梯度结构对氧化铝陶瓷涂层接触应力的影响

采用幂指数描述"三明治"式梯度结构形式,建立镍基氧化铝梯度陶瓷涂层在静态接触集中力载荷作用下有限元模型,分析静态接触集中力载荷作用下涂层的Mises应力分布,以及梯度层的厚度、中间层数及结构形式对涂层的Mises应力分布及最大Mises应力发生位置的影响。结果表明:梯度结构对接触区Mises应力大小及分布影响不大,但影响最大Mises应力发生位置;合理的梯度结构能避开最大Mises应力发生在表面强化区及梯度区中,防止陶瓷涂层在接触载荷作用下疲劳脱落。制备层状结构梯度陶瓷涂层时,采用氧化铝层厚度20μm、线性梯度层厚度80μm、8层中间层,可改善Mises应力,适当避开最大Mises应力发生在梯度区。     

单层涂层最佳厚度的有限元分析

采用有限元数值计算的方法对TiN、TiC、Si3 N4及SiC四种材料的硬涂层体系表面下的应力分布进行了模拟分析。结果表明 ,对于TiN材料 ,当涂层厚度与接触半宽之比t/a <0 .3时 ,表面下的最大剪应力分布对提高轴承疲劳寿命较为有利 ;t/a =0 .5时 ,涂层系统的摩擦力学性能最差。涂层厚度较薄时 ,位于赫兹接触中心附近的涂层表层上的最大剪应力要远大于基体内的最大静态剪应力 ;当t/a >0 .1时 ,涂层表面上的最大剪应力对提高轴承疲劳寿命较为有利 ;涂层材料与基体材料的弹性模量之比小于 2 .0时 ,有利于提高涂层系统的疲劳寿命     

高速钢上TiN涂层残余应力的曲率测试和有限元分析

采用多弧离子镀在W6Mo5Cr4V2高速钢上沉积五种不同厚度TiN涂层,用曲率法和有限元法研究TiN涂层残余应力和构成。结果表明涂层厚度对其残余应力有很大影响,特别是对本征应力。当涂层厚度从3μm变化到11μm时,TiN涂层总残余应力分布在-3.12～-2.29GPa之间;热应力分布在-1.96～-1.92GPa之间;本征应力分布在-1.17～-0.37GPa之间。其中热应力所占的比例较大,约占62%～68%。当膜基比ξ0.017时,总残余应力随ξ的增加呈非线性增加;当ξ=0.017时,该值达到最大值-3.12GPa;当ξ0.017时,该值随ξ的增加而下降。造成这种变化的主要原因是涂层本征应力受涂层结构影响较大,随着涂层厚度的增加,涂层中孔洞、过冷液滴以及界面微裂纹等缺陷也随之增加,导致涂层中本征应力得到有效释放。     

磨粒磨损的磨粒接触热分析

针对磨粒磨损机制,采用球形磨粒模型和分形磨粒2种模型,利用有限元软件ANSYS分析磨粒磨损的滑动过程,探讨磨粒与磨损表面接触区內的温度变化、热应力分布及其随表层深度的变化情况,并对2种模型的分析结果进行对比分析。研究结果表明:球形磨粒模型中磨粒温度较高,接触体温度较低,磨粒与磨损表面温差较大,磨粒与表面接触处的Mises应力和剪应力分布比较分散;而分形磨粒模型中接触体温度较低,磨粒温度更低,磨粒与磨损表面温差较小,磨粒与表面接触处的Mises应力和剪应力分布比较集中,并且应力最大值比球形磨粒模型的大。     

梯度结构对氧化铝陶瓷涂层抗冲击载荷性能的影响

梯度结构陶瓷涂层以其优异的抗热震性表现出巨大的工程应用前景。为推动梯度陶瓷涂层在机械零件表面强化上的应用,采用“三明治”式梯度结构形式,建立镍基氧化铝梯度陶瓷涂层在冲击载荷作用下有限元模型,分析冲击载荷作用下涂层的力学性能,以及梯度层的结构形式、厚度及层数等参数对涂层的力学性能影响。结果表明：较无梯度结构陶瓷涂层相比,梯度结构能有效减缓涂层与基体结合面上的应力突变,涂层内部最大Mises应力明显降低,合理的梯度结构能改善涂层内部Mises应力分布,改变应力分布特征,减缓表面陶瓷涂层的冲击应力,从而防止陶瓷涂层在冲击载荷作用下脱落。最后对制备层状结构梯度陶瓷涂层时,如何进行梯度层结构设计进行了探讨,并提出了采用0.25次方幂指数梯度结构,得出10层中间层就可有效减缓冲击载何、降低Mises应力突变的结论。     

水泥环破碎器矩形异形活塞密封性能分析

针对传统圆柱形液压活塞承载力不足问题,提出一种矩形异形活塞,研究其在不同工况下的密封性能。基于Abaqus软件建立异形活塞有限元模型,研究介质压力、密封间隙、活塞运动状态以及摩擦因数对密封性能的影响,并分析异形密封环不同位置处的应力分布和翻转情况。结果显示：静密封时,介质压力越大,密封环的最大Mises应力和最大接触应力越大;密封间隙越小,最大Mises应力与最大接触应力越大;相比静密封,内行程过程中最大Mises应力和最大接触应力都有明显增加,且随摩擦因数增加而增加,而外行程中最大Mises应力和最大接触应力相比静密封差异较小;各工况下应力最大值均出现在密封环圆弧段;在活塞运动过程中密封圈并未发生翻转,只是存在位置的平移情况。研究结果证明了异形活塞的可行性以及良好的密封性能,为活塞结构设计与优化提供了依据。     

固体润滑滚子轴承的接触表面应力分析研究

为获得固体润滑滚动轴承滚动体与滚道处的接触应力,通过固体润滑滚子轴承拟动力学分析并考虑涂层的影响,获得了滚子轴承稳定运行过程中滚动体的力载分布。通过建立带涂层接触的平面应变问题的力学模型,将涂层与基底两种材料的特性等效为一种材料来求解滚子与接滚道触应力分布情况,并与轴承的拟动力学分析相结合,获得了滚子轴承中滚动体与固体润滑膜接触表面的接触变形、接触半径与外加载荷之间的关系,讨论了不同涂层的弹性模量以及不同涂层厚度对接触界面应力分布的影响。当涂层弹性模量比基底大时,涂层的存在使得接触半宽减少,最大名义接触应力增加;涂层弹性模量比基底小时,则与之相反。当涂层的厚度<0.01mm时,涂层的存在对固体润滑滚子轴承的接触表面应力分布影响较小;在一定范围内,当涂层的厚度逐渐增大时,涂层对轴承接触表面应力分布的影响增大。     

磨粒磨损的接触分析

磨粒磨损作为磨损的主要类型之一,影响机械使用寿命。针对犁沟磨损机制,采用球形磨粒模型和分形磨粒模型,对于磨粒磨损的压入、滑动和压碎3个过程,利用有限元软件ANSYS,分析磨粒与磨损表面接触区的Mises应力和剪应力分布以及应力随表面深度的变化情况,并对2种模型的分析结果进行对比。研究结果表明,球形磨粒模型中,磨粒与表面接触处的Mises应力和剪应力分布比较分散,且应力峰值较小,在相同材料和压力下磨粒和表面均未压碎;然而分形磨粒模型中,磨粒与表面接触处的Mises应力和剪应力分布比较集中,且应力峰值较大,磨粒和表面均压碎。2种模型中,采用分形方法构造的分形磨粒形状与实际情况中的磨粒形状更加相似。     

等离子喷涂8YSZ热障涂层隔热效果及内应力演变有限元模拟

采用等离子喷涂法制备质量分数8%氧化钇稳定氧化锆(8YSZ)热障涂层，并进行隔热和热震循环试验；构建简易有限元模型对热障涂层的隔热性能和热震循环中的内应力演变进行模拟，并对破坏机理进行分析。结果表明：模拟得到热障涂层的隔热温度在167.60～262.22℃,隔热效果良好，与试验结果的相对误差在10%以内；热障涂层的隔热效果随厚度增加而增强；热震循环产生的应力在涂层的界面边缘处集中，与试验得到的在涂层边缘处出现裂纹和脱落并逐渐延伸至中心的失效方式相吻合；随涂层厚度增加，热震循环升温和降温后的应力增大。     

AZ31B镁合金单点渐进热成形工艺的模拟优化

通过数值模拟研究了AZ31B镁合金在不同成形温度、压下量和进给速度下的单点渐进成形过程,建立了各参数与最大Mises应力和最大厚度减小率的响应面模型,并进行了以最大Mises应力和最大厚度减小率为约束的多目标优化。结果表明:随着成形温度的升高,板料温升逐渐减小,当成形温度超过200℃后,板料不同位置的温度变化不大;各参数按对最大Mises应力和最大厚度减小率的影响由大到小排序为成形温度、进给速度、压下量;多目标优化得到的最佳工艺参数为成形温度273℃、压下量0.51mm、进给速度1 340mm·min~(-1),在最佳工艺参数下模拟和实测成形件厚度的误差较小,证明了数值模型及响应面模型的准确性。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.