry (TG) and differential thermal analyzer (DTA). It was found that the lattice parameter c of obtained Ti₃C₂ was up to 24.9 Å, and the larger interplanar spacing Ti₃C₂ was more stable than the sample exfoliated by HF. The transition temperature in air from NH₄HF₂-etched Ti₃C₂ to anatase TiO₂ thoroughly is more than 500 ℃, and the multilayered structure of Ti₃C₂ could be well retained even afer 900 ℃ heat treatment, while the value of HF-etched Ti₃C₂ is less than 350 ℃. This work is important for exploring a safe synthesis method and well understanding the thermal stability of 2D MXene materials.