纯铝粉末烧结体锥形件高压扭转有限元模拟及实验

采用有限元法对锥形件高压扭转成形过程进行了数值模拟,着重分析了成形过程的应变和相对密度的分布及变化趋势。通过实验对纯铝粉末烧结体试样变形前后相同部位的金相组织、显微硬度和相对密度进行了对比分析。研究结果表明:高压扭转工艺对试样有着显著的致密效果,模拟中试样的相对密度超过0.996,实验中试样的密度达0.980;试样不同部位的等效应变和显微硬度不同,边缘处的等效应变最大,达到4.55,该处的显微维氏硬度值也最高,达61.12HV0.1/10。     

压扭成形关键工艺参数对铝合金杯形件性能的影响

采用压扭复合成形工艺实现某型号Al-Zn-Mg-Cu合金杯形件成形,采用金相观察、拉伸试验和扫描电镜等分析测试手段,研究了不同工艺参数对Al-Zn-Mg-Cu合金杯形件微观组织、力学性能和断裂方式的影响。结果表明,Al-Zn-Mg-Cu合金杯形件压扭成形最佳温度为400℃,此时微观组织几乎全部由细小等轴晶组成,材料抗拉强度最高为430MPa,强度提高了49.8%;当变形温度高于300℃时,Al-Zn-Mg-Cu合金压扭变形后其断裂方式为塑性断裂,而当成形温度低于300℃时,其断裂方式呈现一定程度的脆性断裂;Al-Zn-Mg-Cu合金杯形件压扭成形扭转圈数不宜过大(不大于5圈),当扭转圈数较小(不大于5圈)时,Al-Zn-Mg-Cu合金压扭变形后其断裂方式为塑性断裂,且随着扭转圈数的增大,微观断口表面韧窝数量增加,韧窝深度加深;当扭转圈数较大(大于5圈)时,其断裂方式呈现一定程度的脆性断裂。     

镁合金板形件扭-挤成形载荷的主应力法求解模型

结合挤压工艺和高压扭转工艺的优势提出一种扭-挤成形工艺新方法及开发了模拟装置,该工艺不仅能够保证成形,而且还能够有效的细化晶粒.通过分析扭-挤成形工艺金属流动和变形区特点,建立了镁合金扭-挤成形载荷的主应力法求解模型,该模型将变形区划分为四个区域,依次推导了不考虑扭转和考虑扭转成形载荷的求解模型,剪切屈服强度考虑温度和应变速率的效应.通过与成形试验的载荷对比,模型计算结果与试验的结果误差在8％以内.采用该模型分析了不同参数对成形载荷的影响,结果表明随着扭转轴转速的增加,不仅坯料剪切变形增加,且成形载荷减小;成形载荷随坯料半径的增加而增加,随坯料高度的增加呈线性增加,随板件宽度的增加而减小,随板件高度的增加先骤减后平缓减小,且坯料半径和板件高度对成形载荷影响显著.     

不同沉积路径冷金属过渡电弧增材制造H13钢成形件的显微组织和硬度

在不同沉积路径下采用冷金属过渡电弧增材制造技术制备了H13钢成形件,基于热-弹塑性有限元法对成形件的热历程进行了分析,并通过试验研究了成形件的显微组织和硬度。结果表明：同向和双向路径沉积得到5层单道和单层5道成形件的热历程基本一致,双向沉积5层单道成形件第3层中间点的峰值温度远高于双向沉积单层5道成形件第3道中间点,5层单道成形件的热累积效应更明显;5层单道成形件的板条状马氏体组织比单层5道成形件的粗大;同向沉积5层单道成形件在同一高度上的硬度略高于双向沉积成形件,同向沉积和双向沉积单层5道成形件在水平方向的硬度分布基本相同,5层单道成形件的平均硬度略低于单层5道成形件。     

激光-TIG复合填丝焊接工艺对6061铝合金焊缝组织与硬度的影响

采用激光-TIG复合热源填丝焊接5 mm厚T651态6061铝合金,研究电弧电流对复合填丝焊接焊缝成形的影响,分析了优化工艺参数下的焊缝显微组织及显微硬度特征,并与单独TIG填丝焊接进行综合对比。结果表明：采用激光-TIG复合热源填丝焊接T651态6061铝合金,能够有效改善焊缝成形,当TIG电弧电流为140 A时焊接过程稳定,焊缝成形效果良好;复合填丝焊接焊缝中心区域的显微组织为等轴晶,熔合区组织由大量枝状晶组成;复合填丝焊接显微硬度高于单独TIG填丝焊接,焊缝区均存在软化现象,在选择的测试点范围内,复合填丝焊接焊缝中心区域的平均硬度为66.91 HV,约为母材硬度的62.0%,比单独TIG填丝焊接提高约13.1%。     

铝合金超声波喷丸成形制件表面完整性研究

采用试验方法对AA2024-T351进行数控超声波喷丸成形,研究了超声波喷丸成形制件的显微硬度、残余应力场、表面形貌、表面粗糙度及半高宽等随超声波喷丸过程参数变化的规律,定性地探讨了AA2024-T351超声波喷丸后表面完整性的改善状况。结果表明:超声波喷丸后,制件的显微硬度得到了明显提高（最大增幅为20%）,同时在材料表面产生了一定厚度的硬化层（深度约为300μm）;制件内部引入数值较高、分布呈现梯度形式的残余压应力场,残余压应力场的临界深度在500~650μm之间,在距表面200μm处产生了最大残余压应力;制件表面形成一道道犁沟,表面喷丸区域的粗糙度Ra有一定程度的增大;制件表面层的半高宽值变大,深度在125μm左右,半高宽的增大表明材料冷作硬化程度加大、晶体内部位错密度有一定程度的增大。显微硬度的提高、残余压应力场的引入及表面层组织的细化有助于喷丸成形制件疲劳寿命、抗磨损和抗腐蚀性能的提高。     

Al-Zn-Mg-Cu合金高压扭转变形微观组织及力学性能

以Al-Zn-Mg-Cu合金为研究对象,在不同变形工艺条件（扭转圈数、变形温度）下对其进行高压扭转试验,利用扫描电子显微镜（SEM）、能谱仪（EDS）、X射线衍射技术（XRD）以及硬度测试等手段分析变形工艺参数对合金微观组织和力学性能的影响规律。研究结果表明：原始铸态组织呈等轴状,分布不均匀,粗大的第二相粒子（Al2Cu、MgZn2）沿晶界呈链状分布;高压扭转变形过程中,随着变形温度的升高、扭转圈数的增多,基体组织中粗大的第二相粒子数量明显减少,分布更加均匀,第二相粒子回溶进Al基体,获得过饱和固溶体;高压扭转变形后的Al-Zn-Mg-Cu合金位错密度显著上升,并且扭转圈数越多,变形温度越高,位错密度增加幅度也越大,微晶尺寸则随着扭转圈数的增大和变形温度的升高而减小;高压扭转变形后Al-Zn-Mg-Cu合金显微硬度值总体上随扭转圈数增大和变形温度升高而增大。     

激光冲击MAG复合增材工艺与组织性能研究

为了研究激光冲击熔化极活性气体保护焊(Metal Active-Gas welding, MAG)复合增材工艺规律,通过构建复合热源模型,对比研究激光加入前后电弧及熔池的变化,并通过改变激光功率参数,分别分析其对增材成形件宏观形貌、微观组织和力学性能的影响。结果表明,在激光的冲击作用下,电弧产生吸引和压缩现象,可提高电弧的稳定性和热源利用率、增加熔池内气体逃逸时间、细化成形件晶粒尺寸,以及提高成形件的力学性能。激光功率900 W为最佳工艺参数,此时增材成形件表面较为光滑、晶粒尺寸最小范围为5～16μm,平均显微硬度为(182.5±8.7)HV,抗拉强度为566 MPa,断后伸长率为10.35%,气孔率为0.74%。对比单电弧增材成形件,平均显微硬度、抗拉强度和断后伸长率分别提高了9.3%、13.4%、37.5%,气孔率减少了43.1%。     

冷金属过渡加脉冲电弧增材制造4043铝合金薄壁件的组织与拉伸性能

采用冷金属过渡加脉冲(CMT+P)电弧增材制造4043铝合金薄壁件,对比了不同工艺参数下薄壁件的成形性能,研究了成形性能良好薄壁件的组织与拉伸性能,并与CMT工艺下的进行了对比。结果表明:CMT+P工艺下,当焊接速度为8 mm·s-1和送丝速度4 m·min-1时,薄壁件的成形性能最好,且其成形效果接近CMT工艺下的; CMT+P工艺下薄壁件的单层组织由焊道上层的细晶区和焊道下层的粗晶区组成,焊道间存在穿过界面生长的粗大柱状枝晶,CMT工艺下的显微组织为分布均匀的细小柱状晶; CMT+P工艺下薄壁件的拉伸性能优于CMT工艺下的; CMT+P工艺下横向和纵向拉伸试样断裂方式均为韧性断裂,横向与纵向抗拉强度各向异性百分比仅为4%,说明薄壁件的力学性能不存在各向异性。     

薄壁锥形件拉深成形条件研究

在考虑了薄壁锥形件拉深过程中侧壁压缩失稳和小端拉裂两种破坏方式后,利用薄板在板平面内难以承受压应力,锥壁纬向收缩靠经向拉伸的变形特点,根据薄壁锥形件小端危险面所能提供的最大经向拉应力,求得了锥壁纬向无压缩失稳的最大相对拉深高度;根据薄壁锥形件的最大拉深载荷与毛坯外径的关系,求得了薄壁锥形件小端无破裂的最大相对拉深高度;从而建立了薄壁锥形件拉深的成形条件。针对板材性能的影响,提出了相对锥顶半径特征方程和特征值的概念。以Spcc深拉深钢板和S754铝合金板的试验表明,理论计算与实测结果相近。     

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.