卧式水电机组用径向滑动轴承热弹流特性分析

研究轴颈挠度和瓦块表面热弹变形对卧式水电机组径向滑动轴承静态润滑性能的影响。推导考虑轴颈挠度和轴瓦热弹变形后的油膜厚度表达式;用中心差分法结合ANSYS软件联立求解雷诺方程、能量方程、固体热传导方程、密度方程、黏度方程和轴瓦热弹变形等,得到径向滑动轴承的热弹流润滑(TEHD)特性,并与不计入轴颈挠度及轴瓦热弹变形的油膜动压润滑特性进行比较。结果表明:在考虑轴颈挠度和轴瓦瓦面热弹变形的影响后,油膜压力、温度、厚度沿着轴承宽度中心线的对称特性消失;油膜压力峰值增大,峰值点位置由轴向中心区偏移至出口区;油膜温度峰值增大,最高温度发生在出口区;润滑区内的最小油膜厚度大幅度减小,油膜最小厚度处于出口侧边界附近;轴承润滑流量减小,损耗略有增大;轴承稳态运行时,轴颈偏位角基本一致。     

铝硅聚苯酯封严涂层切向载荷作用下应力分布的有限元分析

在封严涂层弹性模量试验的基础上,建立封严涂层摩擦有限元模型,对民航发动机铝硅聚苯酯封严涂层的摩擦过程进行有限元分析。分析了摩擦系数、涂层厚度和粘结层厚度等参数对涂层/粘结层/基体系统应力分布的影响。分析结果表明:在切向载荷的作用下,随着摩擦系数的增大,涂层表面、涂层与粘结层的界面以及粘结层和基体界面处的应力峰值均增大;随着涂层厚度的增大,涂层表面及两界面处的应力峰值均减小,但当涂层厚度达到一定程度后,继续增加涂层厚度对降低应力峰值的效果不明显;粘结层厚度在一定范围内的变化对涂层表面和涂层与粘结层界面处的应力变化影响不大,但随着粘结层厚度的减小,粘结层与基体界面处的应力峰值均增大。     

一种圆锥面无键联接接触压力和应力的解析计算方法

推导了计算圆锥无键联接的接触压力的解析公式,给出了心轴和套筒轴的径向应力、轴向应力、切向应力、Mises等效应力以及压入轴向力的方程。对解析解与等效直径的圆柱面无键联接近似解法、有限元法的计算结果进行了比较。在不考虑端部应力集中时,3种方法计算出的接触压力和Mises等效应力结果差别不大。进一步验证了近似解法的可行性,并为计算圆锥联接传递的扭矩和胀紧套的应力分析提供了依据。     

一种圆锥面无键联接接触压力和应力的解析计算方法

推导了计算圆锥无键联接的接触压力的解析公式,给出了心轴和套筒轴的径向应力、轴向应力、切向应力、Mises等效应力以及压入轴向力的方程.对解析解与等效直径的圆柱面无键联接近似解法、有限元法的计算结果进行了比较.在不考虑端部应力集中时,3种方法计算出的接触压力和Mises等效应力结果差别不大.进一步验证了近似解法的可行性,并为计算圆锥联接传递的扭矩和胀紧套的应力分析提供了依据.     

封装热效应及粘结层对微芯片应力和应变的影响

针对不同的基板和粘结层,运用COMSOL Multiphysics软件分析了由封装引起的热失配对MEMS芯片的内部应力和应变的影响及其影响规律。分析不同基板对SiC芯片的应力和应变的影响,通过有限元计算分析得知,当基板的热膨胀系数跟芯片的热膨胀系数越接近,封装对芯片导致的应力应变和位移的影响越小。研究表明:粘结层的厚度对SiC芯片的应力等参数同样存在一定的影响,当粘结层的厚度增加时能够降低SiC芯片由封装引起的热应力,同时也会降低SiC芯片的第一主应变。基板厚度增加会增加SiC芯片由封装引起的热应力,温度场由高到低会增加SiC芯片由封装引起的热应力。     

等离子喷涂热障涂层中应力分布的有限元模拟

采用热弹性有限元方法研究了热载荷条件下由数值模拟方法生成的热障涂层冷却至室温后的应力分布,分析了热生长氧化物(TGO)层及其厚度对热障涂层应力分布的影响,并与文献的试验结果进行了对比。结果表明:不含TGO层的热障涂层,陶瓷层和粘结层的凸起处为拉应力,凹陷处为压应力;TGO层形成后,陶瓷层凸起处表现为压应力,凹陷处表现为拉应力;界面附近的陶瓷层在TGO层达到一定厚度时出现应力反转现象,且该现象的出现随着界面粗糙度的增大而延迟;模拟预测的应力与文献报道的结果相近,证明了模拟结果的正确性。     

反射镜无热装配中胶层厚度的计算及控制

为了实现空间遥感器反射镜无热装配,对反射镜粘接镶嵌件时胶层厚度的计算及控制胶粘厚度的方法进行了研究。首先介绍了工程中常用的计算反射镜无热装配胶层厚度的方法及胶层厚度控制工艺,主要描述了工装保证法、精密测量法和工装测量结合法,给出了各种方法的优缺点及局限性。针对目前胶粘工艺控制胶层厚度存在的问题,提出采用具有不同直径规格的空心玻璃微珠来控制胶层厚度的方法。拉伸试验验证了添加了空心玻璃微珠的光学环氧胶比纯光学环氧胶的力学性能提升了20%;利用平面反射镜粘接镶嵌件的试验表明,依靠填充空心玻璃微珠保证胶层厚度的胶粘工艺方法能够保持反射镜面形值,同时证明了胶层计算方法可以应用于空心玻璃珠的直径选择。提出的胶层厚度计算方法及玻璃微珠胶粘工艺可以实现反射镜无热装配,目前已应用于某在研项目。     

轴线偏斜对多瓦径向滑动轴承热润滑性能的影响

分析轴线偏斜对多瓦可倾瓦径向滑动轴承热流体动力润滑性能的影响。计及轴线偏斜与瓦块自由度,推导可倾瓦径向滑动轴承的油膜厚度方程,建立数学模型,计算单自由度、双自由度2种瓦块支承的径向滑动轴承在不同偏斜程度时的最小油膜厚度、压力和三维温度分布,并分析偏斜对这2种轴承热流体动力润滑性能的影响。结果表明,轴线偏斜对单自由度瓦径向滑动轴承有较大影响,会使单自由度瓦块的可倾瓦径向滑动轴承的油膜压力在轴向分布不对称,导致瓦块支承处产生不平衡的力矩,而对双自由度瓦径向滑动轴承的润滑性能几乎没有影响。     

热障涂层抗氧化夹层界面残余应力分析

通过喷涂等工艺预制的Al2O3夹层能有效抑制热障涂层高温不规则氧化生长及其所导致的失效.但是,预制的Al2O3夹层又会导致其界面应力重新分布.针对热障涂层界面三维形貌特征,考虑陶瓷层(ZrO2层)、夹层(Al2O3层)、氧化层及粘结层,建立了三维四层球模型,并推导出相应的应力解析式.凹凸两种界面形貌下抗氧化夹层的算例分析表明,抗氧化夹层厚度对热障涂层界面残余应力分布规律有很大的影响.     

磷酸锌水门汀厚度对义齿粘结面和骨结合面影响的有限元分析

利用三维有限元软件研究磷酸锌水门汀厚度对义齿粘结界面和骨结合界面的影响。将下颌第一前磨牙位的种植义齿三维模型在有限元软件A N SY S W orkbench中进行分析,再使用W orkbench中的D esign Exploration模块,分析粘结剂层厚度的变化对义齿摘除过程中应力应变的影响。通过局部灵敏度图可知,粘结层厚度的变化对基台等效应力的灵敏度、粘结剂最大主应力灵敏度、最大剪切应力灵敏度的影响最大,通过全局灵敏度图可知,粘结层厚度为51μm左右时,在牙冠颈部舌侧施加冲击载荷,对种植义齿各界面的损伤风险最小,且能保证产生的应力可以使牙冠脱位。     

The role of athermal mechanisms in the activation of tribodesorption and triboluminisence in miniature and lightly loaded friction units

Analysis of how the size of the tribocontact influences temperature rise in the contact zone has revealed that the maximum temperature rise in tribocontact with micro- and nanodimensions does not exceed 10 K. As the contact zone shrinks, each surface point is in contact for a shorter time so that the thermal activation leaves various friction-induced processes in the contact zone more or less unaffected. Thus, there should be athermal processes of activation of tribostimulated phenomena. The athermal mechanisms are considered that are likely to activate tribodesorption of gases and triboluminscence.     

红外3.2～4.5μm波段折射/衍射光学系统的减热差设计

研究了折射/衍射光学元件的温度效应及红外系统的设计理论及具体实例,给出了在红外3.2～4.5μm波段,5°视场范围,冷光栏效率100%,在-40～80℃温度变化范围情况下的红外混合减热差系统的设计结果.结果表明,使用折射/衍射光学系统的减热差设计方案,可令相应的传统光学系统减少一片元件,并且节省了昂贵的硒化锌红外材料.不仅能在较大视场内得到接近衍射极限的成像质量,较宽的温度工作范围,而且结构简单,体积小,重量轻.     

径向金属密封唇部结构接触力学研究*

由于初始过盈量和介质压力的作用,井下流量控制阀径向金属密封唇部的应力和应变梯度变化很大,很容易发生塑性变形。为研究径向金属密封唇部接触力学行为,提出径向金属密封唇部的圆弧结构,基于接触力学建立径向金属密封唇部轴对称结构的圆弧-平面接触模型,得出径向金属密封唇部结构接触力学参数的理论关系式,并基于有限元方法进行验证。径向金属密封唇部接触力学参数的理论解与数值解相符,接触宽度、最大接触应力、初始过盈量和平均接触应力的平均相对误差分别为8.86%、6.96%、8.88%和4.33%,满足工程设计要求。研究表明：径向金属密封唇部的最大接触应力与初始过盈量、径向金属密封唇部径向厚度和轴向厚度成正比,与径向金属密封唇部圆弧半径成反比,因此可通过增加初始过盈量、径向金属密封唇部径向厚度和轴向厚度来增加径向金属密封唇部的最大接触应力。研究结果为井下流量控制阀径向金属密封的设计提供了理论指导。     

Plastic Deformation Mechanism in Double-Roller Clamping Spinning of Flanged Thin-Walled Cylinder

Double?roller clamping spinning(DRCS) is a new process for forming a thin?walled cylinder with a complex surface flange. The process requires a small spinning force,and can visibly improve forming quality and production e ciency. However,the deformation mechanism of the process has not been completely understood. Therefore,both a finite element numerical simulation and experimental research on the DRCS process are carried out. The results show that both radial force and axial force dominate the forming process of DRCS. The deformation area elongates along the radial direction and bends along the axial direction under the action of the two forces. Both the outer edge and round corner of the flange show the tangential tensile stress and radial compressive stress. The middle region shows tensile tangential stress and radial stress,while the inner edge shows compressive tangential stress and radial stress. Tan?gential tensile strain causes a wall thickness reduction in the outer edge and middle regions of the flange. The large compressive thickness strain causes material accumulation and thus,an increase in the wall thickness of the round corner. Because of bending deformation,the round corner shows a large radial tensile strain in addition. The inner edge of the flange shows small radial compressive strain and tensile strain in thickness. Thus,the wall thickness on the inner edge of the flange continues to increase,although the increment is small. Furthermore,microstructure analysis and tensile test results show that the flanged thin?walled cylinder formed by DRCS has good mechanical properties. The results provide instructions for the application of the DRCS process.     

Effects of substrate materials on fracture toughness measurement in adhesive joints

To understand the effects of substrate materials on the fracture behavior of adhesive joints, experimental studies and finite element analyses have both been conducted for double-cantilever-beams (DCB) with aluminum and steel substrates at different bond thickness (h). Numerical results show that the region dominated by the crack singularity is much smaller than by the bond thickness. Very small plastic deformation may hence violate the requirements for small-scale yielding where the crack-tip field can be characterized uniquely by the stress intensity factor. Both critical strain energy release rate and J-integral for the joints with steel substrate are lower than those for the joints with aluminum substrate. Compared to the critical strain energy release rate, the critical J-integral is less sensitive to the substrate material if small plastic deformation occurs before cohesive failure takes place through the adhesive layer. For the joints with aluminum substrate, the fracture toughness initially increases and then decreases with bond thickness. Elastic–plastic crack-tip analysis indicates that at the same level of loading, a higher opening stress is observed in the joint with a smaller bond thickness. A self-similar stress field can be obtained by the normalised loading parameter, J/hσ₀.     

Molecular dynamics study on external field induced crystallization of amorphous argon structure

A molecular dynamics study has been conducted on an external-force-field-induced isothermal crystallization process of amorphous structures as a new low-temperature athermal crystallization process. An external cyclic-force field with a dc bias is imposed on molecules selected randomly in an amorphous-phase of argon. Multiple peaks smoothed out in the radial distribution functions for amorphous states appear very clearly during the crystallization process that cannot be achieved otherwise. When the amorphous material is locally exposed to an external force field, crystallization starts and propagates from the interfacial region and crystallization growth rates can be estimated.     

Surface stresses in coated steel surfaces—influence of a bond layer on surface fracture

Thin hard coatings in the thickness range of only a few micrometers deposited by physical vapour deposition (PVD) on components or tools can improve the friction and wear properties by several orders of magnitude. A 2 μm thick TiN (E=300 GPa) coating on a high-speed steel substrate with a bond layer at the interface between the coating and the substrate was modelled by micro-level three-dimensional finite-element method (3D FEM) in order to optimise a coated surface with regard to coating fracture. Both compliant low modulus (E=100 GPa) and stiff high modulus (E=500 GPa) bond layers at the coating/substrate interface of 200 and 500 nm thickness were investigated. First principal stresses were simulated for scratch test geometry in the load range of 7.5-15 N. Very high stress concentrations of above 5700 MPa tensile stresses were observed in the bond layer just behind the contact zone for the stiffer bond layer. The stiff bond layer generated 5 times higher tensile stress maxima compared to the compliant bond layer. There was approximately 3.5 times larger strain in the compliant bond layer compared to the stiff bond layer. The general coating design advice based on this exercise is that when a bond layer is used e.g. for coating/substrate adhesion improvement should the bond layer be less stiff than the coating not to generate high and critical tensile stresses. The thickness of the bond layer may vary and is not critical with respect to generated stresses in the surface.     

Application of a variable flow stress machining theory to helical end milling

A methodology of modeling chip geometry of flat helical end milling based on a variable flow stress machining theory is presented in this article. The proposed model is concerned with the variation of the width of cut thickness. The nonuniform chip thickness geometry is discretized into several segments based on the radial depth of cut. The chip geometry for each segment is considered to be constant by taking the average value of the maximum and minimum chip thickness. The maximum chip thickness for each chip segment is computed based on the current width of cut, feed per tooth and the cutter diameter. The subsequent radial depth of cut is subtracted from the discretized size of the width of cut to obtain the minimum chip thicknesses. The forces for each segment are summed to obtain the total forces acting on the system of the workpiece and the tool. The cutting forces can be predicted from input data of work material properties, cutter configuration and the cutting conditions used. The validation of the proposed model is achieved by correlating experimental results with the predicted results obtained.     

卧式螺旋卸料沉降离心机转鼓的有限元仿真

应用VisualNastran有限元仿真软件对转鼓在各种载荷工况下的应力应变进行了仿真分析，并调整转鼓壁厚参数来研究参数的变化对转鼓的强度和径向变形的影响。仿真结果表明：转鼓的最大应力位于靠近大端鼓底的柱形筒体的内壁上；物料离心液压引起的最大应力和最大径向位移随着转鼓壁厚的减小而增大；转鼓自身质量离心力在壁内产生的最大应力和最大径向位移与鼓壁厚度无关。