共查询到20条相似文献,搜索用时 15 毫秒
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针对熔融金属填充焊接工艺过程中液流冲蚀形成小孔的过程进行数值模拟研究. 分析确定该过程的控制方程和边界条件,建立二维轴对称模型. 利用Fluent软件,从物理过程出发建立凝固熔化模型以及热源模型. 利用VOF模型追踪金属相与气相界面,获得液流在不同的焊接条件下,冲蚀形成小孔的过程. 并通过获得的流场,温度场分析形成不同形貌小孔的原因. 利用锡铅合金为试验材料在堆焊过程中得到的焊缝截面形貌,试验结果表明,模拟计算得到结果与试验结果基本吻合. 相似文献
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金属液在旋转电磁搅拌器作用下的流动分析 总被引:4,自引:1,他引:4
对自行研制的电磁搅拌器中金属液的电磁场和流场进行数值模拟,并进行实验验证。结果表明:在旋转磁场搅拌器作用下,金属液中除存在横截面上的旋转离心流动外,还存在着纵向的大环流,但二者速度不同,前者比后者高出一个数量级:金属液表面的磁感应强度风与电流频率成反比,与输入的电压成正比:金属液所受电磁力的最大值与磁感应强度B0的平方成正比,与频率的n次方成反比,其中1/2≤n≤3/2:n与金属液的电阻率有关,电阻率越小则n越小:对于纯铝n为1/2,对于纯锡和纯铅n为1;金属液的转速与磁感应强度R0成正比,与金属液密度的平方根成反比。 相似文献
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We examine size scale and strain rate effects on single-crystal face-centered cubic (fcc) metals. To study yield and work hardening, we perform simple shear molecular dynamics simulations using the embedded atom method (EAM) on single-crystal nickel ranging from 100 atoms to 100 million atoms and at strain rates ranging from 107 to 1012 s−1. We compare our atomistic simulation results with experimental data obtained from interfacial force microscopy (IFM), nano-indentation, micro-indentation and small-scale torsion. The data are found to scale with a geometric length scale parameter defined by the ratio of volume to surface area of the samples. The atomistic simulations reveal that dislocations nucleating at free surfaces are critical to causing micro-yield and macro-yield in pristine material. The increase of flow stress at increasing strain rates results from phonon drag, and a simple model is developed to demonstrate this effect. Another important aspect of this study reveals that plasticity as reflected by the global averaged stress–strain behavior is characterized by four different length scales: (1) below 104 atoms, (2) between 104 and 106 atoms (2 μm), (3) between 2 μm and 300 μm, and (4) above 300 μm. 相似文献
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为研究激光深熔焊中表面张力对熔池流动行为及熔池形貌的影响,获得活性剂对Q235低碳钢和304L不锈钢焊缝截面形貌的影响规律. 基于有限元计算软件Fluent,计算分析了激光深熔焊时表面张力在改变熔池流动行为中的重要作用. 结果表明,未添加活性剂焊接时,熔池液态金属的表面张力温度系数为负,熔池表面熔融金属以匙孔为中心由内向外流动,焊缝横截面形貌宽且浅. 添加活性剂焊接后,表面张力温度系数为正值,在熔池表面形成了由外向内的反向流动,形成了窄且深的焊缝形貌. 随表面张力温度系数绝对值的增大,表面张力变大,流体流动速度增大. 相似文献
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Frederico de Carvalho Nunes Luiz Henrique de Almeida André Freitas Ribeiro 《Journal of Materials Engineering and Performance》2006,15(6):717-721
HK steels are among the most used heat-resistant cast stainless steels, being corrosion-resistant and showing good mechanical
properties at high service temperatures. These steels are widely used in reformer furnaces and as superheater tubes. During
service, combustion gases leaving the burners come in contact with these tubes, resulting in corrosive attack and a large
weight loss occurs due to the presence of vanadium, which forms low melting point salts, removing the protective oxide layer.
In this work the external surface of a tube with dramatic wall thickness reduction was analyzed using light microscopy, scanning
electron microscopy, and transmission electron microscopy. The identification of the phases was achieved by energy dispersive
spectroscopy (EDS) analyses. The results showed oxides arising from the external surface. In this oxidized region vanadium
compounds inside chromium carbide particles were also observed, due to inward vanadium diffusion during corrosion attack.
A chemical reaction was proposed to explain the presence of vanadium in the metal microstructure. 相似文献
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利用CAE技术对2种尺寸的自行车座在同一副注射模中成型时熔料的流动平衡状态进行分析,提出对原浇口结构进行改进的方案,并对改进的方案进行模拟分析。根据分析的结果,对原浇注系统尺寸进行改进。结果表明:CAE技术在熔料填充模具型腔的流动平衡设计过程中,具有快速、准确、高效等优势,可以缩短模具制造周期,降低制造成本,提高生产效率。 相似文献
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采用离子色谱、火焰吸收等方法分析反应器中的残渣和尾气凝液,结果表明:残渣的主要成分为FeCl_2/FeCl_3、NiCl_2、CrCl_2/CrCl_3和CaCl_2,其中以铁的氯化物含量最高;凝液主要由HCl、HClO、H_2O以及金属氯化物所组成。分析认为反应器内的气体包括:Cl_2、HCl、HClO、H_2O、金属氯化物蒸气和通入的氩气等。模拟计算表明,在常用的1.0L/min的氩气流量下,难以将反应器内的HCl、HClO等腐蚀性气体及时排出反应器,它们与反应器内壁发生反应形成金属氯化物,对设备造成严重腐蚀,并且会对电解过程产生一定的影响。通过模拟计算不同流量的氩气在反应器内的流动状况,并结合尾气吸收实验,确定在2 h的预电解期,氩气通入量宜改为5.0 L/min。在不同的氩气通入方案下电解TiO_2发现,改进后的氩气通入方案有利于电解速度的提高,且设备的腐蚀情况有所缓解。 相似文献
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基于AutoCAD的冷冲压工艺卡片的设计与应用 总被引:1,自引:0,他引:1
分析了常规冷冲压工艺卡片的结构特点。讨论了AutoCAD环境下冷冲压工艺卡片的设计思想。介绍了这种工艺卡片的使用方法。最后,指出其存在的几个问题。 相似文献
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根据相似原理,采用模拟试验的方法研究了与铝液相似的模拟液在负压作用下渗流动力学规律。实验得到了控制铝液渗流过程的相似准则为:对直径1.5~3.5mm的颗凿介质为Froude准则,对直径0.5mm的颗粒介质为Reynolds准则。在相似准则指导下,原型铝液和模型中模拟液的渗流过程是相似的。 相似文献
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RH钢水环流控制技术 总被引:1,自引:0,他引:1
RH钢水环流控制是RH钢水精炼系统中的一项重要技术,本文通过对多套RH钢水精炼系统的分析、研究,形成了一套具有良好效果的RH钢水环流控制专有技术和标准设计,对于保证和提高RH钢水精炼处理能力和质量起到了重要作用. 相似文献
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Ni Chang-jiang Lu Gao-chun Zhang Qing-dong Jing Tao Wu Jun-jiao Yang Lin-long Wu Qin-fang 《中国铸造》2016,13(1):22-29
Core shooting process plays a decisive role in the quality of sand cores, and core box vents distribution is one of the most important factor determining the effectiveness of core shooting process. In this paper, the influence of core box vents distribution on the flow dynamics of core shooting process was investigated based on in situ experimental observations with transparent core box, high-speed camera and pressure measuring system. Attention was focused on the variation of both the flow behavior of sand and pressure curves due to different vents distribution. Taking both kinetic and frictional stress into account, a kinetic-frictional constitutive model was established to describe the internal momentum transfer in the solid phase. Two-fluid model(TFM) simulation was then performed and good agreement was achieved between the experimental and simulated results on both the flow behavior of sand and the pressure curves. It was found that vents distribution has direct effect on the pressure difference of different locations in the core box, which determines the buoyancy force exerting on the sand particles and significantly influences the filling process of core sand. 相似文献
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基于电子束焊接过程的传热与受力物理过程分析,建立相应模型,对电子束定点焊接304不锈钢的温度场与流场进行数值模拟,研究电子束焊接熔池流动行为及焊缝成形规律.结果表明,电子束加热阶段,熔池上表面温度梯度达到106 K/m,熔池表面峰值温度高,在沸点温度附近波动,强烈的金属蒸汽反作用力成为熔池流动的主要作用力,促使熔池中心下凹并不断波动,熔池冷却凝固阶段,金属蒸汽反作用力下降,熔池金属表面张力梯度引起的Marangoni对流成为熔池金属流动主要驱动力,促使焊缝表面熔宽增大,熔池凝固后焊缝上表面宽度为1.9 mm,中心处宽度为1.6 mm,下表面宽度为1.8 mm. 相似文献
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We report a significant entropic effect on creep of nanocrystalline metal using molecular dynamics. Our simulations reveal that the activation entropy may contribute a multiplicative factor of many orders of magnitude to the steady-state creep rate. The relationship between activation entropy and enthalpy obeys an empirical Meyer–Neldel compensation rule. The activation volume is found to decrease with increasing temperature for dislocation nucleation creep, which agrees well with experimental results. The study opens up an avenue for quantitatively discussing the entropic effects on various thermally activated deformations in nanocrystals. 相似文献
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采用循环伏安法研究了700℃时46.5LiF-11.5NaF-42KF(摩尔分数,%)熔盐中Ti(Ⅳ)(c(K2TiF6)=0.2 mol/L)和B(Ⅲ)(c(KBF4)=0.4 mol/L)在铂电极上的电化学还原机理,计算了各还原步骤传递的电子数。研究了LiF-NaF-KF-K2TiF6-KBF4(c(K2TiF4)=0.3 mol/L,c(KBF4)=0.3,0.6,0.9 mol/L)熔盐中电化学合成TiB2的阴极过程机理。结果表明:Ti(Ⅳ)的电化学还原为三步电荷传递反应,且阴极过程近似可逆;B(Ⅲ)在铂电极上的电化学反应机理为简单的三电子一步反应,阴极过程近似可逆;Ti(Ⅳ)和B(Ⅲ)可在同一电位下发生共沉积并反应生成TiB2。 相似文献
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针对AZ91D镁合金焊接熔池的气—液两相流系统,在质量守恒和动量守恒的基础上,建立了真空电子束焊接熔池二维气泡流数学模型,模拟计算了熔池中的气相分布、气泡流流动现象,分析了对空腔型缺陷形成、分布的实际影响.结果表明,完全穿透型焊缝熔池中的气体逸出可能性大大高于非穿透型焊缝,使其出现空腔型缺陷的几率在一定程度上低于非穿透型焊缝.典型空腔型缺陷的形成过程与电子束焊特有的深熔焊缝熔池中气泡流的流型及其流动特征有密切关系.较高的液相对流速度更有利于熔池中气体的逸出,从而使焊缝最终的含气率较低. 相似文献