永磁铁氧体烧结过程应力场有限元分析

利用有限元法对永磁铁氧体材料烧结过程的瞬态应力场进行了数值模拟分析,讨论了温度场变化对铁氧体磁瓦内部热应力的影响,得出磁瓦在烧结过程中的等效应力分布云图,结合分布图与热传导方程讨论了磁瓦烧结开裂问题中产生边裂和角裂的原因.同时分析了升温速率对应力场的影响,该分析结果反映了升温速率对磁瓦内部热应力最大值的影响规律.模拟结果为磁瓦烧结工艺制度的制定提供理论依据.     

低温烧结NiCuZn铁氧体的微结构和磁性能研究

采用固相法制备了Ni0.2Cu0.2Zn0.6Fe2O4铁氧体,在850℃进行预烧结,通过添加不同量的Bi2O3-HBO3-ZnO(BBZ)助熔剂,在不同温度烧结成型。研究了烧结温度和BBZ添加量对NiCuZn铁氧体材料微观结构和磁性能的影响。通过XRD、SEM、VSM和磁谱分析,结果表明,BBZ的加入起到了良好的低温烧结作用,在不同的烧结温度下性能呈现一定的规律。加入2%(质量分数)BBZ、950℃烧结的NiCuZn铁氧体晶粒生长较均匀,饱和磁化强度为51.9emu/g,起始磁导率μ′=349.9,磁谱损耗角正切值tanδ在0.02左右。     

烧结工艺对锶铁氧体永磁材料性能及结构的影响

研究了锶铁氧体烧结过程中烧结温度、恒温时间对锶铁氧体磁性能及结构的影响.结果表明,随烧结温度的升高,Br和(BH)max均增大,HCJ减小;随恒温时间的延长,变化趋势相同.优化试验结果为:烧结温度1180～1215 ℃,恒温时间2～3 h.     

升温速率和烧结温度对纳米晶MnZn粉体直接制备功率铁氧体性能的影响

采用纳米晶粉体直接造粒压制成块材烧结的方法制备MnZn铁氧体,研究了不同的升温速率和烧结温度对样品微观结构、磁性能的影响。研究表明,与传统的制备方法相比,直接烧结纳米晶MnZn铁氧体粉体,可以降低烧结温度。采用低的升温速率有利于提高样品的密度和初始磁导率,降低比损耗因子,并且低温烧结可以形成良好的微观结构和磁性能。     

Bi掺杂对Ni-Zn-Cu铁氧体的烧结与磁性能的影响

低温烧结软磁铁氧体是表面组装元件（ＳＭＤ）中的一类关键材料。本文对Ｂｉ掺杂的低温烧结Ｎｉ－Ｚｎ－Ｃｕ铁氧体从烧结性质、结构与相组成、显微形貌、磁结构和磁性质（磁导率、品质因数及频谱）方面进行了研究，在此基础上分析了Ｂｉ掺杂对材料形成过程和磁化机制的影响，发现Ｂｉ对材料磁性能的改进所起的作用主要产生于它对材料显微结构（晶粒、晶界和气孔）的调制。     

液氮-水相变传热传质特性分析及数值模拟

研究低温液体水下直接排放的传热传质问题,分析在常压和超临界压力下,低温液体与水的传热传质过程特性,建立相应的数理模型,采用Fluent软件进行数值模拟,得出不同排放条件下低温液体的生存距离和温度场及浓度场.模型的计算结果可为低温液体排放装置的设计提供依据.     

预烧温度对MnZn功率铁氧体烧结活性及温度稳定性的影响

采用氧化物陶瓷工艺制备了MnZn功率铁氧体.研究了预烧温度对MnZn功率铁氧体烧结活性及磁性能、温度稳定性的影响.结果表明,MnZn功率铁氧体预烧料粉体的活性随预烧温度的升高而降低.预烧料粉体的活性对其烧结样品的微观结构有很大影响.预烧温度在870℃时样品具有最佳的磁性能和温度稳定性.     

Mg—Cu—Zn铁氧体材料的低温烧结及其在片式电感上的应用研究

采用固相反应法制备低温烧结的Mg-Cu-Zn铁氧体（Mg0.68-xCuxZn0.32O）（Fe2O3）0.96（其中x在0.12~0.28变化）,通过XRD对不同CuO含量的Mg-Cu-Zn铁氧体的成相进行了分析,研究了CuO含量及预烧温度对材料性能的影响。在此基础上,利用LTCC技术制作Mg-Cu-Zn铁氧体片式电感,结果显示,低温烧结的Mg-Cu-Zn铁氧体有望成为制备叠层片式电感器的基体材料。     

微波烧结Mn-Zn 铁氧体的微观结构演变特征

以传统氧化物法合成的Mn-Zn铁氧体前驱体和外购前驱体为实验原料,经压制成形后用频率为2.45 GHz的微波在1 200~1 400℃烧结制备Mn-Zn铁氧体软磁材料.对烧结过程样品的微观结构和形貌进行了研究,并探究了烧结过程致密化特性及微波加热温度对Mn-Zn铁氧体密度的影响.研究表明:微波烧结的Mn-Zn铁氧体具有典型的尖晶石结构,样品主体相为Mn0.4Zn0.6Fe2O4;用SEM观察样品形貌,发现在1 350~1 400℃烧结的样品结晶状况良好,晶界平直,烧结组织均匀;微波烧结温度对密度有较大影响,在1 200~1 400℃,随着烧结温度升高样品密度增高,密度为4.80~5.28 g/cm3,在1 400℃烧结样品比较致密.微波烧结可以实现样品的快速致密.     

低温烧结Cu、Zn掺杂Co2-Y平面六角铁氧体及其频率特性

报道了通过BiO3的掺杂而获得的较低温度（870℃左右）下烧成的Y型平面六角结构软磁铁氧体的烧结工艺,结构特征及其磁导率和介电常数的频率特性,研究发现Cu,Zn掺杂的Co2Y型软磁铁氧体材料（Ba2Co1.2-xZnxCu0.8Fe12O22)在甚高频段具有良好的磁性能和介电性能,且此种材料烧结温度低,易于实现低温烧结,是一种可以用于甚高频段的理想的软磁材料。     

钛合金锥形件温热剪旋热力耦合有限元模拟

成形过程中的温度场变化对钛合金锥形件温热剪旋成功与否,以及产品的精度影响很大.在数值模拟时叠加符合实际的热源边界条件显得非常重要.针对TC4钛合金锥形件建立了三维热力耦合有限元模型,在有限元模拟过程中叠加了火焰加热边界条件.计算了成形过程中工件和芯轴上温度场的分布情况.所建立的有限元模型更加符合实际工况,模拟结果更加真实可靠.     

多层多道焊温度和热应力场对角变形影响分析

为探究Q235中厚板多层多道焊温度与热应力耦合场作用下对工件角变形的影响,利用有限元软件COMSOL对中厚板多层多道焊温度和热应力耦合场进行分析.通过建立中厚板多层多道焊温度与热应力耦合场模型,对工件不同方向温度场、热应力场的变化以及工件最终角变形情况进行模拟,并将模拟结果与相同工艺条件下焊接试验结果进行比较验证.结果表明：仿真分析结果与焊接实验结果具有较好的重合度;温度和热应力耦合场主要作用于工件的横向和纵向,对厚度方向的角变形影响较小.这为后续多层多道焊接角变形问题的进一步研究奠定了基础.     

TA15钛合金筒-锥复合曲母线构件旋压成形工艺研究

TA15钛合金作为一种高比强度结构材料具有良好的室温和高温强度、热稳定性能,广泛应用于飞机、导弹和发动机等飞行器,实现关键受力构件的减重要求.本文针对钛合金筒-锥复合曲母线构件的特点,重点开展了TA15钛合金薄壁曲母线构件热旋压成形技术的研究,采用剪切旋压预成形,强力旋压/普通旋压多道次复合旋压终成形的工艺方案,获得了成形质量较好的TA15钛合金筒-锥复合曲母线旋压件.建立了多道次曲母线构件的有限元模型,结合旋压实验解释了强旋/普旋复合成形过程中出现的典型缺陷产生机制.对热旋压过程坯料的显微组织观察分析发现,剪切旋压对显微组织具有一定程度的晶粒破碎作用,多道次强旋/普旋复合旋压成形后显微组织沿构件轴向和切向都发生伸长.经历剪切旋压和多道次强旋普旋复合旋压成形后,坯料的微观组织更加细化,且均匀性得到改善.TA15钛合金旋压成形工件的单向拉伸实验结果表明,相对于原始坯料旋压件强度明显提高,塑性略有下降.     

The effect of tool flank wear on the temperature distribution of a machined workpiece

Abstract

Temperature distributions in the chip, workpiece and tool during orthogonal machining were calculated numerically by the finite element method. The solution of the problem takes into account the thermal properties of the machined workpiece and the tool materials, which are the function of temperature. The effects of different flank wear under different cutting speeds on the temperature distributions of the machined workpiece were analyzed. It also provided an assumption for measuring the frictional force and the normal force on the flank face. The assumption was verified by experimental data.     

Analysis on Simulation of Quasi-Steady Molecular Statics Nanocutting Model and Calculation of Temperature Rise During Orthogonal Cutting of Single-Crystal Copper

This paper uses quasi-steady molecular statics method to carry out simulation of nanoscale orthogonal cutting of single-crystal copper workpiece by the diamond tools with different edge shapes. Based on the simulation results, this paper analyzes the cutting force, equivalent stress and strain, and temperature field. For the three-dimensional quasi-steady molecular statics nanocutting model used by this paper, when the cutting tool moves on a workpiece, displacement of atoms is caused due to the effects of potential on each other. After a small distance that each atom moves is directly solved by the calculated trajectory of each atom, the concept of force balance is used. And Hooke-Jeeves direct search method is also used to solve the force balance equation, and obtain the new movement position. When chip formation and the size of cutting force during cutting are calculated, further analysis is made. After the position of an atom's deformation displacement is acquired, the shape function concept of finite element is employed to obtain the atomic-level equivalent strain. With the stress-strain curve obtained from experiment of the numerical tensile value of nanoscale copper film taken as the foundation, regression treatment is made, and then the flow stress-strain relational equation is acquired. The flow stress-strain curve is used to calculate the equivalent stress produced under equivalent strain of element. This paper further supposes that workpiece temperature is mainly produced from two heat sources: plastic deformation heat and friction heat. Thus, this paper uses the acquired equivalent stress and strain to calculate plastic deformation heat. Besides, this paper additionally develops a method to calculate the numerical value of friction heat produced by the workpiece atoms on the tool face and the numerical value of temperature rise of workpiece atoms on tool face. Finally, the temperature rise produced from the two heat sources is added up for calculation of temperature field of the cut single-crystal copper workpiece during nanoscale orthogonal cutting, and for making analysis.     

铝合金薄板的铣削动力响应特性仿真与实验研究

铣削加工时铣削力周期性变化,引起的工件动态应力和应变对残余应力及振动有重要影响,明确铣削过程中的动力响应规律可以有效调控残余应力的产生与再分布。以铝合金工件为例,基于ABAQUS仿真软件建立了三维动态铣削仿真模型,获得了不同铣削时刻工件应力场的分布规律,分析了铣削不同位置时工件的动力响应特性。通过铣削实验测量了工件的动态应变和铣削力,并分析了加载频率对动力响应的影响。结果表明:铣削加工边缘时更易出现应力波峰和应力集中现象;不同加载频率下应变的波动频率恒定为267 Hz,应变波动的最大范围为40με;工件的动力响应与铣削位置紧密相关。     

A Discussion on Evolution of Microstructures and Influence Factors during Continuous Rolling of Compact Strip Production

The evolution of microstructures and influence factors of ultrathin hot strips of low carbon steel produced by compactstrip production (CSP) techniques were investigated. The steel blocking samples of CSP six-passes were obtained,and microstructures at the different positions of workpiece for each pass were studied. At the same time, anexplicit finite element technique was used to reveal the continuous rolling process. By combining experiment resultswith simulation analysis, the effects of plastic strain, temperature, precipitation and interval time on evolution andrefinement of crystal grains have been investigated. The results are useful for the development of high strength hotstrips.     

TA15 钛合金板材不贴模加热旋压成形规律研究

目的揭示工艺参数对钛合金锥形件柔性加热旋压成形过程的影响。方法采用基于ABAQUS平台建立的TA15钛合金柔性热旋有限元仿真模型和基于正交试验设计的模拟方案,研究了芯模预热温度、工件加热温度、旋轮与芯模间隙和旋轮进给比对该过程中,工件的切向拉应变和壁厚差的影响显著性与规律。结果获得了合理的工艺参数组合与回归方程。结论较小的旋轮进给比有利于抑制工件的破裂;适中的工件加热温度有利于获得较为均匀的壁厚。     

FEM analysis of temperature distribution and experimental study of microstructure evolution in friction interface of GH4169 superalloy

The linear friction welding (LFW) process is a very effective solid-state welding method. Friction process is very significant for temperature distributions on the surface between two contacting workpieces during LFW process. In this paper, a finite element method (FEM) model is implemented to analyze the temperature distributions in friction interface of GH4169 superalloy cylindrical specimens. The simulation studies were conducted using ABAQUS software. Temperature distributions during the simulation of one rotation of the pressure head on the specimen were simulated. Temperature distributions of specimens in the end of different rotations were also investigated. The validation experiments were conducted to validate the simulation results. The detailed microstructure investigations demonstrate that the temperature distributions obtained in the present model are correct. This friction model is able to simulate the friction process of the GH4169 superalloy, but further research about FEM models is still needed for more precise prediction of microstructure evolution in the friction process of this alloy.