偏心误差影响下齿轮副啮合行为及振动响应

为探究偏心误差对齿轮传动动态特性的影响规律，采用Adams动力学软件建立了含偏心误差激励的直齿圆柱齿轮副6自由度弯扭耦合振动模型，代入理论计算的平均啮合刚度和轴承支撑刚度，采用GSTIFF积分法求解获得了表征系统啮合行为及动态响应的数值解。分析表明，受偏心误差影响，齿轮副中心距、啮合角、重合度、齿侧间隙、传递误差、传动比等啮合相关参数均表现出动态时变特征，使齿轮系统振动和动载荷幅值增大，且呈现调制特征，在啮合频率附近出现一系列与偏心误差相关的边频带；此外，偏心误差的存在改变了系统的振动状态，使系统由理想条件下的单周期响应转变为拟周期响应

Microstructural Evolution of Shear Localization in High-Speed Cutting of CoCrFeMnNi High-Entropy Alloy

Shear localization is one of the most important failure mechanisms subjected to high-strain-rate deformation and has significant effects on the process, plastic deformation, and catastrophic failure of a material. Shear localization was observed in serrated chips produced during the high-speed cutting of the CoCrFeMnNi high-entropy alloy. Electron backscatter diffraction was performed to systematically investigate microstructural evolution during shear banding. The elongation and subdivision of the narrow grains were observed in the areas adjacent to the shear band. The microstructure inside the shear band was found to be composed of equiaxed ultrafine grains. The results reveal that grain subdivision and dynamic recrystallization might have significant roles in the microstructural evolution of shear bands. These results offer key insights into our understanding of shear localization and high-speed machining behavior for high entropy alloys

Eutectic high entropy alloy syntactic foam

High strength metallic foams have a wide range of applications in engineering as lightweight structural and energy absorbing materials. However, it is challenging to obtain metallic foam with both good energy absorption performance and high strength. Here, we developed a novel metal matrix syntactic foam fabri cated with AlCoCrFeNi2.1 eutectic high entropy alloy and alumina cenospheres that exhibits a remarkable combination of high strength and energy absorption performance under both quasi static and dynamic compression. The porous structure of syntactic foam fully exploits the properties of the AlCoCrFeNi2.1 alloy matrix with a unique FCC/B2 dual phase eutectic microstructure and thus yields exceptional per formance. We discovered that this dual phase microstructure not only provides high strength but also allows the pores to collapse in a progressive and diffusive way, which enables the formation of a high and smooth energy absorption platform. It is found that the heterogeneity between the two phases in the matrix can provide back stress strengthening, and it also induces multiple micro shear bands and microcracks as additional energy dissipation modes as the deformation proceeds. This unique mechanism ensures the strength of microstructures and makes them fracture promptly, which causes the balance of strengthening and softening on the macro scale. This work opens the avenue for developing advanced high strength lightweight structural and energy absorbing materials.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology

Research on Multi-AGVs Path Planning and Coordination Mechanism

Reasonable automatic guided vehicle path planning can shorten the transportation time of materials and improve the production efficiency of the intelligent assembly workshop. Ant colony algorithm is a widely used path planning method, however, it suffers from the shortcomings that being easy to fall into local optimum and low search efficiency. To overcome these shortcomings, first, this paper proposes a step optimization method to improve the search efficiency of the ant colony algorithm, and a path simplification method to avoid getting blindly tortuous paths; Second, to overcome the problem that the ant colony algorithm is easy to fall into the local optimum, this paper proposes an adaptive pheromone volatilization coefficient strategy, which uses different pheromone volatilization coefficients at different stages of the search path; third, for the path conflict problem of multiple automatic guided vehicles, this paper proposes a load balancing strategy to avoid it, which is based on the consideration that, path conflicts are caused by excessive concentration of multiple automatic guided vehicles paths. Extensive simulation results demonstrate the feasibility and efficiency of the proposed methods.</p

Lattice distortion and magnetic property of high entropy alloys at low temperatures

Deformation mechanisms and magnetic properties of medium and high entropy alloys (MEA/HEAs) closely relate to lattice distortion and are strongly temperature-dependent, in particular, at low temperature ranges. However, little attention has been paid to the evolution of lattice distortion with temperature decreasing and its effects on deformation behavior and magnetic state transition. In this work, we carry out in situ synchrotron radiation based X-ray powder diffraction (SR-XRD) experiments from 293 to 123 K aiming for determining lattice distortion evolutions of CrCoNi MEA, CrFeCoNi and CrMnFeCoNi HEAs. Magnetic measurements at corresponding low temperatures and cryogenic ranges are further conducted. The in situ SR-XRD results demonstrate a general reduction of lattice distortion magnitude with temperature decreasing, which shows a similar tendency with that of reported stacking fault energy (SFE) values. It is thus suggested that lattice distortion reduction possibly makes a critical contribution to deformation mechanism transition. The magnetic measurement results show a clear ferromagnetic transition of CrFeCoNi HEA when temperature is below 173 K. While, no obvious magnetic state transition is observed for CrCoNi MEA and CrMnFeCoNi HEA. The present findings on lattice distortion evolutions will pave the way for designing targeted HEAs with particular properties. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology

Crystalline Structure and Thermal Stability of an Unknown ZIF L300 Phase

In recent years, the synthesis, crystalline structure, and applications of zeolite imidazole frameworks (ZIFs) have attracted extensive attention. Since the ZIF L phase was synthesized, a new phase was observed during the heating process, but its crystal structure is unknown. The unknown new phase, which was named ZIF L300 in this study, was confirmed again. In this study, the X ray powder diffraction technique and Rietveld refinement were used to solve the crystalline structure of the unknown ZIF L300 phase. The results demonstrate that ZIF L300 has the same chemical formula (ZnC8N4H10) as in ZIF 8 and belongs to a hexagonal structure with a space group of P61. The lattice parameters have been determined as follows: a = b = 8.708(7) angstrom, c = 24.195(19) angstrom, alpha = beta = 90 degrees, and gamma = 120 degrees. The X ray absorption fine structure (XAFS) technique was also used to extract the local atomic structures. The in situ X ray diffraction (XRD) technique was used to monitor the structural evolution of the as prepared ZIF L in a temperature range from room temperature to 600 degrees C. The results show that the sample experiences a change process from the initial ZIF L orthorhombic phase (420 degrees C). These sorts of structural information are helpful to the application of ZIF materials and enrich the knowledge of the thermal stability of ZIF materials

Probing temperature effects on lattice distortion and oxidation resistance of high-entropy alloys by in situ SR-XRD and XANES

To investigate lattice distortion evolutions of CrCoNi medium-entropy alloy (MEA), CrFeCoNi, and CrMnFeCoNi high-entropy alloys (HEAs) with temperature increasing from 300 to 1323 K, we conduct in situ synchrotron-radiation-based X-ray diffraction experiments. Electron backscattering diffraction, energy-dispersive X-ray spectroscopy and X-ray absorption near edge fine structure spectra (XANES) are further carried out to uncover variations of microstructure, morphology and oxidation resistance. Generally, the lattice will expand continuously with temperature increasing, however, the expansion rate is affected by grain growth and oxidation. The oxidation resistance of CrCoNi MEA is slightly higher than CrFeCoNi HEA, and much higher than CrMnFeCoNi HEA.The XANES spectra demonstrate higher oxidation resistance of Ni, Co, and Fe than Cr and Mn. Formation of local short-range order structures around Ni and Co is observed, but no such features are observed around Fe and Mn. The present findings are significant on deepening the understandings of correlations between atomic structure and mechanical properties in advanced HEAs

Chemical composition dependent local lattice distortions and magnetism in high entropy alloys

A distinguish feature of high-entropy alloys (HEAs) is well-defined crystalline structure with chemical disorder. While, local lattice distortion is a longstanding issue in HEAs and more challenging than traditional alloys. However, reports on local lattice distortion of HEAs are rarely related to chemical compositions. Here, we use synchrotron radiation facility based XRD and X-ray absorption fine structure (XAFS) to examine averaged lattice distortion and element specified local lattice distortions in CrCoNi medium-entropy alloy (MEA), CrFeCoNi and CrMnFeCoNi HEAs. The results showed that averaged lattice distortions observed from XRD patterns are subtle. The distortion magnitude centred around certain alloying element observed in XAFS spectra keeps in the same order, generally, Ni > Co > Fe > Cr > Mn. The observed positive strains are proposed to counteract negative strains and thus leading to observation of subtle averaged lattice distortion. The XANES results suggested that local electron structure flexibility of element might be one factor that contributes to local lattice distortions. The magnetic measurements indicated a paramagnetic state of all the studied alloys at ambient conditions. This study provides key information on local lattice distortion and its correlations with chemical compositions in HEAs, which is of crucial importance in tailoring properties of advanced HEAs and other multicomponent alloys

一种抑制低能光电子共振电离产生负离子的装置

本实用新型涉及质谱分析的电离装置技术领域，具体涉及一种抑制低能光电子共振电离产生负离子的装置，包括紫外光源、推斥电极，聚焦电极，磁铁环，引出电极，金属孔电极和金属栅网，利用紫外光源照射金属孔电极表面产生光电子，通过在金属孔电极表面设置一个金属栅网并施加一定的电压将溢出的光电子从金属孔电极表面加速提取，减小低能的光电子与样品中的分子发生共振被捕获后产生负离子，获得高能的电子在电离区与样品发生碰撞电离而产生正离子，正离子被探测器检测，为了增加高能光电子与样品分子在电离区的碰撞电离效率，在电离区设置了磁铁