Toward revealing atomic deformation mechanics in lithium disilicate and β-quartz containing glass-ceramics

The mechanics of glass-ceramics subjected to sharp contact or other loading conditions remain elusive, even after being commercialized in many industrial applications. We present work herein to reveal atomic details of such deformations that are otherwise extremely difficult to probe experimentally for a lithium disilicate (LS2) and β-quartz containing glass-ceramics via molecular dynamics simulations. Specifically, the materials are comprised of LS2 and β-quartz nanocrystals in a residual glass matrix. Regardless of the deformation mechanism, whether it be nanoindentation or crack propagation for samples with pre-existing flaws, we observe that the LS2 nanocrystal itself undergoes substantial deformation, either by activating dislocations, forming an amorphization zone, or by initiating microcracks at glass-crystal interfaces or weak crystallographic planes. In contrast, the β-quartz nanocrystal is not easily deformed and remains almost intact with minimal plastic deformation, thereby forcing shear flow and crack propagation pathways to predominately occur in the residual glass and/or at interfaces. The dramatic difference between the crystalline phases also manifests itself in the deformation mode of interfaces under pure shear loading, in which shear bands preferably occur at the LS2-glass interfaces, while cavities form at the β-quartz-glass interfaces. These observations significantly advance our understanding of glass-ceramics and pave ways to exploit the understanding for more applications.     

Electrical performance and ferroelectric phase transition characteristic in different oriented 0.73PMN-0.27PT single crystals

The electrical and optical properties of (001)- and (110)-oriented 0.73 Pb(Mg_1/3Nb_2/3)O₃-0.27PbTiO₃ single crystals are systematically investigated at various temperatures, both of which present a series of ferroelectric phase transition processes. Dielectric performance measurements reveal that the ferroelectric phase transition occurs over a temperature range, rather than at one temperature point. By testing the ferroelectric hysteresis P–E curves as well as bipolar and unipolar electric field-induced strain S–E curves, the values of remnant polarization, coercive field, maximum strain, and converse piezoelectric constant d₃₃^* change considerably near the phase transition temperatures. Simultaneously, the 0.73PMN-0.27PT single crystals with (001)- and (110)-orientations under a low electric field show ultrahigh d₃₃^* values of 3540 and 2817 pm/V, respectively, which can be attributed to the electric field-induced monoclinic and orthorhombic phases, respectively. The series of ferroelectric phase transitions upon heating, that is, from rhombohedral ferroelectric to monoclinic/orthorhombic, followed by from monoclinic/orthorhombic to tetragonal, and finally from tetragonal to cubic paraelectric, are further investigated via polarized light microscopy and Raman spectroscopy.     

Hybrid CuO-Co3O4 nanosphere/RGO sandwiched composites as anode materials for lithium-ion batteries

Hybrid CuO-Co₃O₄ nanosphere building blocks have been embedded between the layered nanosheets of reduced graphene oxides with a three dimensional (3D) hybrid architecture (CuO-Co₃O₄-RGO), which are successfully applied as enhanced anodes for lithium-ion batteries (LIBs). The CuO-Co₃O₄-RGO sandwiched nanostructures exhibit a reversible capacity of~847 mA·h·g^-1 after 200 cycles' cycling at 100 mA·g^-1 with a capacity retention of 79%. The CuO-Co₃O₄-RGO compounds show superior electrochemical properties than the comparative CuO-Co₃O₄, Co₃O₄ and CuO anodes, which may be ascribed to the following reasons:the hybridizing multicomponent can probably give the complementary advantages; the mutual benefit of uniformly distributing nanospheres across the layered RGO nanosheets can avoid the agglomeration of both the RGO nanosheets and the CuO-Co₃O₄ nanospheres; the 3D storage structure as well as the graphene wrapped composite could enhance the electrical conductivity and reduce volume expansion effect associated with the discharge-charge process.     

Ideality analysis and general laws of bubble swarm microflow for large-scale gas-liquid microreaction processes

The flow ideality of bubbly microflow remains unclear even though it is vital for the design of microreactors, especially the ideality of bubble swarm microflow for large-scale gas-liquid microreaction processes. This work is the first time to report the ideality analysis of the microbubble swarm in a relatively large microchannel. The bubble swarm microflow has undergone two conditions: quasi-homogeneous plug flow and liquid phase/gas-liquid quasi-homogeneous phase two-phase laminar flow. Both the deviations of void fraction and bubble velocity from the ideal plug flow can divide into two parts, and the two transition points simultaneously happen at the velocity ratio of 1.25. There exists a critical capillary number to maintain the quasi-homogeneous plug flow, which could be regarded as the general laws for the design of gas-liquid microreactors. Finally, a novel model is developed to predict the bubble velocity. This work could be very helpful for the large-scale gas-liquid microreactors design.     

铜熔炼渣综合回收铜铅锌基础研究

采用化学分析、X射线衍射、扫描电镜微观分析三种方法分析铜熔炼渣的基础物化性质;利用热力学计算软件对铜熔炼渣中所需回收金属化合物进行理论计算,使用100kW感应炉及碳化硅石墨坩埚进行10kg级铜熔炼渣综合回收有价金属试验。结果表明,铜熔炼渣中有91.06%的Cu以硫化物状态存在,在无烟煤配比10%、黄铁矿配比10%条件下,保温120min,获得尾渣中Cu、Pb、Zn含量分别为0.28%、0.013%、0.0062%;为搭配处理炼铜烟尘和更经济的综合回收,无烟煤配比3%、黄铁矿配比3%,搭配处理6%炼铜烟尘,保温70 min,实现尾渣中Cu、Pb、Zn含量分别为0.39%、0.049%、0.028%。     

Geometric error compensation for five-axis ball-end milling by considering machined surface textures

Arbitrarily adjusting tool poses during error compensation may affect the quality of surface textures. This paper presents one tool center limitation-based geometric error compensation for five-axis ball-end milling to avoid the unexpected machined textures. Firstly, the mechanism of cutter location generation with cuter contact (CC) trajectory is analyzed. Due to zero bottom radius of ball-end cutter, CC points of the surface are only related to the tool center of the cutter. Realizing that, tool center limitation method of ball-end milling is established based on the generation of movements of all axes in order to ensure the machined textures. Then, geometric error compensation of ball-end milling is expressed as optimizing rotation angles of rotary axes by limiting tool centers of cutter locations. Next, particle swarm optimization (PSO) is intergraded into the geometric error compensation to obtain the compensated numerical control (NC) code. The limited region for particles of rotation angles is established, and moving criterion with a mutation operation is presented. With the help of the tool center limitation method, fitnesses of all particles are calculated with the integrated geometric error model. In this way, surface textures are considered and geometric errors of the machine tool are reduced. At last, cutting experiments on five-axis ball-end milling are carried out to testify the effectiveness of the proposed geometric error compensation.     

Analysis of tool-chip interface characteristics of self-lubricating tools with nanotextures and WS<Subscript>2</Subscript>/Zr coatings in dry cutting

The environmental obligations of manufacturing industries have resulted in the development of new cutting tools during metal machining without cutting fluids. According to the green manufacturing principles and to further improve the cutting performance of tools in dry cutting, novel cutting tools combined with nanotextures and WS₂/Zr coatings (AN-AW) are developed, and cutting tests without cutting fluids on hardened steel exhibit that the AN-AW tool is the most effective in reducing the cutting forces compared with the WS₂/Zr-coated tool (AS-W) and conventional tool (AS). Based on the experiments and theoretical models, the tool-chip interface characteristics are further investigated quantitatively to analyze the mechanism of the AN-AW tool. Results show that the AN-AW tool has a significant effect on the tool-chip interface characteristics. The AN-AW tool is the most effective in reducing the friction coefficient and tool-chip contact length; meanwhile, it changes the stress distribution at the tool-chip interface. The reduced tool-chip contact length and sticking-total contact length ratio as well as the lubricant film formed by the WS₂/Zr coatings at the tool-chip interface may be responsible for the changes of friction and stress distribution for the AN-AW tool.     

Configuration Design of an Under-Actuated Robotic Hand Based on Maximum Grasping Space

Capture is a key component for on?orbit service and space debris clean. The current research of capture on?orbit focuses on using special capture devices or full?actuated space arms to capture cooperative targets. However, the structures of current capture devices are complex, and both space debris and abandoned spacecraft are non?cooperative targets. To capture non?cooperative targets in space, a lightweight, less driven under?actuated robotic hand is proposed in this paper, which composed by tendon?pulley transmission and double?stage mechanisms, and always driven by only one motor in process of closing finger. Because of the expandability, general grasping model is constructed. The equivalent joint driving forces and general grasping force are analyzed based on the model and the principle of virtual work. Which reveal the relationship among tendon driving force, joint driving forces and grasping force. In order to configure the number of knuckles of finger, a new analysis method which takes the maximum grasping space into account, is proposed. Supposing the maximum grasped object is an envelope circle with diameter of 2.5m. In the condition, a finger grasping maximum envelope circle with different knuckles is modeled. And the finger lengths with corresponding knuckles are calculated out. The finger length which consists of three knuckles is the shortest among under?actuated fingers consists of not more than five knuckles. Finally, the principle prototype and prototype robotic hand which consists of two dingers are designed and assembled. Experiments indicate that the under?actuated robotic hand can satisfy the grasp requirements.     

Static Force Analysis of Foot of Electrically Driven Heavy-Duty Six-Legged Robot under Tripod Gait

The electrically driven six-legged robot with high carrying capacity is an indispensable equipment for planetary exploration, but it hinders its practicability because of its low efficiency of carrying energy. Meanwhile, its load capacity also affects its application range. To reduce the power consumption, increase the load to mass ratio, and improve the stability of robot, the relationship between the walking modes and the forces of feet under the tripod gait are researched for an electrically driven heavy-duty six-legged robot. Based on the configuration characteristics of electrically driven heavy-duty six-legged, the typical walking modes of robot are analyzed. The mathematical models of the normal forces of feet are respectively established under the tripod gait of typical walking modes. According to the MATLAB software, the variable tendency charts are respectively gained for the normal forces of feet. The walking experiments under the typical tripod gaits are implemented for the prototype of electrically driven heavy-duty six-legged robot. The variable tendencies of maximum normal forces of feet are acquired. The comparison results show that the theoretical and experimental data are in the same trend. The walking modes which are most available to realize the average force of distribution of each foot are confirmed. The proposed method of analyzing the relationship between the walking modes and the forces of feet can quickly determine the optimal walking mode and gait parameters under the average distribution of foot force, which is propitious to develop the excellent heavy-duty multi-legged robots with the lower power consumption, larger load to mass ratio, and higher stability.     

化学需氧量和总磷对猪场废水产磷化氢的影响

以猪场原液和沼液作为研究对象,在遮光密闭的环境中,于厌氧序批式反应器(ASBR)内利用钼酸铵分光光度法分别测定单位时间内不同COD和TP浓度下PH3的产生量。结果表明:猪场原液和沼液PH3释放量分别达0.048、0.033 mg/h;COD和TP都能促进磷化氢的产生。