Spontaneous ignition of high-pressure hydrogen and boundary layer characteristics in tubes

Hydrogen is efficient and environmentally friendly, but the danger of self-ignition resulted from the leakage of high-pressure hydrogen cannot be ignored. In this work, the self-ignition of high-pressure hydrogen released through different conditions was studied. 700-mm-length tubes with different diameters were adopted in our experiments. It summarized the characteristics of shock waves' attenuation and evolution process of hydrogen jets in tubes. In addition, effects of the boundary layer on the leading shock waves, the contact surface, and expansion waves were discussed. Results indicate that minimum pressure when self-ignition occurs for 15-mm-diameter tube is similar to 10-mm-diameter. And they have closely velocity of shock waves. Simulations show that the greater the release pressure, the more ignition products of hydrogen. Higher release pressure and smaller diameter can create a thicker boundary layer in micro shock tubes, and the boundary layer can lead to a change in the velocity of shock waves’ structures.     

Void evolution in nanocrystalline metal film under uniform tensile stress

A theoretical model to describe the nucleation and growth of voids at triple junctions of nanocrystalline metal film under uniform tensile loading is suggested. The void growth rate controlled by grain boundary diffusion under the combined influence of void surface energy, grain boundary interface energy and elastic energy stored in the solid is evaluated. Stress relaxation during uniform tension deformation is finally discussed; the effective stress relaxation distance is also calculated. The stress relaxation not only suppresses the nucleation of voids and cracks, but also influences the void growth rate.     

Numerical simulations of the phase separation properties for the thermal aged CDSS with Phase Field Model

Experiments and numerical simulations with Phase Field Model and Finite Element Analysis were carried out to investigate the phase separation dynamic properties and the corresponding thermal aging degradation mechanism. Experimental results from transmission electron microscopy and atomic force microscopy show that thermal aging causes the Cr-rich phase precipitate and form clusters. A phase field dynamic model was developed with constitutive relations and empirical potential functions to investigate the phase separation dynamics in the ferrite phase. Numerical results integrated with cell dynamical system method show clearly the micro structure morphology and the phase separation coarsening with aging time. The evolution process of the phase separation was quantitatively illustrated and reproduced macroscopically. The scattering pattern becomes clearer and the corresponding radius becomes smaller along with the increasing aging time. The average characteristic length increases firstly then decreases and enters a more stable stage. With the increment of the local Cr concentration, the evolution of the phase morphology was quite different. Finite Element Analysis simulation results with the Gurson-Tvergaard-Needleman void model show that the damage initiated more easily in the ferrite matrix for the Cr atoms forming clusters with increasing aging time. The phenomenological simulations with Phase Field Model and Finite Element Analysis were in remarkably good agreement with experimental results and analytical considerations.     

Effect of nano-metal particles on the fracture toughness of metal–ceramic composite

A theoretical model is proposed to study the influence of nano-metal particles (NMPs) on the fracture toughness of metal–ceramic composites (MCC). In the framework of the model, the crack tip intersects the grain boundary of the NMPs. Stress concentration at crack tip initiates edge dislocations which makes a shielding effect on the crack and leads to fracture toughness of the MCC. The dependence of critical crack intensity factors on grain size of the NMPs was calculated. The calculation suggested that the existence of the NMPs lead to an increase of critical crack intensity factors by 14%.     

SiO2/S涂层及乙酸钾抗结焦性能的对比

  以石脑油为裂解原料,在850℃下对退役  HP40炉管内表面进行结焦试验,并对比了 SiO₂/S 涂层与乙酸钾的抗结焦性能。采用场发射扫描电子显微镜(FE-SEM)和透射电镜(TEM)表征了焦炭形貌,采用热重(TGA)、元素分析和拉曼光谱考察了焦炭结构。结果表明,由于退役 HP40炉管内表面状态的改变,加剧了催化结焦。SiO₂/S 涂层可以有效地抑制催化结焦,其结焦抑制率达到65%,但是 SiO₂/S 涂层剥落后,焦炭以催化焦为主,同时夹杂着部分热裂解焦。当乙酸钾质量分数为400 μg/g 时,抑焦率达到60%。当乙酸钾质量分数分别为0、100、200和400 μg/g 时,丝状焦直径分别为100、60、45和35 nm。SiO₂/S涂层与乙酸钾对焦炭结构影响较小,退役 HP40炉管内表面焦炭为高沸点、缩合度较高的大分子,石墨化程度较低。     

一种新型大刚度高灵敏度的并联六维力传感器设计研究

腕力传感器是一类重要的机器人传感器,腕力传感器的结构设计好坏直接影响到传感器的各项指标。在分析了并联力传感器的力变换原理,利用并联传感器的空间力传递关系,直接推导出感测力的六维雅可比矩阵,并将六维力雅可比矩阵用具体的结构参数解析表达,在此基础上设计了一种新的并联六维力传感器,新设计的附加弹性体的采用,使该传感器具有很大的刚度,同时具有很高的检测灵敏度,从而很好地解决了传感器的刚度与灵敏度之间的矛盾,探索了传感器设计的新方法和途径。     

基于ADAMS的数控转台蜗轮副传动精度的研究

利用Solidworks建立了蜗轮蜗杆传动副的三维实体模型,然后导入多体动力学分析软件ADAMS,根据Hertz弹性撞击理论,在蜗轮蜗杆之间施加碰撞力,给出了模型参数的确定方法。对蜗轮蜗杆啮合过程进行了运动仿真分析,将仿真结果与理想情况进行对比,结果表明所建虚拟样机模型正确可靠。在此基础上,分析了不同安装误差条件下,各项安装偏差对蜗轮副传动精度的影响,并比较了三种偏差影响程度的大小,为提高数控转台精度提供依据,具有较大的工程应用价值。     

节能型搪瓷涂层烧成工艺及其性能研究

介绍了一种低温搪瓷釉的助熔剂,有效将搪瓷的烧成温度降至800℃以下,研究了烧成温度和保温时间对搪瓷层耐酸性能、抗机械冲击性能以及耐温急变性能的影响。结果表明:所制备搪瓷层的耐酸性能、抗冲击性能以及耐温急变性能都达到了国家优等品的标准,随着烧结温度的提高和保温时间的延长,搪瓷层的耐酸性能和抗机械冲击性能均提高。最后,运用有限元分析软件ANSYS分析了搪瓷层的传热性能,以及热应力对搪瓷层稳定性的影响。     

Finite element modelling of brazed residual stress and its influence factor analysis for stainless steel plate-fin structure

This paper presents a finite element modelling of brazed residual stress in a stainless steel plate-fin structure applied to recuperators in microturbines. The effects of nine influence factors on residual stress are investigated. The results show that the brazed joint creates large residual stresses due to the mechanical properties mismatching between base metal and filler metal. Strength in the middle joint is affected mainly by longitudinal stress. The residual stress gradient around the interface between base metal and filler metal is very large, which can have a great effect on interface strength. The material mismatching, brazing gap, pressure loading, fin pitch, fin thickness, fin height and plate thickness significantly affect the residual stress distribution, while the brazing temperature and the number of fin layers have little impact on residual stress. This work provides a reference for optimizing the brazing procedure and decreasing the residual stress for stainless steel plate-fin structures.