热压烧结法制备氧化铝/透辉石陶瓷复合材料

采用热压烧结法制备了氧化铝/透辉石复相陶瓷材料,分析了复合材料的微观结构,测试了复合材料的断裂韧度、硬度和抗弯强度与透辉石颗粒含量的对应关系.结果表明:在28 MPa、1 450℃×30 min条件下热压烧结制备的复相陶瓷材料,其抗弯强度、断裂韧度均有明显提高,最高达到442.5 MPa和4.76 MPa·m1/2.     

纳米复相陶瓷刀具材料的研究现状

纳米复相陶瓷刀具材料的研究成功有望从根本上解决陶瓷材料的脆性问题，比起传统刀具陶瓷刀具材料，它具有更高的抗弯强度、断裂韧度等力学性能。本文介绍纳米复相陶瓷的增韧补强机理；总结了现阶段以Al2O3、Si3N4、ZrO2和Ti（C、N）四种陶瓷为基体的纳米复相陶瓷刀具材料的显微结构和力学性能之间的关系，并且指出了纳米复相陶瓷刀具材料今后的研究方向。     

Si_3N_4/SiC(N)纳米复相陶瓷的制备与性能研究

采用极性分散剂和超声分散技术 ,在微米Si3 N4基体中加入SiC纳米颗粒 ,用真空热压烧结法制备出Si3 N4/SiC(N)纳米复相陶瓷。研究结果表明 :加入SiC纳米颗粒可显著降低烧结温度 ,阻止 β Si3 N4晶粒的过度生长 ,细化晶粒组织 ,提高复合陶瓷材料的致密度和机械性能 ;含 15wt%SiC纳米颗粒的复相陶瓷具有最佳断裂韧度和较高抗弯强度 ,可作为高速切削刀具和模具的候选材料。     

石墨烯添加量对无压烧结石墨烯/碳化硅陶瓷复合材料性能的影响

在碳化硅粉中添加质量分数为1%~5%的石墨烯,采用无压烧结工艺在2 190℃保温1h制备石墨烯/碳化硅陶瓷复合材料,研究了石墨烯添加量对复合材料物相组成、密度和力学性能的影响。结果表明:该复合材料由碳化硅相及少量石墨相组成;随着石墨烯添加量的增加,复合材料的密度下降,相对密度变化较小,抗弯强度和断裂韧度先增大后减小,硬度下降;当石墨烯的质量分数为3%时,复合材料的抗弯强度为395 MPa、硬度为89HRA、断裂韧度为6.0 MPa·m1/2,综合力学性能最好。     

Al_2O_3-20%TiB_2/Al_2O_3-20%TiC对称型叠层陶瓷刀具的切削性能

以Al2O3为基体,以TiB2和TiC为增强相,通过粉末叠层以及热压烧结工艺制备了Al2O3-20%TiB2/Al2O3-20%TiC对称型叠层陶瓷刀具材料,对其抗弯强度与断裂韧度进行了测试,采用该材料刀具对淬火45钢进行高速切削试验,并与Al2O3-20%TiC陶瓷刀具的切削性能进行了对比。结果表明:对称型叠层陶瓷刀具材料的抗弯强度和断裂韧度分别为651 MPa和4.59 MPa·m1/2,比Al2O3-20%TiC陶瓷的分别提高了11 MPa和0.59 MPa·m1/2;对称型叠层陶瓷刀具的切削力和磨损均较小,切削性能明显优于Al2O3-20%TiC陶瓷刀具的。     

短切碳纤维C_(sf)含量对TiC基复合陶瓷刀具材料微观组织及力学性能的影响

金属烧结剂选择Ni和Co,增强相选择短切碳纤维C_(sf),采用真空热压烧结技术,在1500°C下制备了短切碳纤维C_(sf)含量不同的TiC基复合陶瓷刀具材料。研究了C_(sf)的含量对TiC基复合陶瓷刀具材料微观组织和力学性能的影响,结果表明:加入C_(sf)后,复合陶瓷刀具材料断裂方式为穿晶断裂和沿晶断裂方式并存,在C_(sf)含量增加的过程中,TiC基复合陶瓷刀具材料的硬度逐步下降,抗弯强度和断裂韧度先变大后减小;当增加到2wt%C_(sf)时,获得了最佳的力学性能,硬度为14.32±0.16GPa,断裂韧度为8.70±0.15MPa·m~(1/2),抗弯强度为695.63±15.01MPa。     

第二级时效工艺对7050铝合金厚板组织及性能的影响

研究了第二级时效工艺对7050铝合金厚板拉伸性能、断裂韧度及电导率的影响，并采用透射电镜及扫描电镜分析其强韧化机理。结果表明：该合金厚板在双级时效的第一级时效条件相同时，随第二级时效温度的升高或时效时间的延长，合金中沉淀相的尺寸和间距增大，合金强度下降，断裂韧度和抗应力腐蚀能力提高，切变和穿晶韧窝混合型断裂方式中的韧窝...     

高温高压烧结制备PCBN陶瓷的微观结构与性能

以ZrO₂、Al₂O₃和铝粉作为结合剂,通过六面顶压机在高温(1 300～1 600℃)高压(5.5 GPa)条件下烧结制备聚晶立方氮化硼(PCBN)陶瓷,研究了烧结温度对陶瓷物相组成、力学性能以及加工离心铸铁时切削性能的影响。结果表明:不同温度烧结PCBN陶瓷的主晶相均为cBN、m-ZrO₂、t-ZrO₂、Al₂O₃、AlN和ZrN,结合相颗粒均匀地分散在cBN基体上;随着烧结温度的升高,cBN与结合相的结合更加紧密,陶瓷的相对密度、硬度、抗弯强度和断裂韧度增大;当烧结温度为1 600℃时,陶瓷的综合力学性能最好,硬度、抗弯强度和断裂韧度分别达到32.87 GPa,850.3 MPa,5.1 MPa·m^1/2;当烧结温度为1 400℃和1 500℃时,PCBN陶瓷刀具在切削离心铸铁棒总长度为10 km时,其后刀面磨损量仅分别为171,166μm,切削性能较好。     

短切碳纤维含量对WC-TaC复合陶瓷刀具材料微观组织及力学性能的影响

采用真空热压烧结技术,以Ni为粘结相,短切碳纤维(C_(sf))为增强相,在1550℃下制备了不同C_(sf)含量的WC-Ta C-C_(sf)复合陶瓷刀具材料。研究了C_(sf)含量对WC-Ta C-C_(sf)复合陶瓷刀具材料微观组织和力学性能的影响,结果表明:复合材料中加入一定含量的C_(sf)可以显著细化晶粒。随着C_(sf)含量的增加,硬度逐渐减小,抗弯强度和断裂韧度先增大后减小,当C_(sf)含量为1.5wt%时,材料的综合力学性能最好,硬度、抗弯强度和断裂韧度值分别为12.79+0.28GPa、1072.71+22MPa和14.45+0.2MPa·m~(1/2)。     

纳米SiC晶须增强Ti(C,N)基金属陶瓷的显微组织与力学性能

采用真空烧结法制备了纳米SiC晶须增强Ti(C,N)基金属陶瓷复合材料,用XRD、FESEM、EDS、万能试验机及维氏硬度仪等手段研究了纳米SiC晶须对复合材料显微组织和抗弯强度及断裂韧度的影响。结果表明:复合材料的显微组织具有典型的芯-壳结构,主要由黑色的硬质核心相,灰色的环形相,灰白色的粘结相以及部分分布于外环形相/粘结相界面、部分弥散分布于粘结相中的白色增强相组成;随着纳米SiC晶须添加量的增加,粘结相的体积分数减小,增强相的体积分数增大;与未添加晶须的金属陶瓷相比,复合材料的抗弯强度和断裂韧度均有显著提高,当纳米SiC晶须的体积分数为7.5%时,复合材料的力学性能最佳,抗弯强度为2 346 MPa,断裂韧度为16.82 MPa·m~(1/2)。     

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.