功能梯度斜板的屈曲分析

研究面内荷载作用下功能梯度斜板的屈曲问题.基于经典板理论,假设材料性质为板厚度方向坐标的幂函数,不考虑温度的影响,推导功能梯度板在纵向荷载作用下的平衡微分方程,运用坐标转换关系,建立斜坐标系下功能梯度斜板的屈曲微分方程.采用微分求积法,离散屈曲微分方程,结合边界条件,给出功能梯度斜板在两对边受有均布压力作用下临界屈曲荷载的无量纲数值解.在此基础上,讨论板的几何外形尺寸、夹角、梯度指标以及中面变形等因素对临界屈曲荷载的影响.结果表明:功能梯度板的临界屈曲荷载变化介于相应的均质各向同性板的临界屈曲荷载变化之间;功能梯度材料板的临界屈曲荷载变化随板的相对几何外形尺寸宽长比b/a的减小而减小,随梯度指标κ和夹角θ的增加而减小;中面变形对夹角较小和梯度指标较高的板有较大影响.     

计及不同剪切变形的功能梯度材料梁的弯曲分析

研究矩形截面功能梯度材料(Functionally graded materials,FGM)梁在不同剪切变形理论下的静力弯曲问题。假设FGM梁由金属和陶瓷两种材料构成,其等效物性参数沿厚度方向连续变化,且遵从简单幂率变化规律。基于最小势能原理,建立以轴向位移、横向位移及转角为未知函数的FGM梁的运动微分方程组。对简支FGM梁,采用Fourier级数法获得5种剪切变形理论下FGM梁的挠度、轴向位移及转角曲线,分析梁的长高比、梯度指标对弯曲变形的影响,分析不同剪切变形理论下FGM梁的切应力和正应力的分布特性,并与均质材料梁的静力弯曲特性进行比较。给出FGM梁的中性轴位置随梯度指标的变化曲线并进行分析。     

铝合金三明治板面外承载特性的有限元模拟和试验研究

通过有限元模拟方法研究了点/面载荷作用下不同长宽比和宽厚比铝合金三明治板的面外屈曲特性，并进行试验验证；通过试验研究了不同尺寸参数铝合金三明治板的面外承载特性。结果表明：模拟得到点/面载荷下三明治板的载荷-位移曲线与试验结果基本吻合，平均相对误差小于5%,证明了有限元模拟的可靠性；三明治板在点载荷下发生整体刺穿破坏，在面载荷下发生芯板压缩破坏。在点载荷下，当宽厚比为13.6时，随着长宽比由0.7增大到1.9,三明治板的破坏载荷先升高后趋于平稳，而当宽厚比为21.4时，随着长宽比由0.4增加到1.2,破坏载荷基本不变，宽厚比21.4的破坏载荷大于宽厚比13.6。在面载荷作用下，随着长宽比增大，屈服载荷降低，宽厚比13.6的屈服载荷大于宽厚比21.4。以3 mm为面外屈曲变形临界值时，点/面载荷作用下三明治板的临界屈曲比均为0.093。     

弹性地基上转动功能梯度材料Timoshenko梁自由振动的微分变换法求解

基于Timoshenko梁理论研究弹性地基上转动功能梯度材料（FGM）梁的自由振动。首先确定功能梯度材料Timoshenko梁的物理中面,利用广义Hamilton原理推导出该梁在弹性地基上转动时横向自由振动的两个控制微分方程。其次采用微分变换法（DTM）对控制微分方程及其边界条件进行变换,计算了弹性地基上转动功能梯度材料Timoshenko梁在夹紧-夹紧、夹紧-简支和夹紧-自由三种不同边界条件下横向自由振动的量纲一固有频率,与已有文献的计算结果进行比较,退化后结果一致。最后讨论了不同边界条件、转速、弹性地基模量和梯度指数对功能梯度材料Timoshenko梁自振频率的影响。结果表明：功能梯度材料Timoshenko梁的量纲一固有频率随量纲一转速和量纲一弹性地基模量的增大而增大;在量纲一转速和量纲一弹性地基模量一定的情况下,梁的量纲一固有频率随着功能梯度材料梯度指数的增大而减小。     

梯度功能材料的制备与性能评价

梯度功能材料（FGM）是组分和性能呈连续变化的先进材料,FGM的制备方法与性能评价对其优化设计具有重要意义。对FGM的制备方法与性能评价进行了综述,详细分析了FGM的力学性能、热震性能、压缩性能和热处理性能的评价方法及试验手段,最后指出了FGM性能评价和制备的发展方向。     

磨料喷射喷嘴的应力分析及FGM模型设计

分析表明磨料喷射加工中喷嘴承受的应力在喷嘴入口最大、出口次之、中间区域相对较小。试验显示喷嘴的冲蚀磨损在喷嘴入口最严重、出口次之、中间区域相对较小。试验结果与应力分析结果一致,得出磨料喷射加工中喷嘴入口、出口处承受的高拉应力是造成其冲蚀磨损严重的主要原因的结论。针对提高均质陶瓷材料喷嘴抗冲蚀磨损能力的力度有限,提出运用梯度功能材料(Function gradient material,FGM)理论于喷嘴材料的设计和制造中,研发新型非均质的陶瓷喷嘴材料,将梯度功能陶瓷喷嘴制备中产生的残余压应力引入喷嘴入口、出口,使其减缓磨料喷射加工中喷嘴承受的拉应力,以提高喷嘴抗冲蚀磨损能力。结合喷嘴的冲蚀磨损特点、结构特点及陶瓷喷嘴材料制备工艺性等,建立了梯度陶瓷喷嘴物理模型和成分分布模型。根据本模型设计结果,研制出梯度 SiC／(W,Ti)C陶瓷喷嘴。结果表明,相同条件下制各的梯度SiC／(W,Ti)C陶瓷喷嘴的抗冲蚀磨损能力高于非梯度 SiC／(W,Ti)C陶瓷喷嘴。     

基于有限元的选择性激光熔化薄壁成型的熔池研究

本文主要通过有限元研究了选择性激光熔化(Selective Laser Melting,SLM)加工薄壁过程中的热行为。分析了不同扫描速度及激光功率对熔池尺寸的影响,并与实体加工进行了对比。研究发现,熔池的宽度及深度随激光功率的增加而增加,随扫描速度的提高而减小;熔池的长宽比随功率增大和速度的增大而增大。并且发现,实体加工和薄壁加工中,熔池的宽度与深度在同样工艺参数条件下差别不大,但熔池的长宽比有明显差别,薄壁加工长宽比更大,因此更容易发生球化现象。     

SiCf/SiC陶瓷基复合材料单颗磨粒磨削试验研究

对碳化硅纤维增强碳化硅陶瓷基复合材料（SiCf/SiC）进行了单颗磨粒磨削试验,研究了脆性去除模式下磨削中侧边崩碎规律。研究结果表明：磨削SiC基体时,基体内裂纹易引发磨削中大块侧边崩碎;磨削纤维时,侧边崩碎宽度随纤维与磨削方向夹角的增大而增大;磨削90°纤维时,提高磨削速度可减小侧边崩碎程度;以50 m/s和90 m/s的磨削速度磨削造成的侧边崩碎宽度比以20 m/s磨削时的侧边崩碎宽度分别小30%和60%;在试验参数范围内,增大磨削用量不会增大磨削中侧边崩碎程度,但可以提高材料去除率。     

挤压筒颤振辅助双杯挤压成形过程有限元分析

阐述挤压筒颤振辅助双杯挤压成形机理,运用Deform-3D有限元分析软件进行数值模拟仿真,分析比较不同施振参数下的行程载荷、材料流动速度、杯高比及等效应力分布。仿真结果表明挤压筒颤振可降低平均行程载荷,其平均行程载荷的最大下降值随颤振速度的提高而增加,但对实际挤压力影响不明显;上杯材料流动速度随颤振速度的提高而减小,下杯材料则相反;当颤振速度小于下杯材料流动速度时,杯高比大于无颤振时的值,且随颤振速度的提高而增加,而当颤振速度大于下杯材料流动速度时,上杯材料流动速度方向会出现反向,杯高比小于无颤振时的值,并随颤振速度的提高而减小;邻近挤压筒侧的塑性变形区随颤振周期性上下运动,但并不改变最大等效应力。     

多元梯度自润滑陶瓷刀具材料的研制

针对均质自润滑陶瓷刀具材料不能合理兼顾减摩性能及耐磨性能的难题,运用功能梯度材料的设计思想研制出一种梯度自润滑陶瓷刀具材料。这种新型自润滑刀具材料的特征是固体润滑剂由其表层向内层梯度减少,并且材料表层存在残余压应力。提出多元梯度材料的组成分布模型,按该模型得出的组分梯度设计结果,采用粉末叠层铺填与真空热压烧结工艺制备Al2O3/TiC/CaF2梯度自润滑陶瓷刀具材料。该梯度自润滑陶瓷刀具材料的显微结构呈现出与组成分布一致的梯度变化,表层形成了残余压应力,其抗弯强度、硬度和断裂韧度分别比相应的均质材料提高了21%、16%和5.9%。材料强度的提高主要是由于CaF2由表层到中间层梯度减少,硬度和断裂韧度的提高归因于材料表层的残余压应力。以Al2O3/TiC/CaF2梯度自润滑陶瓷刀具和相应的均质自润滑陶瓷刀具对45钢进行干切削试验,结果表明,梯度刀具的耐磨性能优于均质刀具。     

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.     

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....     

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。     

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.